Originally, radiocarbon dating of older tephra from the volcano suggested that its last previous eruption was in 7420 BC ± 75 years.

Before the current eruption, it was mostly filled by a rhyolite obsidian lava dome that reached a height of 962 metres (3,156 ft), partly devoid of vegetation.

[1] The translucent grey obsidian which had erupted from the volcano was used by pre-Columbian cultures as a raw material for artifacts and has been found as far away as 400 kilometres (250 mi) to the south and north, for example in Chan-Chan.

[1] The Chilean government began an evacuation of the nearby town of Chaitén (population 4,200) and the surrounding area the same day, the main phase of which was completed by May 3, 2008.

[5][6] By the afternoon of May 3, the plume of ash from the eruption had spread across Chile and Argentina to the Atlantic Ocean, contaminating water supplies, and reportedly coating the town of Futaleufú located 75 kilometres (47 mi) southeast to a depth of 30 centimetres (12 in).

[8] A team of scientists from the US was dispatched to the area to assess the air quality and the risks from chemicals in the falling ash.

[16][17] Through the remainder of May and June 2008 the eruption continued as a variable but gradually decreasing emission of ash, with intermittent seismic activity and pyroclastic flows.

[22] Whether the dome will be stable remains uncertain, and there is an ongoing risk of collapse and explosive pyroclastic eruption.

Over the subsequent weeks, the river excavated a new course through Chaitén, completely destroying a significant part of it by July 2008.