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Rheological constraints on martian landslides
Abstract
We use a dynamic finite-difference model to simulate martian landslides in the Valles Marineris canyon system and Olympus Mons aureole using three different modal rheologies: frictional, Bingham, and power law. The frictional and Bingham modes are applied individually. Fluidized rheology is treated as a combination of frictional and power-law modes; general fluidization can include pore pressure contributions, whereas acoustic fluidization does not. We find that general fluidization most often produces slides that best match landslide geometry in the Valles Marineris. This implies that some amount of supporting liquid or gas was present in the material during failure. The profile of the Olympus Mons aureole is not well matched by any landslide model, suggesting an alternative genesis. In contrast, acoustic fluidization produces the best match for a lunar slide, a result anticipated for dry crust with no overlying atmosphere. The presence of pressurized fluid during Valles Marineris landsliding may be due to liquid water beneath a thin cryosphere (<1–2 km) or flash sublimation of CO2.
... This friction estimate is based on the assumption that gravitational potential energy ( ) of a landslide mass ( ) is completely consumed by basal shearing during landslide transport ( ) where is the effective coefficient of basal friction, is gravitational acceleration, and is the landslide transport distance (Iverson, 1997). These simplified physical relationships require that , which is incomplete as kinetic energy must have also contributed to J o u r n a l P r e -p r o o f 49 landslide motion at high speed (Di Toro et al., 2004), basal friction causes heating, and finally mass movement may involve turbulent flow rather than simple frictional sliding (e.g., Harrison and Grimm, 2003). We expand on the early work by exploring and quantifying more geometric attributes of a landslide system, and instead estimate the VM landslide outer-zone coefficient of basal friction from measured surface slope angle in the lateral spreading zone, a more accurate proxy. ...
... Dynamic, analytical, and experimental modeling of VM landslide geometry performed so far has produced contradictory results for dry VM landslide emplacement mechanisms. Dynamic numerical modeling, which computes the initial mass profile and time-varying shape of a given runout path, of a simulated dry (acoustic fluidization) landslide rheology does not match well the cross-sectional geometry of most VM landslides (Harrison and Grimm, 2003). In contrast, statistical comparison of VM landslide geometry (specifically, the power-law relationship between volume and runout distance) with that of terrestrial landslides (Soukhovitskaya and Manga, 2006;Johnson & Campbell, 2017) and extrapolation of laboratory-scale experimental studies of dry granular flows to VM landslides (Lajeunesse et al., 2006) (Lucchitta, 1987;De Blasio, 2011). ...
... High pore water pressure in the basal sliding zones may have reduced the effective frictional coefficient and facilitated the long-distance transport of VM landslides (e.g., Lucchitta, 1987;Harrison and Grimm, 2003). Within this hypothesis, saturation or near-saturation of J o u r n a l P r e -p r o o f 61 sedimentary rocks or sediments at the base would reduce friction to the range of lower-bound values determined for VM landslides in this work. ...
Long-runout landslides with transport distances of >50 km are ubiquitous in Valles Marineris (VM), yet the transport mechanisms remain poorly understood. Four decades of studies reveal significant variation in landslide morphology and emplacement age, but how these variations are related to landslide transport mechanisms is not clear. In this study, we address this question by conducting systematic geological mapping and compositional analysis of VM long-runout landslides using high-resolution Mars Reconnaissance Orbiter imagery and spectral data. Our work shows that: (1) a two-zone morphological division (i.e., an inner zone characterized by rotated blocks and an outer zone expressed by a thin sheet with a nearly flat surface) characterizes all major VM landslides; (2) landslide mobility is broadly dependent on landslide mass; and (3) the maximum width of the outer zone and its transport distance are inversely related to the basal friction that was estimated from the surface slope angle of the outer zone. Our comprehensive Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) compositional analysis indicates that hydrated silicates are common in landslide outer zones and nearby trough-floor deposits. Furthermore, outer zones containing hydrated minerals are sometimes associated with longer runout and increased lateral spreading compared to those without detectable hydrated minerals. Finally, with one exception we find that hydrated minerals are absent in the inner zones of the investigated VM landslides. These results as whole suggest that hydrated minerals may have contributed to the magnitude of lateral spreading and long-distance forward transport of major VM landslides.
... Large, ancient landslides have been recognized on Mars since the Viking missions (Lucchitta 1979(Lucchitta , 1987Shaller 1991). More recently, comparative analysis of different landslides was made possible based on updated data and images with better resolution, also allowing some quantitative studies of slope stability (e.g., Schulz 2002;Harrison and Grimm 2003;Quantin et al. 2004a, b;Soukhovitskaya and Manga 2006;Lajeunesse et al. 2006;Bigot-Cormier and Montgomery 2007;Bulmer 2012;Brunetti et al. 2014). Several landslides cluster in the Valles Marineris (also VM, hereafter), a system of valleys stretching W-E along the equator that had a complex history of extensional tectonics and collapse (e.g., Schultz 1998;Hauber et al. 2010). ...
... Comparatively fewer studies have been dedicated to the dynamics, and the velocity at which these catastrophic events took place remains largely unknown. Analogical simulations (e.g., Lajeunesse et al. 2006) and numerical simulations of landslides in Valles Marineris (Harrison and Grimm 2003;Lucas and Mangeney 2007;Lucas et al. 2011;De Blasio 2011a) attempt at simulating the velocity during the flow and may provide indications on the rheology and geomechanics but, strictly speaking, they are not measurements of the velocity. ...
... The main scarp closer to the ridge has a slope angle between 28°and 30°and average elevation of 3000 m above the basal level of VM, while the two secondary scarps amount to half that height. This landslide has been described earlier in some detail and also simulated numerically (Harrison and Grimm 2003;Quantin et al. 2004a;Lucas et al. 2011). ...
... Large, ancient landslides have been recognized on Mars since the Viking missions (Lucchitta 1979(Lucchitta , 1987Shaller 1991). More recently, comparative analysis of different landslides was made possible based on updated data and images with better resolution, also allowing some quantitative studies of slope stability (e.g., Schulz 2002;Harrison and Grimm 2003;Quantin et al. 2004a, b;Soukhovitskaya and Manga 2006;Lajeunesse et al. 2006;Bigot-Cormier and Montgomery 2007;Bulmer 2012;Brunetti et al. 2014). Several landslides cluster in the Valles Marineris (also VM, hereafter), a system of valleys stretching W-E along the equator that had a complex history of extensional tectonics and collapse (e.g., Schultz 1998;Hauber et al. 2010). ...
... Comparatively fewer studies have been dedicated to the dynamics, and the velocity at which these catastrophic events took place remains largely unknown. Analogical simulations (e.g., Lajeunesse et al. 2006) and numerical simulations of landslides in Valles Marineris (Harrison and Grimm 2003;Lucas and Mangeney 2007;Lucas et al. 2011;De Blasio 2011a) attempt at simulating the velocity during the flow and may provide indications on the rheology and geomechanics but, strictly speaking, they are not measurements of the velocity. ...
... The main scarp closer to the ridge has a slope angle between 28°and 30°and average elevation of 3000 m above the basal level of VM, while the two secondary scarps amount to half that height. This landslide has been described earlier in some detail and also simulated numerically (Harrison and Grimm 2003;Quantin et al. 2004a;Lucas et al. 2011). ...
The flow characteristics and velocities of three landslides in Valles Marineris on Mars are investigated using detailed
morphological analyses of high-resolution images and dynamical calculations based on the run-up and curvature of
the landslide deposits. The morphologies of the landslides are described, especially concerning those characteristics
that can provide information on the dynamics and velocity. The long runout and estimated high velocities, often
exceeding 100 m/s, confirm a low basal friction experienced by these landslides. Because subaqueous landslides on
Earth exhibit reduced friction, we explore the scenario of sub-lacustrine failures, but find little support to this
hypothesis. The environmental conditions that better explain the low friction and the presence of longitudinal
furrows suggest an aerial environment with a basal soft and naturally lubricating medium on which friction
diminished gradually; in this perspective, ice is the most promising candidate.
... [4] Landslide dynamics strongly depend on the underlying topography, on the geometry and volume of the released mass, on the nature and mechanical behavior of the flowing material [e.g., Hungr, 1995;Iverson, 2001, 2004;Harrison and Grimm, 2003;Mangeney-Castelnau et al., 2003, 2005Pudasaini and Hutter, 2007;Sosio et al., 2008;Favreau et al., 2010]. However, none of these parameters are well constrained. ...
... [8] Landsliding in Valles Marineris has important implications for climatic and hydrologic conditions. Triggering mechanisms and emplacement processes have been debated based on geomorphological, experimental and numerical studies [Lucchitta, 1979[Lucchitta, , 1987McEwen, 1989;Shaller, 1991;Legros, 2002;Harrison and Grimm, 2003;Quantin et al., 2004;Soukhovitskaya and Manga, 2006;. Some studies have argued in favor of hydrated conditions for landsliding to occur [Lucchitta, 1978[Lucchitta, , 1979[Lucchitta, , 1987Shaller et al., 1989], whereas others argue in dry conditions [McEwen, 1989;Soukhovitskaya and Manga, 2006;Lajeunesse et al., 2006]. ...
... Some studies have argued in favor of hydrated conditions for landsliding to occur [Lucchitta, 1978[Lucchitta, , 1979[Lucchitta, , 1987Shaller et al., 1989], whereas others argue in dry conditions [McEwen, 1989;Soukhovitskaya and Manga, 2006;Lajeunesse et al., 2006]. In any case, several studies have shown a very high mobility of Martian landslides [Lucchitta, 1979[Lucchitta, , 1987Lucchitta et al., 1992;Melosh 1979;Shaller, 1991;Legros, 2002;Harrison and Grimm, 2003;Quantin et al., 2004;. ...
... Studying these landslides contribute to an understanding of the dynamics of the landscapes and is expected to provide insight into the climatic conditions during emplacement at Amazonian Time [Quantin et al., 2004b] as the potential presence of groundwater in liquid or solid phases. Currently, very few studies focus on the simulation of gravitational flows on Mars [Harrison and Grimm, 2003 ;Barnouin-Jha et al., 2005]. To the authors' knowledge, no simulations of Martian landslides were performed on a real 3D topography. ...
... La distance d'arrêt maximale (runout en anglais) atteinte par les dépôts d'un glissement de terrain est un paramètre souvent utilisé pour la calibration des modèles numériques d'avalanche [Hungr, 1995 ;Denlinger and Iverson, 2001 ;Harrison and Grimm, 2003 ;Mangeney-Castelnau et al., 2003, 2005Pudasaini and Hutter, 2007 ;Sosio et al., 2008]. ...
... g. Hungr, 1995 ;Denlinger and Iverson, 2001 ;Harrison and Grimm, 2003 ;Mangeney-Castelnau et al., 2003, 2005Pudasaini and Hutter, 2007 ;Sosio et al., 2008]. None of these parameters are well constrained. ...
Slope instabilities take part in weathering and transport processes at the surface. The runout distance is extensively used in analysis of landslide dynamics and in the calibration of the rheological parameters involved in numerical modelling. However, the unknown impact of the uncertainty in the shape of the initial released mass on the runout distance and on the overall shape of the deposit questions the relevance of these approaches. Indeed, the shape of the initial scar is generally unknown in real cases. Our study is based on numerical simulations coupled with remote sensing data analysis. The model used in this study has been intensively compared with laboratory experiments and well constrained natural cases in order to establish its range of use. We have also developed a pre-event topographic reconstruction method using remote sensing data allowing the study of the topographic and initial failure plane geometry effects. We show that the runout distance is a robust parameter that is only poorly affected by the initial scar geometry. On the contrary, the extent of the deposits perpendicular to the main mass displacement direction is shown to be controlled by the scar geometry, providing a unique tool to retrieve information of the initial failure geometry, as well as on the released volume. A feedback analysis of Martian landslides shows excellent agreement between numerical results and geomorphological evidence, providing insight into the initial landsliding conditions. In addition, we introduce a new empirical dissipation parameter allowing a good prediction of the runout in the simulation without any calibration for a given geological context.
... The presence of gullies and landslide formations indicates the role of unsaturated soil on Mars, where the melting of ice and thermomechanical effects lead to soil saturation and reduced shear strength, causing downslope movement (Lanza et al., 2006). The detection of ice in the subsurface of Mars has led numerous authors to suggest that ice melting serves as the primary cause of landslides (Harrison andGrimm 2003, De Blasio et al., 2013;Björnsson et al., 2000). Evidence of water-rock interaction and the presence of hydrated phases suggest the existence of past water and the potential for groundwater seepage on Mars (Mitrofanov et al., 2014;Salese et al., 2019). ...
