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Sub-surface ( a ) vertical view parallel to slide direction of an analog avalanche and ( b ) interpretation. a Plan view image for the locations of the cross-sections 1 – 6 . The different sub-areas for collapse and depositional zones and graben are shown in 1 – 6 . The analog has an upper brittle layer where normal faults are evident and a ductile layer underneath with varying thickness throughout the avalanche area. High-angle normal faults ( HANF ) in the upper brittle layer become listric and converge into a low-angle normal fault ( LANF ). These faults accommodate the sliding, tilting, and rotation of edifice blocks in the collapse zone, forming the torevas and their smaller counterpart, first-order type 1 and second-order type 2 hummocks. On the topmost part of the brittle layer are shallower low-angle normal faults that accommodate the sliding, tilting, and rotation of minor blocks at the very top, forming the type 2 hummocks. b A cross-section interpretation of an avalanche
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Hummocks are topographic features of large landslides and rockslide-debris avalanches common in volcanic settings. We use scaled analog models to study hummock formation and explore their importance in understanding landslide kinematics and dynamics. The models are designed to replicate large-scale volcanic collapses but are relevant also to non-vo...
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... cross-sections (Fig. 5a), parallel to the main sliding direc- tion, reveal the avalanche internal structure. The collapse and depositional zones are dissected by normal faults and are separat- ed by a graben. Strike-slip faults, often trending arcuate towards the frontal margin, are difficult to see in this view but are clear in the plan views in Fig. 3. In ...
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... the depositional zone, they create hummocks. Figure 5b shows a cross-sectional interpre- tation and morphology of these structures. ...
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... distinguish two types of hummocks formed in the experiments (Figs. 3 and 5): type 1-primary hummocks and type 2-secondary hummocks. Type 1 hummocks are of two classes: type 1a are the small and generally equant hummocks formed early on through the initial development stages of faulting and may undergo minor breakup during emplacement and type 1b are formed at the same time but are the larger and often ...
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... of avalanche deposits forms the first-order hummocks. Small-scale shear faulting or brittle fracturing separating and detaching the stretched upper layers of the larger primary hummocks forms the type 2 hummocks. They are a boudinage feature of stretched and separated competent layers, such as those seen in many avalanche hummock cuts (e.g., Fig. 5f From the vertical cross-sections, we observe that high-angle normal faults in the upper brittle layer converge into low-angle normal faults towards the lower part, accommodating the sliding, tilting, and rotation of edifice blocks forming the type 1 hum- mocks. The shallower low-angle normal faults or brittle fractures on the topmost ...
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... breaking apart with deformation affecting the surrounding zones. The basal ductile layer becomes thin towards the summit area, and most of it is extruded and spread under the avalanche. The ductile layer may come to the surface due to the high degrees of stretching (the same thing as observed at Socompa ( ). Structures shown in the cross-sections (Fig. 5) are those of late stage 4 when the avalanche is nearly fully ...
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Citations
... However, there is still no direct evidence that toma hills emerge from the fluid-like behavior of rock avalanches. Several laboratory experiments on granular flow have been conducted with focus on rock avalanches (e.g., Pouliquen et al., 1997;Shea and van Wyk de Vries, 2008;Paguican et al., 2014;Valderrama et al., 2018), which were partly able to predict the occurrence based numerical simulations (e.g., Campbell et al., 1995;Mead and Cleary, 2015;Johnson et al., 2016) and for continuum simulations based on the fundamental theory proposed by Savage and Hutter (1989). ...
Toma hills are the perhaps most enigmatic morphological feature found in rock avalanche deposits. While it was already proposed that toma hills might emerge from the fluid-like behavior of rock avalanches, there still seems to be no consistent explanation for their occurrence. This paper presents numerical results based on a modified version of Voellmy's rheology, which was recently developed for explaining the long runout of rock avalanches. In contrast to the widely used original version, the modified Voellmy rheology defines distinct regimes of Coulomb friction at low velocities and velocity-dependent friction at high velocities. When movement slows down, falling back to Coulomb friction may cause a sudden increase in friction. Material accumulates in the region upstream of a point where this happens. In turn, high velocities may persist for some time in the downstream and lateral range, resulting in a thin deposit layer finally. In combination, both processes generate more or less isolated hills with shapes and sizes similar to toma hills found in real rock avalanche deposits. So the modified Voellmy rheology suggests a simple mechanism for the formation of toma hills.
... Statistical analyses of the information retrieved from these measurements allow us to determine the main elongation direction of these hummocks and their morphometric relationships with distance from the source, thus providing valuable information to infer flow kinematics and emplacement dynamics [e.g. Yoshida 2013; Paguican et al. 2014]. ...
