Eyjafjallajökull and Katla: restless neighbours

The Icelandic volcano Eyjafjallajökull has been very restless recently. The current seismicity and apparent inflation may be precursory to an eruption, or it may not – as Hugh Tuffen of Lancaster University observes, this kind of activity has been seen before, associated with dyke intrusion events (although the current seismicity is unusually energetic) and it is not possible at the moment to say whether this time it will end in an eruption: ‘time will tell’. An interesting detail about the current activity comes from a source in Iceland who tells me that magma degassing under Eyjafjallajökull produced an ‘acid pulse’ that led to local water supplies become temporarily acidic about a month ago.

Eyjafjallajökull is an interesting volcano, not least because of its relationship with its near neighbour, Katla. This much larger volcano lies less than 30 km to the east of Eyjafjallajökull, beneath the Myrdalsjökull icecap. Katla is, the Global Volcanism Program reports, ‘one of Iceland’s most active [volcanoes] and is a frequent producer of damaging jökulhlaups, or glacier-outburst floods’. Katla, with more than twenty confirmed eruptions since the sixth century AD, has a much more active eruptive history than Eyjafjallajökull, which has just three eruptions over the same period. It seems, however, that there is a connection between these two closely-spaced volcanoes. Eyjafjallajökull’s most recent eruption, December 1821 to January 1823, was followed by an eruption of Katla in June and July 1823. More recently an intrusion at Eyjafjallajökull in 1999 appears to have been followed by a small subglacial eruption in the Katla caldera.

It’s intriguing that recent earthquake activity around Katla and Eyjafjallajökull has clustered in three areas: (1) shallow quakes around and within the Eyjafjallajökull caldera, (2) shallow quakes largely confined to the eastern part of Katla caldera, and (3) quakes with a deeper focus in the Godabunga area between the first two clusters. One possible interpretation of this pattern is that a cryptodome – an underground lava dome – is active beneath this area. The presence of viscous rhyolitic lava beneath Katla and Eyjafjallajökull makes for potentially explosive eruptive activity, if an eruption occurs.

An Icelandic commenter at Eruptions reports that the Iceland Meteorological Office do not expect an eruption at Eyjafjallajökull. The volcano may get over its current bout of restlessness and calm down again, as happened with the intrusion events of 1994, 1999 and 2009. It clearly needs careful watching, however, as does its large and destructive neighbour, Katla.

[Grateful thanks for information received to ‘a source at the Department of Geophysics, University Of Iceland’.]