Rock slidesExposure to rock flows

Rock slides and rock flows into lakes and sea can create tsunamis. This represents one of the most serious natural hazards in Norway, and over the last 100 years, more than 170 persons in Northwest Norway have lost their lives. The rock slides in Loen in 1905 and 1936 and Tafjord in 1934 are examples of this. Monitoring of the unstable mountain slopes of Åkneset and Hegguruksla in Møre og Romsdal County and Lynge in Troms County are examples of areas under surveillance today.

Knowledge of slide mechanisms

The main element of NGI's work on rock slides and rock flows is an understanding of the mechanisms which lead to them. Land slide experts have divided rock slides into three categories based on size. The size of slide is very important for potential damage.

Rock falls

Rock slides with a volume under 100 cubic metres are called rock falls and only cause incidental damage. Rock falls occur on all types of slope over 30 degrees where there are loose rocks.

Rock fall, Aurland, Norway 2016
 

Rock slides

Slides of from 100 to 10,000 cubic metres of rock are called rock slides and can cause major damage to buildings or other infrastructure in their path. Rock slides occur on large slopes of 50 m height and above where there are weaknesses.

Rock flows

Slides of over 10,000 cubic metres of rock masses are called rock flows. These have led to some of the worst natural disasters experienced in Norway. In northern parts of Western Norway, historical documents show two or three disasters per century stemming from major rock flows and tsunamis. The best-known disasters are the Loen slides in 1905 and 1936 and at Tafjord in 1934. These rock flows caused tsunamis which led to a total of 174 fatalities.

Rock slide research

Much of the research in rock slides in recent years has concentrated on developing realistic slide models. The models can be divided into two groups, stability models and run-out models. Stability models are used to calculate whether a mountain slope is safe and can form the basis for planning stabilisation measures.
Run-out models are used to assess how far a slide will reach after initiation and how quickly it will move. Rockfalls are the most common slide type calculated in this way, and the aim is to find a maximum run-out for comparison with the provisions of the Norwegian Building and Planning Act.

International co-operation

NGI is involved in several international projects for surveying and reducing the risk of land slides, and for knowledge transfer to local authorities. An example is South and Central America, where densely populated areas have repeatedly been hit by land slide incidents due to extreme precipitation and earthquakes. NGI cooperates with slide experts in Italy, Austria, France and Switzerland.

In the period 2002-2012, NGI led the International Centre for Geohazards (ICG), a Norwegian "Centre of Research Excellence" (SFF). ICG carried out research into risk assessment and preventing or reducing damage caused by geohazards. NGI's partners in ICG were the University of Oslo (UiO), the Norwegian University of Science and Technology in Trondheim (NTNU), the Geological Survey of Norway (NGU), and NORSAR.  The centre was also responsible for teaching and supervising Master's and Doctoral graduates.