7 July 2014

Oso landslide: continued small-scale activity

Posted by Dave Petley

Oso landslide

The Oso landslide in Washington State in March remains of great interest to the wider community, not least because of the number of lives lost and the unusually destructive nature of the landslide.  A series of lawsuits have now been started in relation to the landslide.  The Seattle Times has continued to investigate, and yesterday released a video that they obtained through a public-disclosure request showing continued landslide activity on the slope a month after the main failure.  I have tried to embed the video, but if it does not work it can be viewed here.


The video was collected by Jeff Jones, Snohomish County geologist.  It shows ongoing toppling failure from the landslide scarp.  Such behaviour is quite normal as the stresses in the slope rebalance – in some ways this is anomalous to aftershocks after a big earthquake.  Although the video is a bit jerky, the really interesting aspect if the mobility of the debris – even with these small slips the debris easily mobilised into a flow.  Bear in mind that this is in a dry state, whereas the main failure was wet, and that the volume is a tiny fraction of the main event, and it is easy to understand why the main collapse was so destructive.