Seismic imaging offers clues to Santorini eruptions

The Greek island of Santorini is famous for its postcard-perfect views: white buildings perched on high cliffs, rising above the brilliantly blue water of the Aegean sea.

But what most captivates UO geophysicist Emilie Hooft about the island lies beneath the surface—a string of underwater volcanoes that created the island and others in the chain via a series of eruptions.

The island of Santorini is part of the caldera rim of a volcano bearing the same name. About 3,600 years ago, during the Bronze Age, the Santorini volcano erupted dramatically. It set off tsunamis and buried towns in ash, possibly affecting global climate and contributing to the demise of the Minoan civilization.

For almost ten years, Hooft has been using state-of-the-art imaging to study the volcanic systems underneath Santorini. Alongside collaborators from around the world, she hopes to use geophysics to understand the dynamics of Santorini's Bronze Age eruption, as well as predict future geological hazards in the area. Hooft's mapping work continues to pay dividends—it has spurred and supported several new papers examining the complex dynamics of the Santorini volcanic system and other nearby volcanoes.

"Santorini is really unique because so many people have studied it," Hooft said. "It's interesting historically, in terms of the impact on archaeology and development of western civilizations. And we have so much data on it, which allows you to get a really rich picture of one volcano."

Hoof began working on Santorini in earnest in 2015, when she and UO earth scientist Doug Toomey led an international team of scientists on an expedition aboard a research vessel. Hooft and her colleagues planted seismic sensors on the ocean floor and on the island of Santorini itself. Then, they used canisters of compressed air to send powerful sound waves through the ocean, like an underground ultrasound. The speed of those sound waves depends on the kind of material—lava, rock, water—they're moving through. All told, the team collected more than 200,000 data points. They used that to reconstruct a detailed 3D map of Santorini's volcanic plumbing.

But even that top-notch mapping missed a few things, one of Hooft's most recent studies suggests. On the 2015 trip, the research team had also mapped Kolumbo, another underwater volcano just a few miles from Santorini. Recently, Hooft and an international team of collaborators revisited the data with an even more powerful new analysis technique—and discovered an active magma chamber inside of Kolumbo that had gone unnoticed on the first pass of mapping.

The technique, called full waveform immersion, analyzes the same seismic data in more detail, giving a clearer picture. That means it can detect smaller objects that other methods might miss—like a relatively small magma chamber, less than 2 kilometers across.

The magma chamber could be a hazard that warrants future monitoring, Hooft and her colleagues suggest in a paper published in the journal Geochemistry, Geophysics, Geosystems.

More information:
K. Chrapkiewicz et al, Magma Chamber Detected Beneath an Arc Volcano With Full‐Waveform Inversion of Active‐Source Seismic Data, Geochemistry, Geophysics, Geosystems (2022). DOI: 10.1029/2022GC010475

Johan T. Gilchrist et al, Submarine terraced deposits linked to periodic collapse of caldera-forming eruption columns, Nature Geoscience (2023). DOI: 10.1038/s41561-023-01160-z

Provided by University of Oregon