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Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian
Abstract
A variety of Late Amazonian landforms on Mars have been attributed to the dynamics of ice-related processes. Evidence for large-scale, mid-latitude glacial episodes existing within the last 100 million to 1 billion years on Mars has been presented from analyses of lobate debris aprons (LDA) and lineated valley fill (LVF) in the northern and southern mid-latitudes. We test the glacial hypothesis for LDA and LVF along the dichotomy boundary in the northern mid-latitudes by examining the morphological characteristics of LDA and LVF surrounding two large plateaus, proximal massifs, and the dichotomy boundary escarpment north of Ismeniae Fossae (centered at 45.3°N and 39.2°E). Lineations and flow directions within LDA and LVF were mapped using images from the Context (CTX) camera, the Thermal Emission Imaging Spectrometer (THEMIS), and the High Resolution Stereo Camera (HRSC). Flow directions were then compared to topographic contours derived from the Mars Orbiter Laser Altimeter (MOLA) to determine the down-gradient components of LDA and LVF flow. Observations indicate that flow patterns emerge from numerous alcoves within the plateau walls, are integrated over distances of up to tens of kilometers, and have down-gradient flow directions. Smaller lobes confined within alcoves and superposed on the main LDA and LVF represent a later, less extensive glacial phase. Crater size-frequency distributions of LDA and LVF suggest a minimum (youngest) age of 100 Ma. The presence of ring-mold crater morphologies is suggestive that LDA and LVF are formed of near-surface ice-rich bodies. From these observations, we interpret LDA and LVF within our study region to result from formerly active debris-covered glacial flow, consistent with similar observations in the northern mid-latitudes of Mars. Glacial flow was likely initiated from the accumulation and compaction of snow and ice on plateaus and in alcoves within the plateau walls as volatiles were mobilized to the mid-latitudes during higher obliquity excursions. Together with similar analyses elsewhere along the dichotomy boundary, these observations suggest that multiple glacial episodes occurred in the Late Amazonian and that LDA and LVF represent significant reservoirs of non-polar ice sequestered below a surface lag for hundreds of millions of years.
... Surface textures, landscape features, landforms and spatially-continuous landform assemblages reminiscent of current and/or relict glacial-regions on Earth are observed at or near the Mars dichotomy and throughout the mid-latitudes of the northern plains (e.g. Kargel and Strom, 1992;Head et al., 2002Head et al., , 2003Forget et al., 2006;Dickson et al., 2008;Morgan et al., 2009;Baker et al., 2010Baker et al., , 2015Souness and Hubbard, 2013;Hubbard et al., 2014;Sinha and Murty, 2015;Brough et al., 2016;Hepburn et al., 2020;Soare et al., 2021b, c). Their estimated ages shows greater variance (almost present day -~1 Ga) than the candidate periglacial terrain referenced above (e.g. ...
... Their estimated ages shows greater variance (almost present day -~1 Ga) than the candidate periglacial terrain referenced above (e.g. Head et al., 2003;Morgan et al., 2009;Baker et al. 2010;Souness and Hubbard, 2013;Hubbard et al., 2014;Sinha and Murty, 2015;Brough et al., 2016). ...
... Relatively recent work has begun to explore terrain at or close to the Mars dichotomy for geological/geomorphological evidence of similar cyclicity and succession (e.g. Dickson et al., 2008;Morgan et al., 2009;Baker et al., 2010;Head et al., 2010;Souness and Hubbard, 2013;Levy et al., 2014;Sinha and Murty, 2015;Hepburn et al., 2020). ...
The long-term cyclicity and temporal succession of glacial-periglacial (or deglacial) periods or epochs are keynotes of Quaternary geology on Earth. Relatively recent work has begun to explore the histories of the mid- to higher-latitudinal terrain of Mars, especially in the northern hemisphere, for evidence of similar cyclicity and succession in the Mid to Late Amazonian Epoch. Here, we carry on with this work by focusing on Protonilus Mensae [PM] (43-490 N, 37-590 E). More specifically, we discuss, describe and evaluate an area within PM that straddles a geological contact between two ancient units: [HNt], a Noachian-Hesperian Epoch transition unit; and [eHT] an early Hesperian Epoch transition unit. Dark-toned terrain within the eHt unit (HiRISE image ESP_028457_2255) shows continuous coverage by structures akin to clastically-sorted circles [CSCs]. The latter are observed in permafrost regions on Earth where the freeze-thaw cycling of surface and/or near-surface water is commonplace and cryoturbation is not exceptional. The crater-size frequency distribution of the dark-toned terrain suggests a minimum age of ~100 Ma and a maximum age of ~1 Ga. The age estimates of the candidate CSCs fall within this dispersion. Geochronologically, this places the candidate CSCs amongst the oldest periglacial landforms identified on Mars so far.
... Surface textures, landscape features, landforms and spatiallycontinuous landform assemblages reminiscent of current and/or relict glacial-regions on Earth are observed at or near the Mars dichotomy and throughout the mid-latitudes of the northern plains (e.g. Kargel and Strom, 1992;Head et al., 2002Head et al., , 2003Forget et al., 2006;Dickson et al., 2008;Morgan et al., 2009;Baker et al., 2010;Baker and Head, 2015;Souness and Hubbard, 2013;Hubbard et al., 2014;Sinha and Murty, 2015;Brough et al., 2016;Hepburn et al., 2020aHepburn et al., , 2020bSoare et al., 2021bSoare et al., , 2021c. Their estimated ages exhibit greater variance (almost present day -~1 Ga) than the candidate periglacial terrain referenced above (e.g. ...
... Their estimated ages exhibit greater variance (almost present day -~1 Ga) than the candidate periglacial terrain referenced above (e.g. Head et al., 2003;Morgan et al., 2009;Baker et al., 2010;Souness and Hubbard, 2013;Hubbard et al., 2014;Sinha and Murty, 2015;Brough et al., 2016). ...
... Relatively recent work has begun to explore terrain at or close to the Mars dichotomy for geological/geomorphological evidence of similar cyclicity and succession (e.g. Dickson et al., 2008;Morgan et al., 2009;Baker et al., 2010;Head et al., 2010;Souness and Hubbard, 2013;Levy et al., 2014;Sinha and Murty, 2015;Hepburn et al., 2020aHepburn et al., , 2020b. ...
The long-term cyclicity and temporal succession of glacial-periglacial (or deglacial) periods or epochs are keynotes of Quaternary geology on Earth. Relatively recent work has begun to explore the histories of the mid-to higher-latitudinal terrain of Mars, especially in the northern hemisphere, for evidence of similar cyclicity and succession in the Mid to Late Amazonian Epoch. Here, we carry on with this work by focusing on Protonilus Mensae [PM] (43-49 0 N, 37-59 0 E). More specifically , we discuss, describe and evaluate an area within PM that straddles a geological contact between two ancient units: [HNt], a Noachian-Hesperian Epoch transition unit; and [eHT] an early Hesperian Epoch transition unit. Dark-toned terrain within the eHt unit (HiRISE image ESP_028457_2255) shows continuous coverage by structures akin to clastically-sorted circles [CSCs]. The latter are observed in permafrost regions on Earth where the freeze-thaw cycling of surface and/or near-surface water is commonplace and cryoturbation is not exceptional. The crater-size frequency distribution of the dark-toned terrain suggests a minimum age of ~100 Ma and a maximum age of ~1 Ga. The age estimates of the candidate CSCs fall within this dispersion. Geochronologically, this places the candidate CSCs among the oldest periglacial landforms identified on Mars so far, by at least one and possibly two orders of magnitude. Unit HNt is adjacent to unit eHt and shows surface material that is relatively light in tone. The coverage is topographically irregular and, at some locations, discontinuous. Amidst the light-toned surface, structures are observed that are akin to clastically non-sorted polygons [NSPs] and polygonised thermokarst-depressions on Earth. Terrestrial polygon/thermokarst assemblages occur in permafrost regions where the freeze thaw cycling of surface and/or near-surface water is commonplace and the permafrost is ice-rich. The crater-size frequency distribution of the light-toned terrain suggests a minimum age of ~10 Ma and a maximum age of ~100 Ma. The age estimates of the candidate ice-rich assemblages fall within this dispersion. Geochronologically, this places them well beyond the million-year ages associated with most of the other candidate ice-rich assemblages reported in the literature. Stratigraphically intertwined with the two possible periglacial terrains are landforms and landscape features (observed or unobserved but modelled) that are indicative of relatively recent glaciation (~10 Ma-100 Ma) and glaciation long past (≥~ 1 Ga) to decametres of depth: glacier-(cirque) like features; viscous-flow features, lobate-debris aprons; moraine-like ridges at the fore, sides and midst of the aprons; and, patches of irregularly shaped (and possibly volatile-depleted) small-sized ridge/trough assemblages. Collectively, this deeply-seated intertwining of glacial and periglacial cycles suggests that the Mid to Late Amazonian Epochs might be more Earth-like in their cold-climate geology than has been thought hitherto.
... Mid-latitude glacial forms have been documented by a number of researchers [7][8][9][10][11][12][13][14][15][16][17][18]. Baker et al. [7], using crater size frequency distributions, constrained the dating of the youngest of these cold-based glacially emplaced lineated valley fill (LVF) and lobate debris apron (LDA) features to~100 Ma. ...
... Mid-latitude glacial forms have been documented by a number of researchers [7][8][9][10][11][12][13][14][15][16][17][18]. Baker et al. [7], using crater size frequency distributions, constrained the dating of the youngest of these cold-based glacially emplaced lineated valley fill (LVF) and lobate debris apron (LDA) features to~100 Ma. While water ice at these mid-latitude sites is not currently stable [19][20][21][22], using a high-resolution climate simulation model and assuming a modern Mars water cycle, found that mid-latitude, and even low-latitude, sites could maintain water ice at obliquity angles approaching 45 • [20]. ...
... Lobate features on the north face of Mount Sharp. Eleven lobes mapped (0-10) and ten analyzed(1)(2)(3)(4)(5)(6)(7)(8)(9)(10). Lobe (0) is overlapped and partially obscured by lobe (2), therefore, was not included in this study. ...
The presence of buried glacial ice and putative extinct rock glaciers in Mars’ equatorial regions has implications for understanding its climate history and sensitivity to changes in insolation and has significant implications for past global redistribution of the water ice cryosphere. We quantify the morphology of rock glacier- “like” features on the northern slopes of Aeolis Mons (known also as Mount Sharp) within Gale crater and use this information to evaluate a possible rock glacier origin for these forms. Detailed morphometric evaluation of cross and long profiles of these lobate features, which exhibit higher slopes at their heads, lower slopes at their distal edge, and a convex upward cross-sectional profile and oversteepened sides, resembles active terrestrial rock glaciers. However, the absence of a chevron wrinkle pattern and sublimation features could indicate extensive aeolian reworking and the lack of deflation could indicate a higher rock to ice mixture. The lack of cratering surfaces relative to the cratered surfaces that they overly could indicate a younger age and are possibly indistinguishable in age from the capping units of Mount Sharp, which may have once been more laterally extensive and may have been the source of these mass wasting forms.
... Ring-mold craters (RMC) are common on lineated and lobated debris aprons, filling valleys, and concentric crater fills on Mars [32][33][34]. They are interpreted as impacts into ice covered by a thin layer of regolith. ...
... [35] found three classes of ring-mold craters: (1) central pit or bowl craters ( Figure 3A); (2) central mound craters (Figure 3B and C); and (3) central plateau craters (Figure 3B). They show, that ring-mold craters on Ceres are comparable to those on Mars (e.g., [32,33,38]). Both bodies show nearly rimless craters with a circular outer moat and similar interior morphologies, like central pits or bowls, plateaus, and mounds. ...
... The similarities of morphology and location indicate a similar formation process [35]. Although, Martian ring-mold craters with diameters between 697 (mean 225 m; [32]) and 750 m (mean 102 m; [33]) Solar Planets and Exoplanets 6 are smaller than ring-mold craters on Ceres with diameters from ~280 to ~1,520 m with a mean of ~710 m [35]. Ponded material and lobate materials within Occator are supposed to be formed by impact melt or cryovolcanic flows (e.g., [39][40][41]). ...
The exploration of two small planetary bodies by the Dawn mission revealed multifaced surfaces showing a diverse geology and surface features. Impact crater are the most distinctive features on these planetary bodies. The surfaces of asteroid Vesta and the dwarf planet Ceres reveal craters with an individual appearance as caused by different formation processes. Special topographic and subsurface conditions on both bodies have led to the development of special crater types. This chapter present the three most characteristic crater forms fund on both bodies. Asymmetric craters are found on both bodies, whereas ring-mold craters and floor-fractured craters are only visible on Ceres.
... Crown, 2004, 2010;Crown et al., 2004 ). The most favored explanations for the formation of Martian lineated valley fills are that the deposits are volatile-rich material with interstitial ice, similar to terrestrial rock glacier flows ( Squyres, 1978;Mangold, 2003;Pierce and Crown, 2003;Bleamaster and Crown, 2010;Baker et al., 2010 ), or, more probably, debris-covered glacier flows ( Li et al.,20 05;Head et al.,20 06a,20 06b ). However, because most of the craters superposed on the lineated valley fills in Harmakhis Vallis are relatively small, the time during which the surface has been exposed to crater formation must have been relatively short. ...
