Radar monitors snow at Stavbrekka

Cautus Geo radar monitors the snow at Stavbrekka. Avalanches have been technologically documented every winter since 2015.

In 2019, Cautus Geo established a completely new type of radar meter on Strynefjellet. The task is to document the annual avalanches at Stavbrekka. The aim is to safely reopen the winter-closed tourist route from Lom to Geiranger as soon as possible.

County road 63 is closed in winter. In recent years, landslides from Stavbrekka have been radar-documented. The advantage is that the road can be reopened earlier and without the risk of anyone being caught in the avalanche.

- "We are very pleased to have won the contract again. It provides a seamless continuation of the monitoring," says Lars Krangnes of Cautus Geo.

- "Cautus Geo has been chosen because they fulfil all the quality requirements set and had a competitive price," says engineer Andreas Sande Lien of Innlandet County Council.

Guaranteed landslide

It is always uncertain when the avalanche at Stavbrekka will occur, but a major avalanche normally occurs every spring. The tourist road has been monitored by radar for nine years. It started as a research study to see if it is possible to keep the road open in winter.

Cautus Geo AS specialises in monitoring and warning of natural hazards. They have developed various measurement systems for avalanche forecasting.

In March 2019, the company installed the latest radar system at Strynefjellet.

- Radar monitoring is a mature technology that we also use to monitor large rock slides. On Strynefjellet, we monitor a large area of snow with millimetre accuracy. The speed of movement in the snow masses on Stavbrekka indicates when large avalanches will be triggered," says Krangnes.

Continuous

Stavbrekka is monitored automatically and continuously. Data is fed into Cautus Web, Cautus Geoe's proprietary web system.

- The data is analysed continuously and is always available. "The system shows exactly what is happening on the mountain. When the movements in the snow masses increase, the system sends out an alert and the road is closed," says Krangnes.

Uncontrolled landslides from Stavbrekkfonna can have major consequences. The snow masses will both pass over and bury the potentially busy county road over the mountain.

One road - two counties

Innlandet County Council is the client, but the county road over Strynefjellet is a joint venture between Innlandet and Møre og Romsdal. Operation and maintenance is handled by Møre og Romsdal.

- The web solution is absolutely crucial. It shows in real time what is happening on the mountain. We can follow the movements of the snow masses, and the geologists in Møre og Romsdal can predict with great accuracy when the big avalanche will occur. This means we can clear and reopen the road without risk to those milling it," says Sande Lien.

FACTS: Ground-based InSAR

• A new generation of ground-based InSAR is used at Stavbrekka. It moves back and forth on a three-metre rail and takes radar images at close intervals. Each measurement round generates a 2D analysis. Measurement accuracy is less than 1 mm for each measurement cell.
• The radar is not affected by weather conditions, heavy snow drifts or light conditions. It measures and generates 2D analyses around the clock.
• The radar is located 1,000 metres from the measurement area, up on the mountainside on the opposite side of Langevatnet on national road 15 towards Stryn.
• Ground-based InSAR is also used to monitor unstable rocks and structures.

FACTS: Two types of avalanches

• Slideskred, also called flakeskred, is the type of avalanche at Stavbrekka. These avalanches occur when the snow falls along a line with a marked breaking edge. It can be several metres high and several hundred metres wide. At Stavbrekka, the slope is "normally" 150 metres wide and 200 metres long. Such avalanches can reach speeds of 200 metres per hour.
• The second type of avalanche is called a loose snow avalanche. This occurs when the snow is loosened at one point and spreads down the mountainside in a fan. Usually there is not as much snow in loose snow avalanches as in slides.