Insights into Rock-Ice Avalanche Dynamics by Combined Analysis of Seismic Recordings and a Numerical Avalanche Mode

Rock‐ice avalanches larger than 1 × 106 m3 are high‐magnitude, low‐frequency events that may occur in all ice‐covered, high mountain areas around the world and can cause extensive damage if they reach populated regions. The temporal and spatial evolution of the seismic signature from two events was analyzed, and recordings at selected stations were compared to numerical model results of avalanche propagation. The first event is a rock‐ice avalanche from Iliamna volcano in Alaska which serves as a “natural laboratory” with simple geometric conditions. The second one originated on Aoraki/Mt. Cook, New Zealand Southern Alps, and is characterized by a much more complex topography. A dynamic numerical model was used to calculate total avalanche momentum, total kinetic energy, and total frictional work rate, among other parameters. These three parameters correlate with characteristics of the seismic signature such as duration and signal envelopes, while other parameters such as flow depths, flow path and deposition geometry are well in agreement with observations. The total frictional work rate shows the best correlation with the absolute seismic amplitude, suggesting that it may be used as an independent model evaluation criterion and in certain cases as model calibration parameter. The good fit is likely because the total frictional work rate represents the avalanche ’s energy loss rate, part of which is captured by the seismometer. Deviations between corresponding calculated and measured parameters result from site and path effects which affect the recorded seismic signal or indicate deficiencies of the numerical model. The seismic recordings contain additional information about when an avalanche reaches changes in topography along the runout path and enable more accurate velocity calculations. The new concept of direct comparison of seismic and avalanche modeling data helps to constrain the numerical model input parameters and to improve the understanding of (rock‐ice) avalanche dynamics

On characteristics and flow dynamics of large rapid mass movements in glacial environments

