Tonga eruption entombed deep-sea life in ash

In April 2022, a team of scientists was on a research vessel in the Lau Basin near Tonga to study the Animals that live around hydrothermal vents in the deep sea. But when they lowered a remotely operated vehicle (ROV) down to a vent to search for the critters, they found the seafloor, normally a hard basalt surface, blanketed in sediment. They could see few snails and mussels.

"It was like a snow-covered landscape," said Roxanne Beinart, a marine microbial ecologist at the University of Rhode Island who was on the expedition.

Beinart and her colleagues suspected that they were looking at a coating of ash from the January 2022 eruption of the Hunga volcano, one of the most powerful eruptions ever recorded. The ashfall had completely transformed the ecosystem, killing off vulnerable mollusks.

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The group recognized they now had a rare opportunity to document the effects of a volcanic eruption on marine ecosystems. They've published their initial findings in Communications Earth and Environment and intend to track the recovery of these ecosystems through time.

"This is a real opportunity to understand and to study the impacts of a large eruption—where we understand what happened, where we know the processes, we know the timescales involved — and to understand the impacts on the seafloor," said Isobel Yeo, a volcanologist at the United Kingdom's National Oceanography Centre who wasn't involved in the study.

An avalanche of ash

Over 24 days, the scientists surveyed six hydrothermal vent fields using the ROV and scooped up samples of sediment. Under the microscopes aboard the ship, "you could pretty quickly and easily see that it was just full of glass," said Shawn Arellano, a marine ecologist at Western Washington University who coauthored the study. Fine grains of glass are a telltale characteristic of volcanic ash.