Chaitén is a volcanic caldera Template:Convert/km in diameter, 17km west of the elongated, ice-capped Michinmahuida volcano, and Template:Convert/km northeast of Chaitén town in the Gulf of Corcovado, in southern Chile. The most recent eruptive phase of the volcano began on May 2 2008, and is ongoing. According to the Global Volcanism Program, radiocarbon dating of the last lava flow from the volcano suggests that its last previous eruption was in 7420 BC plus or minus 75 years.
The caldera rim reaches 1,122m above sea level. Prior to the current eruption, it was mostly filled by a rhyolite obsidian lava dome that reached a height of Template:Convert/m, partly devoid of vegetation. Two small lakes occupied the caldera floor on the west and north sides of the lava dome.
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. One elderly person died while at sea en route for Puerto Montt.  By the afternoon of 2008-05-03, the plume of ash from the eruption had spread across Chile and Argentina to the Atlantic Ocean, contaminating water supplies, and coating the town of Futaleufú (75km South-East) to a depth of 30cm. 
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.
The initial phase of the eruption was characterised by ash emissions and seismic activity. On May 6 the force of eruption increased significantly, producing pyroclastic flows and possibly some lava explosions, and raising the eruption column to a height of perhaps 30,000 metres. The remaining personnel and almost all inhabitants of Chaitén and nearby villages were evacuated, as was Futaleufú.
In the early phase of the eruption (May 2), two separate vents had developed in the old lava dome. An overflight on 6 May found that these had fused into one vent roughly 800m across. SERNAGEOMIN warned of possible major pyroclastic incidents, and the likelihood of prolonged activity.
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. On 21 May, a new lava dome was observed to be forming in the crater, which by 24 May exceeded the height of the old dome. Initially, the dome extended towards the North side of the caldera, but following the emergence of two new vents in the south of the old dome around June 11 and a later one to the west, the expansion moved to the South, eventually blocking the drainage from the caldera floor  .
As of July 3 2008, Chaitén continues to erupt, with seismic activity, an eruptive column of ash up to 3,000m, and a growing lava dome. Whether the dome will be stable remains uncertain, and there is an ongoing risk of collapse and explosive pyroclastic eruption.
Forest near to the volcano has been burned by pyroclastic flows and lateral explosions, and large parts of Southern Argentina and Chile have been coated with ash, with possible longer term consequences for agriculture, although not only negative as ash adds new minerals to the soil. Large amounts of ash have fallen in some areas, posing a risk of lahars for several communities.Template:Fact
Beginning on May 12, lahars caused flooding in the town of Chaitén, depositing ash mud to a depth of up to a metre or more, damaging many buildings, and completely filling the original course of the Chaitén River past the town. Over the subsequent weeks, the river excavated a new course through Chaitén, completely destroying a significant part of it by July 2008. (n.b. at the time of writing, this process is still ongoing; it is unclear how extensive the damage will ultimately be.) Some defensive work has been undertaken by the government, but it is currently unclear whether the town can be reinhabited.Template:Fact
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