Th. doct.-ing.--Grenoble, I.N.P.G., 1979. N°: DI 134.

Not available / text

Rock and debris avalanches result from sudden rock slope failure; they occur in a variety of materials and landscapes, and often have a catastrophic and lasting impact on the society, infrastructure, and landscape of the area. In order to fully understand these events, the factors leading to failure and those influencing the course of the event must be investigated. In recent years, increased attention has been given to numerous aspects of rock/debris avalanche emplacement: among these is the influence of runout path material on the behaviour of snow and ice avalanches, pyroclastic currents, debris flows, volcanic debris avalanches and non-volcanic rock avalanches. The fact that substrates are involved in rock avalanche emplacement has been known since Buss and Heim remarked on it in 1881, but few detailed studies on the effects of this involvement on avalanche emplacement exist. One popular hypothesis which has emerged is that the long runout of large rock avalanches can be explained by the basal friction reduction due to overrunning or failure of saturated substrate material. However, the present study shows that this is not the case. From analysis of nearly 400 rock and debris avalanche deposit descriptions it is evident that: (1) avalanches inevitably interact with their runout path material; (2) all large (> 10⁶ m³) rock and debris avalanche events have runout distances that exceed simple frictional model predictions regardless of type or degree of substrate interaction; (3) substrates only add complexities to the ‘long-runout’ avalanche events similar to topographic interference. The complexities resulting from substrate interaction include, for example, characteristic deposit surface features such as longitudinal ridges and flowbands, compressional faults and raised margins from rapid deceleration behind e.g. bulldozed substrates; shearing in a basal mixed zone and consequent changes in basal avalanche mechanical properties; volcanic edifice failure on weak underlying sediments with a change in volcano shape; transformation into more mobile debris flows through the entrainment of large quantities of water or water-bearing materials; and many others.

Rock and debris avalanches result from sudden rock slope failure; they occur in a variety of materials and landscapes, and often have a catastrophic and lasting impact on the society, infrastructure, and landscape of the area. In order to fully understand these events, the factors leading to failure and those influencing the course of the event must be investigated. In recent years, increased attention has been given to numerous aspects of rock/debris avalanche emplacement: among these is the influence of runout path material on the behaviour of snow and ice avalanches, pyroclastic currents, debris flows, volcanic debris avalanches and non-volcanic rock avalanches. The fact that substrates are involved in rock avalanche emplacement has been known since Buss and Heim remarked on it in 1881, but few detailed studies on the effects of this involvement on avalanche emplacement exist. One popular hypothesis which has emerged is that the long runout of large rock avalanches can be explained by the basal friction reduction due to overrunning or failure of saturated substrate material. However, the present study shows that this is not the case. From analysis of nearly 400 rock and debris avalanche deposit descriptions it is evident that: (1) avalanches inevitably interact with their runout path material; (2) all large (> 10⁶ m³) rock and debris avalanche events have runout distances that exceed simple frictional model predictions regardless of type or degree of substrate interaction; (3) substrates only add complexities to the ‘long-runout’ avalanche events similar to topographic interference. The complexities resulting from substrate interaction include, for example, characteristic deposit surface features such as longitudinal ridges and flowbands, compressional faults and raised margins from rapid deceleration behind e.g. bulldozed substrates; shearing in a basal mixed zone and consequent changes in basal avalanche mechanical properties; volcanic edifice failure on weak underlying sediments with a change in volcano shape; transformation into more mobile debris flows through the entrainment of large quantities of water or water-bearing materials; and many others.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Joe C. Campbell. Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 121-137). Available also in a digital version from Dissertation Abstracts.

