Abstract
Snow slab avalanches, characterized by a distinct, broad fracture line, are released following anticrack propagation in highly porous weak snow layers buried below cohesive slabs. The ...anticrack mechanism is driven by the volumetric collapse of the weak layer, which leads to the closure of crack faces and to the onset of frictional contact. Here, on the basis of snow fracture experiments, full-scale avalanche measurements and numerical simulations, we report the existence of a transition from sub-Rayleigh anticrack to supershear crack propagation. This transition follows the Burridge–Andrews mechanism, in which a supershear daughter crack nucleates ahead of the main fracture front and eventually propagates faster than the shear wave speed. Furthermore, we show that the supershear propagation regime can exist even if the shear-to-normal stress ratio is lower than the static friction coefficient as a result of the loss of frictional resistance during collapse. This finding shows that snow slab avalanches have fundamental similarities with strike-slip earthquakes.
In April 2000 a large-scale rock avalanche dammed the Yigong Zangpo River, forming an extensive rockslide-dammed lake. The impoundment lasted for 62days before a catastrophic breaching caused a ...massive outburst flood in the Yarlung Zangpo (Tibet) and the Dihang rivers (India) that travelled downstream to the main floodplain of the Brahmaputra in northeastern India. In response to discrepancies in the published literature on the event, we present a review and re-evaluation of the characteristics of the rock avalanche and associated landslide-dammed lake. We use digital topographical data (SRTM-3) and dynamic landslide modelling (DAN-W and DAN3D) to determine the salient characteristics of the damming landslide and to characterise its behaviour. Our analysis indicates that the volume of the damming rockslide was ca. 115Mm3, including 91Mm3 from the initial rockslope failure (bulked during disaggregation to 109Mm3) and 6Mm3 from entrainment during its 10.1km travel down Zhamulong gully. The debris travelled with an average velocity of 15–18m/s and resulted in a landslide dam on the Yigong River with a minimum height of about 55m. Using LANDSAT-7 imagery (obtained before, during, and after impoundment) in conjunction with an SRTM-3 DEM, we reproduced the filling of the lake. We determine that the landslide dam formed an extensive reservoir with an impounded volume of 2.015Gm3 and a maximum possible lake level of 2264masl (rounded to 2265masl). Our figures differ from those previously published but are believed to be well-constrained verifiable estimates of the volumes of the 2000 Yigong events. The outburst occurred after an attempt by army personnel to manually dig a spillway over the landslide debris and resulted in the entire volume of the lake draining in about 12h. The outburst flood travelled over 500km south into India, with a recorded rise in river level of 5.5m at the Pasighat gauging station, 462km downstream. In terms of historical outburst volumes from rockslide-dammed lakes, the volume of the 2000 Yigong event is only exceeded by that of the 1841 outburst flood from the Indus River rockslide-dammed lake, northern Pakistan.
Strongly correlated systems can exhibit unexpected phenomena when brought in a state far from equilibrium. An example is many-body localization, which prevents generic interacting systems from ...reaching thermal equilibrium even at long times1,2. The stability of the many-body localized phase has been predicted to be hindered by the presence of small thermal inclusions that act as a bath, leading to the delocalization of the entire system through an avalanche propagation mechanism3–8. Here we study the dynamics of a thermal inclusion of variable size when it is coupled to a many-body localized system. We find evidence for accelerated transport of thermal inclusion into the localized region. We monitor how the avalanche spreads through the localized system and thermalizes it site by site by measuring the site-resolved entropy over time. Furthermore, we isolate the strongly correlated bath-induced dynamics with multipoint correlations between the bath and the system. Our results have implications on the robustness of many-body localized systems and their critical behaviour.The presence of small thermal regions in a many-body localized system could lead to its delocalization. An experiment with cold atoms now monitors the delocalization induced by the coupling of a many-body localized region with a thermal bath.
Snow is highly sensitive to atmospheric warming. However, because of the lack of sufficiently long snow avalanche time series and statistical techniques capable of accounting for the numerous biases ...inherent to sparse and incomplete avalanche records, the evolution of process activity in a warming climate remains little known. Filling this gap requires innovative approaches that put avalanche activity into a long-term context. Here, we combine extensive historical records and Bayesian techniques to construct a 240-y chronicle of snow avalanching in the Vosges Mountains (France). We show evidence that the transition from the late Little Ice Age to the early twentieth century (i.e., 1850 to 1920 CE) was not only characterized by local winter warming in the order of +1.35 °C but that this warming also resulted in a more than sevenfold reduction in yearly avalanche numbers, a severe shrinkage of avalanche size, and shorter avalanche seasons as well as in a reduction of the extent of avalanche-prone terrain. Using a substantial corpus of snow and climate proxy sources, we explain this abrupt shift with increasingly scarcer snow conditions with the low-to-medium elevations of the Vosges Mountains (600 to 1,200 m above sea level a.s.l.). As a result, avalanches migrated upslope, with only a relict activity persisting at the highest elevations (release areas >1,200 m a.s.l.). This abrupt, unambiguous response of snow avalanche activity to warming provides valuable information to anticipate likely changes in avalanche behavior in higher mountain environments under ongoing and future warming.
