Katla eruption 2011?
This is a fresh picture showing the the seismic activity around the Mýrdalsjökull glacier in Iceland in the past 48 hours. Katla, one of Iceland’s most powerful volcanoes sits directly underneath this glacier. You can always check out a fresh picture of Katla’s activity at the Icelandic Met Office. On any given day you will see earthquakes mapped onto the picture, but today it is quite lively. The color of the dots signify the recentness of the quake, red = 0-4 hrs, orange = 4-12, yellow = 12-24, light blue = 24-36 and dark blue = 36-48. Stars signify quakes over 3 on Richter. If you check out the accompanying table you can see the depth of the quakes. Quakes close to the surface and particularly series of earthquakes reaching closer and closer to the surface are indications of upcoming eruptions.
Katla is long due for an eruption. During the past 1000 years or so, Katla has erupted almost always twice a century. The last Katla eruption was in 1918. Icelanders therefor monitor Katla closely and stay as prepared as possible.
What happens if Katla erupts?
Katla is a powerful volcano situated under the Mýrdalsjökull glacier on the south coast of Iceland. The fact that it is under a glacier affects it a lot. When erupting lava comes in contact with ice an explosion occurs. This explosion is a bit like if you throw water onto an oil fire. Due to this explosive nature, what would otherwise be a calm lava flow (a photographers delight), becomes a great ash eruption. This is best illustrated by the two different eruptions we had last year, the beautiful Fimmvörðuháls eruption, next to the glacier and the much more violent eruption under the Eyjafjallajökull glacier. Ash is bothersome, but not really a danger. It disrupts flights around the world, is a major nuisance for farmers and makes things dirty. So we aren’t really afraid of ash, although many may dread it.
What we do have reason to worry about is the other side effect of subglacial eruptions. An eruption underneath a glacier will of course melt a lot of ice. This will build up a huge bubble of water somewhere underneath the glacier. Once this bubble is large enough it will break its way through the glacier and cause a massive flood. Floods caused by eruptions in Katla are estimated to have reached up to 300.000 cubic meters per second. To give you some kind of idea of how much water that is, it is nearly three times the Amazon river or greater than the three greatest rivers in the world combined.
Since such floods occur on average twice a century, we are somewhat prepared. Of course roads and bridges will be destroyed, but the flood paths are more or less uninhabited sands. The only place in real danger is the town of Vík. Floods may go directly into Vík, but will most likely miss it. However the flood can cause a massive Tsunami like wave towards shore once it hits the sea. This can be a major problem.
Today’s earthquake map is interesting, but no sure indication. There have been a lot of false alarms in the past.
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