Résumé : Depuis les années 1990, environ 12 personnes par année sont tuées des suites d’une avalanche, ce qui en fait maintenant la principale cause de décès liés aux catastrophes hivernales au Canada (Stethem, 2003). Comme l'intérêt pour les activités de plein air telles que la randonnée, la motoneige et le ski de randonnée dans les régions éloignées augmente, l’amélioration de la prévision des avalanches à l'échelle régionale est nécessaire afin d’assurer la sécurité des usagers de l’arrière-pays. La logistique et les mesures de sécurité étant importantes lors de déplacements dans l’arrière-pays, les observations du couvert neigeux (observations d'avalanches, profils stratigraphiques et tests de stabilité) en terrain avalancheux ne sont pas toujours possibles pour les praticiens et prévisionnistes du milieu. Une alternative intéressante est d'analyser le manteau neigeux à distance en utilisant les sorties de modèles physiques de simulation du couvert neigeux. SNOWPACK, un modèle développé par l'Institut WSL sur la neige et les avalanches (SLF) en Suisse, est actuellement utilisé de manière opérationnelle pour la prévision d'avalanches et la recherche dans les Alpes suisses. Le projet vise à adapter SNOWPACK aux différentes conditions météorologiques dans les montagnes canadiennes (climat parfois côtier, transitionnel ou continental) et à l’utiliser dans le contexte de gestion de la prévention d’avalanches d’Avalanche Canada afin d’améliorer les prévisions à l’échelle régionale de la stabilité du couvert neigeux. Ce mémoire présente les traitements et analyses qui ont été menés pour évaluer le potentiel d'utilisation du modèle SNOWPACK forcé à la fois avec des données météorologiques in-situ et des données météorologiques de réanalyses. La validation des données de réanalyses avec les données in-situ pour les hivers de 2013-2014 et de 2014-2015 montre que le modèle météorologique GEM-LAM (Global Environmental Multiscale Limited Area Model) du Centre Météorologique Canadien (CMC) est le plus précis pour les trois contextes climatiques du projet. Un biais sur les données de précipitation proportionnel à l’intensité de celles-ci a toutefois également été identifié. Les sorties des simulations forcées avec GEM-LAM sont les plus proches des mesures observées sur le terrain en ce qui a trait aux indices de densité et de température relative moyenne, montrant des R² supérieurs et des valeurs de RMSE plus faibles. Finalement, l’analyse qualitative de la présence de couches faibles persistantes à l'aide de la plate-forme InfoEX d’Avalanche Canada montre un accord entre les dates de formation de croûte de regel et de givre de surface et les sorties du modèle SNOWPACK, confirmant son potentiel pour une adaptation canadienne. / Abstract : Since the 1990s, approximately 12 people per year are killed on average by avalanches, which are now the primary cause of death related to winter disasters in Canada (Stethem, 2003). As interest in outdoor activities, such as hiking, sledding and ski touring, in remote areas is increasing, there is a strong need for improved avalanche forecasting at the regional scale. Due to important logistical and safety matters, avalanche terrain measurements are not always possible for practitioners/forecasters (avalanche observations, snowpack profiles and stability tests). An interesting alternative is to analyze the snowpack without these challenges by using multilayered snow model outputs. SNOWPACK, a model developed by the WSL Institute for Snow and Avalanche Research (SLF) in Switzerland, is currently used operationally for avalanche prediction and research (Lehning, 1999) in the Swiss Alps. This projects aims to improve largescale predictions of snow stability and avalanches in a Canadian context using SNOWPACK. Thus, this documents presents the analyses that have been conducted to assess the potential of using SNOWPACK driven with both in-situ and forecasted meteorological data. A comparison of meteorological data from in-situ and predicted datasets for the winters of 2013-2014 and 2014-2015 shows that the GEM-LAM model is the most accurate for the three climatic contexts in this project, but also showed a precipitation bias proportional to its intensity/rate. Snow simulations forced with GEM-LAM are the closest to field measurements, showing a higher R² and lower RMSE values. Finally, predictions of persistent weak layers have also been validated using the InfoEx platform from Avalanche Canada. Crust and surface hoar formation dates simulated by SNOWPACK agree with the information reported in InfoEx highlighting the potential for a Canadian implementation.

With an escalating skiing tourism industry where tourists are getting bolder every year in theirsearch for untouched snow, avalanche prediction gets more and more important. Avalancheprediction is often designated manual labour and many years of establishing avalanchedatabases. With GIS and high resolution DEM data it is possible to identify areas withavalanche danger over large areas at low costs. Using parameters as: roughness, inclination,curvature and vegetation models like the ones tested in this study can predict potential releaseareas (PRA). The results that the models present needs to be validated. This can be done eitherby manual labour by avalanche experts or by comparing the results at a validated resolutionfrom another area with avalanche databases. The present study is testing two PRA identifyingmodels on different DEM resolutions trying to identify if higher resolutions yields better resultsthan lower or vice versa. The validation of the results was a challenge, because of the lack ofavalanche databases in Sweden. In this study a 5 m resolution DEM and a model set updeveloped for Davos in Switzerland, was used as a as a reference model. The results showsthat a DEM with a high resolution of 2x2m do not identify PRAs (potential release areas) asgood as the resampled resolutions of 5x5m or 25x25m.

Astronomers need single photon detectors to detect very faint light sources from deep space. An avalanche photodiode in the geiger mode is especially suited for the detection of single photons. Three by three arrays of avalanche photodiodes were fabricated. Breakdown voltages of 200V were measured. Large reverse currents prevented operating the array in the geiger mode. An improved design which minimizes the reverse current is needed. A commercial avalanche photodiode especially made for the geiger mode was tested and compared to a general purpose avalanche photodiode. Using the general purpose avalanche in the geiger mode was found to be unacceptable because when exposed to a weak light source, 90% of the output pulses were dark current pulses. A computer interface circuit was designed to read the time and location where photons were absorbed by the array. The circuit performed its function qualitatively, but it had a false triggering problem.

The thesis describes a method for predicting avalanche activity in Scotland, based primarily on meteorological and topographical data, and this is incorporated into a framework for avalanche forecasting. A literature review identifies the main meteorological and topographical factors causing avalanche release. Snow accumulation, cold temperatures or thaws are identified as the major meteorological factors causing avalanches, and the thesis so distinguishes two basic avalanche types---the direct-action avalanche caused by fresh snow accumulation, and the climax avalanche caused by temperature changes. Slope angle, surface roughness, slope geometry and catchment area are identified as the major topographical controls on the location of avalanche activity. The thesis presents data on avalanche activity in Scotland over the last two hundred and eighty years, with particular emphasis on the Cairngorm Mountains. Avalanche locations, types and magnitudes for almost a thousand avalanches are described. Data on Scottish weather and terrain conditions are also presented, also with particular emphasis on the Cairngorm area. Major periods of snow accumulation, cold temperatures and thaws are identified between the winters of 1977/78 and 1979/80, and the location of steep slopes, smooth surfaces and large catchment areas in the Cairngorms is described. Data on the characteristics of the Scottish snow cover, based on work performed in the Cairngorms by E. Langmuir, B. Beattie and the author are then presented. Correlations between avalanche activity and meteorological, topographical and glaciological conditions are demonstrated, and this enables a predictive model to be developed which assesses avalanche probability on the basis of the amount of fresh snowfall and the prevailing temperature. Fresh snowfall of 200 mm., and either several days of cold weather with maximum temperatures below -4°C or two or three days of warm weather with maximum temperatures above 0°C lead to avalanche activity. The model can be continually up-dated and permits a continuous avalanche probability assessment to be made.