The (A)knes rockslide: Monitoring,threshold values and early-warning

摘要

The (A)knes/Tafjord project is a large investigation,monitoring and early-warning project relatedto some large unstable rockslopes in western Norway. The risk is due to the generation of large tsunamis whenrockslides plunge into the fjords. The (A)knes rockslide is a large rockslide of possible 30-40 million m3,movingwith a velocity of 3-10 cm/year. The monitoring systems is today based on surface extensometers,single lasers,GPS,total station,geophones,climate station and borehole instrumentation (inclinometers and piezometers). Thedata is implemented in an integrated web-based system. Major challenges are linked to the steep terrain,remotesetting and problems with rockfalls and snow avalanches. Major effort has been put on to get reliable operationalpower and communications systems. The movement data so far demonstrates a continuous movement duringthe entire year,but with significant seasonal changes. During snow melt in the spring and heavy precipitationevents,the movement rate can increase up to 10 times the yearly mean. This means a movement of up to1 ram/day. Based on the historical data from the (A)knes rockslide and information from historical rockslideevents elsewhere,preliminary early-warning levels have been proposed (green,blue,yellow,orange and redlevels).