The rock walls of Valles Marineris (VM) valleys on Mars reveal significant gravitational failures, resulting in a sequence of massive landslides spanning several hundred cubic kilometers in volume. For further Mars exploration missions, it is critical to understand which characteristics impact the stability of these rock walls. In this work, ArcGIS is used to identify 30 steep slopes. Utilizing the finite element method, we calculate the proposed seven possibly landslide-prone slopes based on geometry in VM. Using Strength Reduction Method (SRM) in Midas GTS NX, the impacts of variations in cohesion, internal friction angle, unit weight, and elastic modulus of soil and rock on the slope safety factor against landslides are evaluated. The Strength Reduction Method (SRM) is a widely used approach in geotechnical engineering to assess slope stability. It involves systematically reducing the strength parameters of the soil and rock materials within the slope until failure occurs. By iteratively reducing the strength parameters, the SRM calculates the factor of safety against landslides. Internal friction angle is the most critical factor in determining the stability of a slope under low gravity circumstances since it has the widest range of possible alterations. Furthermore, the material’s cohesion and unit weight significantly impact the safety factor, although elastic modulus barely affects slope stability. A modulus of elasticity of more than 35 GPa will not enhance the factor of safety. There is no significant difference in soil suction between Earth and Martian gravities near the surface water table. However, as the groundwater depth increases, soil suction under Martian gravity becomes notably lower than that on Earth. Additionally, consistent with prior investigations, the Vadose zone on Mars is positioned at higher elevations relative to Earth, indicating the presence of a higher capillary fringe. Furthermore, the factor of safety for slope stability consistently outperforms Earth for equivalent slope configurations under unsaturated conditions, with approximately 2.5 times higher factor of safety for higher suctions and approximately 1.5 times higher factor of safety for lower suctions compared to Earth.
... While some studies point to a fluid trigger for the Martian landslides (Carr & Schaber, 1977;Harrison & Grimm, 2003;Quantin et al., 2004), others ruled it out as a necessary condition (Bigot-Cormier & Montgomery, 2007;Brunetti et al., 2014;Soukhovitskaya & Manga, 2006). For their data set, Brunetti et al. (2014) rejected the influence of the inventory completeness on the heavy-tailed PDF; they suggested a lithological control over the lack of medium-sized landslides, relating it to the absence of an upper soil layer and to speculated on large spaces between discontinuities within Mars bedrock (Brunetti et al., 2014;Katz & Aharonov, 2006). ...
Landslides are widely recognized as key components of landscape evolution in areas of steep topography. Here, we present a new framework for examining landslide inventories in the context of the volume‐based impact that different landslide sizes have on shaping the landscape, that is, their geomorphic effectiveness (GE). Focusing on an actively retreating coastal cliff in the Eastern Mediterranean and utilizing a LiDAR‐derived inventory of over 1,100 cliff landslides that occurred between 2014 and 2019, we show that segments of the cliff are characterized by two principal types of GE distributions: (a) A “humped” GE distribution where the accumulated erosion volume of the largest and rarest collapses in the inventory is similar or lower than that of more frequent, mid‐range collapses and (b) Nearly monotonically increasing GE distribution where the cumulative volume of larger collapses consistently surpasses that of smaller magnitude collapses. Regardless of the GE distribution type, we found that the cumulative geomorphic impact of the small and most probable collapses was negligible. Extending this new GE framework to 9 other previously published landslide inventories (coastal and mountainous), we demonstrate that precipitation and seepage‐induced landslide inventories are commonly characterized by monotonic‐type GE distributions, dominated by large landslides (>10⁻¹ of the volume of the largest landslide), and that hump‐shaped GE distributions, dominated by more frequent mid‐size landslides, commonly occur under “dry” triggers (e.g., earthquakes). We propose that the humped GE distribution could reflect the lack of deep mechanical weakening, which exerts a higher probability of the largest landslides in the inventories triggered by “wet” factor.
... Large landslides on Mars were first observed in Valles Marineris through the Mariner 9 images (Sharp, 1973) and then studied with more detail on Viking mission images (Christiansen and Head, 1978;Lucchitta, 1979). In more recent years, many studies investigated and classified large Martian landslides, especially in the Valles Marineris region (e.g., McEwen, 1989;Shaller and Komatsu, 1994;Harrison and Grimm, 2003;Quantin et al., 2004a;De Blasio, 2011;Brunetti et al., 2014;Watkins et al., 2015;Crosta et al., 2018aCrosta et al., , 2018b, where they were formed between the Hesperian and Late Amazonian (Quantin et al., 2004b;Hager and Schedl, 2017). ...
Landslides are geomorphological features observed on many planetary bodies, formed in a wide range of geological, geomorphological and environmental conditions. Hence, study of their morphological and morphometric characteristics, along with their absolute or relative dating, can improve the understanding of
geological and environmental conditions at the time of their emplacement. On Mars, landslides are present over a very large part of the planet, and the most spectacular and best studied are those in Valles Marineris where many mass wasting phenomena occurred between Hesperian and Late Amazonian periods. The present study aims at improving the knowledge of Martian geological and geomorphological evolution including environmental
conditions through absolute dating and morphological analysis of selected large landslides outside of Valles Marineris. These mass wasting features were used as proxies for revealing how active the relatively recent (Middle to Late Amazonian) geological environment of Mars was through the information of their trigger timings and degradation histories. The five landslides of our study, which have never been analyzed previously, are located in the region of Hydraotes Chaos and Tiu Valles near the dichotomy boundary. The geomorphological and morphometric analyses show that the studied landslides, classifiable as rock avalanches, exhibit morphological features and mobility similar to those of other terrestrial and Martian rock avalanches. The results obtained from the absolute dating reveal that these landslides occurred within a time range spanning from 835 Ma (±290) to 252 Ma (±100) ago, consistent with occurrences of other landslides in the equatorial region of Mars. The most plausible triggering factors include ground shaking resulting from meteoric impacts, marsquakes and volcanic events related to the evolution of Tharsis and Elysium regions during the Amazonian period. Local
resurfacing events acting on the studied landslides are probably related to aeolian deflation and deposition, minor mass wasting events and impact cratering. Finally, the geomorphological characteristics of these landslide bodies and their absolute dating reveal a possible recent (< 250–150 Ma) tectonic activity along the flanks of Tiu Valles and the southern Hydraotes Channel.
... In case of terrestrial mass movements, the run-out length is 40 times higher than the drop height (Beddingfield et al., 2020) and similar types of long-run mass wasting has been also observed on icy planetary bodies such as Iapetus, Rhea (Singer et al., 2012) and Ceres (Schmidt et al., 2017). Various mechanisms are responsible in triggering long-run out mass movements such as: riding a cushion of trapped air (Shreve, 1966;1968); lubrication by release due to volatile materials (Lucchitta, 1979;Legros, 2002); aqueous pore pressure support (Johnson, 1978;Harrison & Grimm, 2003); slipping on ice (De Blasio, 2011) or frictionally generated basal melt layers (Erismann, 1979;De Blasio and Elverhøi, 2008;Weidinger & Korup, 2009); sliding on evaporitic salt (De Blasio, 2011); lubrication by rock (Hsu, 1975;Han et al., 2011); mechanical fluidization (Davis, 1982;Campbell et al., 1995); fluidization by acoustic waves (Melosh, 1979;1986;Collins & Melosh, 2003). On Iapetus and Rhea, localized friction reduction was caused at the base of mass movements which release energy during motion (Singer et al., 2012). ...
This work evaluates volatile induced surface features on Vesta and Ceres, two of the largest asteroids present within the asteroid belt. Both the planetary objects have similar surface acceleration but different regolith nature. Vesta is a relatively dry body whereas Ceres is rich with water ice. Direct measurement of volatiles is challenging due to harsh space conditions. However, when they are mixed with regolith, it produces peculiar landforms due to melting and/or sublimation and affects the overall evolution of a planetary body. Therefore, in this study the surface features which have direct or indirect link to ice and/or volatiles are examined in order to understand the volatile distribution. For this, regional and global scale investigations related to ponded deposits, pit chains and mass wasting analysis were conducted on Vesta and Ceres. In the vicinity of Marcia and Cornelia impact craters of Vesta, two types of pond deposits were observed. Type 1 melt ponds have smooth, shallow deposits (depth <100 m) and are produced from the downslope movement of volatile bearing impact melt material. In contrast, type 2 dust ponds deposit consist of rough surface with ~200 m depth. These deposits are produced from the mobility of granular dust via infrequent high-amplitude seismic diffusivity and/or short-lived volatile outgassing activity. Due to low amounts of volatiles, the dusty material did not achieve kinetic sieving and thus do not attain typical smooth pond morphology. The findings of this study strongly support the hypothesis related to presence of low amounts of volatiles within Vesta’s regolith. To understand the volatile distribution on Ceres, the analysis of pit chains is carried out within three impact craters namely; Occator, Azacca and Urvara. Radial pit chain pattern of Occator is related to subsurface laccolith swelling of volatile rich cryomagmatic material. Linear pit chain clusters at floors of Azacca and Urvara are attributed to seasonal thermal contraction of ice layer present near the surface. Additionally, based on the pit chains depth the depicted average minimum thickness of regolith within Azacca, located at equator is ~200 m. On the contrary, within Occator and Urvara, the localized thickness is 30 m and 800 m, respectively, which is attributed to their distinct subsurface condition. Hence, this investigation favors the presence of ice layer within the subsurface layer and reveals that it is not distributed homogeneously on Ceres. Lastly, the global scale comparative examination of the mass wasting process on Vesta and Ceres shows few common and some distinct characteristics. In general, granular sliding on Vesta and flow-like movements on Ceres are observed as dominant population. Further, slides and slumping features are restricted to mid-latitudes on Ceres which implies ice-rock fractionation at regional scale. Additionally, the volatile concentration also influences the deposit mobility on Vesta and Ceres and is analyzed by estimating height, width and effective coefficient of friction; H/L. The outcome suggests that deposits become immobile at shorter distances on Vesta in comparison to Ceres (avg. distance 4.5 km and 11.2 km, respectively). The difference in morphology and mobility is related to contrast in the amounts of volatiles present within regolith of both the bodies. While comparing the effective coefficient of friction of Vesta and Ceres with planetary objects in outer solar system, the examination shows that lower temperature may have more influence on mobility. Together, all the above-mentioned studies summarize the volatile induced surface landforms and provide evidences related to their distribution on Vesta and Ceres. This work also presents the first-time comparative investigation that reveals the influence of volatile content on the morphological characteristics of Vesta and Ceres.
... Hayashi and Self, 1992;Iverson et al., 1997), long-runout landslides exhibit runout lengths that are significantly longer. A variety of formation mechanisms have been suggested for long-runout landslides, including 175 the presence of basal pore water pressures either from water entrained in the landslide material (e.g., Lucchitta, 1987;Harrison and Grimm, 2003;Quantin et al., 2004;De Blasio and Elverhøi, 2008;Iverson, 2016;Watkins et al., 2015), or small amounts of melt generated from localized flash heating at the bases of the landslides during motion during their formations (Erismann, 1979(Erismann, , 1986Goldsby and Tullis, 2011;Singer et al., 2012). Alternatively, some long runout landslides could instead form via acoustic fluidization, which does not require the presence of liquids in the material (Melosh, 1979;Collins and Melosh, 2003;Johnson et al., 2016;Johnson and Campbell, 2017). ...
We identified a large-scale lobate feature that is proximal to a double ridge on Ariel. We analyzed the morphology of this feature to investigate whether it was formed by cryovolcanism or mass wasting. Our results show that the head of the lobate feature is adjacent to a topographically elevated dome on the double ridge, which may have formed via extrusion and emplacement of cryolava in this location. We find that the coefficient of friction of the material that formed the lobate feature is more consistent with a cryovolcanic flow than either a dry or liquid-aided mass wasting flow. Similarly, the estimated yield strength for the neck and terminus of this feature is similar to geologic features that contained some liquid during formation. Alternatively, upwelling of material, in an ascending diapir, could also explain the morphology of this lobate feature, in particular its topographically elevated terminus, which is higher standing than its neck. Higher resolution images are needed to assess the surface texture of the lobate feature to further investigate whether it formed via flowing cryolava or diapirism. Furthermore, without higher spatial resolution images, the possibility of a mass wasting origin for the lobate feature cannot be ruled out and warrants further investigation. The possible presence of cryovolcanic features on Ariel supports the interpretation that this moon is a candidate ocean world that has, or had, a subsurface liquid water layer beneath its icy exterior.
