The study, published in Nature Communications, found that the eruption of Cordón Caulle, Chile, in 2011 caused a large volume of magma – called a laccolith – to rapidly collect perilously close to the earth’s surface, causing dramatic doming of the overlying rocks.

The ability of explosive eruptions to swiftly generate such laccoliths is important for hazard assessments because magma stored at such shallow depths – only hundreds of metres – is prone to trigger further explosions.

Explosive volcanic eruptions, which occur when thick pressurised magma bursts out violently through a vent, are caused by intrusions of magma from the earth’s mantle building up into a high-pressure reservoir kilometres beneath the surface.

Scientists have long thought that magma intrusions such as pancake-shaped laccoliths precede and feed volcanic eruptions.

However, the team, from Lancaster University and the University of Mainz, have used satellite imagery and digital terrain models from before and after the 2011 eruption to show that the laccolith at Cordón Caulle formed during, rather than before the eruption.

The laccolith caused an area of several square kilometres around the volcano to bulge upwards by as much as 200 metres over one month.

This happened when the channel through which erupting magma rose to the surface became blocked, forcing it to instead inject sideways into the neighbouring rocks at a depth of only around 200 metres.