Abstract. Debris flows triggered by glacier lake outbursts have repeatedly caused disasters in various high-mountain regions of the world. Accelerated change of glacial and periglacial environments due to atmospheric warming and increased anthropogenic development in most of these areas raise the need for an adequate hazard assessment and corresponding modelling. The purpose of this paper is to provide a modelling approach which takes into account the current evolution of the glacial environment and satisfies a robust first-order assessment of hazards from glacier-lake outbursts. Two topography-based GIS-models simulating debris flows related to outbursts from glacier lakes are presented and applied for two lake outburst events in the southern Swiss Alps. The models are based on information about glacier lakes derived from remote sensing data, and on digital elevation models (DEM). Hydrological flow routing is used to simulate the debris flow resulting from the lake outburst. Thereby, a multiple-and a single-flow-direction approach are applied. Debris-flow propagation is given in probabilityrelated values indicating the hazard potential of a certain location. The debris flow runout distance is calculated on the basis of empirical data on average slope trajectory. The results show that the multiple-flow-direction approach generally yields a more detailed propagation. The single-flowdirection approach, however, is more robust against DEM artifacts and, hence, more suited for process automation. The model is tested with three differently generated DEMs (including aero-photogrammetry-and satellite image-derived). Potential application of the respective DEMs is discussed with a special focus on satellite-derived DEMs for use in remote high-mountain areas.
The deposit structure of 20 very small to large avalanches that occurred in the Davos area, eastern Swiss Alps, during winters 2004/05 and 2005/06 was investigated. Snow-cover entrainment was significant in the majority of events and likely to have occurred in all cases. Evidence was found both for plough-like frontal entrainment (especially in wet-snow avalanches) and more gradual erosion along the base of dry-snow avalanches. Several of the dry-snow avalanches, both small and large, showed a fairly abrupt decrease in deposit thickness in the distal direction, often accompanied by changes in the granulometry and the deposit density. Combined with other observations (snow plastered onto tree trunks, deposit-less flow marks in bends, etc.) and measurements at instrumented test sites, this phenomenon is best explained as being due to a fluidized, low-density flow regime that formed mostly in the head of some dry-snow avalanches. The mass fraction of the fluidized deposits ranged from less than 1% to ∼25% of the total deposit mass. Fluidization appears to depend rather sensitively on snow conditions and path properties.
A monitoring system for periglacial phenomena has been installed in the Furggentälti (Gemmi) Swiss Alps in the framework of geomorphological field studies aimed at the instruction of students. Various periglacial landforms and processes can be observed in an area of about 1 km2. The research layout includes a survey station for soil and air temperatures, a geodetic surveying triangulation network of a solifluction lobe, and photogrammetric analysis of the soil frost pattern dynamics (stone rings) and a small rock glacier. Geophysical explorations (geoelectric and seismic refraction) and BTS measurements are undertaken on the rock glacier; these measurements have ascertained the presence of permafrost. The temperature survey station records values at levels between 1 m beneath the surface and 1.5 m above the surface; this allows correlation between displacement values of the solifluction lobe and the soil temperatures.
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