First real-time observation of volcanic eruption on a mid-ocean ridge

Researchers aboard the Alvin submersible, operated by the Woods Hole Oceanographic Institution (WHOI), directly witnessed an active volcanic eruption at the Tica hydrothermal vent field on April 29. Located at 9°50’N on the East Pacific Rise, the site lies approximately 2 500 m (8 200 feet) below the Pacific Ocean’s surface and 2 100 km (1 300 miles) west of Costa Rica.

The eruption covered the seafloor with fresh basalt, entombing a hydrothermal ecosystem consisting of giant tubeworms, mussels, crabs, and fish. “Tica was barren,” said Andrew Wozniak, chief scientist and University of Delaware professor. “Almost completely gone.”

The team noticed unusual conditions during their descent, including increased particulate matter and slightly elevated water temperatures. As Alvin’s lights illuminated the seafloor, they revealed fresh lava flows, dead tubeworm clusters, and brief flashes of molten lava hardening in near-freezing seawater. “My brain was trying to understand what was going on,” Wozniak said, “Where did things go?”

Alvin pilot Kaitlyn Beardshear terminated the dive as temperatures neared the submersible’s limits. “When we saw an orange shimmering glow in some of the cracks, it confirmed that a volcanic eruption had taken place and was still actually underway,” Beardshear said. “I decided it was a good idea to leave before we reached the limit.” The submersible, capable of diving to 6 500 m (21 000 feet), returned to the surface for a standard recovery.

The eruption was anticipated based on over seven years of studies funded by the U.S. National Science Foundation (NSF), which monitored chemical changes in hydrothermal fluids and steadily rising vent temperatures recorded every 10 minutes.

“Monday everything was normal, Tuesday it was paved over,” said WHOI marine geologist Dan Fornari, “this will give us a better sense for what the precursors are to an eruption.”

The team had observed a vibrant ecosystem at Tica on April 28, with tubeworms’ crimson tips swaying, mussels clustering, and ghostly fish prowling around vents expelling 400°C (750°F), chemical-rich fluids.

The next day’s eruption left only a single cluster of dead tubeworms amid a jet-black expanse. “It was an incredible sight to see,” Beardshear said. “All the life and features that I had seen just a few days before, wiped away.”

Hydrophones on the research vessel Atlantis, owned by the U.S. Navy and operated by WHOI, detected low-frequency booms and crackling sounds, pinpointing the eruption’s start early on April 29.

The expedition, which began April 11, aimed to study dissolved organic carbon flow from vents, involving scientists from the University of Delaware, Rensselaer Polytechnic Institute, and Middle East Technical University. “It was magical,” Wentzel said of the 70-minute descent, noting bioluminescent jellies before the eruption’s stark scene.

Due to unsafe conditions, further Alvin dives were canceled, but the team lowered instruments from Atlantis to collect data near the vent site. “We were able to very carefully maneuver our sensors and sampling bottles to within meters of the space that had been occupied by the Tica vent structure,” said Sunita Shah Walter, Assistant Professor at the University of Delaware. These measurements will help analyze post-eruption chemical and thermal changes.

The Tica vent, discovered in 1991 during a prior eruption witnessed by Alvin, has experienced three known eruptions, roughly 15–20 years apart, with events in 1991 and 2005–2006. High-resolution seafloor maps created over seven years by the autonomous underwater vehicle Sentry, also operated by WHOI, will enable geologists to determine the eruption’s extent, lava volume, and affected areas. “This has been the closest that we ever come to witnessing the initiation of an eruption,” Fornari said.

The mid-ocean ridge, a 64 000 km (40 000 miles) volcanic mountain chain, generates 80% of Earth’s volcanism by forming new seafloor as tectonic plates diverge.

This eruption, the first active mid-ocean ridge event directly observed, offers a rare chance to study seafloor creation and its impacts. “All of this has to do with understanding this holistic system that is Earth and ocean,” Fornari said. “It’s so intertwined, and it’s both complex and beautiful.”

Hydrothermal vents act as Earth’s plumbing, expelling heated seawater laden with chemicals that sustain unique ecosystems. The team noted bacterial mats, which convert vent chemicals into organic matter, as the first step in ecosystem recovery post-eruption.

“With any volcanically active region, you have a cycle of death and rebirth,” said Sasha Wagner, Assistant Professor at Rensselaer Polytechnic Institute, who visited Tica before the eruption.

“Being there in real time is just this absolutely phenomenal gift,” said Deborah Kelley, a marine geologist at the University of Washington.