During the Late Pleistocene-to-Holocene, the mafic Planchón volcano (35.2 °S, Southern Andes) experienced two important destructive events: a sector collapse to the west and a multiphase explosive eruption transforming the east summit area. We provide new field and laboratory evidence, including geochemical, geochronologic, and geological-morphological analysis, to reconstruct the evolution, triggering mechanisms, and physical parameters of these events.The lateral collapse (48~ka BP) was mainly predisposed by a tectonically westward-inclined substratum and rapid edifice growth rates (0.3–0.48 km3 ka-1). The resulting Planchón-Teno debris avalanche became valley-confined traveling at c. 260 km h-1 up to 95 km distance and forming an 8.6 ± 1.3 km3 deposit. The resulting 4.1 km wide amphitheater was later destroyed at c. 7 ka BP by the multiphase Valenzuela phreatomagmatic eruptions, forming a c. 2.5 km diameter caldera. The case of the Planchón volcano warns that rapidly growing mafic volcanoes imply a substantial catastrophic hazard increase for the surrounding areas.
... Magnarini et al. (2019Magnarini et al. ( , 2021a examined the morphological features of longitudinal ridges and found that the formation of longitudinal ridges could be governed by a unified process associated with stress fluctuations during rock avalanche propagation. Accordingly, previous studies have clearly indicated that the propagation mechanisms of rock avalanches can be inferred from the surficial and internal features of rock avalanche deposits (Dufresne and Davies 2009;Paguican et al. 2014;Wang et al. 2018;Dufresne and Geertsema. 2020). ...
Geomorphological and sedimentological characteristics are key evidences for understanding the emplacement mechanisms of rock avalanches. Based on remote sensing, photogrammetry, and field surveys, the depositional characteristics of the Alasu rock avalanche (ARA) in southern Tianshan, China, were investigated in detail. It is reached that the ARA has a detached rock mass volume of ~ 93 × 106 m3 and propagated 3874 m on rugged terrain with a drop height of 1030 m. Large rock blocks (95,598 rock blocks with sizes ≥ 0.5 m) are widely distributed on the deposit surface. There is no decreasing trend in block size with travel distance for these rock blocks, while jigsaw and sibling structures of megablocks commonly occur in the carapace facies. The size and structural features of megablocks demonstrate that the carapace facies underwent a passive emplacement process with low degrees of fragmentation and disturbance. Furthermore, a series of surficial landforms, including irregular platforms, minor scarps, lateral levees, run-ups, ridges, and troughs, are preserved in the rock avalanche deposit. The most remarkable features are the large, subparallel, curved longitudinal ridges with continuous directional variations and three run-up traces. Extensions of these ridges indicate that the avalanche mass experienced a continuous extension-dominated process in emplacement due to its momentum transfer effect and high energy propagation. These observations and analyses may elucidate the emplacement mechanisms of rock avalanches in rugged landscapes.
... The previous studies were published in which failure mechanisms and modes of the rock avalanche include bulging-slip failure, bulging-toppling, overall slip shear, seismic cracking-slip collapse, block avalanche-slip failure, overall shear dislocation failure, compression-drawing-slip failure (Zhang et al., 2013;Moretti et al., 2015;Zhang et al., 2020b;Moretti et al., 2020;An et al., 2021;Guo et al., 2021;Zhang Y. W. et al., 2022). Regarding the scale of the rock avalanche, researchers suggested that the scale can be divided into individual block collapse or sequential collapse (Paguican et al., 2014;Ouyang et al., 2019). The individual block collapse occurs in a whole rock mass, and the falling rock undergoes consistent motion during the rock avalanche processing. ...
