An experiment to work out why magma travels along vertical and horizontal fractures reveals a previously unrecognised potential trigger for eruptions

This article is more than 5 years old

This article is more than 5 years old

Scientists have discovered a previously unrecognised potential trigger for volcanic eruptions during an experiment involving jelly, lasers and coloured water.



Sandy Cruden, a geologist at Monash University in Melbourne, said the scientists came to the finding by accident during a study of how magma moves through layers of rock in the earth’s crust.

Cruden said working out why magma ascends along vertical fractures, called dykes, before turning along horizontal ones called sills, is a “classic problem in geology”.

Researchers from Monash have teamed up with colleagues from Newcastle and Liverpool universities in the UK to study the plumbing systems of volcanoes with a scaled-down model version in a laboratory.

They filled a tank with two layers of pig skin gelatine of differing strengths as an analogue of the earth’s crust and injected it with coloured water to mimic ascending magma. When the simulated dyke hit the upper layer of gelatine it turned into a sill, travelling between the two gelatine layers.

The gelatine was also injected with tiny fluorescent particles. When hit by a moving laser the particles lit up and could be captured using a high-speed camera.

In the experiment, which took place at Monash, the scientists observed a collapse of the dyke, which would indicate a significant drop in pressure.

Cruden said scientists knew volcanic eruptions were triggered when the side of a volcano collapses, reducing the pressure in a magma chamber. But this was the first time that process has been connected to the collapse of a dyke during the formation of a sill.

Magma was full of dissolved gases, “like champagne or coke”, Cruden said. He likened the process to removing a cap from a shaken bottle of a fizzy drink, with the drop in pressure causing bubbles to form and erupt in a fountain of foam.

While the use of water, rather than gas-filled magma, meant their experiment did not lead to a volcano-like explosion, Cruden and the other scientists calculated its magnitude of pressure and found equated conditions in a natural setting would be enough to produce an eruption.

A still from a video of the experiment showing the pressure drop in the dyke as the sill is formed. Photograph: Monash University

Cruden said the discovery had big implications for predicting when volcanoes would erupt. The 2010 eruptions of Eyjafjallajökull in Iceland was preceded by the formation of dykes and sills, for example.

Volcanoes were inherently dangerous places to work and with much of their activity taking place thousands of metres underground there was little understanding of how they operated, Cruden said. Such challenges put added importance on using models to observe the physics of magma migration.

The work was important to improve the accuracy of volcanic eruption predictions, which Cruden said was “not particularly great” in the scientific community, though still better than their ability to predict earthquakes.

“It’s a bit like reading tea leaves. You’ve got all these signals coming out of the ground. But what we really need is a better understanding of the physical processes that make those signals.”

Cruden said their experiment contributed to a better understanding of the physics behind an eruption and puts volcanologists “in a better position to read those signals, so that we can predict when an eruption is going to occur”.