The dramatic collapse of Indonesia’s Anak Krakatau volcano in December 2018 resulted from long-term destabilization processes and was not triggered by any distinct changes in the magma system that could have been detected by current monitoring techniques, according to news reports. research.
The volcano had been erupting for about six months before the collapse, which saw more than two-thirds of its height slip into the sea as the island’s land area shrank by half. The event triggered a devastating tsunami, which flooded the coasts of Java and Sumatra and killed more than 400 people.
A team led by the University of Birmingham examined volcanic materials from nearby islands for clues as to whether the powerful explosive eruption seen after the collapse had itself triggered the landslide and tsunami. Their results are published in Earth and Planetary Science Letters.
Together with researchers from the Bandung Institute of Technology, the University of Oxford and the British Geological Survey, the team examined the physical, chemical and microtextural characteristics of the erupting material. They concluded that the large explosive eruption associated with the collapse was likely caused by the destabilization of the underlying magma system at the start of the landslide.
This means the disaster was less likely to have been caused by magma forcing its way to the surface and triggering the landslide. Current volcano monitoring methods record seismic activity and other signals caused by magma rising through the volcano, but since this event was not triggered from within, it would not have been detected at using these techniques.
Dr Sebastian Watt, from the School of Geography, Earth and Environmental Sciences at the University of Birmingham, is the lead author of the paper. He said: “This type of volcanic hazard is rare, extremely difficult to predict and often devastating. Our findings show that although there was a dramatic and explosive eruption after the collapse of Anak Krakatau, it was triggered by the landslide releasing the pressure on the magma system, like a plug. popping champagne.
The findings present a challenge for predicting future hazards on volcanic islands. Dr Mirzam Abdurrachman from the Bandung Institute of Technology explains: “If large volcanic landslides occur as a result of long-term instability and can take place without any distinctive change in the magmatic activity of the volcano, this means that they can occur suddenly and without any clear warning.
“This finding is significant for people who live in regions surrounded by active volcanoes and volcanic islands in places like Indonesia, the Philippines and Japan.”
Lead author Kyra Cutler from the University of Oxford said: “Assessing the long-term growth and deformation patterns of volcanoes will help provide a better understanding of the probability of failure – this will be particularly relevant for Anak Krakatau during its reconstruction Identification of sensitive areas, together with efforts to develop non-seismic tsunami detection, will improve overall risk management strategies for at-risk communities.
Professor David Tappin (British Geological Survey, University College, London) led the marine studies that mapped the deposits resulting from the collapse of the 2018 Anak Krakatau eruption (Hunt et al. 2021). He said: “Rarely do we have the opportunity to study such an eruption and tsunami, with the last event, Ritter’s Island, over 100 years ago. The paper’s findings reveal that the driving mechanism stemmed from a long-term destabilization, rather than an instantaneous explosive event. This is a major surprise discovery that will lead to a reassessment of how to mitigate the danger of volcanic failures and associated tsunamis.
Earth and Planetary Science Letters
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Downward propagating eruption after vent discharge implicates no direct magmatic trigger for 2018 Anak Krakatau lateral collapse
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