29 October 2014
Mount Mannen is located in Romsdal in the northernmost part of western Norway; Alesund is the nearest large city. Over the last few days much of Norway has been watching with fascination to see if a large rockslide will occur on the flanks of the mountain. There is sufficient interest in this event that there are live webcams broadcasting the events on the slope. The potential failure is in the order of 120,000 cubic metres, so the final collapse, should it occur, will be quite spectacular.
The issue is a large, actively deforming block high on the mountainside. This is being monitored in detail, and in recent days the block has started to accelerate, with further very heavy rainfall was due overnight (although no failure appears to have occurred). The VG.no website showed this graphic with apparent displacement data:
Whilst in one of the videos on the above webpage a plot was shown with data extending over a longer time frame (apologies for the poor quality of this screenshot)::
This montage of photos in a VG.no article rather nicely shows the block that is causing concern – and in particular the second from right images shows the displacement across the crown of the landslide:
There is also a very nice helicopter video of the slope, which shows why it is causing such concern.
There are very few articles in English on this landslide, but this one from yesterday provides an overview of the current situation. Note that the article was speculating that the failure would occur yesterday though, which did not occur. A more recent article describes quite well the profound difficulties of trying predict reliably these final collapse events, especially where the rockmass is highly fractured and disrupted. There is little doubt that this block will ultimately fail, but whether it will be in the current movement episode is hard to tell. Unfortunately of course if movement of the block slows down then the authorities will have major problems in managing the long term hazard. This is an event that is worth watching. Fortunately, it appears to be a nice clear day on Mount Mannen today, so the webcams have an excellent view of the slope.