... This assumption is also reasonable because several studies have shown that many Martian lineated valley fill features are actually geologically young, having formed in the Mid-Late Amazonian time (e.g. Levy et al., 2007;Morgan et al., 2009;Baker et al., 2010 ). Due to the lack of large craters, it is necessary to use small craters for successful dating. ...
... More detailed analyses show that the scalloped shape of the longitudinal walls is actually caused by small adjacent alcoves. Based on the photogeologic appearance of the alcoves, we interpret them to have formed as a result of periglacial or glacial processes ( Fig. 21 ) ( Baker et al., 2010 ). However, the mass wasting origin cannot be excluded completely, as the alcoves seem to be covered by smooth deposits similar to those found on the other steep slopes and valley walls ( wd ). ...
Harmakhis Vallis is one of the four major outflow channel systems (Dao, Niger, Harmakhis, and Reull Valles) that cut the eastern rim region of the Hellas basin, the largest well-preserved impact structure on Mars. The structure of Harmakhis Vallis and the volume of its head depression, as well as earlier dating studies of the region, suggest that the outflow channel formed in the Hesperian period by collapsing when a large amount of subsurface fluid was released. Thus Harmakhis Vallis, as well as the other nearby outflow channels, represents a significant stage of the fluvial activity in the regional history. On the other hand, the outflow channel lies in the Martian mid-latitude zone, where there are several geomorphologic indicators of past and possibly also contemporary ground ice. The floor of Harmakhis also displays evidence of a later-stage ice-related activity, as the outflow channel has been covered by lineated valley fill deposits and debris apron material.
... Ring-mold craters (RMCs) are a unique morphologic crater class characterized by an interior hummocky zone on the crater floor, surrounded by an inward-facing annulus within the crater interior, and concentric fractures exterior to the crater (Mangold 2003;Kress and Head 2008;Baker et al. 2010;Head and Weiss 2014;Levy et al. 2016). RMCs are interpreted to result from an impact into a massive ice deposit superposed by a thin debris cover (Kress and Head 2008;Baker et al. 2010;Head and Weiss 2014), and thus their presence is used to indicate the presence of buried ice deposits. ...
... Ring-mold craters (RMCs) are a unique morphologic crater class characterized by an interior hummocky zone on the crater floor, surrounded by an inward-facing annulus within the crater interior, and concentric fractures exterior to the crater (Mangold 2003;Kress and Head 2008;Baker et al. 2010;Head and Weiss 2014;Levy et al. 2016). RMCs are interpreted to result from an impact into a massive ice deposit superposed by a thin debris cover (Kress and Head 2008;Baker et al. 2010;Head and Weiss 2014), and thus their presence is used to indicate the presence of buried ice deposits. We report on two RMCs, identified by Levy et al. (2016), that are associated with DLE craters. ...
... 2. The identification of ring-mold craters on the ejecta facies of DLE craters. Ring-mold craters are interpreted to result from an impact into a debriscovered ice deposit (Kress and Head 2008;Baker et al. 2010;Head and Weiss 2014;Levy et al. 2016). 3. The concentration of expanded secondary craters on the ejecta facies of a number of DLE craters demonstrated by Viola et al. (2015Viola et al. ( , 2017. ...
Double-layered ejecta (DLE) craters are distinctive among the variety of crater morphologies observed on Mars, but the mechanism by which they form remains under debate. We assess two ejecta emplacement mechanisms: (1) atmospheric effects from ejecta curtain-induced vortices or a base surge and (2) ballistic emplacement followed by a landslide of ejecta assisted by either surface- or pore-ice. We conduct a morphological analysis of the ejecta facies for three DLE craters which impacted into irregular pre-existing topography. We find that the unique topographic environments affected the formation of grooves and the inner facies, and thus appear to be inconsistent with an atmospheric-effects origin but are supportive of the landslide hypothesis. We distinguish between the two landslide models (lubrication by either surface- or pore-ice) by assessing relationships between DLE crater ejecta and morphologic features indicative of buried ice deposits, including sublimation pits, ring-mold craters, expanded secondary craters, and excess ejecta craters. The association of DLE craters with these features suggests that surface ice was present at the time of the impacts that formed the DLE craters. We also compare the Froude numbers of DLE crater ejecta to landslides, and find that the ejecta of DLE craters are kinematically and frictionally similar to terrestrial landslides that overran glaciers. This suggests that the grooves on DLE craters may plausibly form through the same shear/splitting mechanism as the landslides. In summary, our analysis supports the hypothesis that DLE craters form through meteoroid impacts into decameters-thick surface ice deposits (emplaced during periods of higher obliquity) followed by ejecta sliding on the ice.
... craters-has mostly been confined to single stratigraphic units, such as large VFFs (e.g., Baker et al., 2010;Berman et al., 2015;Dickson et al., 2008;Head et al., 2010;Levy et al., 2007;Morgan et al., 2009) and the NPLD (e.g., Landis et al., 2016). The target strength of ice modifies the size-frequency of the initial craters produced by impacts and their subsequent preservation, relative to other substrates. ...
... There is no clear and obvious record of polyphase glaciation in the Kasei Valles landform assemblage, nor do we consider that crater inheritance exerts a strong control on the variability in model ages (Section 4.3). Although polyphase glaciation is evident elsewhere on Mars (e.g., Baker et al., 2010;Brough et al., 2015;Dickson et al., 2008;Hepburn et al., 2020b;Levy et al., 2007;Morgan et al., 2009), each GLDA depression studied herein has a single sharply defined boundary with the lava flow. Within or beyond GLDA depressions, there are no clearly identifiable features such as moraines or eskers, which may be linked to multiple phases of glaciation. ...
High‐obliquity excursions on Mars are hypothesized to have redistributed water from the poles to nourish mid‐latitude glaciers. Evidence of this process is provided by different types of viscous flow features (ice‐rich deposits buried beneath sediment mantle) located there today, including lobate debris aprons (LDAs). During high‐obliquity extremes, ice may have persisted even nearer the equator, as indicated by numerous enigmatic depressions bounded on one side by either isolated mesas or scarps, and on the other by a lava unit. These depressions demarcate the past interaction between flowing lava and ghost LDAs (GLDAs), which have long since disappeared. We term these features GLDA depressions, about which little is known besides their spatial extent. This collection of depressions implies tropical ice loss over an area ∼100,000 km². To constrain their history in Kasei Valles, we derive model ages for GLDA depressions, mesas, and the lava flow from crater counts. We use a 2D model of glacial ice constrained by the topography of GLDA depressions to approximate the surface and volume of former glacial ice deposits. The model reconstructs former ice surfaces along multiple flow lines orientated normal to GLDA depression boundaries. This reconstruction indicates that 1,400–3,500 km³ of ice—similar to that present in Iceland on Earth—existed at ∼1.3 Ga when the lava was emplaced. Dating shows that the GLDAs survived for up to ∼1 billion years following lava emplacement, before its final demise.
... They can extend several to tens of kilometres from their mesa, and orbital radar observations have confirmed that they can be up to 1 km thick and contain N90% ice (Holt et al., 2008;Plaut et al., 2009). Their ages range from~40-500 Ma (e.g., Mangold, 2003;Morgan et al., 2009;Baker et al., 2010;Hartmann et al., 2014) to~1 Ga (e.g., Levy et al., 2007;Baker and Head, 2015;Berman et al., 2015). The LDAs are the largest reservoir of ice among the VFFs . ...
... In the youngest craters where gullies are found emanating from well-defined bedrock alcoves cutback into the crater rim, de Haas et al. (2015b) estimated headwall retreat rates of 10 −4 to 10 −1 mm y −1 , which correspond to the backweathering rates experienced on rockwalls in Arctic, Nordic, and Alpine environments on Earth. De Haas et al. (2018) classed a crater as glaciated if it contained one or more of the following morphological features: arcuate ridges and/or spatulate depressions at the foot of the slope ( Fig. 3; Arfstrom and Hartmann, 2005;Berman et al., 2005;Head et al., 2008;Hubbard et al., 2011;Jawin et al., 2018), floor-filling CCF indicated by concentric ridges and/or pitted textures within identifiable in-crater deposits (e.g., Levy et al., 2010;Dickson et al., 2012), or crater-scale downslope lobate features that diverge around obstacles on the crater floor and have longitudinal or transverse ridges and/or pitted textures on their surfaces ( Fig. 2; e.g., Baker et al., 2010;Head et al., 2010). Several authors (e.g., Berman et al., 2005Berman et al., , 2009Head et al., 2008;Hauber et al., 2011a;Head, 2011, 2012;Dickson et al., 2015;de Haas et al., 2018;Jawin et al., 2018) have suggested that these glacial landforms represent different stages of ice-deposition and removal (glacial-interglacial cycles) during martian obliquity cycles. ...
The mid- to high latitudes of Mars host assemblages of landforms consistent with a receding glacial landscape on Earth. These landforms are postulated to have formed >5 Ma under a different climate regime when Mars’ orbital obliquity was on average 10° higher than today. Here, we investigate the spatiotemporal relationship between gullies and glacial landforms, both common in the mid-latitudes. Gullies are kilometre-scale landforms with a source alcove, transportation channel, and depositional apron. The glacial landforms comprise (1) extant viscous flow features (VFF) that extend from the base of crater walls into the interior of crater floors and are widely interpreted as debris-covered glaciers containing extant ice, and (2) landforms such as arcuate ridges at the base of crater walls that have been interpreted as relicts of more recent, less extensive glacial advances focussed on crater walls. We measure headwall retreat associated with glacial landforms and date their host-craters to constrain minimum headwall retreat rates. We record headwall retreat rates up to ~10² m My⁻¹ for the youngest suite of glacial landforms, equivalent to erosion rates of wet-based glaciers on Earth and to headwall retreat rates associated with martian bedrock gully systems. We find extensive evidence for a single erosional episode dating 5–10 Ma, which postdates emplacement of the majority of VFF but seems to predate formation of the gullies. We propose that the wet-based glacial episode was associated with glaciation focussed on the crater walls rather than melting of the glacial ice deposits on the crater floors (VFF). This is consistent with our observations of crater wall morphologies, including the presence of arcuate ridges consistent with terrestrial glaciotectonic features that require liquid water to form, textural alteration of the eroded bedrock surface consistent with ice-segregation and frost-shattering, and the presence of downslope pasted-on terrain, tentatively interpreted here as glacial till deposits sourced from glacial erosion of the crater wall. The pasted-on terrain is usually interpreted as a thicker, latitude-dependant mantle located on sloping terrain formed from airfall of ice nucleated on dust, but we suggest that it has been reworked by glaciation and is predominantly glacial in origin. Although our results cannot substantiate that gullies are produced by meltwater, the discovery of this wet glacial event does provide evidence for widespread meltwater generation in Mars’ recent history.
... In the mid-latitude regions, this ice is likely to accumulate on plateaus and in alcoves, and flow downslope to form glacial systems (e.g. Baker et al. 2010). Accordingly, Head et al. (2008) suggested that higher obliquities led to more water in the atmosphere in the mid-latitudes and to the deposition of snow and ice, particularly in favoured and shielded microenvironments such as pole-facing crater interiors at these latitudes. ...
... The dating of glacial landforms, such as lobate debris aprons (LDA) and lineated valley fill, provide evidence for large-scale glacial episodes in the northern and southern mid-latitudes within the last c. 100 myr-1 gyr on Mars (e.g. Dickson et al. 2008;Baker et al. 2010;Hartmann et al. 2014;Fassett et al. 2014;Baker & Head 2015;Berman et al. 2015). Smaller-scale glacier-like forms have probably been active more recently: for example, small-scale lobate glaciers in Greg crater (38.5°S, 113°E) have been dated to have been active 10-40 myr ago (Hartmann et al. 2014). ...
To understand Martian paleoclimatic conditions and the role of volatiles therein, the spatiotemporal evolution of gullies must be deciphered. While the spatial distribution of gullies has been extensively studied, their temporal evolution is poorly understood. We show that gully size is similar in very young and old craters. Gullies on the walls of very young impact craters (< a few Myr) typically cut into bedrock and are free of latitude-dependent mantle (LDM) and glacial deposits, while such deposits become increasingly evident in older craters. These observations suggest that gullies go through obliquity-driven degradation/accumulation cycles over time controlled by (1) LDM emplacement and degradation and by (2) glacial emplacement and removal. In glacially-influenced craters the distribution of gullies on crater walls coincides with the extent of glacial deposits, which suggests that melting of snow and ice played a role in the formation of these gullies. Yet, present-day activity is observed in some gullies on formerly glaciated crater walls. Moreover, in very young craters extensive gullies have formed in the absence of LDM and glacial deposits, showing that gully formation can also be unrelated to these deposits. The Martian climate varied substantially over time, and the gully-forming mechanisms likely varied accordingly.
... Las características lobulares (Figura 3) son comunes en Marte, fundamentalmente en las proximidades de las latitudes medias y suelen estar asociadas a los terrenos desgastados que aparecen a lo largo de la dicotomía global (Colaprete & Jakosky, 1998;Baker et al., 2010;Chuang et al., 2014;Fastook et al., 2014). En el cráter Gale estas morfologías se encuentran localizadas al norte del montículo central (Fairén et al., 2014) y no emanan de un circo obvio, sino de una cuenca cóncava, lo cual es coherente con que estos glaciares tengan su origen en un ambiente periglaciar (Marchant & Head, 2003). ...
