Guest Post: Underneath the Eyjafjallajökull Volcano

June 22, 2010 at 9:28 am 1 comment

Nancy Marie Brown took this photo in Iceland in April.

Editor’s note: The July-August issue of The Penn Stater has a story about Iceland’s Eyjafjallajökull volcano, which began spewing ash in April and wreaked havoc on farms and towns—as well as on international air travel. The piece was written by Nancy Marie Brown ’81, ’85 MA Lib, who lives in Vermont but is a regular visitor to Iceland—and who flew over to Iceland to see the volcano.

Iceland sits on a hot spot where two tectonic plates are drifting apart, making it one of the most volcanically active places on earth, with an eruption about every five years. For scientists, the island is a kind of volcano laboratory whose results apply around the world.

Nancy talked to Kristin Vogfjörd ’86 MS, ’91 PhD EMS, a research seismologist and chief project manager at the Icelandic Meteorological Office; part of Vogfjörd’s job is finding better ways to predict earthquakes and volcanic eruptions.

Here’s what Vogfjörd told Nancy.

When did you first notice the volcano under Eyjafjallajökull was waking up?

We’ve been watching the progress of this lava coming up through the crust of the earth since 1994. We had a swarm of really deep earthquakes at the base of the crust, about 22 kilometers down, in 1996. Usually you don’t have earthquakes that low. Quakes happen when rock breaks, and the rock that deep in the crust is warm and yielding. It bends instead of breaking. The only way you can induce quakes that deep is if you’re forcing magma—molten  lava—in from beneath.

Photo by Nancy Marie Brown

In 1999 there was another series of events that ended in a pool of magma at 6 kilometers down. Then there seemed to be a gap and we got seismic activity up even higher. We think the lava was pooling in between these clusters of earthquakes.

For two months before this last eruption, there was a lot of seismicity. We had 1,000 earthquakes per week, as the lava found its way to the top. On our maps, you can see it forming a dike, then a pipe. It comes up to about 2 kilometers deep and then propagates eastward. The earthquakes were at the spot where the lava was upwelling, but the eruption at first was a little to the north.

How do you “watch” lava moving when it’s 6 kilometers beneath the surface?

It’s like a CAT scan. First you need an array of seismometers. We have a lot of monitors on Reykjanes, a peninsula in the west of Iceland—the power companies paid for them. We have some in the north near Lake Myvatn and some near the Vatnajökull glacier. We would like to have some in other areas, but they’re expensive. We have six in the south around Eyjafjallajökull, including one on the Westman Islands.

Second, you need a lot of tiny earthquakes. For example, between 1991 and 2006, we recorded 860 earthquakes under Eyjafjallajökull.

When an earthquake occurs, you divide the earth into boxes and calculate how long it takes for the waves from that earthquake to get to all the different monitoring stations. Once you record many earthquakes, with many waves passing through each box from lots of different directions, you can calculate  a model of the structure of the earth in that spot.

Photo by Nancy Marie Brown

You’ve recently used earthquakes to map the structure underneath all of Iceland. What have you learned?

We found that the old model we’ve been using all these years for all of Iceland turns out to be only good for the northwest part of the country. There’s a big change in the thickness of the earth’s crust in different parts of the island. That surprised us. The thickness of the crust in the south, near Eyjafjallajökull, is 22 kilometers. In Reykjanes, in the southwest, it’s 17 kilometers. At Grimsvotn, in the southeast, it’s about 40 kilometers.

The new model we’ve developed gives you the location and depth of an earthquake much more accurately. There’s a 1.4-second difference in travel time between the old model and the new one, which is a big difference, considering that we’re working in milliseconds. There’s no way you would have been able to get the right location using the old model.

Our goal is to identify the location where a quake starts. In a volcanic eruption, our model shows you where the molten lava is propagating from. In an earthquake, it shows you where the stress is, so you can map the fault.

Now that you have a better picture of what the earth looks like underneath Iceland, what’s the next step in improving your ability to predict earthquakes and volcanic eruptions?

We’re building portable seismic equipment banks, powered by windmills and solar panels. We’ll have 23 if we get the next round of funding. It took five years to get the right equipment—we wanted them to be able to transmit remotely to our computers here at the Met Office in Reykjavík.

We have six of these portable banks now at Eyjafjallajökull. On April 6, for example, there was a 3.7 magnitude earthquake near there. What the system does is to plot a color-coded map of the arrival times of the seismic waves. It takes about 55 seconds for a wave to travel from the first station to the farthest one. The Shake Map—which shows you where the quake was felt—appears in three minutes. It’s immediately up on the web—the Civil Defense has access to it and can see right away how widely the earthquake was felt. The epicenter of that particular earthquake was 5.4 kilometers south of Basar. The magnitude of the quake—3.7—took the system about two more minutes to calculate. Nobody has to be here watching the instruments; it’s all automatic. This is great for rescue teams, especially since all the big earthquakes and eruptions we’ve had have had foreshocks.


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