Steinunn S. Jakobsdóttir

Eruptions of Eyjafjallajökull Volcano, Iceland

The April 2010 eruption of Eyjafjallajokull volcano (Figure 1), located on Icelands southern coast, created unprecedented disruptions to European air traffic during 15–20 April, costing the aviation industry an estimated

Multiple melt injection along a spreading segment at Askja, Iceland

250 million per day (see the related news item in this issue). This cost brings into focus how volcanoes can affect communities thousands of miles away. Eyjafjallajokull rises to 1666 meters above sea level and hosts agricultural land on its southern slopes, with farms located as close as 7 kilometers from the summit caldera. In the past 1500 years, Eyjafjallajokull has produced four comparatively small eruptions. The eruption previous to 2010 began in December 1821 and lasted for over a year, with intermittent explosive activity spreading a thin layer of tephra (ash and larger ejected clasts) over the surrounding region. In contrast, the explosive 2010 eruption, sourced within the ice-capped summit of the volcano, so far is larger and characterized by magma of a slightly different composition. This may suggest that deep within the volcano, the 1821 magma source is mixing with new melt, or that residual melt from past intrusive events is being pushed out by new magma.

Forecasting and monitoring a subglacial eruption in Iceland

Lower crustal earthquakes (12–25 km depth) have been detected since August 2005 in the Askja volcanic system along the north Iceland rift, in the normally ductile part of the crust. The earthquakes occur in three clusters, which have stable dimensions and locations through time and are interpreted as positions of repeated melt supply from the mantle to the lower crust. Seismic velocity Vp/Vs ratios are consistent with the presence of partial melt in the lower crust at Askja. The spatial separation of the clusters shows that there are multiple positions of melt injection within this one magmatic segment and all three positions are currently active. This pattern of melt supply is more like that observed on fast spreading ridges than slow spreading ridges and is probably a consequence of the increased melt production beneath Iceland compared to the rest of the Mid-Atlantic Ridge. However, the relative number of earthquakes in each cluster shows that two thirds of the melt is supplied to the central volcano Askja (i.e. segment center). During the last major rifting episode shallow lateral melt migration occurred from the magma chamber beneath the volcano. Therefore on long time scales melt supply is probably greater at the segment center, with melt redistribution in the upper crust, even though there are multiple points of lower crustal injection along the segment.

Correction to “Multiple melt injection along a spreading segment at Askja, Iceland”

The recognition of geophysical precursors to volcanic activity is a primary challenge in volcano monitoring. That challenge was successfully met by scientists at the Icelandic Meteorological Office (IMO) before the 1 November 2004 eruption of Grimsvotn, a subglacial volcano beneath the Vatnajokull ice cap,Iceland (Figure 1). Seismic and geodetic precursors were properly recognized, leading to a timely eruption forecast and warning announcements. During the eruption, IMOs monitoring capability was greatly expanded by employing geophysical and meteorological observation tools, which enabled real-time hazard assessment.

Earthquake prediction research in the South Iceland seismic zone and the SIL project

In the paper “ Multiple melt injection along a spreading segment at Askja, Iceland ” by Janet Key et al. (Geophysical Research Letters, 38, L05301, doi:10.1029/2010GL046264, 2011), we regret that an error was made in the calculation of the V p /V s ratios. The correct values are presented in this revised version of Figure 2 and its caption. This change does not affect either the hypocentral locations, for which we used the correct mean V p /V s value of 1.78, nor the overall conclusions of our paper. We still find evidence for relatively elevated V p /V s ratios from the lower crustal earthquakes, consistent with the presence of melt in the lower crust. However the following corrections to the text should be made in light of this discovery.