... En el cráter Gale estas morfologías se encuentran localizadas al norte del montículo central (Fairén et al., 2014) y no emanan de un circo obvio, sino de una cuenca cóncava, lo cual es coherente con que estos glaciares tengan su origen en un ambiente periglaciar (Marchant & Head, 2003). Otro argumento a favor de un origen periglaciar sería la superposición de lóbulos (Figura 3 B), típica de ambientes de permafrost en la Tierra (Marchant & Head, 2003;Baker et al., 2010;Fairén et al., 2014) que, junto con su textura superficial (Figura 3 B), caracterizada por la presencia de surcos transversales consecuentes con fracturas de origen glaciar (Fairén et al., 2014), constituye una prueba más del clima frío y húmedo en el pasado. ...
RESUMEN Hace aproximadamente 3.500 – 3.700 millones de años, Marte sostuvo un ciclo hidrológico, caracterizado por la presencia de glaciares y agua líquida, en forma de ríos y lagos parcial o totalmente helados, configurando un paisaje similar a los que se pueden encontrar actualmente en diversas regiones de nuestro planeta, tal y como evidencia el análisis de imágenes procedentes de orbitadores terrestres y marcianos. El objetivo principal del proyecto consiste en caracterizar los ambientes glaciares, periglaciares y fluviales del marciano cráter Gale, a partir de un estudio morfológico del mismo, que permita comprender cómo fue el clima en el Marte primitivo. Para ello, se empleará el estudio de análogos, es decir, de zonas de nuestro planeta que presentan características geomorfológicas similares a las originadas en el pasado en Marte (Johnsson, 2012). Todo ello se realizará mediante SIG y teledetección, lo cual permite la integración de datos procedentes de los instrumentos a bordo de diversas sondas enviadas a Marte, como son las imágenes, MOLA, HiRISE y CTX, y de orbitadores terrestres como las imágenes procedentes de Google Earth y del satélite Landsat 8. Este SIG permitirá la identificación de diversas estructuras y procesos imperantes en la superficie marciana, gracias a la comparación con sus análogos terrestres, poniendo especial interés en aquellos relacionados con la actividad glaciar, periglaciar y fluvial. Palabras Clave: Geomorfología, Cráter Gale, Marte, Teledetección, Sistemas de Información Geográfica. ABSTRACT Approximately 3.500-3.700 billion years ago, Mars held a hydrological cycle, characterized by the presence of glaciers and liquid water in the form of rivers and lakes partially or completely frozen, forming a similar landscape that can currently be found in various regions of our planet, as evidenced by analyzing images from Mars and Earth orbiters. The main objective of the project is to characterize the glaciers, periglacial and fluvial environments of the Martian Gale crater, from a morphological study of crater, studying its morphology with the aim of understanding the climate on early Mars. To this end, we are used the study of analogues, they are areas of our planet which present similar geomorphological characteristics to those originated in the past on Mars (Johnsson, 2012). This will be done through GIS and remote sensing, which allows integration of data from instruments aboard different probes sent to Mars, such as MOLA, HiRISE and CTX images, and Earth orbiters as images from Google Earth and Landsat 8. This GIS will allow the identification of various structures and processes prevailing on the Martian surface, by comparison with their terrestrial analogs, putting special emphasis on those related to glacier, periglacial, and fluvial activity.
... (1) The Amazonian-aged ∼10 m thick latitude-dependent mantle (LDM) ( Mustard et al., 2001;Kreslavsky and Head, 2002;, up to ∼1 km thick lobate debris aprons (LDAs) (e.g., Peirce and Crown, 2003;Chuang and Crown, 20 05;Head et al., 20 06a;Plaut et al., 20 09;Baker et al., 2010;, lineated valley fill (LVF) ( Head et al., 2006b;Holt et al., 2008;Kress and Head, 2008;Baker et al., 2010 ), concentric crater fill (CCF) ( Levy et al., 2010;Dickson et al., 2010;, and other buried ice deposits (e.g., Viola et al., 2015;Bramson et al., 2015 ) interpreted to be debris-covered glacial deposits that are remnants of regional ice sheets formed in the mid-high latitudes during periods of higher martian obliquity ( Madeleine et al., 2009 ). (2) Amazonian-aged pedestal craters ( Barlow, 2006;Wrobel et al., 2006;Kadish et al., 2008Kadish et al., , 2010 and double-layered ejecta (DLE) craters Head, 2013 , 2014 ) hypothesized to form in ∼20-200 m thick regional surface ice sheets in the mid-high latitudes during periods of higher martian obliquity. ...
... (1) The Amazonian-aged ∼10 m thick latitude-dependent mantle (LDM) ( Mustard et al., 2001;Kreslavsky and Head, 2002;, up to ∼1 km thick lobate debris aprons (LDAs) (e.g., Peirce and Crown, 2003;Chuang and Crown, 20 05;Head et al., 20 06a;Plaut et al., 20 09;Baker et al., 2010;, lineated valley fill (LVF) ( Head et al., 2006b;Holt et al., 2008;Kress and Head, 2008;Baker et al., 2010 ), concentric crater fill (CCF) ( Levy et al., 2010;Dickson et al., 2010;, and other buried ice deposits (e.g., Viola et al., 2015;Bramson et al., 2015 ) interpreted to be debris-covered glacial deposits that are remnants of regional ice sheets formed in the mid-high latitudes during periods of higher martian obliquity ( Madeleine et al., 2009 ). (2) Amazonian-aged pedestal craters ( Barlow, 2006;Wrobel et al., 2006;Kadish et al., 2008Kadish et al., , 2010 and double-layered ejecta (DLE) craters Head, 2013 , 2014 ) hypothesized to form in ∼20-200 m thick regional surface ice sheets in the mid-high latitudes during periods of higher martian obliquity. ...
Fluvial features present around impact craters on Mars can offer insight into the ancient martian climate and its relationship to the impact cratering process. The widespread spatial and temporal distribution of surface ice on Mars suggests that the interaction between impact cratering and surface ice could have been a relatively frequent occurrence. We explore the thermal and melting effects on regional surface ice sheets in this case, where an impact event occurs in regional surface ice deposits overlying a regolith/bedrock target. We provide an estimate for the post-impact temperature of martian ejecta as a function of crater diameter, and conduct thermal modeling to assess the degree to which contact melting of hot ejecta superposed on surface ice deposits can produce meltwater and carve fluvial features. We also evaluate whether fluvial features could form as a result of basal melting of the ice deposits in response to the thermal insulation provided by the overlying impact ejecta. Contact melting is predicted to occur immediately following ejecta emplacement over the course of hundreds of years to tens of kyr. Basal melting initiates when the 273 K isotherm rises through the crust and reaches the base of the ice sheet ∼0.1 to ∼1 Myr following the impact. We assess the range of crater diameters predicted to produce contact and basal melting of surface ice sheets, as well as the melt fluxes, volumes, timescales, predicted locations of melting (relative to the crater), and the associated hydraulic and hydrologic consequences. We find that the heat flux and surface temperature conditions required to produce contact melting are met throughout martian history, whereas the heat flux and surface temperature conditions to produce basal melting are met only under currently understood ancient martian thermal conditions. For an impact into a regional ice sheet, the contact and basal melting mechanisms are predicted to generate melt volumes between ∼10−1 and 105 km3, depending on crater diameter, ice thickness, surface temperature, and geothermal heat flux. Contact melting is predicted to produce fluvial features on the surface of ejecta and the interior crater walls, whereas basal melting is predicted to produce fluvial features only on the interior crater walls. Before basal melting initiates, the ice-cemented cryosphere underlying the crater ejecta is predicted to melt and drain downwards through the substratum, generating a source of water for chemical alteration and possibly subsurface clay formation. These candidate melting processes are predicted to occur under a wide range of parameters, and provides a basis for further morphologic investigation.
... Although water ice is not presently stable across much of Mars' mid-latitudes (Mellon and Jakosky, 1995;Mellon et al., 2004), evidence of pervasive ice-rich landforms between 30 and 60 o latitude has been presented (Sharp, 1973;Squyres, 1978Squyres, , 1979Lucchitta, 1984;Mangold, 2003;Levy et al., 2007;Baker et al., 2010;Dickson et al., 2010;Head et al., 2010, Souness et al., 2012Hubbard et al., 2014;Brough et al., 2016;Sinha and Murty, 2015). Based on evidence from the Shallow Radar (SHARAD) instrument on board the Mars Reconnaissance Orbiter (MRO), the composition of these ice-rich deposits is consistent with water ice (Holt et al., 2008;Plaut et al., 2009), and their surface morphologies are indicative of viscous flow of that ice (e.g. ...
... glaciation (Levy et al., 2007;Dickson et al., 2008;Baker et al., 2010;Sinha and Murty, 2013;Brough et al., 2016). Despite these inferred changes, we currently have limited knowledge of the nature and timing of Mars' LMGM, the volume of ice lost since that time, and whether such GLF recession has been spatially variable (e.g. ...
Mars’ mid-latitude glacier-like forms (GLFs) have undergone substantial mass loss and recession since a hypothesised last martian glacial maximum (LMGM) stand. To date, there is a lack of knowledge of the nature and timing of the LMGM, the subsequent mass loss and whether this mass loss has been spatially variable. Here, we present the results of a population-scale inventory of recessional GLFs, derived from analysis of 1293 GLFs identified within Context Camera (CTX) imagery, to assess the distribution and controls on GLF recession. A total of 436 GLFs were identified showing strong evidence of recession: 197 in the northern hemisphere and 239 in the southern hemisphere. Relative to their parent populations, recessional GLFs are over-represented in the low latitude belts between 25º and 40º and in areas of high relief, suggesting that these zones exert some control over GLF sensitivity and response to forcing. This analysis is complemented by the reconstruction of the maximum extent and morphology of a specific GLF for which High Resolution Imaging Science Experiment (HiRISE) derived digital elevation data are available. Using Nye’s (Nye, J. F. [1951] P. Roy. Soc. Lond. A. Mat., 207[1091]) perfect plastic approximation of ice flow applied to multiple flow-lines under an optimum yield strength of 22 kPa, we calculate that the reconstructed GLF has lost an area of ~6.86 km2 with a corresponding volume loss of ~0.31 km3 since the LMGM. Assuming the loss reconstructed at this GLF occurred at all mid-latitude GLFs, yields a total planetary ice loss from Mars’ GLFs of ~135 km3, similar to the current ice volume in the European Alps on Earth.
... The lobes observed in the Raditladi Basin manifest striking similarities to Martian Lobate Debris Aprons (LDAs), interpreted as ice glaciers covered by debris on Mars (Mangold 2003; Arfstrom & Hartmann 2005;Hauber et al. 2008;Baker et al. 2010;Séjourné et al. 2019). This comparison lends credence given the close match in surface gravitational acceleration between Mars and Mercury-3.71 ...
The discovery of global elemental volatile compositions, sublimation hollows, and chaotic terrains has significantly reshaped our understanding of Mercury's geology. These findings suggest the existence of volatile-rich layers (VRLs) extending several kilometers in depth, challenging the traditionally held view of a predominantly volatile-devoid Mercury crust. However, the precise nature and origin of these VRLs remain to be elucidated. The Raditladi basin exhibits morphologies analogous to terrestrial and Martian glaciers. These geomorphological features are potentially derived from impact-exposed VRLs, likely constituted of halite, other semivolatile salts, or organic volatiles. The distinctive rheological traits of substances such as halite substantiate this hypothesis. The inference posits a potential ubiquity of VRLs on a planetary scale, albeit potentially ensconced at considerable depth in specific regions. North polar chaotic terrains elucidate the VRLs' genesis and temporal evolution. The intense fragmentation of heavily cratered landscapes during their formation indicates a composition dominated by volatiles. This finding postulates a phase of volatile-enriched crustal accretion predating the Late Heavy Bombardment (∼3.9 Ga). Regardless of lost mass, the unaltered basal elevation post-collapse signals a transition to a volatile-free stratum. The exposure of an exhumed lithological substrate within Mercury's stratigraphy, identifiable in gravimetry as an impacted paleosurface, contests the magma ocean differentiation concept for VRL formation. It infers a grand-scale construct originating from depositional processes, possibly due to the collapse of a transient, hot primordial atmosphere. Unified Astronomy Thesaurus concepts: Mercury (planet) (1024); Solar system terrestrial planets (797)
... Lineated valley fill landforms on Mars display similar morphologies to debris-covered glaciers on Earth (Baker et al., 2010). They display parallel ridges along valley walls, extend for 10s of kilometers, and contain signatures of subsurface ice in radar data, with many being 100s of meters thick. ...
Honeybee’s RedWater system is being developed as an in situ resource utilization (ISRU) approach to mining glacial ice on Mars. Our investigation addresses the environmental and geological considerations vital for system success (e.g., site latitude, ice purity, nature of impurities, and constraints on overburden). We will present an assessment of several site locales suitable for the implementation of the RedWater system using existing orbital spacecraft data. A combination of radar sounding, imagery, and other data at landing-site scales will enable constraints to be placed on the thickness, properties, and distribution of ice resources and overburden.
... Moreux crater (Fig. 1) is a~135 km, centered at 41.66 N, 44.44 E in the Protonilus Mensae region in the northern mid latitudes of Mars. This region hosts numerous landforms which contain geomorphic evidences of ice associated with flows cited as evidence of the last wide glaciation (Kargel, 2004;Head et al., 2006;Levy et al., 2007;Dickson et al., 2008;Baker et al., 2010;Murty, 2013, 2015). Moreover, this area is characterized by various buried ice deposits (Plaut et al., 2009). ...