Rock avalanches are a significant threat to transportation or hydraulic infrastructure, as they can also cause catastrophic secondary destruction in large practical engineering or to nearby residents. Earthquake-induced rock avalanches have been the most common and prominent natural hazard phenomena among geological hazards in recent years. Earthquake-induced rock avalanche events usually begin when a massive rock mass or multiple rock masses separate from a rock slope, progressively fragmenting and transforming into fast-moving, cohesionless rock falls. Earthquake-induced sequential collapse often occurs on weathered and fractured rock cliffs in horizontal strata, and its kinematic dynamics and destabilization mechanism are significantly different from those of isolated collapse due to weathering. In this study, the failure characteristics of the initiation and movement process of the avalanche are revealed in detail, through physical model experiments and analytical solutions, thereby obtaining an earthquake-controlled mechanical model equation. Our methods use the inflection points of the displacement time curve at the top of the rock wall and the digital images acquired by the shaking test bench to quantify the critical damage time point and to characterize the critical morphology of continuous collapse. A mathematical model of analytical solution is proposed, which aims to address the kinematic mechanics mechanism of sequential collapse under translational and rotational motion models. The comparative analysis results of the experiment and analytical solutions reveal that the transformed motion pattern is controlled by the ratio between the model stacking height, the rock block size, and the seismic acceleration. Whereas the rotational motion pattern is mainly influenced by the nodal dip angle, model stacking height, and seismic acceleration. The results of the study are of great scientific importance to elucidate the destruction mechanism of the earthquake-induced sequential collapse of rock avalanches and to determine the evolution characteristic of subsequent rockfalls motion of dangerous rocks. The proposed framework for the analysis of rock avalanches can be applied to understand the critical topographic features and mechanical mechanism behavior of analogous geological hazards.
... There are many other microtopographic features common to certain types of landslides ( Fig. 11.2). These may include hummocks, transverse and parallel cracks and ridges, sag ponds, and accumulations of organic debris Dufresne & Davies, 2009;Paguican et al., 2014). In some cases, the rupture surface may be exposed and reveal striations called slickensides. ...
This book introduces an innovative approach to sustainable and regenerative mountain development. Transdisciplinary to biophysical and biocultural scales, it provides answers to the "what, when, how, why, and where" that researchers question on mountains, including the most challenging: So What! Forwarding thinking in its treatment of core subjects, this decolonial, non-hegemonic volume inaugurates the Series with contributions of seasoned montologists, and invites the reader to an engaging excursion to ascend the rugged topography of paradigms, with the scaffolding hike of ambitious curiosity typical of mountain explorers.
Chapter 8 is available open access under a Creative Commons Attribution 4.0 International License via link.springer.com.
... There are many other microtopographic features common to certain types of landslides ( Fig. 11.2). These may include hummocks, transverse and parallel cracks and ridges, sag ponds, and accumulations of organic debris Dufresne & Davies, 2009;Paguican et al., 2014). In some cases, the rupture surface may be exposed and reveal striations called slickensides. ...
This chapter begins by giving a brief overview of the forces involved in the geodynamics of mountains and mountain ranges, including the processes needed for the generation of mass movement processes. In the remaining parts of this chapter, the following issues associated with mountain landslides are addressed: the anatomy of landslides, common landslide materials, and landslide movement types, along with landslide causes and triggers. The purpose of the final section of this chapter is to reflect on the extent to which the increasing intensity of human activities on mountainscapes, particularly climate change and urbanization, has magnified potential disaster risk for downslope settlements.
... Similar observations of toma transport within highly fluidized mass movements were reported from the Fernpass site (Prager et al., 2006) and analogue models (Paguican et al., 2014). Prager et al. (2006) interpreted the onlapping sediments as post-rockslide fluvial clasts. ...
Rockslides and rock avalanches are amongst the most destructive natural hazards in the alpine environment. The Flims rockslide is the largest known rock-slope failure in the Alps, which provides excellent outcrops and has fascinated researchers since the early 20th century. The postulated impact of the Flims rockslide on Lake Bonaduz caused intensely fluidized rock material, which formed the Bonaduz Formation and toma hills, probably accompanied by a catastrophic impact wave. So far, this hypothesized sequence of events is based only on sedimentological and geomorphic analyses. We present electrical resistivity tomography (ERT) profiles, which we correlated with the sedimentological information obtained from outcrops and drill logs. Here, geophysical evidence on a metre and decametre scale complements prior outcrop and sample intervals with much smaller representativeness. Our study provides new insights into the distribution, thickness, and internal structure of the Bonaduz Formation and the toma hills as well as other flood deposits around the Ils Aults, where we studied the sediment to a depth of up to 160 m. There is geophysical evidence that the Bonaduz Formation formed an onlap onto the Ils Aults and is thus the stratigraphically younger unit. The toma hills consist of blocky cores with an agglomeration of smaller mixed sediments, which drift and override the toma core, causing their smoothly shaped top. We consider simultaneous transport of the hills within the Bonaduz Formation but a slightly slower movement at the front due to a bulldozing effect. This study contributes to an improved understanding of (i) the complex stratigraphical context of the Tamins and Flims deposits, (ii) water-rich entrainment in rock avalanches, and (iii) the genesis and transport of toma hills.