Current developments of the climate involve dramatic changes in the high-mountain cryosphere, such as glacial retreat, permafrost degradation, development of new glacial lakes, release of huge masses of friable and often steep debris, and altered precipitation patterns. Consequences are increased mass turnover rates, characterized by higher frequencies and magnitudes of rock falls, debris flows and slow slope movements, but also by large (V > 106 m3) and rapid mass movements such as landslides, rock-, debris- or ice-avalanches and debris flows. Large rapid mass movements in or from glacial and periglacial high mountain environments can be attributed by extraordinary mobility, flow transformations or chain reactions implying high hazard potentials if they are reaching populated areas such as demonstrated by a number of disastrous events during the last decades. The present study concentrates on the propagation and deposition of large rapid mass movements in glacial environments. This includes aspects from general landslide long-runout mechanisms, several case studies in volcanic and non-volcanic glacial environments, numerical runout modeling, seismic data analysis, physical flow experiments in the laboratory and an empirical analysis of specific flow characteristics of large rapid mass movements in glacial environments. Simple empirical runout modeling of mass movements was applied for preliminary regional hazard assessments. For specific retrospective local case studies, physically-based dynamic numerical simulations were performed. Besides required geometric similarities between the modeled and real event, the rheologic model input parameters could be better constrained by fitting dynamic model output parameters to seismic data. As a result, insights into flow dynamics of rock-ice avalanches can be improved, such as by more accurate velocity estimations that is of interest for hazard mitigation measures. Laboratory experiments in large vertically rotating drum flumes were used to quantify the influence of ice on the friction coefficient of granular gravel-ice mixtures to make conclusions on the effects of ice on the mobility of natural rock-ice avalanches. The friction coefficient was found to decrease linearly with increasing volumetric ice content by a maximum of ~20%. For longer process durations, melting ice caused partial or complete liquefaction of the mass with a consequent reduction of the friction coefficient by nearly 50%. An empirical analysis of 64 large rock-ice avalanches has shown that the effect of the ice content is not a dominant factor in natural events. The mobility of the events revealed a correlation with the relative flow path length leading over a glacier, confirming quantitatively that the low-friction glacier surfaces effectively contribute in extending the runout distance of rapid mass movements as hypothesized by previous authors. Furthermore, rock-ice avalanches with high water content are often among the most mobile events. However, the most disastrous rapid mass movements from glacial environments have often shown a combination of features, such as large volumes, flow paths over glaciers or smooth bedrock, confined flow, high ice and water contents, strong material entrainment and flow transformations or chain reactions. Despite the broad variety and complex process interactions in large rapid mass movements in glacial environments, insights to several aspects were deepened. The findings should be extended in future by similar and additional methods to serve once as a strong basis for scenario-based modeling. Die heutige Entwicklung des Klimas beinhaltet dramatische Veränderungen der Hochgebirgs-Kryosphäre, beispielsweise die Bildung neuer glazialer Seen, die Freigabe grosser Mengen an lockerem, häufig steilem Schutt, sowie veränderten Niederschlagsbedingungen. Die Folgen sind verstärkte Massenumsatzraten, welche durch erhöhte Frequenzen und Magnituden von Felsstürzen, Murgängen und langsamen Hangbewegungen, jedoch auch durch grosse (V > 106 m3) und schnelle Massenbewegungen wie zum Beispiel Bergstürze, Fels-, Schutt- oder Eislawinen und Murgänge in Erscheinung treten. Grosse schnelle Massenbewegungen in oder von glazialen und periglazialen Hochgebirgs- gebieten charakterisieren sich durch ausserordentliche Mobilitäten, Fliesstransformationen oder Kettenreaktionen, welche ein grosses Gefahrenpotenzial beinhalten sofern besiedelte Gebiete erreicht werden – wie es durch einige katastrophale Ereignisse in den letzten Jahrzehnten gezeigt wurde. Die vorliegende Studie konzentriert sich auf das Fliessen und die Ablagerung von grossen schnellen Massenbewegungen in glazialen Gebieten. Dies beinhaltet Aspekte allgemeiner Mechanismen für grosse Auslaufdistanzen von Bergstürzen, einige Fallstudien in vulkanischen und nicht-vulkanischen glazialen Gebieten, numerische Auslaufmodellierungen, Analysen seismischer Daten, physikalische Fliessexperimente im Labor, sowie eine empirische Analyse spezifischer Fliesseigenschaften von grossen schnellen Massenbewegungen in glazialen Gebieten. Für vorläufige regionale Gefahrenbeurteilungen wurden einfache empirische Auslaufmodellierungen von Massenbewegungen verwendet während in spezifischen retrospektiven lokalen Fallstudien physikalisch-basierte dynamische Auslaufmodellierungen durchgeführt wurden. Neben den nötigen geometrischen Ähnlichkeiten zwischen den modellierten und den echten Ereignissen, konnten die rheologischen Eingangsparameter durch Einpassung dynamischer Modell-Ausgangsparameter an seismische Daten besser eingeschränkt werden. Das Ergebnis ist ein besserer Einblick in die Fliessdynamik von Fels-Eislawinen, wie beispielsweise genauere Geschwindigkeitsabschätzungen welche für Massnahmen der Gefahrenreduzierung von Interesse sind. Um den Effekt von Eis auf den Reibungskoeffizienten granularer Kies-Eisgemische und damit auf den Einfluss von Eis auf die Mobilität von natürlichen Fels-Eislawinen zu quantifizieren, wurden Laborexperimente in grossen vertikal rotierenden Trommelgerinnen durchgeführt. Es wurde festgestellt, dass der Reibungskoeffizient mit steigendem volumetrischem Eisgehalt linear bis maximal ~20% abnimmt. Bei längerer Prozessdauer verursachte schmelzendes Eis eine teilweise oder komplette Verflüssigung der Masse mit folgender Abnahme des Reibungskoeffizienten von beinahe 50%. Eine empirische Analyse von 64 grossen Fels-Eislawinen zeigte, dass der Einfluss von Eis in natürlichen Stürzen kein dominanter Faktor ist. Die Mobilität der Ereignisse zeigte einen Zusammenhang mit der über einen Gletscher führenden relativen Fliesspfadlänge, wodurch quantitativ bestätigt wurde, dass Gletscheroberflächen mit geringer Reibung zu verlängerten Auslaufdistanzen beitragen – wie bereits von früherer Autoren angenommen. Ausserdem gehören Fels-Eislawinen mit hohem Wassergehalt häufig zu denjenigen mit den grössten Auslaufdistanzen. Die verheerendsten schnellen Massenbewegungen aus glazialen Gebieten beinhalten jedoch oftmals Kombinationen von Eigenschaften wie ein grosses Volumen, Fliesspfade über Gletscher oder glatten Fels, eingeengtes Fliessen, hoher Eis- und Wassergehalt, starke Erosion von Lockermaterial sowie Fliesstransformationen oder Kettenreaktionen. Trotz der grossen Vielfalt und Komplexität der Prozessinteraktionen in grossen schnellen Massenbewegungen in glazialen Gebieten, konnten Einblicke in diverse Aspekte vertieft werden. Die Erkenntnisse sollten in Zukunft durch ähnliche und zusätzliche Methoden ausgeweitet werden um dereinst als fundierte Basis für Szenarien-basiertes Modellieren zu dienen

7.18 Long-Runout Landslides

This chapter provides an overview of large (>10⁶ m³) volcanic and nonvolcanic long-runout landslides characterized by high velocities, large release and deposit volumes, and excess runout. Large long-runout landslides are very rare events and pose substantial challenges to quantitative hazard assessments. Despite several mechanistic theories, there is no commonly agreed-upon explanation of excess runout, which would also entail superposition of processes such as dynamic fragmentation, material bulking, and partial lubrication. Water as a lubricant plays only a minor or limited role given the ample evidence of dry excess runout. Numerical models based on shallow water equations provide some of the best means to realistically simulate rapid flow- and avalanche-like motion over three-dimensional terrain. However, such models critically depend on reliable initial conditions, such as failure volume and scar, material properties, and runout topography