Our research focuses on the detailed study of the aeolian deposits within Moreux crater using multi-resolution imaging and spectral data from the Mars Reconnaissance Orbiter. The morphometric analysis on the dune slip faces and wind streak orientations allowed us to reconstruct the sand transport pathways and the changes of the transport pattern. We used a new automatic procedure based on the Line Detection algorithm in PCI Geomatics’ Geomatica software to characterize small scale aeolian structures as ripples within Moreux crater from HiRISE images. After validation on a previously studied area in Herschel crater, we apply this method to reconstruct the wind regime at high spatial resolution in Moreux and reconstruct the wind circulation forming the aeolian bedforms. Moreover, we used three pairs of CTX images to perform a multi-temporal analysis of the wind streaks. We mapped more than 500 features with data acquisition spanning over four Earth years and the observed wind streak changes may reflect present day atmospheric variations due to local winds. CRISM datasets show an olivine and clinopyroxene mixture characterizing most of the dunes within Moreux crater, while the dark dunes in the northern sector of the crater showed an enrichment in Mg-olivine. This composition is similar to that detected in the central peak bedrock suggesting that central peak erosion contributes to the formation of the northly dunes meanwhile recent northeast wind flows and Moreux topography influence the wind circulation and determine the formation of the sand transport pathways within the crater. These results are consistent with the hypothesis that aeolian sands are generally sourced locally on Mars.
... Linear valley fills and lobate apron deposits have been found to be widespread in this region and are hypothesized to be related to Amazonian glacial deposits [Head et al., 2006;Dickson et al., 2008;Baker et al., 2010]. Using Mars SHAllow RADar sounder (SHARAD) radargrams, extensive subsurface ice deposits have been detected in the Deuteronilus Mensae region and are correlated with surface morphology features, e.g. ...
Amazonian‐aged Lyot crater is the best‐preserved and deepest peak‐ring impact crater (diameter, D=220km) in the northern lowlands of Mars. Morphological features including scouring channels emanating from its ejecta and small channels within the crater have been examined previously to understand hydrological activity associated with the crater. In this study, we analyze images acquired by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the Mars Reconnaissance Orbiter (MRO) to investigate the mineralogical record in Lyot and its surroundings, which are presently enriched in ground ice, to understand the associated aqueous processes, their relative timing, and a possible role for ground ice in hydrous mineral formation. We find diverse hydrous minerals, including Fe/Mg phyllosilicates, chlorite, illite/muscovite and prehnite in Lyot crater walls, central peak, and ejecta, as well as in two craters to the west of Lyot. The exposure and distribution of the hydrous minerals suggests they are related to the impact process, either exposed by the excavation of hydrothermally altered rocks or formed through syn‐depositional hydrothermal alteration immediately after impacts. The Lyot impact induced channel formation to the north, but no mineralogical evidence of aqueous alteration associated with the channels is observed. The sinuous channels within Lyot, diverted by bedrock units with hydrous mineral detections, did not cause mineralization but likely represent the last stage of water activity in Lyot crater. The separate episodes of water activity indicate flow of liquid water on Mars' surface during the Amazonian but limited to no aqueous alteration to generate hydrous minerals.
... Although these "wrongly oriented" lobes have been detected in one region of Mars, they represent a rather unique phenomenon and were interpreted as remnants after the lowering of the original surface of ice (Dickson et al., 2008). The vast majority of the viscous flows on Mars flow down the local slopes (Mangold and Allemand, 2001;Milliken et al., 2003;Li et al., 2005;Baker et al., 2010). Thus, the lobes of the Deuteronilus contact are unlikely to represent edges of either individual or coalescing glacier tongues. ...
In this paper, we present the results of our detailed study of morphology, topography, and age of the Deuteronilus contact that outlines Vastitas Borealis Formation (VBF) in the northern plains and the Isidis Planitia unit. The Deuteronilus contact represents a sharp and distinct geological boundary that can be traced continuously for many hundreds to thousands of kilometers. In the northern plains, segments of the Deuteronilus contact occur at two distinct topographic levels. In the northern plains, the long-wavelength topography of the Deuteronilus contact occur at two distinct topographic levels. In the Tempe, Chryse, Acidalia, and Cydonia-Deuteronilus regions (the total length is ∼14,000 km), the contact is at the mean elevation of about −3.92 km (the decile range is 180 m, from −4.01 km to −3.83 km). In the Pyramus-Astapus, Utopia, and Western Elysium regions (the total length is ∼7700 km), the mean elevation of the contact is about −3.58 km (the decile range is 270 m, from −3.73 km to −3.46 km). These levels to large extent (but not completely) correspond to the model geoids that may have been characterized the shape of Mars at the time of the VBF emplacement. Largest deviations of the actual topographic position of the contact from the model geoids occur in the Tantalus and Phlegra regions where the deviations are due to the post-VBF changes of the regional topography. The fact that the model geoids satisfactory describe the shape of the largest portion of the contact provides additional evidence for both the emplacement of the VBF edges near an equipotential surface and for relative stability of the shape of Mars during a long time interval of about 3.6 Ga. Within the northern plains in the Tempe Terra, Acidalia Planitia, Cydonia-Deuteronilus, Pyramus-Astapus, and the southern Utopia regions, the absolute model ages of the VBF surface near the Deuteronilus contact are tightly clustered around the age of ∼3.6 Ga, which we interpret as the age of the VBF emplacement. The surface of the VBF-like Isidis Planitia unit is distinctly younger, ∼3.50 ± 0.01 Ga, which suggests that this unit formed independently. Neither volcanic nor glacial modes of emplacement are consistent with the topographic configuration and the shape of the Deuteronilus contact within both the northern plains and in Isidis Planitia. The broad flooding and formation of extensive water/mud reservoirs remains to be the most plausible mode of formation of the VBF in the northern plains and the VBF-like unit on the floor of the Isidis basin.
... Their interpretation envisages a permafrost ((2) "interstitial ice") model. Baker et al. (2010) defined rock glaciers as "being a debris-rich feature formed by the deformation and mobilization of interstitial ice and ice lenses." A debris-covered glacier was used as a rock glacier subtype having remnant cores of glacier ice, a slow-moving "debris-covered glacier" as a "nearly pure ice body overlain by a thin till layer that is generated from the build-up of rock-fall and aeolian material as near-surface ice is sublimated." ...
... Several studies have also pointed out that GLFs appear to be distinctive from the underlying ice-rich (LDA or LVF) material onto which they appear to have flowed (e.g., Levy et al., 2007;Baker et al., 2010;Sinha and Murty, 2013). This material contrast has been interpreted as signifying the possibility of a marked age difference between the two surfaces, suggesting two or more glacial events with at least one smallscale or "local" glacial phase advancing over an earlier "regional" glaciation (e.g., Levy et al., 2007;Dickson et al., 2008;Sinha and Murty, 2013). ...
More than 1300 glacier-like forms (GLFs) are located in Mars' mid-latitudes.
These GLFs are predominantly composed of ice–dust mixtures and are visually
similar to terrestrial valley glaciers, showing signs of downhill viscous
deformation and an expanded former extent. However, several fundamental
aspects of their behavior are virtually unknown, including temporal and
spatial variations in mass balance, ice motion, landscape erosion and
deposition, and hydrology. Here, we investigate the physical glaciology of
martian GLFs. We use satellite images of specific examples and case
studies to build on existing knowledge relating to (i) GLF current and
former extent, exemplified via a GLF located in Phlegra Montes; (ii)
indicators of GLF motion, focusing on the presence of surface crevasses on
several GLFs; (iii) processes of GLF debris transfer, focusing on mapping
and interpreting boulder trains on one GLF located in Protonilus Mensae, the
analysis of which suggests a best-estimate mean GLF flow speed of 7.5 mm a−1; and
(iv) GLF hydrology, focusing on supra-GLF gulley networks. On the basis of this information, we summarize the current
state of knowledge of the glaciology of martian GLFs and identify future
research avenues.
... Their interpretation envisages a permafrost ((2) "interstitial ice") model. Baker et al. (2010) defined rock glaciers as "being a debris-rich feature formed by the deformation and mobilization of interstitial ice and ice lenses." A debris-covered glacier was used as a rock glacier subtype having remnant cores of glacier ice, a slow-moving "debris-covered glacier" as a "nearly pure ice body overlain by a thin till layer that is generated from the build-up of rock-fall and aeolian material as near-surface ice is sublimated." ...
... Interesting terrain types include: a) dune gullies 25,28 and b) lobate aprons 29 and lineated valley fill potentially associated with glaciers. 30 With a descent imager, intriguing targets could include peering into 'caves' or fresh impact craters (some of which may have exposed ice). ...
From canyons to glaciers, from geology to astrobiology, the amount of exciting surface science awaiting us at Mars greatly outstrips available mission opportunities. Based on the thrice-flown Aerospace Corporation Earth Reentry Breakup Recorder (REBR), we present a method for accurate landing of small instrument payloads on Mars, utilizing excess cruise-stage mass on larger missions. One to a few such microlanders might add 1-5% to the cost of a primary mission with inconsequential risk. Using the REBR and JPL Deep Space 2 starting points for a passively stable entry vehicle provides a low mass and low ballistic coefficient, enabling subsonic deployment of a steerable parawing glider, capable of 10+ km of guided flight at a 3:1 glide ratio. Originally developed for the Gemini human space program, the parawing is attractive for a volume-limited microprobe, minimizing descent velocity, and providing sufficient remaining volume for a useful scientific payload. The ability to steer the parawing during descent offers unique opportunities, including terrain-relative navigation for landing within tens of meters of one of several specified targets within a given uncertainty ellipse. In addition to scientific value, some Mars human exploration Strategic Knowledge Gaps could be addressed with deployment of focused instruments at multiple locations.
The long-term cyclicity and temporal succession of glacial-periglacial (or deglacial) periods or epochs are keynotes of Quaternary geology on Earth. Relatively recent work has begun to explore the histories of the mid- to higher-latitudinal terrain of Mars, especially in the northern hemisphere, for evidence of similar cyclicity and succession in the Mid to Late Amazonian Epoch.
Here, we carry on with this work by focusing on Protonilus Mensae [PM] (43–49⁰ N, 37–59⁰ E). More specifically, we discuss, describe and evaluate an area within PM that straddles a geological contact between two ancient units: [HNt], a Noachian-Hesperian Epoch transition unit; and [eHT] an early Hesperian Epoch transition unit. Dark-toned terrain within the eHt unit (HiRISE image ESP_028457_2255) shows continuous coverage by structures akin to clastically-sorted circles [CSCs]. The latter are observed in permafrost regions on Earth where the freeze-thaw cycling of surface and/or near-surface water is commonplace and cryoturbation is not exceptional.
The crater-size frequency distribution of the dark-toned terrain suggests a minimum age of ~100 Ma and a maximum age of ~1 Ga. The age estimates of the candidate CSCs fall within this dispersion. Geochronologically, this places the candidate CSCs among the oldest periglacial landforms identified on Mars so far, by at least one and possibly two orders of magnitude.
Unit HNt is adjacent to unit eHt and shows surface material that is relatively light in tone. The coverage is topographically irregular and, at some locations, discontinuous. Amidst the light-toned surface, structures are observed that are akin to clastically non-sorted polygons [NSPs] and polygonised thermokarst-depressions on Earth. Terrestrial polygon/thermokarst assemblages occur in permafrost regions where the freeze thaw cycling of surface and/or near-surface water is commonplace and the permafrost is ice-rich. The crater-size frequency distribution of the light-toned terrain suggests a minimum age of ~10 Ma and a maximum age of ~100 Ma. The age estimates of the candidate ice-rich assemblages fall within this dispersion. Geochronologically, this places them well beyond the million-year ages associated with most of the other candidate ice-rich assemblages reported in the literature.
Stratigraphically intertwined with the two possible periglacial terrains are landforms and landscape features (observed or unobserved but modelled) that are indicative of relatively recent glaciation (~10 Ma - 100 Ma) and glaciation long past (≥ ~ 1 Ga) to decametres of depth: glacier-(cirque) like features; viscous-flow features, lobate-debris aprons; moraine-like ridges at the fore, sides and midst of the aprons; and, patches of irregularly shaped (and possibly volatile-depleted) small-sized ridge/trough assemblages. Collectively, this deeply-seated intertwining of glacial and periglacial cycles suggests that the Mid to Late Amazonian Epochs might be more Earth-like in their cold-climate geology than has been thought hitherto.
We examine unconformable lobate deposits along the north-facing slopes of Alba Patera (40°N 250°E with an elevation of ~6 km), Mars, using data from the Mars Reconnaissance Orbiter Context Camera, High-Resolution Imaging Science Experiment, and the Mars Orbiter Laser Altimeter. We interpret the lobate north-facing slope deposits (NSFDs) to be small (<3 km from source to toe) lobate debris aprons (LDAs), making them the highest-elevation LDAs yet identified on Mars. The total volume of the deposits along the caldera walls is ~5–11 km3. Deposits filling impact craters around the Alba Mons summit appear to be similar to the NFSDs. These NFSDs bear two distinct textures either singly or together: a hummocky surface of decameter-scale hills and a smooth surface. Smooth-textured NFSDs have lobate margins and convex-up topographic profiles, and show evidence of having flowed; hummocky NSFDs have concave or linear topographic profiles and are generally found on steep slopes. These deposits likely formed due to reduced insolation on north-facing slopes, which allowed for the preferential accumulation or preservation of water ice. The presence of small LDAs restricted to north-facing slopes could indicate that Alba Patera was only a marginal environment for glaciation, possibly because little water vapor was available at such a high elevation. The hummocky material is interpreted to be the eroded remnants of a mantle of ice-cemented dust that was superposed on the NFSDs. This mantle has been almost completely removed in smooth-textured areas. This difference in rates of ice removal was the result of either lower insolation on steep north-facing slopes than on shallow slopes or the greater mobility of the thicker, lobate portions of NFSDs producing a more densely-fractured mantle.
