(CN) — Indonesia’s 2018 Anak Krakatau volcanic eruption is not what caused large portions of the southwestern side of the island to collapse, according to new research.
The collapse was instead caused by a long-term destabilizing process and not any distinct changes in the magmatic system that might have been detected by current monitoring techniques, according to a study published Friday evening in the journal Earth and Planetary Science Letters.
“This type of volcanic hazard is rare, extremely hard to predict and often devastating,” Sebastian Watt, a professor in the University of Birmingham’s School of Geography, Earth and Environmental Sciences, and senior author on the paper, said in a statement.
“Our findings show that, although there was a dramatic, explosive eruption after the collapse of Anuk Krakatau, this was triggered by the landslide releasing pressure on the magma system – like a champagne cork popping,” Watt explained.
One important next step following the report, researchers say, is the development of non-seismic tsunami detection to predict rare instances of tsunamis that are the result of external rather than internal forces, such as the 2018 Indonesian tsunami.
Anak Krakatau, located in a caldera in the Sunda Strait between the islands of Java and Sumatra in the Indonesian province of Lampung, emerged from the caldera, which formed in 1883 by a volcanic eruption that destroyed the island of Krakatoa.
Sporadic eruptive activity has happened at the site since the late 20th century and culminated with a large underwater collapse of the volcano and the ensuing deadly tsunami in December 2018.
The volcano had been erupting for around six months before the collapse, during which two-thirds of its height slid into the sea and Anak Krakatau lost half its size.
The collapse unleashed a massive tsunami with waves measuring five meters (or 16.4 feet). Four hundred and thirty-seven people were killed, and more than 14,000 were injured. The tsunami is considered Indonesia's deadliest volcanic tsunami this century. The 2004 Indonesian tsunami, which killed over 227,000 people, was caused by an earthquake.
The large explosive eruption associated with the collapse was probably caused by destabilization to the underlying magmatic system as the landslide got underway, rather than by magma forcing its way to the surface and triggering the landslide, researchers concluded.
Professor David Tappin from the British Geological Survey at University College in London led the marine surveys that mapped the deposits left by the eruption and collapse, and called the discovery that the collapse was the result of destabilization “a major surprise discovery.”
Tappin said the discovery will “lead to re-evaluation of how to mitigate the hazard from volcanic failures and their associated tsunamis.”
The team was headed by researchers from the University of Birmingham and also included researchers from the Bandung Institute of Technology and the University of Oxford and the British Geological Survey. Together, they looked at the physical, chemical and microtextural characteristics of the erupted material and concluded that current monitoring techniques could not have been useful in detecting the massive landslide and tsunami.
Current monitoring methods record seismic activity and other signals caused by magma as it rises through a volcano but would not have been able to detect the activity of that event since the collapse wasn’t triggered from within, researchers said.
This conclusion presents a challenge for future predictions of hazards at volcanic islands.
“If large volcanic landslides occur as a result of long-term instability and can take place without any distinctive change in the magmatic activity at the volcano, this means they can happen suddenly and without any clear warning,” said Mirzam Abdurrachman, a researcher from the Bandung Institute of Technology.
“This finding is important for people who live in regions surrounded by active volcanoes and volcanic islands in places such as Indonesia, Philippines and Japan,” Abdurrachman said in a statement.
The findings of this research will help inform at-risk communities located near volcanos, lead author Kyra Cutler from the University of Oxford said in a statement.
“Evaluating longer-term growth and deformation patterns of volcanoes will help to provide a better understanding of the likelihood of failure,” Cutler said. “This will be particularly relevant for Anuk Krakatau as it rebuilds. Identifying susceptible areas, along with efforts to develop non-seismic tsunami detection, will improve overall hazard management strategies for communities who are at risk.”
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