Latterly, its dormant status meant it warranted little attention from scientists.
But Chile is one of the most volcanically active regions in the world. It sits on the edge of the South American tectonic plate at a point where it forces the neighbouring Nazca plate, which holds the Pacific Ocean basin, into the earth’s mantle.
This creates a weak point in the crust, allowing magma to force its way up.
Experts believe that magma has been trickling through the crust into a chamber beneath Chaiten, increasing the pressure as more of the liquid rock and gas filled the void left by the last explosion.
This week’s eruption was caused by magma forcing its way up through the crust beneath the volcano.
Scientists in Chile are now frantically collecting data in an attempt to measure how much magma has built up under the volcano.
"This could be an isolated incident or the start of quite a long period of rumbling," said Prof Clive Oppenhiemer, a volcanologist at Cambridge University.
Chaiten is a caldera volcano, which can explode in a cataclysmic eruption, emptying the magma chamber and causing the dome and surrounding land to collapse into the void beneath.