Buried ice in the Martian mid-latitudes is of high interest for In-Situ Resource Utilization (ISRU) by future crewed missions, as well as for its scientific value as a record of climate history on another planet. "Lobate debris aprons," widely considered to be debris-covered glaciers, constitute a large reservoir of such ice. Many have been probed by Mars Reconnaissance Orbiter's Shallow Radar (SHARAD) sounder, which imaged their base and constrained their internal composition to >80% water ice. The basal contact is not imaged by SHARAD for all aprons, however, which introduces the possibility that these features contain significantly less ice. In this study, we used SHARAD survey results in tandem with high-resolution digital terrain models to show that these "non-detections" can be attributed to surface roughness, which through scattering reduces the coherent signal that penetrates the aprons. We quantified this effect using a fractal backscattering model and found that the roughest surfaces coincided with the location of basal non-detections. There is thus no need for reduced ice content to explain nondetection of lobate debris apron bases with SHARAD. This result leads us to interpret all lobate debris aprons as likely debris-covered glaciers, due to the similarities in their gross morphology and surface textures to aprons with basal detections.
We provide an up-to-date review on the different landscapes and landforms that have been attributed to the action of liquid water in the Amazonian epoch on Mars and the current state of the art regarding their interpretation. This chapter accompanies the chapter by Dundas, where the counterarguments are presented. The Amazonian epoch is thought to be dominated by hyper-arid climate conditions hostile to surface liquid water, and our review reveals that this steady state is likely to be punctuated by episodic appearances of liquid water at the surface. The proposed sources of liquid water are varied: groundwater, thawing of surface-ice, deliquescence, ground-ice or glaciers, with triggers as variable as microclimates, climate-shifts, geothermal anomalies, and impact cratering.
Our review covers recently active surface processes in the form of slope streaks, dark dune flows, and recurring slope lineae, all hypothesized at one point or another to be seeps of liquid water. We then cover landscapes and landforms that are proposed to be a result freeze–thaw cycles in the recent past, including gullies, lobate forms on hillslopes, pingo-like mounds, low-centered polygons, patterned ground, and ice-loss landscapes. We present evidence that liquid water has been produced at the base of glacial landforms during the Amazonian, resulting in sinuous ridges (eskers), and enhanced crater-wall erosion. Liquid water brought up from depth is thought to have produced mud-volcanoes and other features related to sedimentary volcanism in the Amazonian and small fluvial channels among other features are thought to be related to melting induced by periodic impact events.
We end by summarizing the importance of the search evidence of liquid water on Mars and by proposing solutions to the current impasses where progress is hindered due to limitations in data or our understanding.
Small-sized mounds that exhibit a sweep of similarities, that is, shape, scale (in height and long axes), surface features, and framing landscapes with perennially ice-cored mounds on Earth, that is, pingos, occur within and adjacent to the Moreux impact-crater (42.1°N; 44.4°E). The crater is located in northern Arabia Terra and lies astride the Martian crustal-dichotomy.
Here, we do three things:
1.Describe the possible glacial and periglacial landscapes in which the Moreux mounds are ensconced and attempt to synthesize each of these landscape types with “open” or “closed” pingo formation-pathways.
2.Suggest that the closed-system hypothesis, if valid, places mound origin in a scale of time that is neither current nor in the recent past.
3.Suggest that the open-system hypothesis, if valid, situates mound origin in a scale of time that could be current or in the recent past.
Lobate debris apron (LDA) in the Mars' mid-latitudes substantiate extensive glaciation during the Late Amazonian. Detailed investigation of these landforms is imperative because different areas distributed at different latitudes, distinct geologic settings and varied regional topography may have responded to climate in different ways. In this study, mapping of LDA deposits in Erebus Montes region in the flat, low-lying plains of the northern mid-latitudes has been undertaken and examined at a detail previously not attempted to infer new insights on the history of extensive glaciation. LDA deposits show convex-up, steep terminus profiles consistent with typical down-gradient flow characteristics, and integrated flow patterns akin to the glacial landforms reported along the dichotomy boundary. Evidence for a broad piedmont-like lobe, down-gradient flow within a possible oblique-impact crater, and infilled craters, suggest focused localized flow and glaciation. Lobate flows emanating from small alcoves and superposed on the main LDA are not observed, which likely suggests that there is a lack of multi-stage glaciation facilitated by the alcove microclimatic conditions in the region. Linear-curvilinear ridges on the LDA deposits could be the remnant of the internal flow lineations, and are most likely produced by the sublimation of debris-rich ice. Brain-terrain textures, polygonal cracks and ring-mold craters are ubiquitous on the upper surface of LDA deposits, which provides the morphological evidence for the past accumulation of LDM in the region. Hitherto, radar-based investigations do not provide substantial evidence for the presence of extant water ice beneath LDA deposits. We find that the LDA deposits examined here are more consistent with the cold-based glacial behavior - morphological observations supports existence of the sublimation process in the region. We suggest that the derived best-fit age of the ~30 Ma for the LDA deposits indicates age of the debris apron that has been mantled and the mapped LDA deposits in our study should be better represented by a broad age range of ~10–100 Ma. Together, our findings add another well-documented case to support the rapidly accumulating evidences for widespread extensive debris-covered glacial landsystems in the northern mid-latitudes of Mars in the Late Amazonian geological history.
Debris-covered glaciers from around the world offer distinct environmental, climatic, and historical conditions from which to study the effects of debris on glacier-ice evolution. A rich literature on debris-covered glaciers exists from decades of field work, laboratory studies, remote-sensing observations, and numerical modeling. In general, the base of knowledge established by studying periglacial, glacial, and paraglacial landforms on Earth has been applied to aid interpretation of ice-rich or ice-remnant landforms on Mars, but research has progressed on both planets. For Mars, the spatial distribution of lobate debris aprons and glacier-like forms, in particular, is critical to constraining past climate conditions when such features were active, reconstructing past ice extent, and estimating the total inventory of buried ice remaining in the mid-latitudes of Mars. This review spans a range of knowledge about debris-covered glaciers on Earth, in order to add context to investigations of dust and debris-covered ice on Mars and to put research on both planets in a perspective aimed at maximizing process-based understanding of glacier evolution. The state of knowledge and some gaps in knowledge on Mars are discussed in relation to possible avenues for future research in how landforms are classified, advances in comparative planetology, and new understanding from future missions. While this review is focused primarily on processes controlling active debris-covered glaciers, a key to understanding glacier change through time is to consider individual landforms in context with the full-system environment in which they are found. For Earth, this includes understanding local and regional controls on current glacier change, and how these processes relate to landform development in the past as well as what may develop in the future. For Mars, this includes evaluating how present-day landforms elucidate past ice activity and environmental conditions during epochs when orbital parameters, climate, and water ice distribution were substantially different.
Mars has experienced widespread glaciation across the mid-latitudes during the Late Amazonian. Deglaciation has altered these mid-latitude regions, and the characteristics of deglaciation can be useful in determining the variability in environmental response to climate change. The paraglacial period describes the period over which deglaciation occurred, and is characterized by a suite of features that form due to ice loss. Glaciated craters in the martian mid-latitudes were documented for evidence of paraglacial activity to determine how local crater setting affects deglaciation. Five paraglacial features were identified: spatulate depressions, washboard terrain, gullies, polygons, and broad pits, and their occurrence in each glaciated crater was recorded. 71% of glaciated craters (~450 craters) contained some evidence of paraglacial activity. Relatively more southern hemisphere glaciated craters contained paraglacial features (89%) than northern hemisphere glaciated craters (42%). The spatial density of paraglacial features varies with location. Different combinations of paraglacial features were found in each crater, although some features were preferentially associated, including washboard terrain and gullies, and broad pits and polygons, suggesting dependent formation mechanisms. More types of paraglacial features (up to all five features) were found in small craters (~5–10 km) at a range of elevations, and at modest latitudes (~35–45°), which corresponds to a large region of the southern highlands. Few or no paraglacial features were found in craters containing glacial fill exceeding ~70% of their predicted depth. The thickness of crater fill appears to be the dominant control on paraglacial response, which is affected by crater diameter, and partly by latitude. The variation in thickness of crater fill is attributed to variable accumulation and ablation rates during peak glacial periods during the Late Amazonian. The similarity in paraglacial feature morphology across the mid-latitudes of both hemispheres suggests that deglaciation and paraglaciation operate via similar mechanisms, although climatic conditions and geologic setting at each crater will determine the specific pathway for paraglacial activity to occur. These observations can be used to predict where future paraglacial activity will occur, and where it may be inhibited.
Martian gullies are landforms comprising an alcove, channel and debris apron. In some gullies lobate deposits have been observed, implying a debris-flow-like process, but uncertainty remains as to the importance of this process in the gully-population and whether lobate deposits are related to a specific context. We document evidence of overlapping lobate deposits on gully-fan surfaces within craters emplaced between 30°-75° in both hemispheres. We have identified 26 craters in which lobate deposits occur in gullies, of which 6 were previously reported. This corresponds to 3.39% of the 765 gullied craters studied using 1004 HiRISE images. We show that gullies with lobate deposits (1) do not show any location preference, (2) are poleward-facing, (3) are found in craters with and without latitude dependent mantle (LDM) and/or glacier-like-forms, (4) are emplaced at average slopes of 22° and 15° at the foot of fans in the northern and southern hemispheres, respectively, and (5) form in craters of all ages. We infer that preservation of lobate deposits in gullies is the main factor leading to their relative paucity within the gully-population. Additionally, we find that the size of the clasts embedded in the lobes does not seem to vary with host-crater age and the presence of LDM and/or glacial landforms. Further, we observe morphological features associated with terrestrial wet-debris flows including: overlapping tongue-shaped terminal lobes, levees, channel backfilling, plug formation and avulsion. We have not observed any significant present-day changes in the morphology and topography of gullies and/or lobes. We conclude that a debris-flow-like process is likely responsible for the majority of sediment transport in gully-landforms, but whether the fluidising agent is or was liquid water or CO2 sublimation remains unknown.
At the high northern latitudes of Mars, there are two impact craters (70.3°N 266.45°E and 67.25°N 249.45°E) with lobate moraine-like ridges (LMLR) on the inner slopes. In addition to these craters, a nearby plain (74°N 95°E) also displays remnants of water ice layered deposits with similar series of lobate ridges. The formation of these ridges has been hypothesized to be caused by either viscoplastic flow of CO2 ice deposits or a catastrophic down-slope movement of an H2O ice massif, which produced long-distance avalanches or fast-running glacier surges. In past climatic epochs, the formation of water ice massifs on high latitudes was possible under low (<20°) planet obliquity. Destabilization of water ice massifs on the craters’ steep inner slopes could lead to down-slope movement, followed by the destruction of the massifs and the production of long-distance water ice avalanches or surges. In this work, we focus on the avalanche formation hypothesis. The down-slope movement of a water ice massif has several possible causes, with the main one being excessive accumulation of water ice on slopes, which then reaches a critical unstable condition. Modeling of long-distance avalanche processes in Martian environments was carried out with Rapid Mass Movement Simulation (RAMMS:AVALANCHE) software, using the graph-analytical method of estimating avalanche velocity and maximum distance. As a result of the modeling, the volume of down-slope movement was defined, confirming the that LMLR were formed by the catastrophic down-slope movement of H2O ice masses in the form of long-distance avalanches.
Reconstructing Mars's glacial history informs understanding of its physical environment and past climate. The known distribution of viscous flow features (VFFs) containing water ice suggests that its mid‐latitudes were glaciated during the Late Amazonian period (the last several hundred million years). The identification of a subgroup of VFFs—called superposed glacier like forms (SGLFs)—flowing onto other VFFs, indicates multiple glacial phases may have occurred during this time. To explore the history and spatial extent of these glaciations, we record the distribution of SGLFs globally and use impact‐crater counting to date the SGLFs and the VFFs onto which they flow. Our inventory expands the handful of SGLFs reported in earlier literature to include 320 located throughout the mid‐latitudes. Our dating reveals these SGLFs to be much younger than their underlying VFFs, which implies a spatially‐asynchronous glaciation. SGLFs have been forming since ∼65 Ma, and their ages are clustered in two distinct groups around 2–20 and 45–65 Ma, whereas the ages of their underlying VFFs span the last ∼300 Ma diffusely. We discuss these results in the light of well‐known uncertainties with the crater‐dating method and infer that while ice sheets decayed over the Late Amazonian period, alpine glaciers waxed and waned in at least two major cycles before their final demise approximately two million years ago.