... McEwen (1989) argued in favour of dry rock avalanches instead, and Lucchitta et al. (1992) suggested that they may have initiated as dry flows that incorporated water and ended up as mud flows. More generally, as for terrestrial landslides, several hypotheses have been proposed to explain the high mobility of Martian landslide such as fluidisation by liquid or gas in Valles Marineris (Harrison and Grimm 2003;Johnson and Campbell 2017), lubricating due to the presence of clays (Watkins et al. 2015) or ice (Lucchitta 1979(Lucchitta , 1981De Blasio 2011;Mazzanti et al. 2016;De Blasio and Crosta 2017;Crosta et al. 2018), the impact of seismic triggering with activation or reactivation of summital faults (Mège and Bourgeois 2011). Johnson and Campbell (2017) suggest on the contrary that Martian landslides may be less mobile than landslides on Earth, while Lucas et al. (2014) found no clear difference between empirical friction weakening with volume (or velocity) for terrestrial and Martian landslides. ...
Understanding what controls the travelling distance of large landslides has been the topic of considerable debate. By combining observation and experimental data with depth-averaged continuum modelling of landslides and generated seismic waves, it was empirically observed that lower effective friction had to be taken into account in the models to reproduce the dynamics and runout distance of larger volume landslides. Moreover, such simulation and observation results are compatible with a friction weakening with velocity as observed in earthquake mechanics. We investigate here as to whether similar empirical reduced friction should be put into discrete element models (DEM) to reproduce observed runout of large landslides on Earth and on Mars. First we show that, in the investigated parameter range and for a given volume, the runout distance simulated by 3D DEM is not much affected by the number (i.e. size) of grains once this number attains ~ 8000. We then calibrate the model on laboratory experiments and simulate other experiments of granular flows on inclined planes, making it possible for the first time to reproduce the observed effect of initial volume and aspect ratio on runout distances. In particular, the normalised runout distance starts to depend on the volume involved only above a critical slope angle > 16–19°, as observed experimentally. Finally, based on field data (volume, topography, deposit), we simulate a series of landslides on simplified inclined topography. The empirical friction coefficient, calibrated to reproduce the observed runout for each landslide, is shown to decrease with increasing landslide volume (or velocity), going down to values as low as 0.1–0.2. No distinguishable difference is observed between the behaviour of terrestrial and Martian landslides.
... The following mechanisms have been offered for explaining long-runout MTDs on extraterrestrial environments: 1. Self-lubrication by released groundwater, wet debris, or mud (Lucchitta, 1979(Lucchitta, , 1987. 2. Aqueous pore-pressure support (Harrison and Grimm, 2003 (Singer et al., 2012a,b). 7. Seismic energy released during meteorite impacts . ...
... Lucas et al., 2011;Schultz, 2002;Bigot-Cormier and Montgomery, 2007;Neuffer and Schultz, 2006;Crosta et al., 2013]. These analyses help at constraining the mechanical properties of the rock, the presence of water, ice, clay and evaporites [e.g., Harrison and Grimm, 2003;Shaller, 1991;De Blasio, 2011;Crosta et al., 2013]. It appears that impact cratering processes have been important in determining many of the landslides not only by seismic shaking of the ground [Crosta et al., 2013], but also as a predisposing factor through the process of impact gardening [Frattini et al., 2014]. ...
Landslides have been observed in different terrestrial environments and also on planets, satellites, and asteroids. Long runout landslides are strongly dependent on the initial mass position, material and slope path properties, topographic relief, and presence of volatiles. Therefore, landslides represent a means for the description of rock properties and environment of deposition prevailing at the time of occurrence, and may assist understanding the geological and climatological history of the planetary surfaces. Concerning Mars, previous studies have concentrated on Valles Marineris, where among the largest and longest landslides have been observed. Using different imagery, we present and analyse an original database of 3,118 Martian landslides of deposit area greater than 0.1 km2 throughout the planet between 60°n and 60°S, resulting in a dataset far richer than previously done. After a distinction is made between different typologies of landslides, their position and the statistical distribution of their geometrical properties are examined. Large landslides cluster along the Noctis Labyrinthus – Valles Marineris – Margaritifer Terra system. Rock avalanches within craters are widespread, but no significant large landslides have been found at latitudes higher than 40°S and 46°N. The magnitude-frequency distribution follows a power-law with scaling exponent ranging between 1.02 and 1.57, for the entire dataset, and varies according to the geomorphological settings, the landslide typology, and mobility. A volume-area power law relationship (exponent: 1.12-1.24) is proposed, based on the reconstruction of 222 landslide geometries, and compared to those for similar terrestrial landslides (1.39). Similarities with respect to terrestrial landslide, distribution with respect to impact craters and impact energy, and cryosphere extent are also discussed.
... F: example of MOLA points for the sector number 10. G: Example of a section showing in detail the essential geometrical quantities. These are the additional pristine radius of Olympus Mons (overhang length L OV ), the corresponding overhang height H OV , the runout and fall height R , H , the change of the centre of mass coordinates of the collapsed sector, R CM , H CM , the sliding level, and the pre-aureole slope angle α. Harrison and Grimm (2003) , who found little correspondence between simulated and observed deposit. The presence in the N aureole deposit of blocks with tilted lava flows originally concordant with the free surface of the volcano confirms the scenario of a catastrophic landslide and the provenance from the edifice of Olympus Mons . ...
The tallest volcano in the solar system, Olympus Mons on Mars, is bordered by at least ten enormous sub-circular hummocky deposits forming a welded halo, termed the aureole. The aureole units (or simply aureoles), which are the deposits of landslides from Olympus Mons, have dramatically transformed the pristine size and shape of the volcanic edifice. Topographic data are used to determine the amount of collapsed material, and so reconstruct the original outline of Olympus Mons before the landslides took place, under the assumption that the edifice did not start failing until it had reached this maximum size. Due to post-aureole deposition on the eastern and southern flanks and to the uncertainty of the slippage level on the northern side, the reconstruction is sufficiently precise along the western and north-western Olympus Mons flank, it is more uncertain for the northern flank, while it is not feasible around the rest of the volcano.
It appears that the radius along the western and north-western Olympus Mons before the collapse of the aureole landslides was approximately 200 km longer or more. The results show that the volume of the aureoles, even if enormous, is insufficient to fill the ideal conical edifice which would be obtained prolonging the Olympus Mons flanks with present slope angles. Thus, an overhang remains in the pre-aureole reconstructed Olympus Mons, which would also explain the onset of instability that led to the aureole collapse.
Further, a drape deposit blanketing the southern Acheron Fossae ridge just at the front of the western (W) aureole landslide deposit and a fan-channel system carved on the same W aureole are investigated, and it is suggested that these morphologies have been emplaced in subaqueous setting. While the drape may indicate a landslide-thrust water splash akin to a tsunami deposit caused by the fast travelling W aureole landslide, the fan-channel system is similar to certain morphologies in the terrestrial oceans. A numerical model of the collapse of the western aureole unit in water shows final runouts on both Acheron ridge and Amazonis Planitia compatible with observations provided that the friction angle is extremely small, of the order of a tenth of degree. Simulations indicate that the W aureole could have reached Acheron Fossae ridge with velocities in excess of 100 m/s, which would explain the several tens of km long distance reached by the landslide-thrust tsunami deposit. In short, morphological and numerical lines of evidence would indicate a subaqueous origin for the largest, W aureole landslide.
... Long-runout landslides on the Earth and Mars appear to be relatively dry and are distinguished from saturated terrestrial debris flows (Legros, 2002;McEwen, 1989;Soukhovitskaya & Manga, 2006). Other authors, however, argue that water or ice plays an important role in the reduction of friction of these landslides (De Blasio, 2011;Harrison & Grimm, 2003;Iverson, 2016;Lucchitta, 1987;Quantin et al., 2004;Watkins et al., 2015). ...
Long runout landslides are landslides with volumes of 105 m3 or more, which move much farther from their source than expected. The observation that martian landslides are generally less mobile than terrestrial landslides offers important evidence regarding the mechanism responsible for the high mobility of long runout landslides. Here we simulate landslides as granular flow using a soft-particle discrete element model. We show that, while surface gravity plays a negligible role, observed differences in fall height naturally reproduce the observed differences in mobility of martian and terrestrial landslides. We also demonstrate that landslides on Iapetus may fit this trend. Our simulations do not include any fluid and indicate a mechanism similar to acoustic fluidization can explain the high mobility of long runout landslides. This implies that long runout landslides on Mars should not be considered as evidence for ice, saturated clays, or liquid water.
... Researchers have concentrated on a general description of the landslides [1][2][3][4][5][6][7], gathering statistical data [3,4,7,8], on the landslide dynamics in relation to the geometry, rheology and flow environment [9][10][11][12][13][14], and stability of the headwalls against catastrophic failure [15][16][17]. A recent database [8] of more than 3000 landslides on Mars demonstrates the pervasive role of mass wasting during the evolution of Mars. ...
Landslides on Mars exhibit features such as steep collapse, extreme deposit thinning, and long runout. We study the flow dynamics of Martian landslides particularly in Valles Marineris, where landslides are among the largest and longest. Firstly, we observe that landslides in Valles Marineris share a series of features with terrestrial landslides fallen onto glaciers. The presence of suspected glacial and periglacial morphologies from the same areas of Valles Marineris, and the results of remote sensing measurements suggest the presence of ice under the soil and into the rock slopes. Thus, we explore with numerical simulation the possibility that such landslides have been lubricated by ice. To establish a plausible rheological model for these landslides, we introduce two possible scenarios. One scenario assumes ice only at the base of the landslide, the other inside the rock-soil. A numerical model is extended here to include ice in these two settings, and the effect of lateral widening of the landslide. Only if the presence of ice is included in the calculations, do results reproduce reasonably well both the vertical collapse of landslide material in the scarp area, and the extreme thinning and runout in the distal area, which are evident characteristics of large landslides in Valles Marineris. The calculated velocity of landslides (often well in excess of 100 m/s and up to 200 m/s at peak) compares well with velocity estimates based on the run-up of the landslides on mounds. We conclude that ice may have been an important medium of lubrication of landslides on Mars, even in equatorial areas like Valles Marineris. © 2017, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
... The forces that triggered the landslides have also generated large discussion. The discovery of ice in the Martian subsurface (Boynton et al. 2002;Möhlmann 2004) has prompted many authors to propose ice melt as the main landslide trigger (Mangold et al. 2000;Harrison and Grimm 2003;Wang et al. 2005;De Blasio 2012). In contrast, other authors suggest slope failure under dry static conditions (yielding transverse ridge morphologies and hummocky structures) as sufficient to mobilize materials without the need for elevated surface or subsurface water. ...
The Valles Marineris canyon system in Mars shows large landslides across its walls, which can be 40 km wide and up to 60 km long, with fall scarps height as high as 7 km. These landslides were produced through a large mass movement at high speed by gravity across the trough floor. Although the triggering factors are unclear, several mechanisms have been proposed as, among others, large amounts of subsurface water, quake produced through normal faulting close to the canyon walls, and meteoritic impacts. In this work we examine the limit equilibrium slope stability of three landslides (placed respectively at Ius, Candor, and Melas Chasmata), which can be considered representative, with the aims of constraining their formation conditions. Our results suggest that external factors (as high pore fluid pressure, seismic loading or rock mass disturbance) do not seem necessary for the failure of slopes if they are composed of unconsolidated materials, while high pore water pressure or ground acceleration are needed to trigger slides in slopes composed of strong basaltic-like materials. Moreover, the presence of sub-surface ice would contribute to slope stability. As a whole, our findings point to ground shaking due to meteorite impacts as the main triggering force for most landslides in the Valles Marineris.
... Comparison of landslide characteristics, e.g., the mass movement type and size (area, volume) on various planetary bodies would help to understand the effect of physical and environmental conditions on landslide initiation and propagation. Numerical and analytical investigations that provided insights on the landslide dynamics have been done on Mars by many authors (e.g., Harrison and Grimm, 2003; Lucas and Mangeney, 2007; De Blasio, 2011; Lucas et al., 2011; Watkins et al. 2015). Bigot-Cormier and Montgomery (2007) explored the stability of rock walls in Valles Marineris, Mars, and attributed the higher elevation of martian reliefs to the reduced gravity acceleration (3.7 m/s by atmospheric or crustal volatiles (Xiao et al., 2013; Xiao and Komatsu, 2013). ...
... Comparison of landslide characteristics, e.g., the mass movement type and size (area, volume) on various planetary bodies would help to understand the effect of physical and environmental conditions on landslide initiation and propagation. Numerical and analytical investigations that provided insights on the landslide dynamics have been done on Mars by many authors (e.g., Harrison and Grimm, 2003;Lucas and Mangeney, 2007;De Blasio, 2011;Lucas et al., 2011;Watkins et al. 2015). Bigot-Cormier and Montgomery (2007) explored the stability of rock walls in Valles Marineris, Mars, and attributed the higher elevation of martian reliefs to the reduced gravity acceleration (3.7 m/s 2 ). ...
