Submarine volcanoes are enigmatic and mysterious because they are cloaked by the overlying ocean, yet their activity represents 75% of earth’s volcanism.
Submarine volcanoes influence ocean chemistry, sustain specially-adapted biological communities, and when they grow to shallow depths they can be extremely hazardous. Often, we only know if submarine volcanoes are erupting when we detect big commotions at a distance but recent work shows that they can also erupt quietly and undetected.
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Left (A) Bathymetry collected in July 2026 by the Exploration Vehicle Nautilus, showing the crater formed during the September 2023 eruption with a new lava dome growing in the bottom. Right (B) Depth differences between the survey in March 2026 by the Research Vessel Thomas G. Thompson and the one in July 2026 by Exploration Vehicle Nautilus. Red area shows elevation change due to dome growth within the crater, which is outlined in black.
This was the case for a recent eruption of Ruby seamount in the Commonwealth of the Northern Mariana Islands, located about 50 kilometers (31 miles) north-northwest of the island of Saipan in the west Pacific Ocean. On September 14–15, 2023, the US Geological Survey’s Alaska Volcano Observatory (AVO) detected large underwater explosion signals from Ruby on seismometers throughout the Pacific and on hydrophones over 2,200 km (1,370 miles) away at Wake Island. AVO scientists also observed a large plume of discolored water at the ocean surface near Ruby in satellite imagery for 2 days. Then everything went quiet. What had happened on the seafloor?
We didn’t know until the Research Vessel Thomas G. Thompson was able to remap Ruby with its multibeam sonar system in March 2026. That bathymetric survey, by colleagues at University of Washington, showed dramatic depth changes, including new eruptive deposits, scars from landslides on the volcano’s flanks, and a large new summit crater 700 by 350 meters wide (2,300 by 1,150 ft).
Where the summit of the volcano had previously been at a depth of 175 meters (575 ft) before the two-day long explosive eruption, the floor of the new crater was now 275 meters (900 ft) deeper. That was presumably the end of the story, since the September 2023 eruption had apparently been short-lived and there was no evidence of any activity since then. However, we often don’t really know what submarine volcanoes are up to, due to our limited monitoring capabilities in the oceans.
A recent collaborative expedition on the Ocean Exploration Trust’s Exploration Vehicle (E/V) Nautilus in July 2026 provided the first post-eruption opportunity to make direct observations to investigate what happened at Ruby. Using the remotely operated vehicle (ROV) Little Hercules, scientists aboard the E/V Nautilus explored the new summit crater, and the ship remapped the volcano once again for good measure, not expecting to see any changes. But that’s the value of exploration—often you find things you didn’t expect.
The new bathymetry collected in July showed that the floor of the summit crater was now about 110 meters (360 ft) taller than it had been in March! Our first thoughts were that this change could either have been caused by collapse of material from the crater rim accumulating into the bottom of the crater, or by the eruption of new lava onto the crater floor. At the bottom of the crater the ROV encountered fresh lavas, which immediately confirmed the second hypothesis.
Comparing the March and July bathymetric surveys showed that the only changes were indeed at the bottom of the crater where a new lava dome had formed. The ROV video showed that the new dome lavas had distinct striations on some of the fracture surfaces, which is likely evidence of incremental crack growth during slow lava extrusion, similar to what has been observed on lava domes growing at volcanoes on land, like Mount St. Helens.
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Video frame grab from remotely operated vehicle (ROV) Little Hercules dive in July 2026 at Ruby seamount showing striations on freshly erupted lava at the bottom of the new summit crater.
We learned a lot more about what had happened during the September 2023 eruption at Ruby seamount by simply remapping it in March 2026, and we learned even more by remapping it again in July 2026 and making a single ROV dive. This shows that revisiting and remapping submarine volcanoes, even with no evidence they are active, can reveal a lot about their secret lives.
Ruby had been quietly erupting between March and July 2026, but no one knew it. Was it still slowly erupting in July? Maybe. Will it continue to rebuild the summit cone that was destroyed during the September 2023 eruption? The only way to find out is to keep coming back and looking. Bathymetric and ROV surveys are one of the ways we can learn more about submarine volcanoes: how they grow, what their range of activity is, how often they are active, and what hazards they pose as their activity evolves.
*Interagency co-authors:
Bill Chadwick: Cooperative Institute for Marine Ecosystems and Resource Studies (CIMERS), Oregon State University, Newport, OR, USA
Jeffrey Beeson: Cooperative Institute for Marine Ecosystems and Resource Studies (CIMERS), Oregon State University, Newport, OR, USA and College of Earth Ocean and Atmospheric Sciences (CEOAS), Oregon State University, Corvallis, OR, USA
Jeremy Powell: College of Earth Ocean and Atmospheric Sciences (CEOAS), Oregon State University, Corvallis, OR, USA
Ashton Flinders: U.S. Geological Survey, Hawaiian Volcano Observatory, Hilo, HI, USA
Larry Mayer: University of New Hampshire, Center for Coastal and Ocean Mapping, Durham, NH, USA
Samantha Wishnak: Ocean Exploration Trust, University of Rhode Island, Kingston, RI, USA
Today's article is by Oregon State University scientist Bill Chadwick and a team of scientists from other agencies*.