The Martian mid-latitudes contain numerous small water-ice deposits, collectively termed viscous flow features (VFFs). The shape and topography of the deposits contain information on their past flow history and formation process. In order to access this information, it is imperative to get information on their deformational properties. Here we use a high-resolution digital topography map and ice-penetrating radar data in combination with an inverse method to constrain the deformational properties of a lobate debris apron, a class of VFF, in the southern hemisphere of Mars. We find that while the creep parameter and accumulation rates are not well constrained in absolute values, their ratio is robust. We also find that the creep exponent is most likely n ≤ 3.
One of the main tasks of the Dawn mission is to characterize the potentially ice-rich crust of the dwarf planet Ceres. Ongoing studies reveal morphological features related to ice-rich material such as pits or particular landslides. Here we report the identification of ring-mold craters within the huge impact crater Occator. The Cerean ring-mold craters exhibit strong morphological similarities to the ring-mold craters on Mars, where ice-rich material is thought to be involved in such crater development. We discuss the occurrence of water ice reservoirs in the subsurface and assume that ice-rich material likely plays an important role in the development of ring-mold craters on Ceres. The occurrence of ring-mold craters on the surface of Ceres is not only a sign of water ice reservoirs in the subsurface but can also be used for the study of habitable zones on planetary bodies.
Outflow channel formation on the eastern Hellas rim region is traditionally thought to have been triggered by activity phases of the nearby volcanoes Hadriacus and Tyrrhenus Montes: As a result of volcanic heating subsurface volatiles were mobilized. It is however under debate, whether eastern Hellas volcanism was in fact more extensive, and if there were volcanic centers separate from the identified central volcanoes. This work describes previously unrecognized structures in the Niger–Dao Valles outflow channel complex. We interpret them as volcanic edifices: cones, a shield, and a caldera. The structures provide evidence of an additional volcanic center within the valles, and indicate volcanic activity both prior to and following the formation of the outflow events. They expand the extent, type and duration of volcanic activity in the Circum-Hellas Volcanic Province, and provide new information on interaction between volcanism and fluvial activity.
Lobate debris aprons (LDA) and lineated valley fill (LVF) have been broadly recognized in the mid-latitudes of Mars and their subsequent analyses using data from the SHAllow RADar (SHARAD) instrument has suggested evidence for contemporary ice preserved beneath these features. In this study, we conduct detailed characterization of newly identified LDA flow units within the Tanaica Montes region (39.55˚ N, 269.17˚ E) of Mars to assess and understand the similarities in their emplacement with respect to LDA flow units mapped in other regions of Mars. We utilize the Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) images and SHAllow RADar (SHARAD) datasets for geomorphic and subsurface analysis and Mars Global Surveyor (MGS) Mars Orbiter Laser Altimeter (MOLA) point tracks for topographic analysis. Geomorphic observation of LDA flow units surrounding the montes flanks and massif walls reveal integrated pattern of convergence and divergence and evidence of bending and deflection within the flow lines that resulted in concentric, loop-like flow patterns in the downslope. Brain-terrain texture and craters with varying morphological characteristics (ring-mold type) is suggestive that LDAs may be similar to ice-rich, debris-covered glaciers. MOLA point tack based convex-up topographic profiles of LDAs suggest that their thickness vary in the range of ∼100-200 m in both the northwestern and southeastern portions of study region. Further, the slope values of mapped LDA surfaces within the study region are within ∼0.1˚-4˚. The extent of mapped LDAs within the study region is such that some of the low elevation (∼0.8-1.3 km) portions of montes flanks are surrounded by relatively less extent (up to ∼0.5-0.8 km) of LDA flow units. Geomorphic and topographic evidence for flow units that appear to be superposed on the main LDA body collectively suggest the possibility of episodic glacial activity in the region. Furthermore, based on the alignment of subsurface reflectors with the surrounding plains when a permittivity of ice (3.2) is assumed and the radargram is depth-corrected, we infer that some of the portions of LDA flow units have preserved ice in their subsurface up to ∼300-500 m depth. Crater size frequency distribution of craters counted on LDA surface indicates that the best-fit age is ∼110 Ma. In addition, the LDA surfaces exhibit different best-fit ages for different types of crater morphologies (bowl-shaped, ring-mold and infilled craters) included in the crater count statistics. Together, these observations and the interpretations suggest that most, if not all, of the LDAs in the study region are like classical LDAs mapped in other regions of Mars (e.g. along the mid-latitude dichotomy boundary and eastern Hellas region). These results indicate that a widespread accumulation and preservation of ice has occurred during the Late Amazonian as suggested in previous studies.
Evidence for mid-high latitude glacial episodes existing within the Late Amazonian history of Mars has been reported from analysis of variety of glacial/periglacial landforms and their stratigraphic relationships. In this study, using the Context Camera (CTX) images, we have surveyed the interior of craters within the Alba Mons region of Mars (30°–60°N; 80°–140°W) to decipher the presence of ice-related flow features. The primary goals of this study are to (1) suggest from observations that the flow features identified in the interior of Alba Mons craters have flow characteristic possibly different from concentric crater fill (CCF) landforms and (2) interpret the extent of glacial activity that led to formation of flow features with respect to previously described mid-latitude ice-related landforms. Our geomorphic investigation revealed evidence for the presence of tongue-like or lobate shaped ice-related flow feature from the interior of ∼346 craters in the study region. The presence of ring-mold crater morphologies and brain-terrain texture preserved on the surface of flow features suggests that they are possibly formed of near-surface ice-rich bodies. We found that these flow features tend to form inside both the smaller (<5 km) and larger (>5 km) diameter craters emplaced at a wide range of elevation (from ∼ −3.3 km to 6.1 km). The measurement of overall length and flow direction of flow features is suggestive that they are similar to pole-facing small-scale lobate debris apron (LDA) formed inside craters. Crater size-frequency distribution of these small-scale LDAs reveals a model age of ∼10–100 Ma. Together with topographic and geomorphic observations, orientation measurements, and distribution within the study region, we suggest that the flow features (identified as pole-facing small-scale LDAs in the interior of craters) have flow characteristic possibly different from CCF landforms. Our observations and findings support the results of previous analyses that suggests Mars to have preserved records of multiple debris-covered glacial episodes occurred in the Late Amazonian.
Analyzing the density of impact craters on planetary surfaces is the only known technique for learning their ages remotely. As a result, crater statistics have been widely analyzed on the terrestrial planets, since the timing and rates of activity are critical to understanding geologic process and history. On the Moon, the samples obtained by the Apollo and Luna missions provide critical calibration points for cratering chronology. On Mercury, Venus, and Mars, there are no similarly firm anchors for cratering rates, but chronology models have been established by extrapolating from the lunar record or by estimating their impactor fluxes in other ways. This review provides a current perspective on crater population measurements and their chronological interpretation. Emphasis is placed on how ages derived from crater statistics may be contingent on assumptions that need to be considered critically. In addition, ages estimated from crater populations are somewhat different than ages from more familiar geochronology tools (e.g., radiometric dating). Resurfacing processes that remove craters from the observed population are particularly challenging to account for, since they can introduce geologic uncertainty into results or destroy information about the formation age of a surface. Regardless of these challenges, crater statistics measurements have resulted in successful predictions later verified by other techniques, including the age of the lunar maria, the existence of a period of heavy bombardment in the Moon's first billion years, and young volcanism on Mars.
We conclude our radar imaging survey of Mars, which maps spatial variations in depolarized radar reflectivity using Arecibo S-band (λ12.6 cm) observations from 2005–2012. Whereas our earlier paper (Harmon et al., 2012, Arecibo radar imagery of Mars: the major volcanic provinces. Icarus 220, 990–1030) covered the volcanic regions of Tharsis, Elysium, and Amazonis, this paper includes non-volcanic regions where hydrologic and impact processes can be the dominant resurfacing agents affecting radar backscatter. Many of the more prominent and interesting radar-bright features outside the major volcanic provinces are located in and around Chryse Planitia and Xanthe Terra. These features are identified with: a basin in northeast Lunae Planum containing the combined deposits from Maja Vallis and Ganges Catena outflows; channel outwash plains in western and southern Chryse basin; plateaus bordering chasma/chaos zones, where surface modification may have resulted from hydrologic action associated with incipient chaos formation; and some bright-ejecta craters in Chryse basin, of a type otherwise rare on Mars. Dark-halo craters have also been identified in Chryse and elsewhere that are similar to those seen in the volcanic provinces. Although the cratered highlands are relatively radar-bland, they do exhibit some bright depolarized features; these include eroded crater rims, several unusual ejecta flows and impact melts, and terrain-softened plains. The rims of large impact basins (Hellas, Argyre, Isidis) show a variety of radar-bright features provisionally identified with massif slopes, erosion sediments, eroded pyroclastics, impact melts, and glacial deposits. The interiors of these basins are largely radar-dark, which is consistent with coverage by rock-free sediments. Tempe Terra and Acheron Fossae show bright features possibly associated with rift volcanism or eroded tectonic structures, and northwest Tempe Terra shows one very bright feature associated with glacial or other ice processes in the dichotomy boundary region. The first delay-Doppler images of the radar-bright features from the north and south polar icecaps are presented. Both poles show the circular polarization inversion and high reflectivity characteristic of coherent volume backscatter from relatively clean ice. The south polar feature is primarily backscatter from the residual CO2 icecap (with a lesser contribution from the polar layered deposits), whose finite optical depth probably accounts for the feature's strong S/X-band wavelength dependence. Conversely, the north polar radar feature appears to be mostly backscatter from the H2O-ice-rich polar layered deposits rather than from the thin residual H2O cap. The north polar region shows additional radar-bright features from Korolev Crater and a few other outlying circumpolar ice deposits.
Rock glaciers, regarded as cryospheric ice/water resource in the terrestrial-glacial systems based on their tongue/lobate-shaped flow characteristic and subsurface investigation using ground-penetrating radar. We examined the subsurface, geomorphology, climate-sensitivity and thermophysical properties of a Lobate Flow Feature (LFF) on Mars (30°-60° N and S hemispheres) to compare/assess the potentials of rock glaciers as an analog in suggesting LFFs to be a source of subsurface ice/water. LFFs are generally observed at the foot of impact craters’ wall. HiRISE/CTX imageries from MRO spacecraft were used for geomorphological investigation of LFF using ArcMap-10.0 and subsurface investigation was carried out using data from MRO-SHARAD (shallow radar) after integrating with SiesWare-8.0. ENVI-5.0 was used to retrieve thermophysical properties of LFF from nighttime datasets (12.57 μm) acquired by THEMIS instrument-onboard the Mars Odyssey spacecraft and derive LFFs morphometry from MOLA altimeter point tracks onboard MGS spacecraft. Integrating crater chronology tool (Craterstats) with Arc Map, we have derived the formation age of LFF. Our investigation and comparison of LFF to rock glaciers revealed: (1) LFFs have preserved ice at depth ~50m as revealed from SHARAD radargram and top-layer composed of rocky-debris material with thermal inertia (~300-350 Jm⁻² K⁻¹s-1/2). (2) LFF formation age (~10-100 Ma) corresponds to moderate scale debris covered glaciation of a shorter-span suggesting high sensitivity to obliquity-driven climatic shifts. (3) Presence of polygon cracks and high linear-arcuate furrow-and-ridges on the surface indicates presence of buried ice. This work is a significant step towards suggesting LFF to be a potential source of present-day stored ice/water on Mars.
Lobate debris aprons (LDAs) are midlatitude deposits of debris-covered ice formed during one or more periods of glaciation during the Amazonian period. However, little is known about the climate conditions that led to LDA formation. We explore a hypothesis in which a single, extended period of precipitation of ice on the steep slopes of Euripus Mons (45°S, 105°E-east of the Hellas Basin) produced a flowing ice deposit which was protected from subsequent ablation to produce the LDA found at this location. We test this hypothesis with a numerical ice flow model using an ice rheology based on low-temperature ice deformation experiments. The model simulates ice accumulation and flow for the northern and southern lobes of the Euripus Mons LDA using basal topography constrained by data from the Shallow Radar (SHARAD) and a range of ice viscosities (determined by ice temperature and ice grain size). Simulations for the northern lobe of the Euripus LDA produce good fits to the surface topography. Assuming an LDA age of ∼60 Myr and an expected temperature range of 200 to 204 K (for various obliquities) gives an ice grain size of ≈2 mm. Simulations of the southern section produce poor fits to surface topography and result in much faster flow timescales unless multiple ice deposition events or higher ice viscosities are considered.
Ice-walled melt ponds on the surfaces of active valley-floor rock glaciers and Matthes (Little Ice Age) moraines in the southern Sierra Nevada indicate that most of these landforms consist of glacier ice under thin (ca. 1 - 10 m) but continuous covers of rock-fall-generated debris. These debris blankets effectively insulate the underlying ice and greatly reduce rates of ablation relative to that of uncovered ice. Such insulation explains the observations that ice-cored rock glaciers in the Sierra, actually debris-covered glaciers, are apparently less sensitive to climatic warming and commonly advance to lower altitudes than do adjacent bare-ice glaciers. Accumulation-area ratios and toe-to-headwall-altitude ratios used to estimate equilibrium-line altitudes (ELAs) of former glaciers may therefore yield incorrect results for cirque glaciers subject to abundant rockfall. Inadvertent lumping of deposits from former debris-covered and bare-ice glaciers partially explains an apparently anomalous regional ELA gradient reported for the pre-Matthes Recess Peak Neoglacial advance. Distinguishing such deposits may be important to studies that rely on paleo-ELA estimates. Moreover, Matthes and Recess Peak ELA gradients along the crest evidently depend strongly on local orographic effects rather than latitudinal climatic trends, indicating that simple linear projections and regional climatic interpretations of ELA gradients of small glaciers may be unreliable.
