Every year, several roads in Norway are affected by avalanches, which in the worst case can cause major damage and lead to loss of human life. At Sandneslia along Fylkesvei 472 in Gildeskål municipality in Nordland, a stretch of approximately 1 km experience several avalanches annually. The Norwegian Public Roads Administration in Nordland therefore wanted a system that could register when an avalanche was triggered in the exposed area and a way to warn and prevent road users from driving into the exposed area if a landslide is on its way.

NGI was given the task of developing and installing an automatic system that could detect avalanches and give notice of this.

Sanneslia skredvarslingssystem 600

Wireless sensor network with geophones up to 700 meters in the mountain side for automatic avalanche warning in Sandneslia at Fv472 in Gildeskål municipality in Nordland

Landslides monitored by geophones

In the known avalanche paths in Sandneslia directly above the exposed stretch of road, geophones were installed at strategically selected locations. The geophones register vibrations that pass through the rock masses. An avalanche on its way down one or more avalanche paths in the mountainside will create vibrations as long as the avalanche masses are in motion. External incidents such as animal footsteps, gusts of wind or heavy rainfall can also create vibrations, but these have a different characteristics.

If the gophone system detects vibrations for a period longer than approx. 3 seconds, this will be an indication of a landslide. Then the system will send an avalanche warning to the traffic lights on the road below, at the same time as Transportation centre in Mosjøen is notified.

Quick warning will save lives

Red lights at each end of the avalanche-prone stretch of road effectively prevent cars from entering the avalanche-prone zone. Cars that may be inside, between the traffic lights, have ample of time to get out into the avalanche-safe zone. The registration of landslides on the mountainside is very fast, based on wireless sensor networks.

NGI receives avalanche alerts by email when landslides are triggered in one of the places where geophones are installed. The measuring system is so sensitive that it shook for more than 3 seconds when an earthquake occurred off the coast of Western Norway in November 2017. Even small avalanches are registered and warned. Many of these do not reach the road and will therefore be perceived as "false warning".

When the road is closed, the Norwegian Public Roads Administration will inspect the area. They announce that the notification system is working properly and that it encompasses the requested features.