Janine Krippner
Submarine eruptions – eruptions that occur below our oceans – are fascinating.
Volcanology has been learning a lot more about them in the past decade or so, but there is still so much we don’t know. This is an exciting area of research.
We do observe eruptions as they approach the surface and begin ejecting wet plumes of volcanic ash and steam, known as Surtseyan eruptions. However, very few eruptions in deeper water have been directly witnessed or recorded.
As of 2025, only 209 submarine eruptions have been directly observed in some way and another 136 have been detected remotely. That is a tiny fraction of what we have seen on land, and we cannot collect the same amount of data to understand them. This also means that when a submarine eruption is observed, it is incredibly valuable.
Janine Krippner
About 71 per cent of our gorgeous planet is covered by oceans, and volcanic landforms are abundant. There are many thousands of volcanic cones scattered across our seafloor. The majority of activity is “effusive”, meaning lava flows erupt from and spread outward from a vent.
“Explosive” activity does occur, but it is different to explosive volcanism on land. In the ocean, eruptions occur under pressure because of the enormous weight of water. On land, the rapid expansion of gas drives explosive eruptions, blowing apart or fragmenting rock into volcanic ash.
Because of the increasing pressure as you add more water above a volcano, when the water is deeper, how the volcano erupts changes.
People out at sea sometimes see signs of volcanic activity that include floating pumice, the smell of sulphur, or muddy-looking water. Seismic networks can detect shaking that is involved in eruptions on the sea floor. Sometimes, scientific research expeditions have been lucky enough to come across recent volcanic activity when cameras or submersibles are sent down below. Sadly, one sign of activity is the death of the incredible creatures that live on the seafloor and thrive around hot volcanic vents.
While most submarine eruptions occur without us having any idea, they can still pose a hazard. Critical submarine infrastructure, including internet cables, cross volcanic regions and can be damaged. We saw this happen with the 2022 Hunga Tonga–Hunga Ha’apai eruption. Much of society relies on internet cables, and most of that travels below oceans.
When growing volcanic cones reach the ocean surface, eruptions can become highly explosive. If this occurs near populations, steam-rich pyroclastic flows can travel across the water and impact communities. If an eruption releases large volumes of gas bubbles into the water column, it can lower the density of the surrounding water. If an unlucky boat travels over that spot, it can sink.
We also rely on global shipping and marine transport, and we do not have a global monitoring and warning network like we do for volcanic ash and aviation. Submarine eruptions are scientifically fascinating, and it is also critical to understand them from a hazards and impacts perspective.