A thin glacial diamicton, informally termed Granite drift, oc- cupies the floor of central Beacon Valley in southern Victoria Land, Antarctica. This drift is ,1.0 m thick and rests with sharp planar contacts on stagnant glacier ice reportedly of Miocene age, older than 8.1 Ma. The age of the ice is based on 40 Ar/ 39 Ar analyses of presumed in situ ash-fall deposits that occur within Granite drift. At odds with the great age of this ice are high-centered poly- gons that cut Granite drift. If polygon development has reworked and retransported ash-fall deposits, then they are untenable as chronostratigraphic markers and cannot be used to place a mini- mum age on the underlying glacier ice. Our results show that the surface of Granite drift is stable at polygon centers and that enclosed ash-fall deposits can be used to define the age of underlying glacier ice. In our model for patterned- ground development, active regions lie only above polygon troughs, where enhanced sublimation of underlying ice outlines high-cen- tered polygons. The rate of sublimation is influenced by the devel- opment of porous gravel-and-cobble lag deposits that form above thermal-contraction cracks in the underlying ice. A negative feed-
The Nilosyrtis Mensae region is important among dichotomy boundary fretted terrain outcrops, as it provides evidence of overprinting of ancient landscapes by a suite of glacial features, providing a composite view of the variety of midlatitude glacial modification processes that can occur during recent Martian ice ages. On the basis of a series of criteria developed for the identification of a glacial origin for lineated valley fill and lobate debris aprons, we interpret stratigraphic, topographic, and textural relationships between lineated valley fill and lobate debris apron morphological units as evidence of local and regional glacial overprinting of the landscape during the recent Amazonian. We document (1) stratigraphic relationships between lineated valley fill subunits, including the presence of apparently superposed and small-scale lobate features, (2) the regional integration and flow of lineated valley fill material, (3) lineated valley fill degradation, and (4) the nature and stratigraphic position of lobate debris aprons. These observations suggest multiple phases or episodes of midlatitude valley glacier activity. These observations, together with those of surface units elsewhere in northern Arabia Terra interpreted as glacially modified landforms, suggest the possibility of midlatitude glacial deposits extending over broad portions of the Martian dichotomy boundary within the past several hundred million years.
Restoration of the dichotomy boundary to its original position to assess
its origin requires a thorough knowledge of processes responsible for
its degradation and retreat. The unique fretted terrain, located along
the Deuteronilus-Protonilus Mensae northern mid-latitude portion of the
boundary, has been long held to provide clues to dichotomy degradation
processes. We use new spacecraft data to show that fretted valleys
display a multitude of characteristics typical of integrated valley
glacial systems on Earth (multiple theater-headed, alcove-like
accumulation areas; sharp arete-like ridges typical of glacial erosion;
converging patterns of downslope valley flow; valley lineation patterns
typical of folding and shear; wrap-around features indicative of flow
around obstacles; and broad piedmont-like lobes as the valley fill
extends out into the northern lowlands). The single integrated system
containing these features covers about 30,000 km2, and is one
of dozens of fretted valleys along the dichotomy boundary in this
region. These relationships suggest that the boundary area was subjected
to very large-scale regional glaciation during the Amazonian.
Recognition and documentation of this important late-stage process
provides information critical to reconstructing the original dichotomy
boundary.
Several contentious issues have arisen from rock glacier nomenclature, for example, whether the term “rock glacier” implies genesis from glacial ice or genesis from permafrost. The situation is compounded since rock glacier classification may be based on several different parameters, some of which are measured and quantified, others inferred. These include: gross morphology, dynamics, processes of formation, location, internal characteristics, thermal regime and age. Uncertainties in specifying the genesis in the light of the potential complexity means that definitions should be related to recognisable topographic forms which allow mapping of such features.The distinction is made between rock glaciers (sensu stricto), which follows the original descriptions and typology of the early years of the 20th century, and protalus lobes. The forms can usually be differentiated in terms of length/ breadth ratios as well as by their relative locations. Some of the most common issues of contention within rock glacier research can be solved by this approach.
Ring-mold shaped craters, interpreted to represent impacts into
relatively pure ice and resulting spallation, are common in lobate
debris aprons near the dichotomy boundary on Mars; their abundance
suggests a debris-covered glacial origin for LDA.
A large number of anomalous landforms on Mars can be attributed to glaciation, including the action of ice and meltwater. Glacial landscapes are concentrated south of lat -33° and in the Northern Plains suggesting vast Austral and Boreal ice sheets. Crater densities on the glaciated terrains indicate that the final glacial epoch occurred late in Martian history. Thus, Mars may have had a relatively warm, moist climate and dense atmosphere much later than previously believed.
Radar sounding data from SHARAD aboard Mars Reconnaissance Orbiter
provide evidence for a substantial component of ice in lobate debris
aprons in the Deuteronilus Mensae region of the mid-northern latitudes
of Mars.
An ⁴⁰Ar/³⁹Ar chronology of in-situ to near in-situ volcanic ashfall deposits indicates that the surficial stratigraphy of Arena Valley extends back at least to middle-Miocene time. Wet-based glacial ice occupied part of Arena Valley more than 11.3 Ma ago. Thick, northeast-flowing ice subsequently engulfed Arena Valley, again more than 11.3 Ma ago. Only minor glacier expansion occurred during Pliocene and Pleistocene time. The maximum Pliocene thickening of Taylor Dome, 35 km inland of Arena Valley, was certainly less than 475 m and probably less than 250 m. Maximum thickening of Taylor Dome was less than 160 m during the Pleistocene.
The preservation of Miocene-and Pliocene-age ashes on steep valley slopes indicates that the major bedrock land-forms of Arena Valley are relict and that little slope evolution/colluviation has occurred during the last 11.3 Ma. The geologic record of Arena Valley glaciation and landscape evolution shows persistent cold-desert conditions and hence implies stability of the adjacent East Antarctic Ice Sheet for at least the last 11.3 Ma.
ABSTRACT: 15.1 INTRODUCTION The concept of the glaciated valley landsystem was introduced by Boulton and Eyles (1979) and Eyles (1983b), to describe the characteristic sediments and landforms associated with valley glaciers in upland and mountain environments. By focusing on the scale of the whole depositional basin, the glaciated valley landsystem has a broader compass than most of the other landsystems explored in this book, which are specific to particular depositional environments. Indeed, glaciated valley landsystems may incorporate ice-marginal, supraglacial, subglacial, proglacial, periglacial and paraglacial landsystems, recording the juxtaposition and migration of very different depositional environments. Additionally, because glaciated valleys occur in every latitudinal environment from equatorial to polar regions, the dimensions of climate and glacial thermal regime add even more variability. Thus the 'glaciated valley landsystem' should be regarded as a family of landsystems, which exhibits considerably more variety than suggested by the original Boulton and Eyles model (Fig. 15.1). Despite this variability, landsystems in glaciated valleys tend to have certain recurrent features, as a result of two main factors: 1. the strong influence of topography on glacier morphology, sediment transport paths and depositional basins 2. the importance of debris from supraglacial sources in the glacial sediment budget. In this chapter, we emphasise the contrasts between glaciers with limited supraglacial debris ('clean glaciers') and glaciers with substantial debris covers in their ablation zones ('debris-covered glaciers'), although it should be recognized that intermediate forms occur between these end members. Before examining the landsystems of glaciated valleys, we begin by considering debris sources and transport pathways through valley glaciers, and the ways in which debris cover influences glacier dynamics. 15-Evans-Glacial-15-ppp 5/27/03 2:38 PM Page 372
Full-text · Article · Jan 2004
An 40Ar/39Ar chronology of in-situ to near in-situ volcanic ashfall deposits indicates that the surficial stratigraphy of Arena Valley extends back at least to middle-Miocene time. Wet-based glacial ice occupied part of Arena Valley more than 11.3 Ma ago. Thick, northeast-flowing ice subsequently engulfed Arena Valley, again more than 11.3 Ma ago. Only minor glacier expansion occurred during Pliocene and Pleistocene time. The maximum Pliocene thickening of Taylor Dome, 35 km inland of Arena Valley, was certainly less than 475 m and probably less than 250 m. Maximum thickening of Taylor Dome was less than 160 m during the Pleistocene. The preservation of Miocene- and Pliocene-age ashes on steep valley slopes indicates that the major bedrock landforms of Arena Valley are relict and that little slope evolution/colluviation has occurred during the last 11.3 Ma. The geologic record of Arena Valley glaciation and landscape evolution shows persistent cold-desert conditions and hence implies stability of the adjacent East Antarctic Ice Sheet for at least the last 11.3 Ma.
Four different dating methods (cosmogenic dating, satellite
interferometry, Ar/Ar analysis of ash fall, and glaciological modeling)
confirm a multi-million year old age for the Mullins Valley
debris-covered glacier in the Antarctic Dry Valleys.
Variations in the Martian water and CO2 cycles with changes
in orbital and rotational parameters are examined using the Geophysical
Fluid Dynamics Laboratory Mars General Circulation Model. The model
allows for arbitrary specification of obliquity, eccentricity, and
argument of perihelion as well as the position and thickness of surface
ice. Exchange of CO2 between the surface and atmosphere is
modeled, generating seasonal cycles of surface ice and surface pressure.
Water is allowed to exchange between the surface and atmosphere, cloud
formation is treated, and both cloud and vapor are transported by
modeled winds and diffusion. Exchange of water and CO2 with
the subsurface is not allowed, and radiative effects of water vapor and
clouds are not treated. The seasonal cycle of CO2 is found to
become more extreme at high obliquity, as suggested by simple heat
balance models. Maximum pressures remain largely the same, but the
minima decrease substantially as more CO2 condenses in the
more extensive polar night. Vapor and cloud abundances increase
dramatically with obliquity. The stable location for surface ice moves
equatorward with increasing obliquity, such that by 45° obliquity,
water ice is stable in the tropics only. Ice is not spatially uniform,
but rather found preferentially in regions of high thermal inertia or
high topography. Eccentricity and argument of perihelion can provide a
second-order modification to the distribution of surface ice by altering
the temporal distribution of insolation at the poles. Further model
simulations reveal the robustness of these distributions for a variety
of initial conditions. Our findings shed light on the nature of
near-surface, ice-rich deposits at midlatitudes and low-latitudes on
Mars.
Detailed geological studies across the highland-lowland boundary in
north central Arabia Terra, Mars provide constraints on the age and
nature of processes responsible for a complex array of structures and
landforms. The area studied is bounded by 27.5° and 47.5°N,
330° and 335°W. Highland basement was formed in Early Noachian
and was extensively resurfaced in Late Noachian. Materials underlying
highland plateaus were emplaced in Middle Noachian. Erosion responsible
for fretted terrane and fretted channels most likely occurred in Early
Hesperian but definitely prior to the middle of the Hesperian and during
or after Middle Noachian. There is good evidence for the involvement of
liquid water in fretted channel formation. Within the area mapped, the
presence of fretted terrane correlates with evidence for extensive
development of large grabens. All lowland materials were emplaced after
the erosion that formed fretted terrane and channels; the earliest of
these materials were emplaced in mid-Hesperian, and the youngest were
emplaced in Late Amazonian. Morphological evidence supports debris flow
or rock glacier processes for the formation of the youngest materials.
Debris flow materials on the floors of fretted channels are much too
young to be related to channel formation. The entire region exhibits a
northerly tilt of ~0.1°-0.15° that formed after deposition of
the oldest lowland materials but before emplacement of Upper Hesperian
and younger debris flow/rock glacier materials. The nature and ages of
structures and landforms in this region are not consistent with the
presence of a Late Noachian to Early Hesperian convergent plate boundary
in northern Arabia Terra.
Phoenix for the first time directly studied ice on Mars and the SHARAD
instrument detected clear evidence for glacial deposits in the
equatorial regions of Mars. We study with the BMST model if these
deposits are the remnants of an earlier climate cycle.
Removal of thick sedimentary sequences on Mars can dramatically alter
surface ages inferred from crater statistics. Hesperian surfaces can
appear to be Amazonian and Amazonian can appear to be newly emplaced.
Analysis of ring-mold crater populations on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars and of ice-impact experiments suggest crater-count-derived ages may be erroneously old.
We reassess the age of the Medusae Fossae Formation using evidence from ancient contacts between the formation and adjacent lava flows. These relationships add stratigraphic information and suggest a Hesperian age for some parts of the formation.
Dry Valley debris-covered glaciers are the last stages of a previously much larger East Antarctic ice sheet and provide clues to the extent of the plateau icefield that covered the Mars dichotomy boundary in the Amazonian; LVF/LDA represent the waning stages.
There is new radar evidence for the presence of debris-covered glacier at 36°N latitude in the Phlegra Montes region of Mars. The depth of the glacier is estimated at about 180 m. This is the closest glacier to the equator found by SHARAD to date.
We compile an inventory of non-polar ice deposits on Mars to estimate water abundance with time during different ancient climate conditions. We find that significant volumes are removed from the system and sequestered in non-polar ice reservoirs.
