Møre og Romsdal

Møre og Romsdal is the county with the highest number of historic rock avalanche events. Many of them caused deadly displacement waves in the fjords. NGU has mapped 90 unstable rock slopes, which might form rock avalanches in the future.
Scar of the 1934 Langhammaren rock avalanche in the Tafjord (Photo: T. Oppikofer, NGU).

Møre og Romsdal is a county in western Norway characterized by numerous fjords and valleys surrounded by high mountains. These steep mountainsides have led to several large rockslides and rock avalanches since the last glaciation. NGU has made a systematic inventory of 119 rock avalanche deposits in the Storfjord (NGU report 2009.002). Many of them occurred between 11 000 and 9 000 years ago, i.e. shortly after the deglaciation.

Several rock avalanches have occurred in historic times and lead to numerous casualties, mainly because of displacement waves (tsunamis) created by the rock avalanche when impacting a fjord or a lake. The last major event in Møre og Romsdal was the rock avalanche from Langhammaren in Tafjord in 1934, which caused an up to 63 m high displacement wave and killed 40 people in nearby villages. Other fjords and valleys in Møre og Romsdal were also affected by several rock avalanches in the past, such as the Romsdal Valley where tens of rock avalanche deposits are mapped.

NGU has performed systematic mapping of unstable rock slopes in Møre og Romsdal since 2005. Out of more than 280 investigated sites, 90 unstable rock slopes with signs of past or present movements have been detected by NGU in collaboration with the County geologist of Møre og Romsdal. The systematic investigation of these unstable rock slopes is still ongoing and will result in the hazard and risk classification of all the unstable rock slopes. These investigations will be made public in the database on unstable rock slopes. Periodic displacement measurements are currently being conducted on 22 unstable rock slopes in Møre og Romsdal, using for example differential Global Navigation Satellite Systems (commonly known as GPS), terrestrial laser scanning, satellite-based InSAR, ground-based InSAR, as well as extensometers. Significant displacements have been measured on four unstable rock slopes (Børa in Romsdal Valley, Gikling in Sunndal Valley, Middagstinden in Innfjorddal Valley and Oppstadhornet on Otrøya Island) with average velocities ranging from 0.1 to 2.1 cm/year.

Three unstable rock slopes were classified as high-risk sites in the 2000s and are now continuously monitored and equipped with an early-warning system operated by the Åknes/Tafjord Early-Warning Centre (now taken over by NVE). The Åknes rockslide in the Sunnylvsfjord was studied within the Åknes/Tafjord Project with a very high level of detail using a multitude of surface and subsurface investigations and continuous monitoring instruments. The rock slope instabilities at Hegguraksla in the Tafjord and a large rockslide at Mannen in the Romsdal Valley were also investigated in detail and continuously monitored. NGU participated in these detailed investigations and collaborates with the Åknes/Tafjord Early-Warning Centre.

Links: 

  • NGU report 2013.053
  • NGU report 2013.014
  • NGU report 2009.002
  • NGU report 2008.049
  • NGU report 2007.043
  • NGU report 2006.052
  • NGU report 2002.016
Det ustabile fjellpartiet Oppstadhornet på Otrøya nær Molde
Large unstable rock slope at Oppstadhornet on Otrøya island near Molde (Photo: M. Böhme, NGU).