Impact craters are the most common surface features on the Moon and Mercury. On these two bodies, we recognized and mapped large landslides on the walls of impact craters. Through visual inspection of high-resolution imagery, we compiled an inventory of 60 landslides on the Moon and a second inventory of 58 landslides on Mercury. Adopting categories used to catalog terrestrial mass movements, we classified the landslides on the Moon and Mercury as rock slides. We determined the probability density distribution of their planimetric area, and we compared the distributions with similar distributions for terrestrial and martian landslides using data from the literature. We found that rock slides mapped in impact craters on the Moon are, on average, larger than analogous rock slides on Mercury. The relationship between the area of the individual rock slides and the area of the hosting crater suggests that rock slides on Mercury initiate in smaller craters. We hypothesize that the above findings are an effect of the weaker surface gravity of the Moon compared to that of Mercury and/or an effect of the rock material properties.
... George Allen & Unwin, London Bridge JS (2003) Each process tends to create landforms with a distinctive morphology and internal material structure. This allows inferences on the probable origin of extraterrestrial flow-like deposits through morphological comparisons with apparently similar terrestrial events (e.g., Harrison and Grimm 2002;Collins and Melosh 2003). ...
DefinitionA relatively flat, largely horizontally-bedded alluvial landform adjacent to a river channel, separated from the channel by banks which may be levéed, normally underlain by unconsolidated sediment. Terrestrial active floodplains of perennial rivers are subjected to regular flooding, usually annually (Ritter et al. 2002). Floodplains develop in many alluvial valleys, on alluvial fans and deltas. The lowland where floodplains occur is called a floodbasin (Bridge and Demicco 2012, p. 430).SynonymsAlluvial plain; Braid plain; Coastal plain; Delta plain; Flooding surface; Plain (bordering a river); Tidal plainDescriptionThe surface of a floodplain is classically flat or slightly convex if channels are accompanied by levées. However at the outer margins, towards bounding hills, colluvium may elevate the level slightly. The floodplain surface can also include linear and sinuous hollows that indicate former river course (abandoned channels, palaeomeanders; oxbow lakes) as well as sma ...
... Although submarine MTD show much longer runout distances than those of subaerial MTD on Earth, the longest runout distance of 2500 km has been documented for an extraterrestrial MTD on Mars (Montgomery et al., 2009, their Figure 9). The following mechanisms have been offered for explaining long-runout MTD on extraterrestrial environments: 1) Self-lubrication by released groundwater, wet debris, or mud (Lucchitta, 1979(Lucchitta, , 1987 2) Aqueous pore-pressure support (Harrison and Grimm, 2003) 3) Continental-scale salt tectonics coupled with overpressured fluids (Montgomery et al., 2009) 4) Movement on ice (De Blasio, 2011) 5) Movement on evaporitic salt (De Blasio, 2011) 6) Friction reduction during flash heating (Singer et al., 2012) 7) Seismic energy released during meteorite impacts (Akers et al., 2012). Similar explanations were offered previously for landslides on the Moon (Guest, 1971;Howard, 1973). ...
The synonymous use of the general term “landslide”, with a built-in reference to a sliding motion, for all varieties of mass-transport deposits (MTD), which include slides, slumps, debrites, topples, creeps, debris avalanches etc. in subaerial, sublacustrine, submarine, and extraterrestrial environments has created a multitude of conceptual and nomenclatural problems. In addition, concepts of triggers and long-runout mechanisms of mass movements are loosely applied without rigor. These problems have enormous implications for studies in process sedimentology, sequence stratigraphy, palaeogeography, petroleum geology, and engineering geology. Therefore, the objective of this critical review is to identify key problems and to provide conceptual clarity and possible solutions. Specific issues are the following: (1) According to “limit equilibrium analyses” in soil mechanics, sediment failure with a sliding motion is initiated over a shear surface when the factor of safety for slope stability (F) is less than 1. However, the term landslide is not meaningful for debris flows with a flowing motion. (2) Sliding motion can be measured in oriented core and outcrop, but such measurement is not practical on seismic profiles or radar images. (3) Although 79 MTD types exist in the geological and engineering literature, only slides, slumps, and debrites are viable depositional facies for interpreting ancient stratigraphic records. (4) The use of the term landslide for highvelocity debris avalanches is inappropriate because velocities of mass-transport processes cannot be determined in the rock record. (5) Of the 21 potential triggering mechanisms of sediment failures, frequent short-term events that last for only a few minutes to several hours or days (e.g., earthquakes, meteorite impacts, tsunamis, tropical cyclones, etc.) are more relevant in controlling deposition of deep-water sands than sporadic long-term events that last for thousands to millions of years (e.g., sea-level lowstands). (6) The comparison of H/L (fall height/runout distance) ratios of MTD in subaerial environments with H/L ratios of MTD in submarine and extraterrestrial environments is incongruous because of differences in data sources (e.g., outcrop vs. seismic or radar images). (7) Slides represent the pre-transport disposition of strata and their reservoir quality (i.e., porosity and permeability) of the provenance region, whereas debrites reflect post-transport depositional texture and reservoir quality. However, both sandy slides and sandy debrites could generate blocky wireline (gamma-ray) log motifs. Therefore, reservoir characterization of deep-water strata must be based on direct examination of the rocks and related process-specific facies interpretations, not on wireline logs or on seismic profiles and related process-vague facies interpretations. A solution to these problems is to apply the term “landslide” solely to cases in which a sliding motion can be empirically determined. Otherwise, a general term MTD is appropriate. This decree is not just a quibble over semantics; it is a matter of portraying the physics of mass movements accurately. A precise interpretation of a depositional facies (e.g., sandy slide vs. sandy debrite) is vital not only for maintaining conceptual clarity but also for characterizing petroleum reservoirs.
... In order to analyze the possible dependence of the average landslide thickness from the gravity, I assume that Martian slope failures are a Bingham fluid (Harrison e Grimm, 2003). A Bingham fluid is a viscoplastic material that behaves as a rigid body at low stresses but flows as a viscous fluid at high stress. ...
... are necessary to explain other cases, such as the very long runout slides observed on Mars (e.g. Lucas and Mangeney, 2007;Harrison and Grimm, 2003). ...
As a complement to experimental and theoretical approaches, numerical
modeling has become an important component to study asteroid collisions and
impact processes. In the last decade, there have been significant advances in
both computational resources and numerical methods. We discuss the present
state-of-the-art numerical methods and material models used in "shock physics
codes" to simulate impacts and collisions and give some examples of those
codes. Finally, recent modeling studies are presented, focussing on the effects
of various material properties and target structures on the outcome of a
collision.
Research into the geological processes operating on Mars relies on interpretation of images and other data returned by unmanned orbiters, probes and landers. Such interpretations are based on our knowledge of processes occurring on Earth Terrestrial analog studies therefore play an important role in understanding the geological features observed on Mars. This 2007 book presents direct comparisons between locales on Earth and Mars, and contains contributions from leading planetary geologists to demonstrate the parallels and differences between these two neighboring planets. Mars is characterized by a wide range of geological phenomena that also occur on Earth, including tectonic, volcanic, impact cratering, eolian, fluvial, glacial and possibly lacustrine and marine processes. The book provides terrestrial analogs for data sets from Mars Global Surveyor, Mars Odyssey, Mars Exploration Rovers and Mars Express, and will therefore be a key reference for students and researchers of planetary science.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
Our knowledge of Mars has changed dramatically in the past 40 years due to the wealth of information provided by Earth-based and orbiting telescopes, and spacecraft investigations. Recent observations suggest that water has played a major role in the climatic and geologic history of the planet. This textbook covers our understanding of the planet's formation, geology, atmosphere, interior, surface properties, and potential for life. This interdisciplinary textbook encompasses the fields of geology, chemistry, atmospheric sciences, geophysics, and astronomy. Each chapter introduces the necessary background information to help the non-specialist understand the topics explored. It includes results from missions through 2006, including the latest insights from Mars Express and the Mars Exploration Rovers. Containing the most up-to-date information on Mars, this textbook is essential reading for graduate courses, and an important reference for researchers.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
Research into the geological processes operating on Mars relies on interpretation of images and other data returned by unmanned orbiters, probes and landers. Such interpretations are based on our knowledge of processes occurring on Earth Terrestrial analog studies therefore play an important role in understanding the geological features observed on Mars. This 2007 book presents direct comparisons between locales on Earth and Mars, and contains contributions from leading planetary geologists to demonstrate the parallels and differences between these two neighboring planets. Mars is characterized by a wide range of geological phenomena that also occur on Earth, including tectonic, volcanic, impact cratering, eolian, fluvial, glacial and possibly lacustrine and marine processes. The book provides terrestrial analogs for data sets from Mars Global Surveyor, Mars Odyssey, Mars Exploration Rovers and Mars Express, and will therefore be a key reference for students and researchers of planetary science.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
With the advent of the space age, planetary geomorphology has become a stand-alone discipline. This contribution provides a summary of the different processes that have been identified to form landscapes and landforms on planetary bodies in our Solar System, including rocky planets, icy planets and moons, dwarf planets, comets and asteroids. I highlight the insights these landforms have provided into the workings of these bodies and how what has been learnt in space has often taught us new lessons about the Earth. Finally, I conclude that despite the limitations imposed by remote sensing, planetary geomorphology has a bright future in planning future missions to explore our Solar System as well as understanding the data that will be returned.
The exploration of the solar system has shown that mass movement is a common process on the surface of the terrestrial planets (Mercury, Venus, Mars) and on many moons, including our own. However, it is on Mars that mass movements represent a major geomorphologic force both in terms of frequency, volume (often greater than 10 km³, with a record volume of 10⁶ km³), and runout, normally longer than several tens of kilometers. The study of landslides and more in general of mass movements on Mars has important implications for assessing the rock and solid properties and is a tool for understanding the geologic and climatic history of the planet. In contrast to our planet, where a landslide deposit is erased or covered after few thousands of years, mass movements on Mars are still perfectly preserved after times that may be greater than 1 billion years, making of such impulsive events a key for understanding the conditions of the planetary surfaces deep in time. In particular, landslides and their associated primary and secondary deposits may shed light on the possible presence of water or ice on the planet at the instant of flow, which is of great astrobiological importance.
Firstly, we describe the different types of landslides on Mars. Many types are similar to those on Earth, albeit often at a larger scales. We document the characteristics of slumps and rock avalanches, most of which occur in Valles Marineris, a 4000 km-long system of 6–8 km deep gorges. Landslides in Valles Marineris exhibit a variety of morphologies on their surfaces, such as Toreva blocks, longitudinal grooves, pressure ridges, run-ups on pre-existing mounds indicating high speed of emplacement. Other forms of mass movements are dubious of at least not as common as they are on Earth. Rockfalls have been documented in some cases, but their smaller size can be spotted only with high-resolution cameras. The presence of slow-expanding lateral spreads may indicate deep clay layers. Some landforms may be interpreted as debris flows and may thus be related to water. Narrow and thin slope lineae may be replenished from under a rock cap, an occurrence that, if genuine, has astrobiological implications. Mixed ejecta-landslides are a peculiar class of movements unknown on Earth. Outside Valles Marineris, mass movements occur especially but not exclusively at the craters rims or inside outflows channels. The largest landslides on Mars and of the whole solar system, the aureoles, can be identified at the borders of the Olympus Mons volcano, with runouts up to 700 kilometers. The analysis of many events demonstrates that similar to Earth, the ratio between the fall height and the runout, which is a proxy for the friction coefficient, diminishes with the mass movement volume. This may be related to environmental constraints.
Recent acquisition of high‐resolution satellite imagery of the Martian surface has permitted landslides to be studied on a global scale on Mars for the first time. We apply the Scoops3D software package to compute slope stability for select regions of the Martian surface, combining calculations of slope stability with number of observed landslides (Crosta, Frattini, et al., 2018; Crosta, De Blasio, et al., 2018), as reported in a recently published inventory of Martian landslides, to understand controls on the global distribution of landslides on Mars. We find that the distribution of landslides does not simply follow the distribution of unstable slopes. In particular, there is an abundance of landslides around Tharsis, and especially in Valles Marineris and Noctis Labyrinthus, which is not explained by an abundance of unstable topography alone. We analyzed for but did not find a clear large‐scale lithologic or stratigraphic control on landslide occurrence from subsurface heterogeneities. Other possibilities to explain the increased occurrence of landslides in Tharsis include (1) thin weak unit(s) that is regionally widespread and at multiple stratigraphic levels, such as from interbedded ashes; (2) seismic activity related to the Tharsis's geological activity, and (3) possible groundwater near Valles Marineris into the Amazonian. Given the apparently young ages of many landslide deposits in Valles Marineris (Quantin et al., 2004), continued modern day analysis of lithologies in Valles Marineris and observations of Martian seismicity may act to strengthen or rebut the first two hypotheses.
