Chaitén update, 31 May 2008

The latest from SERNAGEOMIN is the following bulletin, dated 30 May 2008:

30.05.2008 SERNAGEOMIN bulletin concerning the Chaitén volcano

Permanent eruptive activity continues in a subplinian phase.

On 28 May the eruptive column remained between 3.5 and 4km above sea level and the plume was blown in a northerly/north-westerly direction, affecting areas hundreds of kilometres to the north and forcing the closure of airports in Puerto Montt, Osorno, Temuco and Valdivia.

At lower altitudes, orographic winds from the east dispersed ash westwards to affect areas along the coast between Chaitén and Chumildén, in addition to the island of Talcán. This zone was covered by a dense haze produced by ash in suspension, which prevented the carrying out of overflights.

[Caption for the above image: Crater of Chaitén volcano and southern flank of the old volcanic dome on 26 May 2008. Towards the north two columns of gases and ashes can be seen, the southernmost of which contains a large amount of water vapour, while the other has more abundant emissions of ash and pumice. On the left the western part of the active dome can be seen.]

Seismic activity

During the past few days the VT [volcano-tectonic] earthquakes have continued to decline, both in number and magnitude. No hybrid [quakes] have been detected, that would be associated with the growth of the dome, nor long-period earthquakes that are associated with the movements of magma and gases. The foregoing confirms a continuing decrease in seismic activity.

In consequence, the decline in seismicity has coincided with a decrease in the heights of the eruptive columns, as confirmed over the week. Finally, although seismic activity and the intensity of the explosions have fallen, we cannot exclude the possibility of the occurrence of major explosions caused by obstruction of the eruptive conduit, which could produce the partial destruction of the dome and the generation of pyroclastic flows.

The latest GOES-12 satellite image from the Argentine Servicio Meteorológico Nacional, taken at 17:45 UTC on 30 May 2008, shows a smallish northward-trending plume from Chaitén, with ash fallout visible across a large area to the west of the plume. Below is a detail view of the Chaitén area: the volcano is slighly left of centre. The full-size image from which this detail comes is here.

ONEMI says there was an earthquake at 22:25 local time yesterday in the Hornopirén area north of Chaitén (the same locality as the quakes of 28/29 May), level 3 on the Mercalli scale, but no-one else seems to have any information about it. Nothing in the press, nor from the USGS or any of the other earthquake reporting services, nor even Chile’s own Servicio Sismológico. UPDATE: the Servicio Sismológico now have a report about the quake: their bulletin is here. They say it was a 4.5M quake, at a depth of only 6.2km.

For all our Chaitén coverage: Chaitén « The Volcanism Blog.

Information
Global Volcanism Program: Chaitén – summary information for Chaitén (1508-41)
ONEMI, Oficina Nacional de Emergencia – Chilean government emergencies office (Spanish)
SERNAGEOMIN – volcanology information from the Servicio Nacional de Geología y Minería (Spanish)