Bárðarbunga has been expanding, which could be a sign of magma accumulation ahead of a possible volcanic eruption, or the volcano could still be changing as it settles down from its last eruption, at Holuhraun, in 2014-15. Geophysicist Páll Einarsson believes recent earthquakes at the East Iceland volcano were likely caused by uplift.
Páll told Morgunblaðið that the pressure has decreased enough for the volcano to start drawing magma in from below.
There were two fairly large earthquakes under Bárðarbunga on Tuesday evening, of magnitude 3.9 and 4.5, according to Met Office data. Initial Icelandic readings indicated the quakes were smaller, while the United States Geological Survey initially recorded them as larger than they were.
Páll says it is difficult to know which of the two theories on the volcano’s behaviour is correct at this stage, but that seismic activity could be a sign of a new eruption. If Bárðarbunga is preparing to erupt, it is not likely it will do so imminently, however.
Seismic activity levels dropped when the Holuhraun eruption finished in 2015, increased again for a while, and then dropped off again until recently. Scientists are also closely monitoring Öræfajökull and Grímsvötn.