Chaitén: latest SERNAGEOMIN bulletin

SERNAGEOMIN have just released their latest bulletin on the Chaitén eruption. It’s the fullest and most interesting report to come from them so far. The translation of the complete text is as follows:

On account of the conditions being monitored by SERNAGEOMIN specialists in the area, the service is maintaining a Red Alert. The possibility of future major explosions and the collapse of the eruptive column cannot be discarded.

On 8 May the volcano was hidden from view between 07:15 and 15:15 hrs. During this period, despite the low cloud cover, grey swirls were clearly seen along the north-south valley immediately east of the volcano Chaitén which drains into the Rayas river, descending towards the river and producing marked evaporation in the north-south valley. This phenomenon is interpreted as being caused by small pyroclastic flows that descend from the volcano into this valley and, heating the river water, produce the resulting evaporation.

Between approximately 15:00 and 16:30 hours the prevalent cloud dissipated allowing observation of the volcano and the mushroom-shaped column of gases and ashes, which reached an altitude of 14 km at 16:00 hrs, with a plume dispersing in a north-eastern direction. We saw evidence, moreover, that the western part of the column of ash was more dense and of a medium to dark grey colour, which could be due to the opening of a new crater on the western side of the dome.

On Thursday 8 May, for reasons of safety, it was decided to relocate the Muelle uniaxial station from the town of Chaitén to Talcán island. The data retrieved from the station showed a marked increase in seismic activity produced by the large explosion at 23:35 on 7 May.

With regard to the number of volcano-tectonic (VT) events, these have not increased, reaching up to 35 events per day, with their activity concentrated in the vicinity of the volcano. Finally, SERNAGEOMIN staff are in the process of transferring the other two stations (PUMA in Caleta Gonzalo and YELCHO at the lake of the same name) to more accessible places where their data can be obtained on a more regular basis.

Seismic activity

The precursory earthquakes of the LP type, although previously detected in advance of the two large explosions observed on 6 and 7 May, indicate the existence of significant movements of fluids, probably at shallow levels, which would confirm the existence of a magma chamber at no great depth (hypocentre calculation suggests that the chamber is located at a depth of less than 5 km).

The occurrence of earthquakes of the HB [hybrid] type (earthquakes generated by the breaking of rocks followed by the movement of fluids), following the two large explosions which occurred in the preceding days, would be associated with a significant ascent of magma, which is displacing the rocks surrounding the main conduit through which the magmatic fluids move and causing them to fracture.

This vertiginous ascent would produce a sudden evacuation of fluids (gases and magma) provoking these big explosions occasionally reaching about 30 km in altitude, which release large quantities of ash and gases into the atmosphere, generating a partial vacating of the upper zone of the chamber and a subsequent ascent of magmas fragmented by rapid nucleation.

The main concern continues to focus upon possible future major explosions and the collapse of the eruptive column, which could cause the destruction of the dome and the generation of pyroclastic flows that would descend radially from the volcano through the adjacent valleys.

Thus SERNAGEOMIN maintains a Red Alert for the volcano. Our specialists monitoring the eruption will continue to operate from the [naval] ship Aquiles, with periodic overflights, operated by helicopter or boat, to make observations and measurements and retrieve data from ground stations. In this way, the processing, analysis and interpretation of related seismic activity will continue.

The notion of overflights by boat is vaguely comical, but that is what the original says. On the point about local rivers being heated by pyroclastic surges from the volcano, SERNAGEOMIN volcanologist Luis Lara is quoted in yesterday’s Patagonia Times article as reporting ‘a noted temperature increase (of between 7 and 17 degrees Celsius) in the nearby Chaitén and Raya Rivers’.

For all our Chaitén coverage: Chaitén << The Volcanism Blog