Right call to issue eruption alert

„Right now we're analyzing what was going on. As of now we don't know, but we'll keep analyzing and add it to the data pool," says Sigrún Karlsdóttir, director of the Nature Watch at the Icelandic Meteorological Office, when asked what exactly gave such clear signs that a small eruption had started under the Dyngjujökull glacier on Saturday.

False signs

Low frequency waves that were detected by seismographs around noon on Saturday were interpreted by experts at the Icelandic Meteorological Office that a small amount of magma had erupted under Dyngjujökull. This activity went on for several hours but reduced in strength as time passed.

Readings from on board the Coast Guard's helicopter, as well as readings from the water level system showed no significant changes. As the day drew on, it became obvious that this had not been an eruption. Sigrún claims that the experts at the Icelandic Meteorological Office had not reacted too quickly, but it had been necessary to react to the signs detected. In the case of a real eruption, the series of events can be very quick to happen.

"It was the right decision at the time. In prior eruptions these signs have indicated that an eruption had started. We thought it right to react immediately," says Sigrún. No other evidence has surfaced to indicate than the activity signaled that an eruption had started.

Groundwater?

Magnús Tumi Guðmundsson, professor of geophysics, says that no one knows what caused this particular activity that was interpreted as the beginning of an eruption. Opinions differ on the topic.

"We've never monitored a situation like this with our current equipment. We'd have to go back to the Gjálp eruption in 1996 to find a comparable event, but we had different equipment back then and it didn't reach as far onto the highland. We're always learning from past experience. We don't know everything about how these instruments behave or what signals they send under various circumstances," states Magnús Tumi, adding that one plausible theory is that the magma under the Dyngjujökull glacier came into contact with groundwater, and the resulting reaction was picked up by the instruments. But as is this is only an unproven theory.

Magnús also eliminates the possibility of an equipment malfunction. "It was a real signal, just not an eruption."

270 million cubic meters

As of late last night (Sunday) there had been close to 2000 registered earthquakes, both by the Bárðarbunga caldera and at the north end of the subterranean cavern at the edge of the Dyngjujökull glacier. Most of the quakes originate from the north end of the cavern, but seismic activity is now registering north of the glacier, and it also seems that the magma has slowed down in speed. Two earthquakes greater than 5 on the Richter scale have been registered near the Bárðarbunga caldera, they are the largest earthquakes registered in the area since 1996.

The latest data from GPS readings indicate that magma is still flowing into the cavern under Dyngjujökull and that it is reaching further north. 3D models based on the date indicate that the total volume of magma in the cavern is now 270 million cubic meters.

Added probability

Haraldur Sigurðsson, volcanologist, ponders in a blog post late last night what would happen if the magma flow would reach Askja, but the magma flow has changed course and is now on a direct course towards the Askja caldera. The magma would only have to travel 25 kilometers to reach it, and there are plenty of examples of subterranean caverns that have traveled such distances. History shows us, according to Haraldur, that magma always reaches the surface where rock caverns break through the earth's crust at altitudes close to sea level. "That means that now is the greatest chance of an eruption, as the cavern makes its way through the crust underneath the sands north of the Dyngjujökull glacier and south of Askja," Haraldur writes.