Rock avalanches occur when a large volume of stone blocks loosens from a mountainside.
Once in a great while, large sections of a mountainside will come loose. This can have enormous consequences on both settlement and infrastructure in large areas around the location of the slide. The greates threat posed by a slide is when large sections of a mountain crash into fjords, creating towering tidal waves.
Slides consisting of one or more smaller stone blocks is called rock falls.
Where do rock avalanches occur?
Rock avalanches commonly occur on steep, unstable mountainsides. In some locations, cracks in the mountain increase the risk of avalanches, while in other locations it could be large stone blocks that slide on weaker layers of the bedrock.
In Norway, counties in Western Norway, Nordland and Troms in Northern Norway are particularly vulnerable to rock avalanches.
What triggers rock avalanches?
The combination of steep mountainsides and bedrock zones with weaknesses are important preconditions for triggering rock avalanches.
Finding out exactly what triggered an avalanche can be difficult. The most common causes are considered to be water pressure, rock pressure, frost wheathering or earthquakes.