Detailed sedimentological studies concerning different facies types and the factors influencing their development (such as lithology, topography, substrates, etc.) were carried out at the carbonate ...Tschirgant rockslide-rock avalanche deposit in the Eastern Alps of Austria. Several depositional facies and sub-facies have been identified at this and other sites by many researchers. These facies are found throughout the debris, regardless of depth or travel distance, and result from highly heterogeneous stress distributions in time and space during emplacement. One of the most important recent observations in terms of emplacement dynamics is that shear is not confined to the base, but is distributed throughout the debris (except the coarse carapace). Due to the preservation of source stratigraphy in these non-turbulent mass movements, any horizontal facies or grain size variations need to be regarded in context since they strongly depend on source stratigraphy and hence the spatial distribution of lithologies (i.e. geological units of different mechanical properties). For example, some lithologies do not form a boulder carapace due to absence of large in-situ blocks in the source rock mass. However, at Tschirgant, slight facies “maturation” with distance (within the same lithology) is observed, i.e. clast fragmentation progresses to create the distinct, facies-characteristic grain size distribution only after some distance travelled. These details are revealed through facies-based sampling and analysis. Studies based on bulk sampling, in some cases, observed progressively reduced grain sizes with distance and depth – which might be a function of added variations within different facies sampled together. In this paper, the wealth of observations on rockslide and rock avalanche sedimentology of the past decades is combined with a detailed case study of a (lithologically) relatively simple deposit, to outline global and site-specific depositional structures and facies with the aim to summarize, review, and refine the current state of knowledge on rock avalanche and rockslide emplacement processes.
Surficial mass movements, such as debris avalanches, rock falls, lahars, pyroclastic flows, and outburst floods, are a dominant hazard at many volcanoes worldwide. Understanding these processes, ...cataloging their spatio-temporal occurrence, and detecting, tracking, and characterizing these events would advance the science of volcano monitoring and help mitigate hazards. Seismic and acoustic methods show promise for achieving these objectives: many surficial mass movements generate observable seismic and acoustic signals, and many volcanoes are already monitored. Significant progress has been made toward understanding, modeling, and extracting quantitative information from seismic and infrasonic signals generated by surficial mass movements. However, much work remains. In this paper, we review the state of the art of the topic, covering a range of scales and event types from individual rock falls to sector collapses. We consider a full variety of volcanic settings, from submarine to subaerial, shield volcano to stratovolcano. Finally, we discuss future directions toward operational seismo-acoustic monitoring of surficial mass movements at volcanoes.
•Surficial mass movements are common in volcanic areas and generate signals that are recorded by seismic and acoustic arrays.•Our understanding of the relation of these signals to characteristics of the mass movement is limited but improving.•We review the literature on the study of mass movements at volcanoes using seismic and acoustic monitoring.•We discuss future research directions and steps toward operational monitoring.
Water accumulating on microstructural transitions inside a snowpack is often considered a prerequisite for wet snow avalanches. Recent advances in numerical snowpack modeling allow for an explicit ...simulation of this process. We analyze detailed snowpack simulations driven by meteorological stations in three different climate regimes (Alps, Central Andes, and Pyrenees), with accompanying wet snow avalanche activity observations. Predicting wet snow avalanche activity based on whether modeled water accumulations inside the snowpack locally exceed 5–6% volumetric liquid water content is providing a higher prediction skill than using thresholds for daily mean air temperature, or the daily sum of the positive snow energy balance. Additionally, the depth of the maximum water accumulation in the simulations showed a significant correlation with observed avalanche size. Direct output from detailed snow cover models thereby is able to provide a better regional assessment of dangerous slope aspects and potential avalanche size than traditional methods.
Key Points
Simulations of water accumulating on microstructural transitions inside a snowpack can be used to predict wet snow avalanche activity
Using the presence of water accumulations provides a higher prediction skill than the snow energy balance or air temperature
The depth below the snow surface where the water is accumulating was found to provide an estimate of avalanche size
Experiments in various neural systems found avalanches: bursts of activity with characteristics typical for critical dynamics. A possible explanation for their occurrence is an underlying network ...that self-organizes into a critical state. We propose a simple spiking model for developing neural networks, showing how these may "grow into" criticality. Avalanches generated by our model correspond to clusters of widely applied Hawkes processes. We analytically derive the cluster size and duration distributions and find that they agree with those of experimentally observed neuronal avalanches.
One of the largest concentrations of giant landslides (≥108 m3) in Patagonia is in the eastern part of Lago Cochrane/Pueyrredón (LP) valley in Argentina. In addition to minor earthflows and rock ...slides, this landslide cluster is dominated by rock and debris avalanches that affect the northern slope of Meseta Belgrano, the largest of which have volumes >1 km3 and a runout of >10 km. To determine the chronology of these large landslides and their relationship to the geological setting and the glacial history related to the Last Glacial Maximum (LGM) ∼20–18 ka ago, we combined geomorphological mapping with absolute dating (luminescence and radiocarbon dating) and numerical modelling of slope stability. Dating and cross-cutting relationships with glaciolacustrine deposits suggest that some of the largest rock avalanches collapsed directly into a glacial lake between ∼17 and ∼12 ka, soon after deglaciation, but some were pre-glacial and landslide activity continued until today, posing a potential hazard to the area. In agreement with these data, numerical modelling suggests that slope stability was only marginally affected by ice retreat and glacial lake drainage, and landslides were most likely favoured by relatively low rock strength, related glacially-conditioned topography, and, possibly, seismic activity. A newly identified active fault at the base of the Meseta Belgrano, whose activity was likely enhanced by postglacial rebound, was probably the key factor that concentrated postglacial rock avalanches into the LP valley. We conclude that exceptionally large (km-scale) landslides can occur on slopes made of relatively weak rocks in a glacially-conditioned topographic setting even without a strong direct triggering effect of deglaciation, while fatigue due to long-term seismicity may promote collapse.
•Meseta Belgrano hosts the largest rock avalanches in Patagonia.•Most of the landslide volume mobilized between ∼17 and 12 ka.•Recurrent landslides continuing to a lesser extent in the Holocene.•Long-term seismicity is a likely cause of slope instability.•Largest rock avalanches likely triggered by stronger postglacial earthquakes.
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