Wednesday, February 8, 2012

Large Earthquake Swarm at Reyjanes Ridge, Iceland

A large and long duration earthquake swarm hit the Reykjanes ridge of the SW coast of Iceland today, and is ongoing. The largest events were slightly above 3.0 magnitude, with many smaller events. The Reykjanes Ridge is part of the underwater seafloor spreading system that occurs between the North American plate, and the European plate, and is prone to frequent submarine eruptions and seismicity. It is unclear at this time from reading bad Icelandic translations from whether they are saying this is an eruption, or simple seismicity (I suspect the translated word "eruption" is misplaced in this article, and might mean "swarm", but as I do not speak the language, that's a guess!).

Tremor Graph from Reyjanes Ridge. Image copyright Iceland Meteorological Office.
Locations of the earthquake swarm (SW). Image copyright Iceland Meteorological Office.

Judging from the placement, location, and size of these quakes, it could be reasonable to assume that an underwater eruption might be occurring, however the depths, weather, and other factors could easily prevent direct observation, and volcanologists would have to infer an eruption from instrument readings (which can sometimes lie). At this point, nothing has been confirmed nor denied.

The GVP characterizes this area as such:

"The submarine Reykjaneshryggur volcanic system off the SW tip of Iceland is part of the Mid-Atlantic Ridge, which is exposed subaerially in Iceland. Numerous submarine eruptions at Reykjaneshryggur dating back to the 12th century have been observed during historical time, some of which have formed ephemeral islands. Basaltic rocks of probable Holocene age have been recovered during dredging operations, and tephra deposits from earlier Holocene eruptions are preserved on the nearby Reykjanes Peninsula."

There are no volcanoes on the Reykjanes ridge that have breached the sea surface in historical time. There is a small 'chunk' of an island along the ridge that was formerly (most likely) a volcanic feature that has since been eroded to a steep walled 'plug', named Eldey, which has the sad distinction of being the last known location of the 'great auk', a penguin-like bird that was hunted to extinction, and the last known living specimens strangled and their eggs squashed by careless hunters. The Wikipedia article on this bird is particularly sad.

I will keep my eyes peeled on the Reykjanes ridge for the time being, and post updates if anything new develops.


  1. They are actually talking about magma movements (a dike intrusion) which is the most likely cause for this quake series. So Reykjanes might get more active.

  2. Looks as if the swarm has ended for now. I'll keep my eye on it!


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