Mapping hazards from glacier lake outburst floods based on modelling of process cascades at Lake 513, Carhuaz, Peru

Recent warming has had enormous impacts on glaciers and high-mountain environments. Hazards have changed or new ones have emerged, including those from glacier lakes that form as glaciers retreat. The Andes of Peru have repeatedly been severely impacted by glacier lake outburst floods in the past. An important recent event occurred in the Cordillera Blanca in 2010 when an ice avalanche impacted a glacier lake and triggered an outburst flood that affected the downstream communities and city of Carhuaz. In this study we evaluate how such complex cascades of mass movement processes can be simulated coupling different physically-based numerical models. We furthermore develop an approach that allows us to elaborate corresponding hazard maps according to existing guidelines for debris flows and based on modelling results and field work

Detecting potential climate signals in large slope failures in cold mountain regions

Concern and interest are rising that climate change may have an adverse impact on slope stability in mountain regions. Rock slopes in high mountain areas with glaciers and permafrost are particularly sensitive to atmospheric warming. In fact, several large rock slope failures have been observed in high mountain areas around the world in recent years. However, the detection of changes in the frequency or magnitude of such slope failures is fraught with a number of difficulties and has only recently been addressed. Here we outline several approaches that could be used to detect a change in high mountain slope failure activity. Rather than present research results, we provide a conceptual design of how research in this field could be strengthened

Prozesskaskaden und ihre Modellierung

Naturgefahren im Hochgebirge lassen sich häufig nicht auf einen einzelnen, isolierten Prozess beschränken, sondern beinhalten viel mehr ganze Ketten von interagierenden Prozessen. Solche Prozesskaskaden stellen eine besondere Herausforderung an die Beurteilung und Modellierung der Gefahrenprozesse und nicht zuletzt auch an deren Kartierung. Am Beispiel eines Ausbruchs eines Gletschersees in den Peruanischen Anden wird in diesem Artikel eine solche Prozesskette erläutert und auf verschiedene Aspekte der Modellierung und Gefahrenkartierung solcher Phänomene eingegangen. Diese Arbeit wurde im Rahmen des von der DEZA finanzierten „Proyecto Glaciares“ durchgeführt und wurde von Schneider et al. (2014) publiziert. En haute montagne, les dangers naturels ne sont souvent pas limités à un processus unique et isolé, mais sont plutôt constitués d’enchaînements de processus qui interagissent. De telles successions de processus représentent un défi particulier pour l’évaluation, la modélisation des dangers et notamment pour leur cartographie. A travers l’exemple d’un débordement d’un lac glaciaire dans les Andes péruviennes, cet article illustre un tel enchaînement de processus et aborde différents aspects de la modélisation et de la cartographie des dangers pour ce type de phénomènes. Ce travail a été réalisé dans le cadre du „Proyeto Glaciares“ financé par la DDC. Il a été publié par Schneider et al. en 2014

Numerical modeling of the mount Steller landslide flow history and of the generated long period seismic waves

International audienceThe rock-ice avalanche that occurred in 2005 on Mount Steller, Alaska and the resulting long period seismic waves have been simulated for different avalanche scenarios (i.e., flow histories), with and without erosion processes taken into account. This 40-60 Mm3 avalanche traveled about 10 km down the slope, mainly on top of a glacier, eroding a significant amount of ice. It was recorded by 7 broadband seismic stations. The simulations were compared with the recorded long period seismic signal and with the inverted flow history. The results show that, when erosion processes are taken into account, the simulations reproduce the observed signal at all the stations over a wide range of azimuths and source-station distances (37-623 km). This comparison makes it possible to constrain the rheological parameters involved which should help constrain the volume of eroded material. Because landslides are continuously recorded by seismic networks, this method could significantly broaden quantitative insights into natural flow dynamics

Energetic connectivity of diverse elasmobranch populations - implications for ecological resilience.

Understanding the factors shaping patterns of ecological resilience is critical for mitigating the loss of global biodiversity. Throughout aquatic environments, highly mobile predators are thought to serve as important vectors of energy between ecosystems thereby promoting stability and resilience. However, the role these predators play in connecting food webs and promoting energy flow remains poorly understood in most contexts. Using carbon and nitrogen isotopes, we quantified the use of several prey resource pools (small oceanic forage, large oceanics, coral reef, and seagrass) by 17 species of elasmobranch fishes (n = 351 individuals) in The Bahamas to determine their functional diversity and roles as ecosystem links. We observed remarkable functional diversity across species and identified four major groups responsible for connecting discrete regions of the seascape. Elasmobranchs were responsible for promoting energetic connectivity between neritic, oceanic and deep-sea ecosystems. Our findings illustrate how mobile predators promote ecosystem connectivity, underscoring their functional significance and role in supporting ecological resilience. More broadly, strong predator conservation efforts in developing island nations, such as The Bahamas, are likely to yield ecological benefits that enhance the resilience of marine ecosystems to combat imminent threats such as habitat degradation and climate change