In Switzerland, glaciers play an important role as water reservoirs for hydro-power production (generating 50% of all electricity). Glacier are also an important economic factor for tourism. Moreover, they were frequently associated with natural hazards, endangering humans and infrastructure in this densely populated mountain region. Their well documented retreat since 1850 (up to 2 km) is a key indicator for climate warming. In 1973 an inventory of all Swiss glaciers (obtained from aerial photography) reveals 1828 glaciers covering 1342 km2. Since 1973, major changes in glacier extent have taken place.
Glacier changes from Landsat TM
Landsat TM data have been used to derive a new Swiss glacier inventory for the year 2000. Glacier change between two dates can be visualized by digital overlay of classified TM images (left). Since 1985, most glaciers have retreated, and some small glaciers have totally disappeared. Glacier extent in 1850 was reconstructed from old maps and field surveys. These glacier outlines and satellite imagery were overlayed on a Digital Elevation Model (DEM) to visualize glacier retreat in perspective view.
Between 1850 and 1973 Swiss glaciers lost 27% of their area. Based
on satellite observation, a sample of 270 glaciers also lost 20%
of their area between 1973 and 1998. This value is close to the
30% expected as derived from model calculations for 2025.
The relative loss of glacier area increases with decreasing glacier size. Glaciers smaller than 1 km2 account for about 40% of the total area loss, although they cover only xx% of the total area. Only satellite observation is able to reveal these changes at tolerable costs for large and remote areas. For climate change detection, hazard prevention or assessment of drinking water resources such space-borne monitoring will be an inevitable source of information.
Ice avalanches represent a prevailing threat to some alpine communities and have repeatedly caused disasters in the Swiss Alps. Steep glaciers are often periodically susceptible to ice breaking off. Glaciers advancing or retreating may alter the hazard situation. Methods have been developed to detect and observe steep and hanging glaciers which have the potential to produce ice avalanches. High-resolution satellite images and digital elevation data are used. GIS-models are then applied to simulate potential ice avalanche paths giving indications of particularly critical locations. Ice avalanches are also important to consider for combined hazards, for instance when triggering snow avalanches in winter or displacement waves in lakes (possibly leading to lake outbursts).
|The 1996 ice avalanche from Gutz Glacier, near Grindelwald, affected road infrastructure and injured tourists (left).|
|Modelled ice avalanches in the Loetschental, near Brig, and possible effects on settlements and road infrastructure (steep glaciers shown in blue, ice avalanche run-out paths in red and settlements in the valley bottom in yellow).|
|On 25 June 2001, a debris flow which originated from a glacial lake overflowed and heavily damaged the village of Tasch, in the southern Swiss Alps.|
|The lake outburst flood in Tasch as simulated by a GIS-model and draped over a DEM together with a TM scene from 1998 (DEM25 by L+T: BA00 XX)|
|The central part of the "Grosser Aletschgletscher", (24 km long, 86 km2 area), is now formally a part of the UNESCO world heritage "Aletsch, Bietschhorn, Jungfrau".|
Environmental impacts from glacier hazards: Lake outbursts and ice avalanches
In the Swiss Alps, lake outbursts and subsequent
debris flows have caused a large number of deaths and severe damage
to alpine villages and other installations. The steep alpine valleys
in Switzerland, the dense population and the intense tourism development
increase the risk of adverse effects. Detection and monitoring of
potentially hazardous lakes has been achieved by satellite remote
sensing and subsequent detailed photogrammetric studies. Models
using satellite information can simulate lake outburst floods and
indicate areas potentially at risk.
Glacier retreat can lead to the formation of glacier lakes, typically in the recently deglaciated areas in front of a glacier. Such lakes are often dammed by large moraines consisting of loose glacial sediment. The potential instability of moraine dams makes the lakes prone to water outbursts.