Evidence suggests that the lobate flow feature that extends ~72 km outward from the western rim of Tsiolkovskiy crater is a long runout landslide. This landslide exhibits three (possibly four) morphologically different parts, likely caused by local conditions. All of these, plus the ejecta of Tsiolkovskiy crater, and its mare fill are approximately of the same crater model age, i.e., ~3.55 ± 0.1 Ga. The enormous size of this landslide is unique on the Moon and is a result of a combination of several geometric factors (e.g., its location relative to Fermi crater), and that Tsiolkovskiy crater was an oblique impact that produced an ejecta forbidden zone on its western side (Schultz, 1976). The landslide formed in this ejecta free zone as the rim of Tsiolkovskiy collapsed and its debris flowed across the relatively smooth, flat floor of Fermi crater. In this location, it could be easily identified as a landslide and not ejecta. Its mobility and coefficient of friction are similar to landslides in Valles Marineris on Mars, but less than wet or even dry terrestrial natural flows. This suggests that the Mars landslides may have been emplaced dry. The high density of small craters on the landslide is likely an illusion caused by the effects of age related differences in regolith thickness on crater morphology, and the presence of the abundant young, circular secondary craters produce by debris ejected from distant fresh craters.
The Tharsis region of Mars is a vast volcanic plateau which hosts the immense Tharsis Montes shield volcanoes. The Tharsis region is suggested by multiple lines of morphologic and modeling evidence to have been a site of coincident volcanic and glacial activity throughout the majority of the geologic history of Mars. The prolonged and overlapping histories of volcanism and glaciation within the Tharsis region raise the likelihood of widespread surficial glaciovolcanism, a possibility which is supported by the recognition of glaciovolcanic landforms in the region by past investigations. Given this likelihood, we perform an exploratory study to assess the potential role that surficial glaciovolcanism may have played in the geologic and hydrologic history of the Tharsis region. We first review the history and characteristics of volcanism and glaciation in the Tharsis region, as well as previously documented evidence for past glaciovolcanic activity, in order to outline relevant conditions and parameters. The outlined volcanic and glacial conditions are then used in conjunction with results and predictions from past modeling of surficial glaciovolcanic processes to assess the potential role of glaciovolcanism in the formation of the Tharsis region's major tectonic and hydrologic features. We conclude that surficial glaciovolcanism may plausibly have contributed to the formation of many of the tectonic and fluvial features in the Tharsis region, offering advantages over prior formation models, particularly for the large basin/chaos-sourced outflow channels concentrated in the area. The formation of a range of investigated features in the Tharsis region by surficial glaciovolcanism does not require ambient warm and wet climate conditions therefore suggesting potential consistency between the observed features and a predominantly cold and icy climate. Consequently, this analysis represents an incremental contribution to better understanding the climatic and hydrologic evolution of Mars. However, analyses performed in this work indicate that the glaciovolcanic origin models we considered are unable to viably account for the complete range of explored features, indicating that future work is required to better resolve the processes involved in their formation.
Several disasters have been caused by landslides and rock avalanches falling onto natural or artificial water basins. The most studied case occurred in northern Italy on October 9th, 1963, when a volume of \( 270 \times {10^6}\;{{\hbox{m}}^3} \) of limestone collapsed into the artificially dammed Vaiont lake. The dam survived the impact, but water overtopped the dam by about 200 m; the ensuing water wave took 2,000 lives. Many investigations have been devoted to the Vaiont failure, mostly related to the hydraulic and mechanical history prior to the landslide. Probably the disaster could have been avoided if the danger of landslides falling at high speed in water reservoirs and their capability of displacing the water had been recognized.
In this paper, the research on mechanism of conversion of landslides to debris flow is summed up. The progress up to date in this research area is stressed. The direction for farther research is expounded. The subject of conversion of debris flow from landslides lies on the crossing of landslides dynamics and debris flow kinematics. It is on the fringe and also the foreland of the study. The conversion of landslide to debris flow is a fluidization process related to soil liquefaction; it is the result of violent interaction of soil and water. The key of the mechanism is the production and maintenance of excess pore fluid pressure. Iverson's work on this subject promotes the theory of landslide fluidization. His Coulomb mixture theory is a breakthrough to traditional debris flow kinematical model based on rheology. The influence of clay granule to the process needs farther research. The mechanism of landslide translating to debris flow in ravine is more complex and is the central task for the future.
Impact craters with ejecta flows and/or central pits have been found on Venus, the Moon, Earth, Mars, and some icy satellites. Using the MESSENGER camera data obtained during the orbital mission, we found craters with ejecta flows and central pits on Mercury. The ejecta flows differ from normal ballistically emplaced ejecta deposits in their long mobilized distances. They all flowed in downslope directions and exhibited a layered morphology. Analog study suggests that the ejecta flows probably have formed by fluidization in the ejecta deposits. Crustal volatiles are not required to form the ejecta flows on Mercury, although they may have helped. The ejecta flows are most likely to be a type of avalanche features in forms of dry granular flows. Central pits in impact craters on Mercury are located on summits of central peaks when viewing in sufficiently high-resolution images, but some of the central pits may occur on crater floors. The central pit craters are all fresh craters located on smooth plains and intercrater plains. The pits are different from the other forms of rimless and irregularly-shaped depressions on Mercury in the size, morphology, and/or occurrence. Crustal volatiles are not required in forming the central pit craters and they may form in a similar way with the central pit craters on the Moon.
DefinitionRugged complex deposit shaped as a gigantic halo surrounding Olympus Mons on Mars. The term has also been used in plural (aureoles) to put emphasis on its composite nature and when distinction between the different sub-units is necessary.SynonymsAureole lobes; Aureoles; Circum-Olympus aureole deposits; Lycus Sulci (part of topographic unit)Description and MorphometryUp to 700 km wide rough-textured halo-shaped deposits surrounding Olympus Mons, Mars, displayed as a series of ~4–11 sub-circular lobes (Figs. 1 and 2). Single lobe-shaped units exhibit up to 1 km high transverse ridges. The maximum distance from the edifice of the Olympus Mons, about 700 km, is reached in correspondence of the NW unit. Single aureole lobes are some hundred meters thick; the maximum thickness (~2,200 m) is recorded along the SE-NW direction as a result of the superposition of more lobes. The total area estimated by Morris and Tanaka (1994) is 8.36 × 105 km2, or nearly one tenth the extension of Eu ...
DefinitionFlow refers to any phenomenon in which gravity drives rapid downslope motion of solid grains, mixed with less dense intergranular fluid (liquid or gas) in a finite, contiguous grain-fluid body that deforms irreversibly as it moves downslope. (Iverson and Vallance 2001)SubtypesFlow phenomena are classified typically according to both types of movement and material properties (Pierson and Costa 1987; Hutchinson 1988; Cruden and Varnes 1996; Hungr et al. 2001). Each process tends to create landforms with a distinctive morphology and internal material structure. This allows inferences on the probable origin of extraterrestrial flow-like deposits through morphological comparisons with apparently similar terrestrial events (e.g., Harrison and Grimm 2002; Collins and Melosh 2003).Granular Mass FlowsRapidly moving flow events involving relatively coarse-grained, non-cohesive materials, whether saturated or unsaturated, are referred to collectively as granular mass flows (Iverson and ...
We thank Shaller (2016) for his Comment on our recent paper
(Watkins et al., 2015), in which we used high-resolution image and
spectral data to constrain long-distance landslide transport mechanisms in
Valles Marineris, Mars. We proposed a clay lubrication transport model
involving the entrainment of clay-bearing trough-floor materials based on
three main lines of support: the discovery of hydrated silicates in the
outer zone of Ius Labes, correlated morphostructural observations
consistent with the presence of these hydrated silicates in the basal
sliding zone of the landslide, and the well documented friction-reducing
mechanical properties of clay minerals.
Laboratory measurements of rock strength provide limiting values of lithospheric stress, provided that one effective principal stress is known. Fracture strengths are too variable to be useful; however, rocks at shallow depth are probably fractured so that frictional strength may apply. A single linear friction law, termed Byerlee's law, holds for all materials except clays, to pressures of more than 1 GPa, to temperatures of 500°C, and over a wide range of strain rates. Byerlee's law, converted to maximum or minimum stress, is a good upper or lower bound to observed in situ stresses to 5 km, for pore pressure hydrostatic or subhydrostatic. Byerlee's law combined with the quartz or olivine flow law provides a maximum stress profile to about 25 or 50 km, respectively. For temperature gradient of 15°K/km, stress will be close to zero at the surface and at 25 km (quartz) or 50 km (olivine) and reach a maximum of 600 MPa (quartz) or 1100 MPa (olivine) for hydrostatic pore pressure. Some new permeabiltiy studies of crystalline rocks suggest that pore pressure will be low in the absence of a thick argillaceous cover.
This paper reports experiments on the flow of bentonite suspensions used as drilling fluid. Thixotropic effects of such fluids depend on structure evolution (rupturing and restoring processes of aggregates). Structure build-up and break down (at rest or under shear) are studied from both rheological and mechanical (flow in a circulating loop), points of view. Different kinetics exist depending on the bentonite kind. Pressure measurements and pulsed ultrasound velocimetry technique are used to get information about the evolution of structure levels with time. An attempt is made to develop a simple structural constitutive model describing all observed phenomena. Experimental flow results are compared with predictions using Rabinowitch equation ; good agreement was obtained.
This paper describes the use of a discrete particle computer simulation to test whether the apparent low friction exhibited by long runout landslides could be explained in terms of simple granular mechanics. The flow structure consists of an active basal shear zone supporting the majority of the landslide, which travels as a relatively solid plug. The observed runout appears to depend on the total energy dissipation which is a trade-off between (1) the inelasticity of the particles, which governs the energy dissipated in each event, and, (2), the size of the dissipating shear zone, which governs the number of particles that are actively dissipating energy. Very inelastic particles quickly dissipate the work performed at boundaries and result in thin dissipative zones. As a result, these two factors balance and the runout is nearly independent of particle inelasticity. Along the same lines, increasing the boundary roughness was found to increase the size of the dissipative shear zone and markedly decrease the runout. Also, a distribution of particle sizes destroyed ordered structures within the body which, once again, increases the dissipation and decreases the runout. Unfortunately, the simulations also indicate that the runout should be independent of the depth of the flow and thus cannot account for the observed volumetric effect on runout.
Field observations, laboratory experiments, and theoretical analyses indicate that landslides mobilize to form debris flows by three processes: (a) widespread Coulomb failure within a sloping soil, rock, or sediment mass, (b) partial or complete liquefaction of the mass by high pore-fluid pressures, and (c) conver-sion of landslide translational energy to internal vibrational energy (i.e. granular temperature). These processes can operate independently, but in many circum-stances they appear to operate simultaneously and synergistically. Early work on debris-flow mobilization described a similar interplay of processes but relied on mechanical models in which debris behavior was assumed to be fixed and gov-erned by a Bingham or Bagnold rheology. In contrast, this review emphasizes models in which debris behavior evolves in response to changing pore pressures and granular temperatures. One-dimensional infinite-slope models provide in-sight by quantifying how pore pressures and granular temperatures can influence the transition from Coulomb failure to liquefaction. Analyses of multidimen-sional experiments reveal complications ignored in one-dimensional models and demonstrate that debris-flow mobilization may occur by at least two distinct modes in the field. 1 The US government has the right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper.
Hillslopes up to 11 km in height can be found along the walls of the Valles Marineris troughs. The widest and deepest troughs are grabens, in which tectonics probably exerted the primary control on the wall morphology. Geographical variations in the wall morphology and profiles show that they result from complex, persistent tectonic influences, and that significant changes in erosional processes occurred during this evolution, from late Hesperian to late Amazonian. Preliminary calculations suggest that about 85–95% of the fault-controlled wall relief probably formed in an “ancient” stage prior to this transitional period. A study of the volatile content of the wall rocks, based upon the morphology and distribution of impact craters on the surrounding plateaus, shows that extreme erosional widening of the Central Valles Marineris troughs occurred during the “ancient” stage of high ground ice content. During the subsequent “recent” stage of tectonic and morphological evolution, the wall materials were partly desiccated.
Fundamentals of Rock Mechanics, 4th edition.
Table of Contents.