... In the absence of direct observations of rock avalanche dynamics, surface features can provide important insights into the dynamics of avalanches. Particularly, the surface features of deposits, which include hummocks, longitudinal or transverse ridges, and extensive fault and fold networks, have been widely used to investigate avalanche dynamic processes and reconstruct emplacement mechanisms (Dufresne and Davies, 2009;Paguican et al., 2014;Dufresne et al., 2018;Strom and Abdrakhmatov, 2018;Zeng et al., 2020). ...
... In fact, these longitudinal ridges were straight when they formed (i.e., along the main movement direction) but curved along the underlying topography owing to lateral debris spreading. Notably, the longitudinal ridges formed in the granular flows were controlled by material density, emplacement velocity, and frictional behavior (Forterre and Pouliquen, 2003;De Blasio, 2014;Paguican et al., 2014;Dufresne et al., 2016). ...
Rock avalanches are characterized by granular flows of dry and disintegrating rock masses detached from a mountain slope. They deposit large volumes of megablocks, which have distinct surface features and are known to cause catastrophic damage. The mechanisms and dynamic processes of such disasters are still under debate, owing to insufficient real-time data. Here, field surveys and high-resolution digital elevation models (DEMs) were used to investigate the dynamic processes of the Tagharma rock avalanche (Kongur Mountain, Eastern Pamir, China), providing a unique case study for determining the long runout mechanisms and dynamic processes of the avalanche based on its morphology and sedimentology. The processes and dynamics of the event were reconstructed through fragmented rock debris combined with surface morphology and substrate implications. We analyzed how fragmentation occurs at impact and studied the generated fragment size distributions. Finally, the emplacement dynamics of the Tagharma rock avalanche were reconstructed. Our results indicate that the dynamic process of the Tagharma rock avalanche consisted of two main stages: (i) foliated megablocks having a strong interaction between the rock avalanche mass and the ground (dynamic rock mass disintegration), and (ii) distal “passive spreading” when the avalanche mass encountered deformable substrates (sediment bulldozing).
... Rock avalanches are notoriously difficult to real-time investigation because they generally occurred in high mountainous regions and lasted a short duration (Hewitt et al., 2008;Strom and Abdrakhmatov, 2018). Thus, it is a significant approach to research on their catastrophic emplacements by observations of surficial and internal sedimentological structures, especially in the recent decade of years as the improvement of field investigation methods (Yarnold and Lombard, 1989;Blair, 1999;Dufresne and Davies, 2009;Paguican et al., 2014;Dufresne et al., 2016aDufresne et al., , 2016bStrom and Abdrakhmatov, 2018;Wang et al., 2018Wang et al., , 2019aWang et al., , 2019bWang et al., , 2020Magnarini et al., 2021). So far, numerous commonly surficial morphological features were recognized, including Toreva blocks, trimlines, superelevation, flowbands, transverse and longitudinal ridges, hummocks, molards, lateral levees, and distal fingers. ...
... Despite a slight deceleration occurred for part avalanche masses when they impacted with the hills, the moving avalanche mass still behaved as a flow-like movement at an extremely high velocity that contributed to the formation of these flexuous flowbands and normal faults. Generally, normal and strike-slip faults are efficient geological evidence of rapid extension processes (Dufresne, 2009;Paguican et al., 2014;Shea and van Wyk de Vries, 2008). Therefore, the development of numerous normal faults in the transition zone of the IRA demonstrates a rapid extension should occur in the transition zone. ...
... Similar observations were also reported in the Round Top deposit (Dufresne et al., 2010) and the Luanshibao deposit (Wang et al., 2018). From the viewpoint of stress regime, they are usually formed under radial extension with the lateral velocity increasing further and being close to the longitudinal velocity (Dufresne and Davies, 2009;Andrade and van Wyk de Vries, 2010;Paguican et al., 2014;Wang et al., 2019b). In the IRA deposit, interestingly, numerous hummocks scatter in the central area, which is similar to the El Magnifico deposit (Crosta et al., 2017b). ...
