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Saturday, 12 November 2011

Landslide in Iceland

This landslide occurred in October, on the flanks of the fjord called Eyjafjordur in North Iceland.  The town of Akureyri is not far away.  This was a big landslide -- reputedly responsible for moving a million tonnes of rock debris down the slope.   What caused it?  An earth tremor linked with volcanic activity?  Possibly......

This got me thinking about some of my earlier posts about pressure release on mountainsides following the withdrawal of glacier ice.  I gave an example of a slumped coastline on the north coast of Pembrokeshire (between Ceibwr and Newport) which may well be linked with pressure release following the retreat of Devensian ice.  This photo shows a huge cliffline near Sudureyri in NW Iceland which has suffered from a whole string of massive landslides.

 The plateau (Tertiary basalts) is in the bottom left corner.  The unstable cliffline runs from bottom R towards top L.  Below that, look at the complex hummocky terrain.  When you walk across it, it is just a jumble of broken bedrock debris that has come down following wholesale cliff collapse.  There are some big landslide lobes too -- the most prominent one almost reaches the buildings and the road in the top R corner.  This one has moved so far that one might speculate as to what the lubrication mechanism might have been.......... and it's possible that the landslide came down onto the surface of a wasting mass of glacier ice, which would have greatly reduced friction and assisted sliding.

I'll hazard a guess on the scale of this series of events, and suggest that hundreds of millions of tonnes have come down here, and that there have been several phases of collapse.  My colleague Eggert Larusson studied this in the 1970's. 

Returning to the theme of super-erratics and the incorporation of vast chunks of bedrock into glaciers, we clearly have a mechanism here which might account for such things.  Indeed, the Foothills Erratic Train (to which I have referred many times in this blog) is a classic example -- with ongoing rockfalls and avalanches from one particular location in the Rockies delivering debris onto a moving glacier surface, to be transported away over a distance of c 700 km.

For this to work, you must have a rock face (which has been subjected to "unloading" and pressure release above the ice surface), and an active flowing glacier below, which continues to flow for centuries after a rockfall or landslide occurs.

2 comments:

BRIAN JOHN said...

Kostas -- comment rejected. I'm thoroughly fed up with your pronouncements which are underpinned by a complete lack of understanding of the processes involved in glacier transport.

BRIAN JOHN said...

Thank you Kostas for off-the-record message. No hard feelings!