During a workshop with the Geological Survey of Norway (NGU) and the Norwegian Water Resources and Energy Directorate (NVE), U.S. geologists studied unstable mountain slopes in Western Norway. Geologist Dennis M. Staley from the United States Geological Survey (USGS) expressed great satisfaction with the workshop.
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First in the world with systematic hazard and risk classification of unstable mountains
During the meeting, participants visited unstable rock slopes around Hardangervidda and Sørfjorden in Western Norway. In 2012, Norway became the first country to systematically classify unstable rock slopes by hazard and risk level.
"Although large parts of Alaska are uninhabited, such events can create displacement waves that may pose a danger to infrastructure, shipping lanes, undersea fiber optic lines, cruise ships, as well as communities in the area. We discussed shared challenges and possible methods for mapping, classifying, and monitoring unstable rock slopes," says geologist Lene Kristensen from NVE's landslide section.
NGU maps unstable rock slopes through:
• Data from satellites and aircraft, along with studies of areas where landslides have previously occurred.
• Detailed field mapping of cracks and structures, which may include movement measurements and sample collection.
• Assessment of areas potentially impacted by landslides, including secondary consequences such as displacement waves, damming of valleys, and related flood zones.
These efforts result in a comprehensive hazard assessment.
NGU's mapping of unstable mountain slopes is accessible via a map.
For more details on slope classification, refer to NGU’s report (PDF).
NVE further develops NGU's data to produce:
• Hazard maps, with collaboration with the consultancy industry for the evaluation of the risk of displacement waves.
• Risk assessments.
• Periodic and continuous monitoring, as needed.
One of the World's largest tsunamis
In Alaska, a large landslide and subsequent displacement wave occurred in Taan Fjord in 2015. According to a paper published in Scientific Reports, this tsunami was 193 meters high, one of the largest ever recorded in the world.
Alaska experiences more frequent rock slope failures than Norway.
"The scientific program put together by NGU and NVE was highly relevant to our work in Alaska. We face similar challenges as in Norway. Observing the complex geological sites and the diversity of hazards you face was invaluable," Stanley says.
Directly affected by landslides
One of the sites visited during the workshop is the unstable rock slope Tussafoten in Eidfjord municipality. The rock slope moves up to eight centimeters per year and has a volume of up to 13 million cubic meters.
Large parts of Øvre Eidfjord could be directly affected by a resulting rock slope failure, according to a report from NGU. A smaller displacement wave in Eidfjordvatnet could also occur if the slope fails, according to NVE.
"At Tussafoten, the Americans saw continuous monitoring of the rock slope in action. While we have had eight rock slope failures with displacement waves in Norway the last hundred years, there have been several landslide-triggered tsunamis in Alaska in just the last ten years. Learning from our American colleagues was beneficial, as Alaska, with its high rate of failures, serves as an excellent natural laboratory," says NGU researcher Reginald Hermanns.
• A total station measures movement at 18 prisms on the unstable mountain slope.
• A ground-based radar measures movements in the mountain from the valley floor.
• Three GPS units – one serving as a reference point on stable ground.
• Four reflectors measured from satellites – one also serving as a reference point on stable ground.
• Camera monitoring and a climate station.
Read more on NVE's website (in Norwgian only).
Climate change could make mountains more unstable
The mountains around Folgefonna in Sørfjorden resemble some Alaskan mountains due to their proximity to glaciers and were visited during the workshop.
"As in Alaska, glaciers are melting in Norway. Climate change in Arctic regions is warming these areas three to four times faster than the global average. This could affect rock slope stability in Norway and Alaska, making it an important topic for further discussion," explains Hermanns.
Discovering far more unstable mountain slopes
InSAR Norway is an interactive map showing radar-based satellite measurements. This enables monitoring of unstable rock slopes, ground movements, and subsidence that can cause structural damage.
In 2018, InSAR Norway became the world's first publicly available map displaying these changes. Since then, similar InSAR technology has spread to cover Europe. By 2020, 100 new unstable rock slopes had been discovered in Norway using the InSAR Norway technology.
"Radar technology is continually improving, so we are discovering more unstable rock slopes that need to be physically mapped to assess the hazard level. The U.S. currently lacks a public platform similar to InSAR Norway, but they are interested in following the technology’s development," says Hermanns.
"We are already looking forward to the new InSAR data that will be available in a few years, allowing us to see more through vegetation," Hermanns adds. Besides InSAR, detailed terrain data are crucial for discovering unstable rock slopes.