Catastrophic rock avalanches are widely distributed on Earth and share a series of common diagnostic features that play a vital role in revealing their emplacement mechanisms. Combined with satellite imagery, field investigation, and statistical analysis, a comprehensive investigation is conducted on the gigantic Iymek rock avalanche (IRA) in eastern Pamir, China. The IRA with a volume of ~0.98 km³ detached mass advanced 16.3 km on an unconfined terrain, covered an area of 48.5 km² with a depth of 10–90 m, and deposited an estimated volume of 1.37 km³ deposits, making it the largest rock avalanche known in China. Its spectacular emplacement landscape provides an excellent laboratory for studying rock avalanches. Morphologically, the IRA deposit exhibits characteristic undulating features, including trimlines, longitudinal ridges, hummocks, transverse ridges, raised distal edge, and raised lateral levees. On the profile, numerous representative landslide-tectonic structures, principally composed of the preserved stratigraphic sequence, pervasive shear bands, spectacular clastic dikes, diapiric intrusion, folds, and normal/thrust faults, are revealed. The sequential assemblage of these morphological landforms and internal structures demonstrates that the propagation of the IRA should behave like a laminar flow with distributed shearing and obey three major stress processes, i.e. extension-dominated process in the proximal area, compression-dominated process in the distal area, and slightly lateral spreading in the central area and the areas adjacent to the margin of the deposit sheet. During its propagation, the strong substrate, mainly composed of gravel-dominated coarse material, should play a decisive role in casting most of the depositional landscapes. Restricted by the strong substrate, prominent lateral levees are well-developed in the accumulation zone with a series of rolling flame structures. This powerfully indicates that the formation of the lateral levees should be attributed to a continuously sideward movement of the frontal mass due to the push from the rear part instead of a particle self-segregation mechanism. Furthermore, the cutting relationship between the clastic dikes and subhorizontal shear bands in local positions indicates that the localized liquefaction of the substrate is not a contributor for the high mobility of the IRA and is only a product of the strong interaction between the sliding mass and the substrate at the final stage. This comprehensive study not only provides important information that contributes to an interpretation of similar features on Earth, but also yields insight into the underlying mechanisms responsible for the emplacement of rock avalanches.
... The study of the sedimentology, internal architecture, and morphology of VDA deposits (VDAD) permits the determination of the internal and external conditions of the flow, such as the nature of the material that collapsed, the rheology of the flow, the trajectory through which the VDA passed, and the syn and post-depositional processes (e.g., Palmer et al., 1991;Dufresne et al., 2021;Waythomas et al., 2000;van Wyk de Vries et al., 2000;Dufresne and Davies, 2009;Paguican et al., 2014;Roverato et al., 2015Roverato et al., , 2018Valderrama et al., 2016). There are various hypotheses related to the dynamic behavior of VDAs that are based on field observations of the deposit's morphology, sedimentology, and structural features. ...
... There are various hypotheses related to the dynamic behavior of VDAs that are based on field observations of the deposit's morphology, sedimentology, and structural features. The proposed models are plug flow (e.g., Voight et al., 1983;Takarada et al., 1999), translational slide (e.g., van Wyk de Vries et al., 2001;Paguican et al., 2014), and sliding over multiple shear zones (e.g., Glicken, 1991Glicken, , 1996Roverato et al., 2015;Paguican et al., 2021). Neither mechanism proposes large-scale turbulence during transport. ...
... These fractures are mainly interpreted as fractures generated due to lithostatic decompression when the mass collapse (e.g., Glicken, 1996;Alidibirov and Dingwell, 2000) or subordinately as a result of the high pressure suffered by the clasts during transport (e.g., Ui et al., 1986;Glicken, 1996). Some authors indicate that when the jigsaw blocks appear throughout the avalanche's longitudinal extent, they indicate a minimum internal deformation during propagation (e.g., Paguican et al., 2014;Dufresne et al., 2016). Component analysis showed that the VDAD is composed mainly of Chimpa and Cajón Units and subordinately by the Basal Unit. ...
Understanding the flow dynamics in debris avalanches is an important tool to advance the knowledge about lateral failures of volcanoes, a fundamental step towards an accurate risk assessment and mitigation in volcanic areas. We describe the morphological, grain-size, and clast surficial textures of the Casana volcanic debris avalanche deposit emplaced by the sector collapse of Chimpa volcano (Central Puna, Argentina). We focused our analysis on the volcanic debris avalanche deposit, characterized by ridges, reduction in downflow matrix grainsize, jigsaw-cracked blocks in the whole extent of the deposit, collision superficial textures in grains (fractures, percussion marks, and voids). Sedimentological and textural analysis show a progressive disintegration and fracturing of the larger particles with greater distance in a dry, granular flow with minimal internal deformation during propagation. Casana avalanche behaved like a rigid body in the proximal area and as a granular flow in the medial and distal reach. Block sliding mechanisms generated the toreva block in the proximal region whereas granular flow produced the debris avalanche deposits. This is an example of how different mechanisms can interact during debris avalanche emplacement, which are strictly related to the cause of the volcano instability, the lithology and the degree of alteration of the source mass, and its interaction with paleotopography. Although the geological risk of the proposed study area is low, the study of Casana VDAD is important to understand similar processes in other volcanoes providing constraints to hazard assessment.
