Trigger For Explosive Volcanic Eruptions Identified
October 13, 2012

Trigger For Explosive Volcanic Eruptions Identified

Lee Rannals for — Your Universe Online

Scientists have identified a trigger for the largest explosive volcanic eruptions on Earth, according to a report published in the journal Scientific Reports.

University of Southampton researchers investigated crystal cumulate nodules and their trapped magma to see what caused eruptions at the Las Cañadas volcanic caldera on Tenerife, in the Canary Islands.

This volcano has generated at least eight major eruptions during the last 700,000 years, which have resulted in eruption columns of over 15 miles high, and have expelled widespread pyroclastic material over 80 miles.

By analyzing crystal cumulate nodules discovered in pryclastic deposits in major eruptions, they found that pre-eruptive mixing within the magma chamber appears to be the repeating trigger in large-scale eruptions.

Dr Rex Taylor, Senior Lecturer in Ocean and Earth Science at the University of Southampton, found that the nodules provided 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," Taylor said in a press release. "Rims of crystals in the nodules grew from a very different magma, indicating a major mixing event occurred immediately before eruption."

He said stirring young hot magma into colder, cooler magma appears to be a common event before these explosive eruptions.

"The analysis of crystal nodules from the volcano documents the final processes and changes immediately prior to eruption — those triggering the catastrophic eruptions," co-author of the study, Dr Tom Gernon, Lecturer in Ocean and Earth Science at the University of Southampton, said in the press release. "The very presence of mushy nodules in the pyroclastic deposits suggests that the magma chamber empties itself during the eruption, and the chamber then collapses in on itself forming the caldera."

The Las Cañadas volcano is an International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Decade Volcano. It is identified by the scientific community as being worthy of a particular study in light of its history of large, destructive eruptions and proximity to populated areas.

"Our findings will prove invaluable in future hazard and risk assessment on Tenerife and elsewhere," said Dr Gernon, who is based at the National Oceanography Centre at Southampton's waterfront campus. "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."

Image 2 (below): The diagram shows the repeating development of the Las Cañadas magma chamber. Credit: Tom Gernon