LONDON: The first detailed analysis of what happened inside the Icelandic volcano that grounded flights across Europe shows it had been rumbling for months before it exploded in April.
In a paper published in Nature, Freysteinn Sigmundsson, of the Nordic Vulcanological Centre at the University of Iceland, describes how one flank of Eyjafjallajokull had been swollen by more than 15 centimetres for 11 weeks before the volcano began erupting. Magma had been flowing from deep underground into shallower compartments under the mountain.
Kurt Feigl, a professor of geosciences at the University of Wisconsin-Madison and a co-author of the study, said the volcano had been showing signs of restlessness.
''Several months of unrest preceded the eruptions, with magma moving around downstairs in the plumbing and making noise in the form of earthquakes,'' he said. ''By monitoring volcanoes, we can understand the processes that drive them to erupt.''
The deformation of the Earth's crust around Eyjafjallajokull, and the resulting small earthquakes, began to increase in January. A few weeks later, sensors and GPS stations began detecting rapid expansion of the mountain.
The first eruption, caused by magma flowing into the mountain from underneath, began on March 20. It continued for three weeks before pausing for two days and then resuming on April 22.
The second time around, the erupting lava punched through the ice at the top of the mountain. The water exploded into steam and rapidly cooled the magma, which turned into a fine-grained dust cloud that rose high into the atmosphere and was blown across the whole of northern Europe.
Sustained, highly variable activity continued until May 22, with an average of 30,000-60,000 litres of magma coming out every second.
Normally, when volcanoes erupt, they deflate as the magma drains out. But for some reason, Eyjafjallajokull kept its shape after the first eruption.
The researchers suggested that this could be because of a limited supply of magma in the first place, and the position of the volcano.
The eruption was probably started by an intrusion of magma deep inside the volcano, though this is something that needs to be confirmed at other volcanoes. The researchers stress that studying the lead-up to the eruption will not necessarily help to predict future events.
''We're still trying to figure out what wakes up a volcano,'' Professor Feigl said.
''The explosiveness of the eruption depends on the type of magma, and the type of magma depends on the depth of its source. We're a long way from being able to predict eruptions. But if we can visualise the magma as it moves upward inside the volcano, then we will improve our understanding of the processes driving volcanic activity.''
Guardian News & Media
