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


Schneider, D. On characteristics and flow dynamics of large rapid mass movements in glacial environments. 2011, University of Zurich, Faculty of Science.

Abstract

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 contents 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.

Abstract

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 contents 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.

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Additional indexing

Item Type:Dissertation
Referees:Haeberli W, Huggel C, Davies T R H, Deline P
Communities & Collections:07 Faculty of Science > Institute of Geography
Dewey Decimal Classification:910 Geography & travel
Language:English
Date:2011
Deposited On:19 Mar 2012 14:27
Last Modified:05 Apr 2016 15:39
Number of Pages:247
ISBN:3-85543-257-0
Additional Information:Ist in der Schriftenreihe Physische Geographie Glaziologie und Geomorphodynamik als Heft 61 erschienen
Official URL:http://www.geo.uzh.ch/fileadmin/files/content/abteilungen/phys3g/docs/phd/2011_Diss_Schneider_Demian.pdf
Related URLs:http://opac.nebis.ch/F/?local_base=NEBIS&CON_LNG=GER&func=find-b&find_code=SYS&request=006753310
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