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Iceland’s Reykjanes Ridge a-rumbling 18 February 2010

Posted by admin in Iceland.
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Earthquake activity in south-west Iceland, 18 February 2010 14:35 UTC (Iceland Meteorological Office map)

Back in November 2009 we reported (thanks to Boris Behncke) that there was significant earthquake activity along the Reykjanes Ridge south-west of Iceland. Well, it seems to be happening again (and again, thanks to Boris for the tip-off). The above detail of the earthquake activity map at the Iceland Meteorological Office website shows the recorded quakes up to 14:35 UTC today; the largest quakes have been between magnitudes 3 and 4. This is a volcanically-active area (part of the Mid-Atlantic Ridge System) and it’s worth keeping an eye on what happens there.

UPDATE 19 February 2010. Erik has posted a very informative piece on the Reykjanes Ridge quakes at Eruptions.

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1. James - 18 February 2010

I’ve not felt anything here in Reykjavik, but I hope to!

There were two large earthquakes in the South Iceland Seismic Zone in July 2000, and numerous aftershocks. You could follow the earthquakes as they propagated to the west along the faults here. Since then there have been a few swarms similar to what we’re seeing now – probably just release of tension left in the system since 2000.

As for the area being volcanically active, there hasn’t been activity on the Reykjanes ridge for thousands of years, but there was an intrusion into the area in July 1978. It’s certainly not a ‘dead’ area, it’s just not very active at this particular moment. There has been more recent volcanic activity out in the ocean, technically still on the ridge, but not really close to Iceland itself – if I recall, there was evidence found for young lava flows possibly dated around the late 1980s to early 1990s.

2. Passerby - 18 February 2010

A recent study of seismic activity at Katla suggested that glacier movement, not magmetic movement, was responsible for an uptick in shakes in 2009.

However, it’s noteworthy that the USGS near-realtime monitoring website has reported shakes at rather unusual (low probability) locations, many at similar depths and magnitudes, despite separation of thousands of miles.

Maybe related to: unusually heavy seasonal precip loading, gravitational tides, rather sudden and large jump in solar flux and lagged return of geomagnetic activity after a protracted quiet period.

3. Boris Behncke - 18 February 2010

@James: here it is important to distinguish the Reykjanes *Ridge* from the Reykjanes *peninsula*. There has been no volcanic eruption on the peninsula since Medieval times (most recently about 1240 AD creating the Illahraun lava field), but the Ridge, which is the submarine prosecution of the ridge, is volcanically quite active, the latest documented eruptive event having possibly occurred in 1970. The Global Volcanism Program entry for Reykjanes (which actually includes both the subaerial peninsula and the submarine ridge) has more details:

4. James - 18 February 2010

@Boris: You’re absolutely right. I brain-farted because I was busy doing other stuff and forgot to differentiate. There is evidence for activity on the ridge (not the peninsula) later than 1970 – some submersible work in the early 1990s found ‘fresh’-looking lava flows, if I remember correctly. I couldn’t remember the exact date of the last eruptive activity on the peninsula, so thanks for that. :)

5. Suzyk2002 - 18 February 2010

Spookily enough we were pricing up a touring holiday of Iceland last night – this must be a sign – we’ll have to book the holiday now!

6. Passerby - 18 February 2010

You can make sense of the earthquake graphic if you superimpose it over another graphic from wikipedia, using a simple graphics rendering program – a simple but effective program (freeware, too) called paint.net works really well.

Paste in the earthquake map above. Go to Wikipedia page on mid-atlantic ridge, http://en.wikipedia.org/wiki/Mid-Atlantic_Ridge The graphic you want is near the bottom, right hand side. Right-click copy it and paste it as a second layer, then, with that being your active layer, go the layer dropdown menu, select layer properties, and slide the tranparency slider to the middle. Then use the image edge boxes of the semi-transparent overlay image to shrink and reposition the overlay until it matches the contours of the Iceland earthquake map underneath. Click to fix it in place.

You should now see that the earthquake pattern matches the ridge contours and that many or most of the shakes lie on the edges of the main glaciers, with the exception of the green-starred quakes.

There is a lovely explanation of the confluence of weather patterns that produced the unusual cold and historic snow pattern of the 2009-2010 winter. This pattern also affected Iceland, and so *may* be a contributing factor to the mild earthquake swarm along the southwestern leg of the mid-Atlantic Ridge underlying Iceland.

Likewise, unusual weather accumulations in the upper Western Plains may explain the mild, shallow Yellowstone swarm of 2009-2010.


7. James - 18 February 2010

Amusingly the winter here in Iceland has been unusually mild this year, apparently – lots of rain and wind, and only occasional spells where it’s regularly below freezing (like right now…). It was getting up to double figures (Celcius) in January which should be the coldest month of the year!

I’m not sure how much of it can be blamed on the glaciers, either. Some of the movement may be due to isostatic adjustment due to snow accumulation on the glaciers during winter, and equally due to ablation in the summer. Certainly the land in Iceland shows a general trend of elevation increase (i.e. it is rising) in glaciated areas, as the average mass of the glaciers decreases due to general climatic warming – this can be seen from GPS measurements.

Equally, a major factor in there being so much seismic activity beneath the glaciers is that most of these glaciers are capping volcanoes. The biggest glacier, Vatnajokull, sits atop a number of volcanoes, themselves sitting almost directly atop the Iceland hot spot – Bardarbunga, Grimsvotn and Gjalp, particularly. These volcanic systems are all quite active (Grimsvotn is arguably ‘due’ another eruption in the next year or so). Likewise, Myrdalsjokull sits within and just over the edges of Katla, which is a huge volcano, and is also showing signs of activity (including general slow inflation shown by GPS measurements).

Certainly the weather and climate may have some link, but in Iceland there is a lot more to it. I would personally say that the Reykjanes peninsula earthquake swarms occuring now are normal tectonic adjustment along South Iceland Seismic Zone’s fault system, possibly considerable as ‘aftershocks’ from the 2000 quakes, but you can never say anything for sure. :)

8. admin - 19 February 2010

I have to agree with James. Given the tectonic context of Iceland as a whole, it seems odd to go looking to the weather for explanations of Icelandic earthquakes. If weather is a factor it is surely marginal, far less significant than what we know is going on beneath the surface – an active spreading plate boundary.

9. jack - 20 February 2010

hi everyone

today I looked at the iceland earthquake page. I think there is something going on at baroarbung, there have been two earthquakes above 3 and 2 above 4. ALSO there have been 43 earthquakes in that area. Could this be related to the volcanoes in this area or the movement of the massive glacier which sit on top of them. in 2004 there was a eruption in this area. i was woundering if this volcano waking up again.

10. SueL - 20 February 2010

Have just come back from Reykjavik today. My perfect holiday was to consist of Aurora Borealis, a little snow and some volcanic or seismic activity. Didn’t feel a thing, except a little rumbling at Keflavik airport this morning wasn’t sure what that was, probably a plane

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