First Documentation of a Volcanic Deep-Ocean Eruption

The ocean floor is much closer to us than outer space, yet reaching and exploring it is no less challenging. Only in the twentieth century did humans begin mapping it, made possible by the invention of sonar. This device, which works on principles similar to radar, emits sound waves and measures the time it takes for them to bounce back from the seabed. From this data, scientists were able to calculate ocean depths and create underwater topographic charts known as bathymetric maps.

One of the most remarkable discoveries from these maps was the existence of vast mountain ranges hidden in the depths of the oceans, later named mid-ocean ridges. Today, we know that these ridges mark the active boundaries where two tectonic plates drift apart. As gaps open, hot magma rises from Earth’s interior, solidifies, and builds new underwater mountains. Over time, this continuous process slowly expands the ocean floor. Older oceans such as the Pacific Ocean are already vast and well developed.  In contrast, the Red Sea is a much younger basin, only recently beginning to open in geological terms, as the Arabian Plate slowly separates from the African Plate.

Although these processes usually unfold over millions of years, on rare occasions scientists are able to witness them in action. Now, for the first time, researchers have documented a volcanic eruption at the heart of the Pacific Ocean’s mid-ocean ridge—an extraordinary glimpse of the forces that shape the ocean floor.

Research Under Extreme Conditions

Following the discovery of mid-ocean ridges, researchers began tracking these vast geological structures to understand how they form, what they are composed of, and the biological systems that thrive around them. However, the extreme conditions of the deep ocean make it incredibly difficult to observe such environments directly. Immense pressure, frigid temperatures, and complete darkness pose formidable challenges to anyone attempting to document underwater volcanic activity.

In recent years, the development of advanced manned submersibles has transformed this research. Unlike most manned submersible, which can only descend a few hundred meters, these specialized vessels are capable of diving to depths of up to six kilometers and remaining there for extended periods.  This advancement enabled scientists to capture real-time footage of an underwater volcanic eruption at the Tika site on the East Pacific Rise—a ridge stretching from the Gulf of California to New Zealand. Using the manned submersible Alvin, the team documented the eruption at a depth of two and a half kilometers, about two thousand kilometers west of Costa Rica. In addition to visual documentation, they successfully gathered live, real-time measurements from the heart of the volcanic event.

Anticipated Eruption

The underwater eruption occurred within the very time window that researchers had anticipated. For years, measurements collected in the Tika region had revealed gradual shifts in chemical composition and temperature—clear signs of intensifying volcanic activity beneath the seafloor.  The accumulation of these unusual readings convinced scientists that an eruption was imminent.

The site had been monitored for years, during which researchers documented thriving colonies of giant tube worms, clams, crabs, and fish clustered around hydrothermal vents, where temperatures can reach up to 400°C. Yet despite the extreme heat, the immense pressure at these depths keeps the water in liquid form, preventing it from evaporating.

The submersible team documented the thriving colonies during their first descent. On the following day, early in the dive, they observed unusual particles in the water and higher-than-normal temperatures. As the vessel approached the seafloor and its lights swept over the site they had studied just a day earlier, the scene was transformed—deserted and lifeless. All that remained were tube worm colonies—dead and encased in hardened magma.

Footage from the submersible showing the seafloor before and after the eruption:

From time to time, the emptiness of the seafloor was broken by bursts of molten magma, which solidified almost instantly upon contact with seawater. “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,” said Kaitlyn Beardshear,  electrical engineer and pilot of the Alvin submersible, of the Woods Hole Oceanographic Institution (WHOI), in an interview with the university’s news site. The researchers maneuvered closer to the active vent, documenting the interaction of magma and water, collecting samples with robotic arms, and monitoring changes in both temperature and the chemical composition of the water surrounding the eruption.

The scientists noted that the eruption offered a rare opportunity to study how volcanic activity shapes the underwater environment and the ecosystems that develop around it. But after spending some time in the extreme conditions, the team was forced to cut the dive short and return to the surface earlier than planned, due to concerns about the submersible overheating.

In addition to the important documentation and measurements made by the researchers, the observation provided scientists with rare and valuable confirmation of their ability to predict volcanic eruptions on the ocean floor. This is a real breakthrough in understanding deep geological processes.

In addition to the critical documentation and measurements collected, the observation also provided powerful validation of scientists’ ability to predict volcanic eruptions on the ocean floor. This marks an important breakthrough in the effort to better understand deep-sea geological processes.