1. Rock as a Material.
2. Analysis of Stress and Strain.
3. Friction on Rock Surfaces.
4. Deformation and Failure of Rock.
5. Linear Elasticity.
6. Laboratory Testing of Rocks.
7. Poroelasticity and Thermoelasticity.
8. Stresses around Cavities and Excavations.
9. Inelastic Behavior.
10. Micromechanical Models.
11. Wave Propagation in Rocks.
12. Hydromechanical Behavior of Fractures.
13. State of Stress Underground.
14. Geological Applications.
References.
Index.
Runout analyses are used for risk assessment and design of remedial measures against rapid landslides such as debris flows, debris avalanches, rockslide avalanches, large-scale liquefaction failures, and slides of fill and mining waste. A continuum model has been developed to simulate the characteristics of these phenomena. The model is based on a Lagrangian solution of the equations of motion and allows the selection of a variety of material rheologies, which can vary along the slide path or within the slide mass. It also allows for the internal rigidity of relatively coherent slide debris moving on a thin liquefied basal layer. The effects of lateral confinement are accounted for in a simplified manner. The model is shown to compare favourably with results of controlled laboratory experiments and other analytical tools for several different materials and problem configurations. Examples of the practical use of the model to predict the runout of coal mine waste flow slides and flows of liquefied granular tailings are presented. Key words : landslides, dynamic analysis, runout prediction, debris flows, debris avalanches, flow slides.
An analysis is carried out of the hydrologic response of a water-rich Mars to climate change and to the physical and thermal evolution of its crust, with particular attention given to the potential role of the subsurface transport, assuming that the current models of insolation-driven change describe reasonably the atmospheric leg of the planet's long-term hydrologic cycle. Among the items considered are the thermal and hydrologic properties of the crust, the potential distribution of ground ice and ground water, the stability and replenishment of equatorial ground ice, basal melting and the polar mass balance, the thermal evolution of the early cryosphere, the recharge of the valley networks and outflow, and several processes that are likely to drive the large-scale vertical and horizontal transport of H2O within the crust. The results lead to the conclusion that subsurface transport has likely played an important role in the geomorphic evolution of the Martian surface and the long-term cycling of H2O between the atmosphere, polar caps, and near-surface crust.
The martian atmosphere contains only minute amounts of water, liquid water is unstable everywhere, and ice has been detected only at the north pole, but the surface shows abundant evidence of erosion by liquid water, and ground ice has been invoked to explain many additional features. The presence of water-worn landforms of different ages has led to the speculation that Mars has undergone major changes in climate. The book summarises the issues and problems concerning the reconciliation of the observational data with evolutionary models. Following an introductory chapter there are 9 further chapters as follows: the present water cycle and stability relations; outflow channels; valley networks; ground ice; climate change; accretion and evolution of water; implications for life; future Mars exploration; and summary and conclusions.
Analysis of landslide dynamics is used for the prediction of hazard areas and for the determination of destructive potential (intensity). Some landslides change their mass by entraining or discarding material along their paths. An existing Lagrangian model has been modified to make it possible to simulate mass changes. The solution uses the concept of a constant 'yield rate' (volume added or subtracted by the moving mass per unit displacement). The model was applied to the back-analysis of a small rock avalanche in the Swiss Alps. The mass changes are shown to have a moderately strong effect on the results of the analysis in case of a frictional rheology, but a much stronger effect occurs when viscous forces are present.
Blackhawk Mountain in southern California rises above southeastern Lucerne Valley at the eastern end of the rugged 4,000-foot escarpment that separates the San Bernardino Mountains on the south from the Mojave Desert on the north. Its summit is a resistant block of marble thrust northward over easily eroded uncemented sandstone and weathered gneiss. Spread out on the alluvial apron at the foot of the mountain is the prehistoric Blackhawk landslide, a lobe of nearly monolithologic marble breccia from 30 to 100 feet thick, 2 miles wide, and 5 miles long. The Blackhawk landslide and an adjacent older landslide, the Silver Reef, have many peculiarities of form and structure in common with the historic Elm, Frank, and Sherman landslides; and in lithology, provenance, size, and "coefficient of friction" they strongly resemble many of the monolithologic breccia deposits of possible landslide origin found associated with Tertiary faults and fanglomerates in the southwestern United States and elsewhere. The older rocks of the Blackhawk area consist of gneiss, quartzite, Carboniferous marble, and Cretaceous quartz monzonite, which originally underlay a landscape of relatively low relief. Uplift of Blackhawk Mountain, first by overthrusting from the south, and then by monoclinal folding along a northwest-trending axis, led in the late Tertiary and Quaternary to deep erosion of the mountain front accompanied by the growth northward of extensive alluvial deposits interspersed with several large-scale landslides, the largest and most recent of which is the Blackhawk landslide. Both the geological evidence and, in the case of the Elm and Frank landslides, the eyewitness reports suggest that the Blackhawk landslide and its congeners started as huge rockfalls, which were launched into the air and then traversed the gently inclined, relatively smooth slopes below as nearly nondeforming sheets of breccia sliding at high speed on a relatively thin, easily sheared lubricating layer. These facts suggest the hypothesis that landslides of this type acquire such high speed in their descent that at a sudden steepening of slope they leave the ground, overriding and compressing a cushion of trapped air upon which they traverse the gentler slopes below with little friction, much as the slipper in a thrust bearing slides on a cushion of oil with no metal-to-metal contact. This air-layer lubrication readily accounts for the low friction, high speed, and nonflowing motion of these large landslides and explains many otherwise puzzling details of their form and structure, such as the striking three-dimensional jigsaw puzzle effect seen in the pervasively fractured larger blocks, the transverse corrugations, soil schlieren, and certain of the peculiar debris cones on the landslide surface, the moraine-like ridges along the sides, and the low rim, steep scarp, and transported debris at the distal end. Thus, it appears that under the right circumstances massive avalanches like the Blackhawk can slide for miles on nothing more substantial than an ephemeral layer of compressed air.
A one-dimensional BK dynamical lattice model (Burridge and Knopoff, 1967) is applied to simulate earthquakes for the study of the scaling relation between frequency and rupture length of earthquakes. Velocity-dependent friction controls the motion of mass elements. The distribution of the breaking strengths (i.e., static friction) is considered to be a fractal function. Simulation results show that the fractal dimension of the distribution of the breaking strengths is a minor factor in affecting the scaling of frequency versus rupture length. A fast velocity-weakening process from static friction to dynamic friction and a slow velocity-hardening one from dynamic friction to static friction are appropriate for interpreting the scaling of the frequency-rupture length (FL) relation. The frictional drop rather than the level of the breaking strength affects the FL scaling. Hence, the friction drop ratio (g) which determines the minimum value of the dynamic frictional force, is an important factor in influencing the FL relation. Smaller g (which a large friction drop) leads to a smaller scaling exponent value in the regime of localized events than larger g (with a smaller friction drop). The stiffiness ratio, which is defined as the ratio of the stiffness of the coil spring to that of the leaf spring of the model, is also a significant parameter affecting the FL distribution. Nevertheless, simulation results show that small s is unable to produce a power-law FL relation.
The equatorial canyon system of Mars extends approximately east-west for about 4000km, from longitude 40° to 110°. It includes the valley network of Noctis Labyrinthus in the west, the linear troughs and wide depressions of the Valles Marineris chasmata in the center, and wide troughs, transitional to out-flow channels, in the east. Individual chasmata are as much as 100km wide but coalesce to form a depression as much as 600km wide in the central part of the canyon system. Their 8 to 10km depths offer excellent three-dimensional views into the upper Martian crust. -from Authors
Large landslides in the Martian equatorial troughs have been investigated with respect to morphology, geologic structure of the troughs, time of emplacement, similarity to terrestrial landslides, and origin and mechanism of transport. The morphologic variations of the landslides can be attributed mainly to their degree of confinement on trough floors. The huge size of many landslides is due to their occurrence on fault scarps that may have attained several kilometers in height in the absence of vigorous fluvial erosion on Mars. The mechanical efficiency of the Martian landslides is high but in accord with predictions from large landslides on earth. -from Author
Very large-scale rockslide mechanisms may be different from those involved in medium- and small-scale slides, and in that case similitude relationships alone provide an invalid means of comparison. This paper considers the application of similitude to medium-scale rotational slides, to large-scale bedding plane slips, and to the question of rock mass avalanches. The possibility of “fluidization” effects are discussed in regard to the avalanche question; it is shown that some collective effect of mass must exist in avalanches, which because of its poorly understood nature, cannot yet be described by similitude laws. Similarly, with large-scale slides, vaporization of water by frictional heating may be a most important scale-dependent mechanism. Such a mechanism can exist only in large slides, because with small slides the required displacement in order to achieve vaporization would be larger than the possible displacement of the slide mass.
Field observations, laboratory experiments, and theoretical analyses indicate that landslides mobilize to form debris flows by three processes: (a) widespread Coulomb failure within a sloping soil, rock, or sediment mass, (b) partial or complete liquefaction of the mass by high pore-fluid pressures, and (c) conversion of landslide translational energy to internal vibrational energy (i.e. granular temperature). These processes can operate independently, but in many circumstances they appear to operate simultaneously and synergistically. Early work on debris-flow mobilization described a similar interplay of processes but relied on mechanical models in which debris behavior was assumed to be fixed and governed by a Bingham or Bagnold rheology. In contrast, this review emphasizes models in which debris behavior evolves in response to changing pore pressures and granular temperatures. One-dimensional infinite-slope models provide insight by quantifying how pore pressures and granular temperatures can influence the transition from Coulomb failure to liquefaction. Analyses of multidimensional experiments reveal complications ignored in one-dimensional models and demonstrate that debris-flow mobilization may occur by at least two distinct modes in the field.
Catastrophic rock falls differ from normal screes in that they tend to spread as a thin sheet over considerable areas of country, the distribution of the debris bearing little relationship to the topography of the low ground over which it is spread. Consideration of ancient and modern examples suggests that the mechanism must involve fluidization with entrapped air, which permits high speed of movement of the fall as a flood of unsorted rock fragments over irregular ground and obstacles.
Dispersions of solid spherical grains of diameter D = 0\cdot 13 cm were sheared in Newtonian fluids of varying viscosity (water and a glycerine-water-alcohol mixture) in the annular space between two concentric drums. The density sigma of the grains was balanced against the density rho of the fluid, giving a condition of no differential forces due to radial acceleration. The volume concentration C of the grains was varied between 62 and 13%. A substantial radial dispersive pressure was found to be exerted between the grains. This was measured as an increase of static pressure in the inner stationary drum which had a deformable periphery. The torque on the inner drum was also measured. The dispersive pressure P was found to be proportional to a shear stress T attributable to the presence of the grains. The linear grain concentration lambda is defined as the ratio grain diameter/mean free dispersion distance and is related to C by lambda =1/(C0/C)1/3-1, where C0 is the maximum possible static volume concentration. Both the stresses T and P, as dimensionless groups Tsigma D2/lambda eta 2 and Psigma D2/lambda eta 2, were found to bear single-valued empirical relations to a dimensionless shear strain group lambda 1/2sigma D2(dU/dy)/eta for all the values of lambda < 12 (C = 57% approx.) where dU/dy is the rate of shearing of the grains over one another, and eta the fluid viscosity. This relation gives T propto \ sigma (lambda D)2 (dU/dy)2 and T propto \ lambda 3/2eta dU/dy, according as dU/dy is large or small, i.e. according to whether grain inertia or fluid viscosity dominate. An alternative semi-empirical relation T = (1 + lambda ) (1 + 1/2lambda ) eta dU/dy was found for the viscous case, when T is the whole shear stress. The ratio T/P was constant at 0\cdot 3 approx. in the inertia region, and at 0\cdot 75 approx. in the viscous region. The results are applied to a few hitherto unexplained natural phenomena.
Large rockfalls commonly generate fast-moving streams of debris that have been called "sturzstroms." The geometry of sturzstrom deposits is similar to that of mudflows, lava flows, and glaciers. Sturzstroms can move along a flat course for unexpectedly large distances and may surge upward by the power of their momentum. A currently popular hypothesis to account for their excessive distance of transport suggests that sturzstroms slide on air cushions. Contrary to that hypothesis, evidence is herein presented to support Heim's contention that sturzstroms indeed flow. The flow of a sturzstrom can be compared to flow of a mass of concentrated cohesionless grains in a fluid medium. Frictional resistance to such grain flow is, according to Bagnold, less than that for sliding of rigid bodies because of the buoyancy of an interstitial fluid which serves to reduce the effective normal pressure of the entrained grains. The presence of sturzstrom deposits on the Moon indicates that the interstitial fluid is not necessarily a compressed gas or a wet mud. The dispersion of fine debris and pulverized rock dust among the colliding blocks may have provided an uplifting stress during the motion of some terrestrial and lunar sturzstroms. Scale models to provide kinematic simulation of sturzstroms may have practical application. Preliminary results suggest that a bentonite suspension of a certain consistency is a suitable material for scale models and that the flow of thixotropic liquids is kinematically similar to sturzstroms. The parameter "excessive travel distance" is introduced to replace the expression "equivalent coefficient of friction" as a measure of mobility of sturzstroms. There is, on the whole, a positive semilog correlation of the excessive travel distance to the size of the fallen mass. Exceptions to the rule include on the one extreme the unusual mobile Huascaran rockfall which gave rise to a sturzstrom with a dense interstitial mud and, on the other extreme, the least mobile Vaiont rockslide which remained a sliding block and failed altogether to generate a sturzstrom.