The distribution of glaciers and deposits formed during build up, maturation, and sublimation of Miocene-age cold-based glaciers (Antarctic Dry Valleys) provides insight into the nature and origin of deposits thought to be of glacial origin on Mars.
Lobate debris aprons examined in new high resolution images show evidence for origin in alcoves as debris-covered glaciers and merging to form lineated valley fill. These deposits suggest periods of glaciation in the Amazonian.
Model investigations of paleo-ice sheets on Mars help identify and interpret glacial deposits observed from orbit and aid in explaining the mechanisms responsible for formation of the ice-rich mantling seen north of ~50N latitude by Mars Odyssey.
We use the geological record of non-polar ice deposits to distinguish between predicted obliquity scenarios for the Late Amazonian climate history of Mars; extended periods of consistently high or low obliquity are unlikely during the last 250 My.
Flow patterns are mapped within lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars. Flowlines are sourced in plateau alcoves and form large, well-integrated systems, consistent with a debris-covered glacier interpretation.
Lobate debris aprons, known to be geomorphic landform indicators of the presence of ground ice, are of special interest for future missions devoted to the research of water on Mars. Lobate debris aprons in fretted terrains of Deuteronilus and Protonilus Mensae (35°–50°N) show typical convex shapes interpreted to be the result of viscous deformation. At the scale of Mars Orbiter Camera (MOC) high-resolution images the surface of these debris aprons shows complex patterns with small pits and buttes. These patterns can be explained by the mantling of dust, the accumulation of interstitial ice, and the subsequent removal of ice by sublimation. The sublimation of the ground ice is especially initiated and accelerated by subsurface heterogeneities like fractures. Theoretical quantification of sublimation rates therefore minimizes sublimation, which is not a homogeneous process, at least over the landforms studied. Crater counts show that the sublimation occurred in the last tens of millions of years up to the recent past. In the point of view of future searching of subsurface ice, only surface layers are submitted to sublimation favoring the conservation of ground ice in deeper layers since the formation of the landform. The geophysical survey of lobate debris aprons would give interesting insights into the subsurface distribution of ice and its seasonal variations, especially in order to measure current sublimation of ground ice.
Lineated valley fill (LVF) in fretted valleys at the dichotomy boundary has been interpreted as glacial in origin. Unknown are (1) the original thickness of the glacier ice, (2) the amount of ice-surface lowering, through sublimation and retreat, to its presently observed level, and (3) whether there were multiple periods of glaciation. We address these questions through analysis of an LVF glacial system. The elevation difference between the upper limit of a previous highstand and the current surface of the LVF at the study site is similar to 920 m. We interpret this difference to be the minimum amount of ice-surface lowering of the glacier system. Consistent with a general lowering of the ice surface are multiple moraines and/or trimlines, and changes in LVF flow patterns, as the ice retreated and decreased in thickness. The superposition of several lobes onto the current surface of the LVF indicates that a phase of alpine glaciation followed the lowering of the valley glacial system. These data suggest that the Late Amazonian glaciation that produced LVF in this region involved significantly larger amounts of ice than previously thought, and that subsequent alpine glaciation followed.
The acquisition of high-resolution photographs of the planet Mars from the Viking orbiters has reinforced former tentative conclusions that permafrost might have played a significant role in landscape development. Despite possible warmer climates and higher heat flows in the past, it appears that conditions favoring permafrost prevailed for extended periods. Different kinds of permafrost phenomena are described, and possible Martian examples are discussed. Attention is given to mass-wasting, chaotic terrain, thermokarst and the formation of alases, canyon features, patterned ground and mantled terrain, and crater morphology.
Impact experiments, cratering and fragmentation, on water ice were performed in order to test the scaling laws previously constructed on rocks and sands for studying the collision process in the planetary history. The installation of a vertical gas gun in a cold room at -18°C (255 K) made it possible to use a projectile of water ice and to get the detailed mass distribution of ice fragments. Experimental results indicated the necessity for large modification of those scaling laws. Material dependence was investigated by using projectiles of ice, aluminum, and polycarbonate. Differences were observed in the morphology and efficiencies of cratering and in the energies required to initiate the fragmentation. Moreover, an abrupt increase of cratering efficiency, suggesting a change of excavation mechanism, was found at a critical diameter of spalled crater. The mass (size) distribution of small ice fragments obeyed a power law with an exponent significantly larger than that in rocks. The exponent was the same as that in Saturn's ring particles estimated from the data by the microwave occultation, which indicates a collisional disruption ring origin.
The Martian fretted terrain between latitudes 30° and 50°N and between 315° and 360°W has been reexamined in light of new Mars Orbiter Camera (MOC) and Mars Orbiter Laser Altimeter (MOLA) data from Mars Global Surveyor. Much of the terrain in the 30°–50° latitude belt in both hemispheres has a characteristic stippled or pitted texture at MOC (1.5 m) scale. The texture appears to result from partial removal of a formerly smooth, thin deposit as a result of sublimation and deflation. A complex history of deposition and exhumation is indicated by remnants of a former, thicker cover of layered deposits. In some hollows and on some slopes, particularly those facing the pole, are smooth textured deposits outlined by an outward facing escarpment. Throughout the study area are numerous escarpments with debris flows at their base. The escarpments typically have slopes in the 20°–30° range. At the base of the escarpment is commonly a deposit with striae oriented at right angles to the escarpment. Outside this deposit is the main debris apron with a surface that typically slopes 2°–3° and complex surface textures suggestive of compression, sublimation, and deflation. The presence of undeformed impact craters indicates that the debris flows are no longer forming. Fretted valleys contain lineated fill and are poorly graded. They likely form from fluvial valleys that were initially like those elsewhere on the planet but were subsequently widened and filled by the same mass-wasting processes that formed the debris aprons. Slope reversals indicate that downvalley flow of the lineated fill is minor. The ubiquitous presence of breaks in slope formed by mass wasting and the complex surface textures that result from mass wasting, deflation, and sublimation decreases the recognizability of the shorelines formerly proposed for this area.
Inverted impact craters (IICs), located in the western Ismenius Lacus region, are evidence of episodes of near-surface ice within the past 5-10 Ma, and are results of surface-deflation due to subsequent climate change.
A summary of techniques used in plasma diagnostics is presented along
with a treatment of the use of lasers for precise interferometric
measurements. The chapter on submillimeter spectroscopy with an
optically pumped laser describes the construction and operation of laser
spectrometers, including a CO2 pumped laser, the theory and performance
of an infrared laser, and a detection system. Dispersive Fourier
transform spectroscopy and electron cyclotron heating in tokamaks are
discussed.
Using climate modeling, we propose a climatic scenario to explain the
formation of glaciers in the northern mid-latitude (e.g.,
Deuteronilus-Protonilus Mensae region) in the recent geological past.
Glaciers in Antarctica provide insight into the origin of debris-covered
glaciers on Mars. The Antarctic analogs suggest that the dichotomy
boundary was largely covered with plateau ice fields during parts of the
Amazonian.
Cold-based glaciers in Antarctica Dry Valleys are characterized by
landforms (drop moraines, sublimation tills, rock glaciers) that are
often different than temperate or wet-based glaciers; these features are
similar to deposits on Mars and may offer clues to their origin.
An integrated system with glacial features exists at 34E, 41N in the
Deuteronilus-Protonilus Mensae region. This 30,000 km2 valley system is
typical of dozens of fretted valleys in this region along the dichotomy
boundary. We compare features described in current geological
observations with results from the University of Maine Ice Sheet Model
(UMISM) that we feel support the glacial interpretation of these
features and also allow speculation as to the timing and processes
responsible for the formation of these features. Geological observations
identify evidence for a number of features that are felt to be
indicative of glacial flow. These include: 1) localized alcoves from
which emanate narrow, lobate concentric-ridged flows interpreted to be
remnants of debris-covered glaciers; 2) alcove depressions perhaps
indicating sublimation of material from relict ice-rich accumulation
zones; 3) plateau-ridge remnants between alcoves typical of glacially
eroded aretes; 4) horseshoe-shaped ridges upstream of topographic
obstacles; 5) convergence and merging of LVF fabric in the down-valley
direction; 6) deformation, distortion and folding of LVF in the vicinity
of convergence; 7) LVF with pits and elongated troughs in distorted
areas; 8) distinctive lobe-shaped termini with associated pitting where
the LVF emerges into the northern lowlands. This evidence defines a
coherent, unified flow regime extending from the upper valley reaches
down to the northern lowlands. Additional support for the glacial
hypothesis comes from a GCM for a dusty-atmosphere Mars with obliquity
set to 35o and a water source in the Tharsis region. The GCM generates a
pattern of ice accumulation in good agreement with these geological
observations. This climate is what one might expect to follow a high-
obliquity excursion of the sort that built ice sheets on the Tharsis
volcanoes. UMISM as used here is an adaptation for the Martian
environment of a thermo-mechanically coupled shallow- ice approximation
terrestrial ice sheet model used for time-dependent reconstructions of
Antarctic, Greenland, and paleo-icesheet evolution on Earth. Starting
with no ice, the model is run for 2 million years. While this is longer
that is expected for any steady climate to hold on Mars, it delivers a
flow pattern that can be compared to the geological interpretations. We
present ice thicknesses, surface elevations, and velocity maps at four
times during the growth of this ice sheet. At 300Ka the flow from the
sides has not yet merged in the centers of the valleys, a configuration
that would not produce the turning flow observed. By 500Ka the beginning
of a coherent downvalley flow is observed with ice from each side of the
valley merging in the center. By 1000Ka there is a well-established
valley glacier extending to the mouths of the valleys. Velocities are as
high as 250 mm/year. By 1500Ka, the glacier extends out of the valleys
onto the northern lowlands. Either 1000Ka or 1500Ka would produce the
observed landforms. We also present comparisons of flow features in
high-resolution THEMIS images with modeled flow at 1000Ka.
Fretted and chaotic terrains are members of a larger family of lowland terrains on the Martian surface. They have formed in equatorial and midnorthern latitudes, within areas reasonably proximate to the extensive volcanic fields of that region. Both are relatively recent developments. Fretted terrain is characterized by extensive, smooth, lowland plains separated from the old cratered upland by an abrupt escarpment of highly irregular planimetric configuration. Chaotic terrain features jumbled assemblages of large, irregular blocks occupying lowlands or depressions within the old cratered upland. Fretted terrain is thought to evolve by recession of a steep bounding escarpment, leaving a smooth lowland floor at a remarkably uniform level. Escarpment recession is speculatively attributed to undermining by evaporation of ground ice exposed within an escarpment face, or, under a different environment, by ground water emerging at its foot. The uniform floor level may reflect the original depth of frozen ground. Removal of debris shed by the receding escarpments could be by eolian deflation, subsequent to weathering by unknown processes to produce material of uniformly small grain size, or by fluvial transport under a vastly different climatic environment. Chaotic terrain is attributed primarily to localized collapse of the cratered upland owing to removal of subsurface material, either ground ice or magma. The ground ice hypothesis suffers from possible quantitative inadequacies, but evacuation of magma seems feasible because of the extensive volcanism in the northern hemisphere. Following collapse, ground ice sapping could have been effective in causing slumps and in modifying the collapsed blocks. Eventually the floors of some areas of chaotic terrain may have been smoothed to the condition of fretted terrain, as suggested by their intimate association. These terrains reflect significant activity on the Martian surface and within the Martian interior during relatively recent times. If liquid water has been the prime agent involved in developing fretted terrain, then it is a fossil feature and carries an implication of an enduring Martian environment vastly different from the environment at present.
The Antarctic Dry Valleys (ADV) are generally classified as a hyper-arid, cold-polar desert. The region has long been considered an important terrestrial analog for Mars because of its generally cold and dry climate and because it contains a suite of landforms at macro-, meso-, and microscales that closely resemble those occurring on the martian surface. The extreme hyperaridity of both Mars and the ADV has focused attention on the importance of salts and brines on soil development, phase transitions from liquid water to water ice, and ultimately, on process geomorphology and landscape evolution at a range of scales on both planets. The ADV can be subdivided into three microclimate zones: a coastal thaw zone, an inland mixed zone, and a stable upland zone; zones are defined on the basis of summertime measurements of atmospheric temperature, soil moisture, and relative humidity. Subtle variations in these climate parameters result in considerable differences in the distribution and morphology of: (1) macroscale features (e.g., slopes and gullies); (2) mesoscale features (e.g., polygons, including ice-wedge, sand-wedge, and sublimation-type polygons, as well as viscous-flow features, including solifluction lobes, gelifluction lobes, and debris-covered glaciers); and (3) microscale features (e.g., rock-weathering processes/features, including salt weathering, wind erosion, and surface pitting). Equilibrium landforms are those features that formed in balance with environmental conditions within fixed microclimate zones. Some equilibrium landforms, such as sublimation polygons, indicate the presence of extensive near-surface ice; identification of similar landforms on Mars may also provide a basis for detecting the location of shallow ice. Landforms that today appear in disequilibrium with local microclimate conditions in the ADV signify past and/or ongoing shifts in climate zonation; understanding these shifts is assisting in the documentation of the climate record for the ADV. A similar type of landform analysis can be applied to the surface of Mars where analogous microclimates and equilibrium landforms occur (1) in a variety of local environments, (2) in different latitudinal bands, and (3) in units of different ages. Documenting the nature and evolution of the ADV microclimate zones and their associated geomorphic processes is helping to provide a quantitative framework for assessing the evolution of climate on Mars.