Powerful volcanic blast not the cause for 2018 Indonesian island collapse

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The collapse of Indonesia's Anak Krakatau volcano in December of last year was not caused by any changes in the magmatic system that could have been detected by current monitoring techniques, according to new research.

The volcano had been active for six months prior to the collapse, which saw more than two-thirds of its height slide into the sea. More than 400 people were killed when a devastating wave hit the coastlines of Java and Sumatra.

A team led by the University of Birmingham looked at volcanic material from nearby islands to see if the powerful eruption seen after the collapse had triggered the landslide and tsunami. Their results are published.

The team looked at the physical, chemical and microtextural characteristics of the erupted material, working with researchers at the Bandung Institute of Technology, the University of Oxford and the British Geological Survey. The collapse was probably caused by the underlying magmatic system becoming destabilised as the slide started.

It is less likely that the disaster was caused by magma forcing its way to the surface. Since this event was not triggered from within, current volcano monitoring methods would not have been able to detect it.

Dr. Sebastian Watt is a senior author on the paper. This type of volcanic hazard is hard to predict and devastating. The eruption was triggered by the release of pressure on the magma system, which was caused by the collapse of Anak Krakatau.

Predicting future hazard at volcanic islands is a challenge. The Bandung Institute of Technology's Dr. Mirzam Abdurrachman says that if large volcanic eruptions occur as a result of long-term instability, they can happen suddenly and without any change in the magmatic activity at the volcano.

This finding is important for people who live in areas with active volcanoes and volcanic islands.

The University of Oxford's lead author said that it will be relevant for Anak Krakatau as it rebuilds. Efforts to develop non-seismic tsunami detection will improve overall hazard management strategies for communities who are at risk.

The surveys that mapped the deposits resulted from the Anak Krakatau eruption collapse. He said that it was rare for us to study an eruption and a wave over 100 years ago. The paper shows that the driving mechanism was from long term destabilisation rather than an explosion. This discovery will lead to a re-evaluation of how to mitigate the hazard from volcanic failures.

ENDS

The Downward-propagating eruption following vent unloading implies no direct magmatic triggering for the collapse of Anak Krakatau. The article is titled "Unanswered questions about the evolution of theepsl."

The Earth and Planetary Science Letters is a journal.

The cause of the Indonesian island collapse was not a powerful volcanic blast.

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