Large rockfalls and debris avalanches constitute spectacular geologic
hazards. A physical basis for the prediction of the extent of runout of
such transport events has remained elusive. We consider the simplest
case in which a mass M of debris and loose rock,
having fallen from a height H , is subjected to a
constant, overall resisting shear stress τ during runout. A
prediction for such behavior is that the area overrun by an avalanche is
proportional to (gMH /τ)2/3, where
the coefficient of proportionality is near unity and a function of the
geometry of the “footprint” of the avalanche deposit. This
scaling results in a good collapse of the data for a wide range of
terrestrial and extraterrestrial phenomena and implies a value of τ
in the range 10 100 kPa. Such shear stress values are comparable to
measures of the yield strength of unconfined, dry debris obtained by
other means. The approach developed here does not give a detailed
description of rockfall motion, but provides new insight for attempts to
delineate the mechanisms that contribute to the mobility of rockfalls
and other densely concentrated flows of geophysical interest.
A computer-based analysis of the runout dynamics of the Madison Canyon rockslide of August 17, 1959, is reported. Three levels of computer representation of the flow are considered. First is a representation of the actual canyon profile, where the model assumes incompressible linear viscous flow. Second is a horizontal profile in which gravitational forces are input by components, and again the flow is approximated by a single viscosity model. Third is a horizontal profile, for which a two viscosity model approaching a Bingham material representation is used. Results of each model are compared to actual slide runout, debris distribution, and maximum speed of the flow. The biviscous model, which depicts an active basal flow layer, also has physical characteristics consistent with measurements made of the Madison Canyon slide following the event.
New observations on details of the aureole and on its relationship to the volcano are presented. It is contended that the pyroclastic hypothesis advanced by Morris (1982) is untenable. The gravitational sliding hypothesis put forward in different forms by Lopes et al., (1980) and Harris (1977) is analyzed, and the suggestion is made that the aureole deposits may have been emplaced as large sheets by gravitational spreading from the ancestral Olympus Mons volcano. The stratigraphy and nomenclature for the aureole lobes used by Morris and Dwornik (1978) are employed. The gravitational spreading mechanism proposed involves imbricate thrusting in distal regions, analogous to terrestrial thrust sheets. It is noted that corrugations in the aureole developed by erosion along imbricate or listric faults and that basal shear stresses on the decoupling surface may have been of the order of 10 to the 6th Pa. Whereas the nature of the decoupling surfaces in the proximal regions is uncertain, it is thought likely to have been the topographic surface in distal parts.
Analysis of the ridge, graben, and fracture patterns on the aureole material surrounding Olympus Mons lends further support to an origin by gravity sliding of the outer flanks of the shield. The patterns provide evidence of the nature of sliding, especially in the last stages of emplacement. No part of the slide need have traveled the whole extent of the aureole. For the slides to occur on a shallow slope, reduction of shear strength of the materials involved is required, possibly by melting of ground ice. Triggering mechanisms could be volcanically related marsquakes and possibly stresses induced on the surrounding area by the growing Olympus Mons volcano.
Very large rock avalanches, involving more than about 10 6 m 3 of rock debris, exhibit anomalously low coefficients of friction. Consequently they travel much farther than conventional slope-stability criteria predict. Discovery of deposits of such landslides of Mars on the moon, however, appears to rule out the fundamental involvement of volatiles or atmospheric gases in the flow mechanism. It appears that large, high-frequency pressure fluctuations due to irregularities in the flow of the debris may locally relieve overburden stresses in the rock mass and allow rapid pseudoviscous flow of even dry rock debris. If the avalanche volume is large enough, the rate of production of this vibrational (acoustic) energy exceeds its loss rate, and sustained motion is possible. -from Author
Measurements of H/L (height of drop/length of
runout) vs. volume for landslides in Valles Marineris on Mars show a
trend of decreasing H/L with increasing volume.
This trend, which is linear on a log-log plot, is parallel to but lies
above the trend for terrestrial dry rock avalanches. This result and
estimates of 104 to 105 Pa yield strength suggest
that the landslides were not water saturated, as suggested by previous
workers. The offset between the H/L vs. volume
trends shows that a typical Martian avalanche must be nearly two orders
of magnitude more voluminous than a typical terrestrial avalanche in
order to achieve the same mobility. This offset might be explained by
the effects of gravity on flows with high yield strengths. These results
should prove useful to future efforts to resolve the controversy over
the mechan-ics of long-runout avalanches.
Despite three decades of exploration, the valley networks on Mars still seem to raise more questions than they answer. Valley systems have formed in the southern highlands, along some regions of the dichotomy boundary and the south rim of Valles Marineris, around the rim of some impact craters, and on the flanks of some volcanoes. They are found on some of the oldest and youngest terrains as well as on intermediate aged surfaces. There is surprisingly little consensus as to the formation and the paleoclimatic implications of the valley networks. Did the valleys require a persistent solar-driven atmospheric hydrological cycle involving precipitation, surface runoff, infiltration and groundwater outflow as they typically do on Earth? Or are they the result of magmatic or impact-driven thermal cycling of ground water involving persistent outflow and subsequent runoff? Are they the result of some other process(es)? Ground-water sapping, surface-water runoff, debris flows, wind erosion, and formation mechanisms involving other fluids have been proposed. Until such basic questions as these are definitively answered, their significance for understanding paleoclimatic change on Mars remains cloudy. I will review what is known about valley networks using data from both past and current missions. I will discuss what we have learned about their morphology, environments in which they formed, their spatial and temporal associations, possible formation mechanisms, relation to outflow channel and gully formation, as well as the possible implications for past climate change on Mars. Finally I will discuss how future, meter to submeter scale imaging and other remote sensing observations may shed new light on the debate over the origin of these enigmatic features.
The composition, mineralogy, physical nature, and distribution of solid
materials exposed at the surface and suspended in the atmosphere of Mars
are examined on the basis of spectroscopic observations (0.3 to 50
microns) coupled with multispectral imaging. Spectroscopic observations
dating back to the early 1960s show a strong absorption in the 3-micron
region due to H2O in some form distributed ubiquitously through the
Martian soils in an abundance of a few tenths of a percent to a few
percent. The spectrum of the retreating south polar cap displays many
absorption features due to CO2 ice. Reflection spectra for dark regions
exhibit an absorption near 1 micron and a more tentative one near 2
microns. Although the mid-IR transmission spectra of Martian airborne
dust were previously suggested as being due to clays, crystalline clays
typically exhibit grater spectral structure than is seen in the Martian
spectrum, particularly near 20 microns.
The structure and chemical composition of the Lafayette meteorite were
examined using several methods. The meteorite contains abundant hydrous
post-magnetic alteration material consisting of ferroan smectite clays,
magnetite, and ferrihydrite. The textural relations, mineralogy, and
composition of these materials were examined and their preterrestrial
nature was documented. Olivine, pyroxene, and glass alteration are
described and the bulk compositions of the alteration veinlets is
discussed. Essential features of the geochemistry of the alteration
processes are described. It is suggested that the alteration of the
Lafayette meteorite occurred during episodic infiltrations of small
volumes of saline water. Constraints placed on water chemistry and
water-rock interactions in the Martian crust are outlined.
Production of Gaseous Pore Pressure During Rock Slides
When a rock mass slips, the local heating of the slip surface transforms pore water into vapour if the surface of failure is deep enough. It is possible to calculate, as a first approximation, a critical displacement of the mass necessary to create vapour in the slide zone. A second approximation gives the relation between critical displacement and rate of shear displacement as the slide mass creeps towards catastrophe.
Mare regolith is fragmental debris of variable thickness that lies upon fractured bedrock. Its origin by impact comminution of primarily local basaltic rocks is widely accepted, but the consequences of such an origin are not appreciated fully. This investigation uses results obtained in an earlier Monte Carlo study by Oberbecket al. (1973) to shed light on those consequences by evaluating regolith growth and mixing as a function of time. Results reported are for average cases and must be used with caution. Each small area of the lunar surface has experienced a unique history and results based on averages may have no application to specific cases. Consideration of average processes is useful, nevertheless, when this limitation is kept in mind. The study demonstrates that regolith growth is self regulated and has the same trend and nearly the same terminal growth rates whatever the history of bombardment: rapid initial accumulation followed by diminishing rates of growth. Mixing and all other processes investigated are growth regulated. Mixing increases as growth slows, but never to the extent that the regolith is homogenized. Because the average regolith is never homogenized, products of growth regulated processes are preserved in the stratigraphy. Differences in material properties are to be expected in vertical sections of the regolith, therefore, but this model is not sufficiently refined to permit prediction of all possible trends. It does indicate, however, that deeper levels contain thinner depositional units, lesser quantities of meteoritic and exotic components, and more debris derived from shallow levels in the mare basalts than material in near surface layers. Additionally, neutron fluence production is regulated by the growth process, but because rates of growth do not differ much over the last aeon, whatever the total age or early bombardment history, values of surface fluence may be similar in many areas whatever their age.
The thermal evolution of the Moon, Mercury, Mars, Venus and hypothetical minor planets is calculated theoretically, taking into account conduction, solid-state convection, and differentiation. An assortment of geological, geochemical, and geophysical data is used to constrain both the present day temperatures and thermal histories of the planets' interiors. Such data imply that the planets were heated during or shortly after formation and that all the terrestrial planets started their differentiations early in their history. Initial temperatures and core formation play the most important roles in the early differentiation. The size of the planet is the primary factor in determining its present day thermal state. A planetary body with radius less than 1000 km is unlikely to reach melting given heat source concentrations similar to terrestrial values and in the absence of intensive early heating such as short half-life radioactive heating and inductive heating.
Studies of individual planets are constrained by varying amounts of data. Most data exist for the Earth and Moon. The Moon is a differentiated body with a crust, a thick solid mantle and an interior region which may be partially molten. It is presently cooling rapidly and is relatively inactive tectonically.
Mercury most likely has a large core. Thermal calculations indicate it may have a 500 km thick solid lithosphere, and the core may be partially molten if it contains some heat sources. If this is not the case, the planet's interior temperatures are everywhere below the melting curve for iron. The thermal evolution is dominated by core separation and the high conductivity of iron which makes up the bulk of Mercury.
Mars, intermediate in size among the terrestrial planets, is assumed to have differentiated an Fe−FeS core. Differentiation and formation of an early crust is evident from Mariner and Viking observations. Theoretical models suggest that melting and differentiation of the mantle silicates has occurred at least up until 1 billion years ago. Present day temperature profiles indicate a relatively thick (∼250 km) lithosphere with a possible asthenosphere below. The core is molten.
Venus is characterized as a planet similar to the Earth in many respects. Core formation probably occurred during the first billion years after the formation. Present day temperatures indicate a partially molten upper mantle overlain by a 100 km thick lithosphere and a molten Fe−Ni core. If temperature models are good indicators, we can expect that today, Venus has tectonic processes similar to the Earth's.
The aureole materials that form an annulus of corrugated terrain surrounding Olympus Mons are considered to be the product of mass movement. The scarp at the mountain''s foot formed as a result of this massive removal of material from the volcano''s outer flanks. This interpretation is supported by a comparison of the amount of material originally available before scarp formation, and the present volume of aureole materials. On the basis of distribution, surface textures and theoretical considerations it is considered that the aureole was produced by a series of megaslides, rather than by a flow mechanism. Production of the megaslides may have been assisted by a period of widespread melting of permafrost.
