Assessing potential ice avalanche hazardsIce breaking off from steep glaciers causes ice avalanches or, in case of breaking into a lake, dangerous flood waves themselves potentially leading to a lake outburst. Compared to lake outbursts and glacier length variations the possibilities to early recognize ice avalanches by means of remote sensing are limited. Reasons are snow cover and shadows (i.e. low optical contrast), difficult topography and the often small size of the object of interest. Because ice falls generally tend to repetition, comparison of glacier geometry and crevasse evolution with earlier stages can help to detect evolving risks. Also, the estimation of volumes to potentially break off might be possible in some cases. Monitoring the velocities of frontal ice lamellas and their typical hyperbolic acceleration before break off, however, will succeed only in rare cases. Whilst space-borne remote sensing is not suitable for early recognition of ice breaking off, satellite-based technology for ice classification (see related project SGI 2000 for more detailed on methods of ice classification) and GIS-analyses of digital elevation models allow for assessing the distribution of steep glaciers and related hazard potentials. If once recognized as potentially dangerous, selected steep glaciers can be monitored by high resolution imagery. In such a way, space- and air-borne remote sensing methods and GIS-modelling complement each other towards a downscaling strategy for detecting ice avalanche risks.
 
 

Results of assessing ice avalanche hazards by satellite remote sensing data fused with GIS models in a test region (Grindelwald):
 
 
 
 

Classification of glacier ice based on a 1998 Landsat-TM scene showing the region of Grindelwald (Bernese Alps)with Eiger (lower left) and
Grosse Scheidegg (upper right). The Classification is based on a ratio image (channel TM4/TM5) and overlain on a the shaded DEM (DHM25, L+T).
 
 
 
 

Slope calculation in the DEM allows for the extraction of those glacier areas which are steeper than 25° and
thus - according to empirical fiindings - potentially prone to ice avalanches assuming temperate thermal ice conditions.
 
 
 
 

Based on hydrological flow modeling within a GIS potential ice avalanche paths are calculated starting from
previously selected glacier areas (flow paths in red).
 
 
 
 

Modeled ice avalanche runout paths (green) compared to a ice avalanche hazard map performed by Bieri (1996)
for Gutzgletscher and Oberer Grindelwaldgletscher.
 
 
 
 

A first order damage potential estimate is possible when the ice avalanche model results are integrated in spatial data
on public and private infrastructure (steep glaciers shown in blue, potential avalanche runout paths in red and infrastructure in yellow. Example from Lötschental, Valais).