Update on activity
Eruption in Eyjafjallajökull, Iceland
Monday 19th the eruption was still ongoing with the height of the plume 2-3,000 ft above the volcano, but the plume ascended to 20,000 ft above
sealevel when it drifted southward. Later in the afternoon reports indicated maximum plume height around 15,000 ft with ash clearly visible in the
clouds. Decreasing windspeed Monday evening will slow the advection of the plume. Southerly winds and rain on Tuesday evening.
On 17 April at least 115 lightning strikes were recorded in the vicinity of the eruption. On 18 April only 17 strikes were detected. Taking this
activity as a measure of ash load in the plume, fewer fine-grained particles are being jetted into the atmosphere. At present, no lightning has
occurred on 19 April; see: andvari.vedur.is...
If phreatomagmatic activity intensifies again and ash is ejected to elevations over 6 km (~20,000 ft) a.s.l., then a low-pressure system presently SE
of Iceland will cause southward-tracking ash clouds to be deflected eastwards toward northern parts of the UK; see:
Details on the composition and grain-size of the erupted tephra are available from the University of Iceland:
Volcanic tremor at a dominant frequency of 0.5 Hz remains continuous. Since ~11:00 GMT on 18 April, tremor levels have intensified beyond levels
maintained since 16 April, as shown in the following real-time plot: hraun.vedur.is...
We presently don't know the
source mechanism behind the heightened low-frequency tremor, although presumably phreatomagmatic conditions still prevail at the eruption site.
Locatable seismicity since the beginning of the Eyjafjallajökull eruption can be seen here: hraun.vedur.is...
epicentres delineate an elongated zone of fracture orientated NNE-SSW. Few earthquakes have occurred beneath Eyjafjallajökull since the pre-eruptive
swarm ended in the early hours of 14 April, as shown here: hraun.vedur.is...
Daily solutions from continuous, 15-s GPS stations around Eyjafjallajökull, operated in conjunction with the University of Iceland, show
centimetre-scale horizontal movements toward the centre of the volcano, with some stations registering centimetre-scale vertical decreases too. An
overview of GPS time-series from nine stations around Eyjafjallajökull is available here: notendur.hi.is...
During overflights on April 19th it was apparent that the ice cauldrons over the eruption site have coalesced to form a larger cauldron.
(See also www.earthice.hi.is...
Following an initial period of glacial flooding on 14-15 April, relatively little water is draining from the northern flank of the ice cap.
Significant ponding of meltwater at the eruption site doesn't seem to be occurring, as there seems to be a largely open pathway for drainage over and
through the Gígjökull glacier.