• Eruption of Chaitén continues without interruption: eruption column 4-5km in altitude
• Town of Chaitén seriously affected by flooding and lahars: more of the same to come
• Ashfall has taken place to the west of the volcano, volcanic material deposited in the sea is being carried northward by the coastal current
• Changes in seismic activity indicate fragmentation and instability around the volcano’s central conduit and beneath the lava dome
• An explosive destruction of the lava dome and collapse of the eruption column, producing pyroclastic flows, remains a possibility
• USGS scientists are arriving shortly to collaborate with SERNAGEOMIN in monitoring the volcano: SERNAGEOMIN is enhancing its seismic network

The Servicio Nacional de Geología y Minería (SERNAGEOMIN) of Chile issued a new bulletin on the situation at Chaitén on 16 May 2008. There’s a lot of information in this latest bulletin so I have summarized the key points as I understand them above, and provided a complete translation of the text below, as follows:

The plinian eruptive activity of the volcano Chaitén is continuing, and over the last two days the column of gases and ashes has been maintained at an altitude not exceeding five kilometres above sea level.

At 07:30 yesterday, 15 May, the upper section of the volcano’s eruption column was observed, reaching an altitude of four kilometres above sea level. The plume was directed towards the north-east due to strong south-westerly winds of up to 140 km/h.

During the day a Bolkow 44 helicopter of the Chilean Navy was able to make a reconnaissance flight over the town of Chaitén and the surrounding area to observe the situation of the Amarillo and Michinmahuida rivers.

Mudflows or lahars were observed which have affected the town of Chaitén, still covering the areas around the channel of the Chaitén river and the southern area of the town, without so far affecting the central plaza, the administrative centre and the areas surrounding the harbour and maritime offices. The airfield, for its part, is covered by water and ash, so entry by both land and air to the town is impeded.

The same helicopter was used to collect data from the seismological stations at Chumildén, Auchemó and Chaitén Norte. In addition, the overflight permitted various observations to be made as follows:

a) Ash has fallen throughout the valley and delta of the rivers Blanco and Rayas and the forests are covered by a mantle of white ash.

b) The marine litoral current, which moves in a northerly direction along the coast of Chile, is carrying a great deal of ash and islands of pumice northwards along the coast. The volcanic material (water coloured light green - milky) is principally from the bay of Chaitén and the Blanco-Rayas river delta. The progress of this ash-bearing body of water was clearly visible as far as Pumalín bay, and it continues to advance northward.

c) Between 12:00 and 13:00 a very cold ‘viento puelche’ [i.e. a cold and dry easterly wind] dispersed fine ash to the west, which even fell on the ship Aquiles and on the island of Talcán. On some parts of the ship the covering of ash reached between 0.5-1.0mm in thickness. During this period ashfall affected the area from the Blanco-Rayas river mouth as far as the mouth of Chaitén fjord.

Mudflows (lahars) and the runoff of large quantities of sediment have continued to fill the channels of the Chaitén and Blanco-Rayas rivers, which can no longer accommodate the normal flow of water. Consequently, the Chaitén river will continue to flood, affecting new areas of the town of Chaitén.

Areas most susceptible to the occurrence of flows of mud and rocks (lahars) and landslips have been identified along the road connecting Chaitén and Futaleufú, in the vicinity of the latter-named town and the other populated areas south-east of the volcano these may be caused by heavy rainfall and occur over a prolonged period.

Seismic activity

Over the past two days marked changes have been witnessed in the seismic activity [of the volcano]. A swarm of earthquakes, mainly of the HB [hybrid] type, has occurred, which is interpreted as related to a fracturing of the main conduit with subsequent ascent of magmatic fluids by the conduit and also through the dome. The later predominance of LP type earthquakes confirms the seismic instability of the system, the origin of which is related to the evident movement of magmatic fluids. In consequence there remains a certain possibility of future major explosions causing the destruction, in whole or in part, of the dome and the generation of pyroclastic flows through the collapse of the column. Nor can the possibility of new lateral explosions be disregarded.

SERNAGEOMIN has reinforced its team on the ground with three additional scientists and technicians and has begun preparations to move its centre of operations to the city of Queilen. In addition, all necessary preparations have been made for the arrival next Saturday of specialists from the Volcano Disaster Assistance Program of the United States Geological Survey, who will collaborate on volcano monitoring with SERNAGEOMIN and will bring additional monitoring equipment.

From next Monday the installation of four new stations with telemetric data transmission and helicopter support will bring about, as soon as possible, the reception of real-time seismic data in Queilen.

In this situation, SERNAGEOMIN maintains Volcanic Red Alert for the area of Chaitén.

End of SERNAGEOMIN bulletin, 16 May 2008.

A press release regarding the Volcano Disaster Assistance Program (VDAP) assistance to Chile was issued by USAID on 16 May 2008. The VDAP is a joint program of the United States Geological Survey and the US Agency for International Development - there’s a recent Volcanism Blog post about it here.

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)