30 December 2020
Gjerdrum: a quick clay landslide disaster in Norway this morning
Overnight, a large quick clay landslide has struck the village of Ask in the municipality of Gjerdurm in Norway. News reports from this landslide are a little confused as I write this – unsurprisingly – but it is clear that the slide has swept away a number of houses. Reports suggest that up to nine people might have been injured. About 700 people have been evacuated so far. It is reported that 14 buildings have been lost to date. Update: as the afternoon ends in Norway reports indicate that 12 people are not accounted for, some of whom are children. Unfortunately, the rescue services have not been able to enter the area affected by the landslide. This is the correct decision – this slope is likely to still be highly unstable. A further three houses have been lost during the day.
The Norwegian Police have described this event as a disaster. The site of the landslide appears to be the area shown in the Google Earth image below – the location is 60.065, 11.036:-
Reports indicate that the alert was sounded at about 4 am local time. The landslide remains unstable, and some retrogression of the head scarp is still occurring. It is not clear how far downslope the landslide extends, but the images suggest that this is a very substantial failure.
Gjerdrum has suffered quick clay (sensitive clay) landslides before. For example, Google Books has a case study of a significant event in 2012.
This is the NVE quick clay hazard map for the area:
The area that has failed is described as being Low hazard
but a loosening area that is within the source zone for landslides (many thanks to those who have helped me to understand this). However, it is immediately adjacent to an area described as medium hazard.
VG TV has a video of a house collapsing into the landslide bowl. It demonstrates that this is a very large failure (unfortunately I cannot embed this video):-https://www.vgtv.no/video/210593/vgs-reporter-om-hus-i-jordskredsomraade-staar-delvis-i-loese-lufta
The Norwegian Police have now released a map showing the area affected by the Gjerdrum landslide (in red). The large area with green hatching is the zone that has been evacuated today.