Update on activity
Eruption in Eyjafjallajökull, Iceland
Eruption similar - 22 April 2010 11:15
Volcanic tremor increased in the afternoon yesterday but after midnight it decreased again and has been relatively stable since then.
The plume rose up to 3-4 km high yesterday afternoon and seems similar this morning according to IMO's radar.
Little changes - 21 April 2010 10:00
Little changes since yesterday. The plume rises up to ca 2 km hight above the volcano but up to ca 5 km south of Iceland.
The volcanic tremor has slightly decreased since yesterday.
Deflation - 20 April 2010 13:30
Latest available results from GPS stations around Eyjafjallajökull showed deflation associated with the eruption. This suggested that the volume of eruptive material which has been ejected already, relieves pressure off the volcano.
No movements associated with the Katla volcano are presently observed.
Sound blasts - 20 April 2010 12:30
Heavy sound blasts have been heard and found near Eyjafjallajökull, especially south and east of the mountain, and more clearly after wind speeds became lower.
The viscosity of the magma from Eyjafjallajökull is higher than on Fimmvörðuháls. This enhances the explosive sound effect. Shock- and soundwaves are carried long distances.
Information received in the last few days
Monday 19th the eruption was still ongoing with the height of the plume 2-3,000 ft above the volcano (upto 1 km), but the plume ascended to 20,000 ft above sealevel (6-7 km) when it drifted southward. Later in the afternoon reports indicated maximum plume height around 15,000 ft (5 km) 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 an automatic list of lightnings.
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 (19 April) will cause southward-tracking ash clouds to be deflected eastwards toward northern parts of the UK; see Volcanic Ash Advisory Centre, London. Details on the composition and grain-size (pdf 0.02 Mb) of the erupted tephra are available from the Institute of Earth Sciences, 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 a real-time plot. 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 on the linked map. The 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 on the linked graph.
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.
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 a report from the Institute of Earth Sciences on Radar observations 15-19 April 2010 (Eyjólfur Magnússon).
Following an initial period of glacial flooding on 14-15 April, relatively little water is draining from the northern flank of the ice cap now (19 April). 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.