Volcanoes awaken more quickly than thought

Mount Rinjani in Indonesia erupts in 1995. Image courtesy Oliver Spalt/Wikimedia.

Instead of taking thousands of years to reawaken, dormant volcanoes require only a few months, according to French volcanologists who have recently updated and tested a more accurate mathematical model for volcanic magma chambers.

'Frozen' magma beneath volcanoes can be quickly re-awakened by the addition of hot molten rock from below, according to Alain Burgisser, from the Orléans Institute of Earth Sciences, France.

“Our model is a significant leap in precision: it predicts reawakening time scales 1,000 times more rapidly than previous models. Our work highlights that what controls the activity cycle of volcanoes is mainly how viscous the magma is in the reservoir,” said Burgisser.

Melting magma inside a volcano

Burgisser included the laws governing mechanical energy caused by melting inside a volcano, known as convection (heat and mass transfer), to make the current model more accurate. To provide quantitative predictions, the laws were solved by a non-linear Newton–Raphson root-finding algorithm.

These algorithms can run on a desktop computer and are designed to find the correct value that makes an equation equal to zero – or the root of the equation. This means that the numerical technique finds the best estimated solution to the complex equations governing the model, while leaving a reasonable margin of error.

Burgisser and his team tested their model on data from the eruption of Mount Pinatubo in the Philippines in March 1991, a devastating eruption that resulted in almost 1,000 deaths. Conventional theories had vastly underestimated the volcano’s reawakening time, estimating it would take hundreds of years when in reality it took two months.

"Awakening a volcano is easier than expected"

The researchers looked at seismic shocks preceding the eruption, which were caused by fresh magma building up inside the volcano.

The new model corroborated actual events predicting between a 20 and 80 day time interval between the initial seismic signals and eruption. This means that, “awakening a dormant volcano is easier than expected,” said Burgisser.

“This model offers a nice explanation for a question that volcanologists have been struggling to explain for some time: how are very large volumes of crystal-rich magma - which appear to need many thousands of years to form - nevertheless prepared for eruption on very short timescales,” said David Pyle, a volcanologist from Oxford University who was not involved in the research.

“In time, this will improve our general ability to forecast eruptions,” he said.