Volcanic eruption in Iceland

[Barb T]

Hi all,

A couple of you have emailed me with questions about the volcanic eruption that started last Saturday night in south Iceland at the big Eyjafjallajokull volcano, so I thought I'd post a little bit on it with a link to a fantastic web cam that's set up across the valley from the eruption. When the sky is clear, you can see the fire fountains really beautifully (particularly late in the day as the sky darkens when the sun is going down). Right now (about 9 am EDT on Thurs., March 25), the sky's a bit murky, and all you can see is a small eruption cloud (looks like probably steam from lava melting snow or ice). But, if the sky clears a bit, it should be as spectacular as yesterday. Here's the web cam site:

http://mila.is/um-milu/vefmyndavelar...thorolfsfelli/

There are also some great photos at the Icelandic Meteorological Office web site at http://en.vedur.is/earthquakes-and-v...ticles/nr/1851 The labeled photo on this web site has essentially the same vantage point as the web cam (although slightly higher), so you can use the photo to tell what you should be seeing from the web cam.

Volcanic eruptions are rare worldwide, so geologists are always really jazzed whenever an eruption happens. The eruption is currently pretty passive and not doing any damage - it's in the best possible place with respect to potential disaster as far as humans go. Geologists had been monitoring earthquakes under the volcano for a couple of weeks, and it wasn't clear whether an eruption would actually happen. But geologists were worried that the eruption might happen under the ice cap of Eyjafjallajokull. If that had happened, a glacier burst (catastrophic meltwater flood) might have done some damage along the southern coast. But, the eruption happened in a snow-covered pass that hasn't seen volcanic activity for over 10,000 years. So, no glacier burst will happen from this particular eruption.

But what everyone is *really* worried about is that this eruption will trigger an eruption in the much more dangerous volcano Katla to the east under Myrdalsjokull. The three eruptions over the last 1000 years in Eyjafjallajokull have triggered an eruption of Katla every time. So, that's the real threat, I think!

One of the main issues with Katla is that the caldera of the volcano is under the glacier, and an eruption there would melt huge volumes of ice. When enough water has accumulated, the edge of the ice sheet will float, and the ponded water will flood out from under the glacier in a flood that will likely last a couple of days and have greater discharge rates than the Mississippi in flood. Katla last erupted in 1918, and the data suggest that a glacier burst is likely to occur and rise to max discharge in a very short period of time, which makes it very dangerous because it will be hard to close the roads in time (unlike the glacier bursts that are more common coming from the big glacier Vatnajokull to the east, which start with a trickle and rise more slowly - probably has to do with subglacial topography).

Since Katla hasn't erupted in any kind of a serious way in nearly 100 years, it's not clear what the precursors for an eruption would be or how far in advance of an eruption they would occur. The earthquake swarms went on for about two weeks before the Eyjafjalljokull eruption. On the other hand, Hekla volcano (which has erupted about every 10 years for the last 40 years), starts its seismic swarm only about an hour before an eruption starts, which makes it very much more dangerous. It's also a popular hike, and, unfortunately, it takes about 2 hours to get down from the summit if you're hiking. And Hekla is inflated beyond where it was in 2000 when it last erupted, so geologists had figured that it would be the one to pop first. Anyway, the whole Hekla thing gives Iceland civil defense authorities agida, because, once the earthquakes start, they don't have time to warn everyone and get them off the mountain before the eruption starts. My research is right north of Hekla, and I can remember on many occasions last summer coming around corners and wondering if I would see a plume rising from the summit!

Katla is also a big stratovolcano, and it could very well erupt in an explosive eruption, not at all like the quiet eruption that's currently taking place in Eyjafjallajokull. The length of time since the last eruption may mean that it will be more explosive than it would be had it erupted more recently.

Wind directions in Iceland are quite variable and not always from the south. In fact, those of us who work in the field in Iceland look forward to the north wind days, because the north wind is dry and it doesn't rain when the wind is from the north. So, if Katla blows in an explosive eruption, the south coast might well see some real destruction, apart from the glacier burst. The glacier burst is probably unlikely to do any real damage if it follows the path that previous glacier bursts from Katla have followed. That's because people have avoided building towns and farms in that part of Iceland precisely because of the threat of a glacier burst. But, if an eruption occurs in a different place under the glacier, all bets are off.