'Trigger' found for explosive eruptions

Posted by Kate Taylor

Scientists say they've identified the trigger for the largest explosive volcanic eruptions on Earth.

The University of Southampton researchers focused on the Las Cañadas volcanic caldera on Tenerife, in the Canary Islands, which has generated at least eight major eruptions during the last 700,000 years.
They resulted in eruption columns over 25km high, with pyroclastic material spreading more than 130km away.

Even the smallest of these eruptions expelled over 25 times more material than the 2010 eruption of Eyjafjallajökull in Iceland.

And, says the team, an examination of crystal cumulate nodules - igneous rocks formed by the accumulation of crystals in magma - has revealed the trigger. Pre-eruptive mixing within the magma chamber, with older cooler magma mixing with younger hotter magma, appears to be what's setting these large-scale eruptions off.

These nodules trapped and preserved the final magma beneath the volcano immediately before eruption. Dr Rex Taylor, Senior Lecturer in Ocean and Earth Science at the University of Southampton, investigated nodules and their trapped magma to see what caused the eruptions. He found that the nodules provide a record of the changes occurring in the magma plumbing right through to the moment the volcano erupted.

"These nodules are special because they were ripped from the magma chamber before becoming completely solid - they were mushy, like balls of coarse wet sand," says senior lecturer Rex Taylor.

"Rims of crystals in the nodules grew from a very different magma, indicating a major mixing event occurred immediately before eruption. Stirring young hot magma into older, cooler magma appears to be a common event before these explosive eruptions."

The hope is that the new information will improve predictions of large-scale eruptions.

"The scale of the eruptions we describe has the potential to cause devastation on the heavily populated island of Tenerife and major economic repercussions for the wider European community," says lecturer Dr Tom Gernon.