24 July 2014

Askja: a very large volcanic landslide in Iceland

Posted by Dave Petley

Askja landslide

A very large an interesting landslide occurred in Iceland on the night of 22nd/23rd July in the flanks of the Askja stratovolcano in Iceland.  This is a very interesting event in a number of ways, not least because the volume appears to be large – estimates at present range from about 24 million cubic metres to about 60 million cubic metres.

Images are appearing of the landslide, which is impressive in its scale:


Source: http://www.mbl.is/frettir/innlent/2014/07/23/vigalegur_mokkur_steig_til_himins/


The landslide is estimate to be about a kilometre in width.  There is a nice video taken from a flight over the landslide on the RUV website too. The landslide entered the lake at the foot of the slope, generating very large tsunami type waves.  A credible witness, Ármann Höskuldsson, who was in the area with a group of students, estimates that the waves were 50 m high.

The cause of the landslide is not clear at present. Some of the articles suggest snow/ice melt, but there is no evidence to support the hypothesis.  The slopes on the southern edge of the Askja massif are steep.  This Google Earth image of what I think is the site suggests that there may have been previous large-scale landslides on this slope:



There is also evidence of large amounts of erosion, suggesting that the slope may have been steadily destabilising with time.  It is entirely possible that this is a progressive landslide with no trigger event.

If the waves were 50 m high then the level of erosion around the lake should be extremely high given the weak materials.  I have yet to see any good images of the scour around the lake.  This must be a golden opportunity to understand better the generation of tsunami waves by rapid, large landslides.