International Geologiical Congress - Oslo 2008

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GHZ-11 Rock slope movements and early warning of catastrophic failure and related tsunamis

 

Real-time monitoring and Early-Warning of the Åknes rockslide in western Norway

 

Lars Harald Blikra, Geological Survey of Norway (Norway)
 

 

The Åknes rockslide, located on the western side of Sunnylvsfjorden, has been the focus of considerable investigations the last 4 years, and the implementation of monitoring and early-warning systems is nearly finished. The risk is due to the generation of large tsunamis when rockslides plunge into the fjords. Geological and geophysical investigations at Åknes indicates that the unstable area covers about 0.7 km2, reaching a volume of 25-70 million m3. The established monitoring demonstrates that it is moving with a velocity of 2-10 cm/year. The inclinometer data in boreholes indicate movement below 100 m depth. The monitoring systems at Åknes is today based on extensometers, single lasers, GPS, total station, geophones, climate station and borehole instrumentation (inclinometers and piezometers). . The movement data so far demonstrates a continuous movement during the entire year, but with significant seasonal changes. During snow melt in the spring and heavy precipitation events, the movement rate can increase up to 10 times the yearly mean. This means a movement of up to 1 mm/day. The data is handled in an integrated web-based system. Major challenges are linked to the steep terrain, remote setting and problems with rockfalls and snow avalanches. Major effort has been put on to get reliable operational power and communications systems. Based on the historical data from the Åknes rockslide and information from historical rockslide events elsewhere, preliminary early-warning levels are implemented.

 

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