Chronology of the May 2008 eruption

On May 1st 2008 Chaiten volcano interrupted a long period of quiescence, generating a sequence of explosive eruptions and causing the evacuation of Chaitén town. The activity was characterized by several explosive events each associated with plumes which reached up to about 20 km a.s.l. (above sea level). The dispersal of tephra during the first week of the eruption affected a vast region (with ash deposited over an area > 2 × 105 km2), from Chile to the Atlantic coast of Argentina. The eruption caused the evacuation of more than five thousand people from a 50 km radius area, led to the eventual abandonment and relocation of the town of Chaitén, and disrupted agriculture, tourism and aviation. This is believed to have been the first major explosive eruption of rhyolite since the eruption of Novarupta (Alaska) in 1912. With so few historical examples of rhyolitic eruptions, it is particularly important to document the onset of Chaitén activity and the associated eruptive dynamics. Other examples of explosive young rhyolite eruptions include Askja 1875 and Taupo 186 AD.

Before the eruption of May 2008, Chaitén volcano was unmonitored, due to its long quiescence and lack of historical unrest. The chronology of the May 2008 main events is as follows:

April 30th–May 1st: A volcano tectonic (VT) seismic event up to a maximum of magnitude 5 is registered by six seismic monitoring stations, located up to 300 km from Chaitén volcano.

May 1st–2nd: The VT activity increases to 20 events per hour in coincidence with the beginning of the eruption, which occurred at 23:38 local time on May 1st, producing a 13–16 km eruptive column sustained for 6 h. The ash is dispersed towards the N and SE. The first observers of the erupting volcano reported the presence of an active crater of ~200 m radius located on the N side of the dome, and of an inactive crater of ~400 m radius, located on the NE side of the dome.

May 3rd–May 5th: A 10 km high sustained plume drifted from SE to E reaching the Atlantic coast of Argentina.

May 6th: Between 8:20 and 9:15 local time, the eruption became more forceful, producing a wide and dark gray ash plume about 20 km high. The explosion generated a single crater with a radius of ~800 m and was followed by a sequence of explosive events of decreasing intensity.

May 7th–8th: Seismicity at Chaitén increased and a new explosive event was reported but cloudy weather prevented visual observations of the characteristics of the explosion.

After May 8th: The intensity of the explosive activity decreased and only ash and steam plumes <10 km high were produced, associated with small dome collapses and/or lateral blasts with associated PDCs that burned the forest on the north-eastern side of the volcano.

May 12th: Seismic data suggest initial extrusion of a lava dome, although it was first observed on May 21st.

May 13th: Production of a lahar which travelled along Rio Blanco reaching the sea damaging about 40 houses in Chaitén town.

After this period, Chaitén remained active and the associated eruption is characterized by the growth and collapse of the new dome with production of small plumes and related tephra-fall and block-and-ash flows. The dome remained active and producing small magnitude events until 2013.


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