The geomorphology of the martian valley networks is examined from a hydrological perspective for the compatibility with an origin by rainfall, globally higher heat flow, and localized hydrothermal systems. Comparison of morphology and spatial distribution of valleys on geologic surfaces with terrestrial fluvial valleys suggests that most martian valleys are probably not indicative of a rainfall origin, nor are they indicative of formation by an early global uniformly higher heat flow. In general, valleys are not uniformly distributed within geologic surface materials as are terrestrial fluvial valleys. Valleys tend to form either as isolated systems or in clusters on a geologic surface unit leaving large expanses of the unit virtually untouched by erosion. With the exception of fluvial valleys on some volcanoes, most martian valleys exhibit a sapping morphology and do not appear to have formed along with those that exhibit runoff morphology. In contrast, terrestrial sapping valleys form from and along with runoff valleys. The isolated or clustered distribution of valleys suggests localized water sources were important in drainage development. Persistent groundwater outflow driven by localized, but vigorous hydrothermal circulation associated with magmatism, volcanism, impacts, or tectonism is, however, consistent with valley morphology and distribution. Snowfall from sublimating ice-covered lakes or seas may have provided an atmospheric source of water for the formation of some valleys in regions where the surface is easily eroded and where localized geothermal/hydrothermal activity is sufficient to melt accumulated snowpacks.
A thermal/diffusive model of H2O kinetics and equilibrium was developed to investigate the long-term evolution and depth distribution of subsurface ice on Mars. The model quantitatively takes into account (1) obliquity variations; (2) eccentricity variations; (3) long-term changes in the solar luminosity; (4) variations in the argument of subsolar meridian (in planetocentric equatorial coordinates); (5) albedo changes at higher latitudes due to seasonal phase changes of CO2 and the varying extent of CO2 ice cover; (6) planetary internal heat flow; (7) temperature variations in the regolith as a function of depth, time, and latitude due to the above factors; (8) atmospheric pressure variations over a 104-year time scale; (9) the effects of factors (1) through (5) on seasonal polar cap temperatures; and (10) Knudsen and molecular diffusion of H2O through the regolith. The migration of H2O into or out of the regolith is determined by two boundary conditions, the H2O vapor pressure at the subsurface ice boundary and the annual average H2O concentration at the base of the atmosphere. These are controlled respectively by the annual average regolith temperature at the given depth and seasonal temperatures at the polar cap. Starting from an arbitrary initial uniform depth distribution of subsurface ice, H2O fluxes into or out of the regolith are calculated for 100 selected obliquity cycles, each representing a different epoch in Mars' history. The H2O fluxes are translated into ice thicknesses and extrapolated over time to give the subsurface ice depth as a function of latitude and time. The results show that obliquity variations influence annual average regolith temperatures in varying degrees, depending on latitude, with the greatest effect at the poles and almost no effect at 40° lat. Insolation changes at the pole, due to obliquity, argument of subsolar meridian, and eccentricity variations can produce enormous atmospheric H2O concentration variations of ≈6 orders of magnitude over an obliquity cycle. Superimposed on these cyclic variations is a slow, monotonic change due to the increasing solar luminosity. Albedo changes at the polar cap due to seasonal phase changes of CO2 and the varying thickness of the CO2 ice cover are critically important in determining annual average atmospheric H2O concentrations. Despite the strongly oscillating character of the boundary conditions, only small amounts of H2O are exchanged between the regolith and the atmosphere per obliquity cycle (<10 g/cm2). The net result of H2O migration is that the regolith below 30–40° lat is depleted of subsurface ice, while the regolith above 30–40° lat contains permanent ice due to the depth of penetration of the annual thermal wave. This result is supported by recent morphological studies. The rate of migration of H2O is strongly dependent on average pore/capillary radius for which we have assumed values of 1 and 10 μm. We estimate that the H2O ice removed from the regolith would produce a permanent ice cap with a volume between 2 × 106 and 6 × 106 km3. This generally agrees with estimates deduced from deflationary features at lower latitudes, depositional features at higher latitudes, and the mass of the polar caps.
The morphologies of Tycho secondary craters and their ejecta deposits were studied using full-Moon, Lunar-Orbiter, and Apollo panoramic photographs. These data were compared with similar data for the secondary craters and light mantle of the Apollo 17 landing site. The results indicate that (1) the central crater cluster and the light mantle can be attributed to Tycho, (2) the dominant mechanism for emplacement of the light mantle was impact by secondary craters that threw material across the valley floor, and (3) level sheets of material may be emplaced locally by secondary impact. Analysis of returned samples confirms that secondary impacts rework mostly local material.
A new model is presented for the Amazonian outburst floods on Mars. Rather than the working fluid being water, with the associated difficulties in achieving warm and wet conditions on Mars and on collecting and removing the water before and after the floods, instead this model suggests that CO2 is the active agent in the “floods.” The flow is not a conventional liquid flood but is instead a gas-supported density flow akin to terrestrial volcanic pyroclastic flows and surges and at cryogenic temperatures with support from degassing of CO2-bearing ices. The flows are not sourced from volcanic vents, but from the collapse of thick layered regolith containing liquid CO2 to form zones of chaotic terrain, as shown by R. St. J. Lambert and V. E. Chamberlain (1978, Icarus34, 568–580; 1992, Workshop on the Evolution of the Martian Atmosphere). Submarine turbidites are also analagous in the flow mechanism, but the martian cryogenic flows were both dry and subaerial, so there is no need for a warm and wet epoch nor an ocean on Mars.Armed with this new model for the floods we review the activity of volatiles on the surface of Mars in the context of a cold ice world—“White Mars.” We find that many of the recognized paradoxes about Mars' surface and atmosphere are resolved. In particular, the lack of carbonates on Mars is due to the lack of liquid water. The CO2 of the primordial atmosphere and the H2O inventory remain largely sequestered in subsurface ices. The distribution of water ice on modern Mars is also reevaluated, with important potential consequences for future Mars exploration. The model for collapse of terrain due to ices that show decompression melting, and the generation of nonaqueous flows in these circumstances may also be applicable to outer Solar System bodies, where CO2, SO2, N2, and other ices are stable.
Detailed study of the Valles Marineris equatorial troughs suggests that the landslides in that area contained water and probably were gigantic wet debris flows: one landslide complex generated a channel that has several bends and extends for 250 km. Further support for water or ice in debris masses includes rounded flow lobes and transport of some slide masses in the direction of the local topographic slope. Differences in speed and emplacement efficiency between Martian and terrestrial landslides can be attributed to the entrainment of volatiles on Mars, but they can also be explained by other mechanisms. Support that the wall rock contained water comes from the following observations: (1) the water within the landslide debris must have been derived from wall rock; (2) debris appears to have been transported through tributary canyons; (3) locally, channels emerged from the canyons; (4) the wall rock apprarently disintegrated and flowed easily; and (5) fault zones within the troughs are unusually resistant to erosion. The study further suggests that, in the equatorial region of Mars, material below depths of 400–800 m was not desiccated during the time of landslide activity (within the last billion years of Martian history). Therefore the Martian ground-water or groundice reservoir, if not a relic from ancient times, must have been replenished.
Gravity sliding and spreading at low strain rates can account for the general morphology and structure of the aureoles and basal scarp of Olympus Mons. Detachment sliding could have occurred around the volcano if either pore-fluid pressures were exceptionally high (greater than 90%) or the rocks had very low resistance to shear (about 1 × 105 Pa or 1 bar). Because of the vast areal extent and probable shallow depth of the detachment zone, development of ubiquitous, high pore-fluid pressures beneath aureole-forming material was unlikely. However, a zone of sufficiently weak material consisting of about 10% interstitial or interbedded ice could have been present. If so, a simple rheologic model for the aureole deposits can be applied that consists of a thin ductile layer overlain by a thicker brittle layer. According to this model, extensional deformation would have occurred near the shield and compressional deformation in its distal parts. Proximal grabens and distal corrugations on aureole surfaces support this model. A submarine slide at Kitimat Arm, British Columbia, is a valid qualitative analogy for the observed features and inferred emplacement style of the aureole deposits. Ground-ice processes have been considered the cause of many geologic features on Mars; a 3% average concentration of ground ice in the regolith is predicted by theoretical models for the ice budget and cryosphere. Ice may have been deposited in higher concentrations below the aureole-forming material; the source of the ice could have been juvenile water circulated hydrothermally by Olympus Mons volcanism. The basal scarp of Olympus Mons apparently demarcates the transition between the upper, stable part of the shield and its lower part that decoupled and formed the aureole deposits. This transition may reflect a change in the bulk shear strength of the shield, caused either by a radial dependence in the abundance of ice or fluid in the shield materials or by the concentration of intrusive dikes within the volcano. Other Martian volcanoes exhibit virtually no evidence of similar large-scale gravity spreading and basal scarps. Perhaps such evidence, if it existed, has been buried by lava flows, or perhaps the smaller size of other volcanoes did not permit the development of these features.
A number of geologic processes, particularly seismic faulting, impact crater slumping, and long runout landslides, require the failure of geologic materials under differential stresses much smaller than expected on the basis of conventional rock mechanics. This paper proposes that the low strengths apparent in these phenomena are due to a state of 'acoustic fluidization' induced by a transient strong acoustic wave field. The strain rates possible in such a field are evaluated, and it is shown that acoustically fluidized debris behaves as a newtonian fluid with a viscosity in the range 100,000 to 10,000,000 P for plausible conditions. Energy gains and losses in the acoustic field are discussed, and the mechanism is shown to be effective if internal dissipation in the field gives a Q approximately greater than 100. Whether such values for Q are realized is not known at present. However, acoustic fluidization provides a qualitatively correct description of the failure of rock debris under low differential stresses in the processes of faulting, crater slumping, and long runout landslides. Acoustic fluidization thus deserves serious consideration as a possible explanation of these phenomena.
The morphology of the landslides in the Martian equatorial troughs, the geologic structure of the troughs, the time of emplacement, the similarity to terrestrial landslides, and the origin and mechanism of transport are analyzed. About 35 large landslides well-resolved on Viking images were examined, and it is found that the major landslides cover 31,000 sq km of the trough floors, and individual slides range in area from 40 to 7000 sq km. The morphologic variations of the landslides can be attributed mainly to their degree of confinement on trough floors. Many prominent landslides appear to be of similar age and were emplaced after a major faulting that dropped the trough floors. Most sliding occurred after the created scarps were dissected into spurs, gullies, and tributary canyons. Emplacement of the landslides approximately coincided with a late episode of major eruptive activity of the Tharsis volcanoes, and it is suggested that the slides may have originated as gigantic mudflows with slump blocks at their heads. The large size of many landslides is due to the fault scarps as high as 7 km on which they formed in the absence of vigorous fluvial erosion. The landslides suggest that Mars is earthlike in some respects, which may be important for further evaluations.
The thermal evolutions of the Moon, Mars, Venus, and Mercury were calculated theoretically starting from cosmochemical condensation models. An assortment of geological, geochemical, and geophysical data were used to constrain both the present day temperature and the thermal histories of the planets' interiors. Such data imply that the planets were heated during or shortly after formation and that all the terrestrial planets started their differentiations early in their history.
Compilation of a simplified geologic/geomorphic map onto digital terrain models of the Valles Marineris permitted an evaluation of elevations in the vicinity of the troughs and the calculation of depth of troughs below surrounding plateaus, thickness and deposits inside the troughs, volumes of void spaces above geologic/geomorphic units, and volumes of deposits. Consideration of the geomorphological relationships of these deposits and their comparison by volume with the troughs in which they lie led to the conclusion that despite their layered form they were of volcanic origin, presumably formed by eruptions beneath an ice sheet. Other processes such as piping may have been involved in the redistribution of material, while broad structural basins control the broad landform pattern. -after Authors
Interior samples of three different Nakhla specimens contain an iron-rich silicate 'rust' (which includes a tentatively identified smectite), Ca-carbonate (probably calcite), Ca-sulfate (possibly gypsum or bassanite), Mg-sulfate (possibly epsomite or kieserite), and NaCl (halite); the total abundance of these phases is estimated as less than 0.01 weight percent of the bulk meteorite. Rust veins are truncated and decrepitated by fusion crust and are preserved as faulted segments in partially healed olivine crystals, indicating that the rust is preterrestrial in origin. Because Ca-carbonate and Ca-sulfate are intergrown with the rust, they are also indicated to be of preterrestrial origin. Similar textural evidence regarding origins of the NaCl and Mg-sulfate is lacking. Impure and poorly crystallized sulfates and halides on the fusion crust of the meteorite suggest leaching of interior (preterrestrial) salts from the interior after Makhla arrived on earth, but coincidental addition of these same salts by terrestrial contamination cannot be exluded. At least the clay-like silicate 'rust', Ca-carbonate, and Ca-sulfate were formed by precipitation from water-based solutions on the Nakhla parent planet, although temperature and pressure conditions of aqueous precipitation are unconstrained by currently available data. It is possible that aqueous alteration on the parent body was responsible for the previously observed disturbance of the Rb-Sr geochronometer in Nakhla at or near 1.3 Ga.