Over 1 million volcanoes sit on the ocean floor — roughly 75% of all volcanic activity on Earth happens underwater, and most of it goes completely unnoticed. We track 114 submarine volcanoes with confirmed eruption data. One of them — Axial Seamount off Oregon — is forecast to erupt in mid-to-late 2026. Another — Hunga Tonga — produced the largest atmospheric explosion in recorded history just four years ago.
In Our Database
114
Recorded Eruptions
355
Active Since 2000
27
Deepest Tracked
5,700m
What Are Underwater Volcanoes?
Underwater volcanoes — also called submarine volcanoes — are volcanic vents and structures that form on the ocean floor. They range from tiny fissures on mid-ocean ridges to massive seamounts that rise thousands of meters from the abyssal plain without ever breaking the surface.
Scientists estimate over 1 million submarine volcanoes exist, but we've only mapped a tiny fraction. Most of the deep ocean floor remains less explored than the surface of Mars. The 65,000 km mid-ocean ridge system — where tectonic plates pull apart and new crust forms — is essentially one continuous volcanic feature, and it accounts for roughly 75% of all magma erupted on Earth each year.
Our database tracks 114 submarine volcanoes with confirmed eruption histories from the Smithsonian Global Volcanism Program. That's a tiny slice of the total, but it includes the ones that matter most for hazard monitoring — the shallow, active seamounts that can generate tsunamis, disrupt shipping, and occasionally build new islands.
By VolcanoDB Research Team. Data: Smithsonian Global Volcanism Program, USGS, NOAA, Oregon State University.
How Underwater Eruptions Differ From Land Eruptions
Water pressure fundamentally changes how volcanoes erupt. At the surface, dissolved gases in magma expand explosively as pressure drops — that's what drives the towering eruption columns at stratovolcanoes. Underwater, the weight of the water column above suppresses gas expansion and dampens explosions.
Eruption Style by Depth
Deep (>1,000m): Effusive pillow lava
At depths below ~1,000 meters, water pressure is so high that magma can't explode. Lava oozes out and solidifies into rounded "pillow" shapes as the outer surface cools against cold seawater while the interior remains molten. Most of the ocean floor is made of pillow basalt. These eruptions are invisible from the surface and detected only by hydrophones (underwater microphones) or seafloor instruments.
Shallow (200-1,000m): Explosive but contained
Gas can partially expand, producing moderate explosions that fragment lava into volcanic glass shards. Plumes of discolored water, floating pumice rafts, and dead fish may appear at the surface. Hot water and volcanic gases rise as hydrothermal plumes.
Very Shallow (<200m): Surtseyan eruptions
Named after Iceland's Surtsey (1963-1967). Seawater flashes to steam on contact with magma, producing violent phreatomagmatic explosions — dramatic jets of black ash, steam columns visible for hundreds of kilometers, and occasionally new islands that may persist or erode away. Kavachi, Fukutoku-Oka-no-Ba, and Home Reef all produce this type of eruption.
The critical depth threshold is roughly 200-300 meters. Above this, submarine eruptions start to behave more like land eruptions — violent, visible, and potentially dangerous. Below it, they're mostly quiet affairs of oozing lava that only scientists with ROVs and hydrophones will ever detect.
Active Submarine Volcanoes in 2026
Several underwater volcanoes are making waves (literally and figuratively) right now:
Oregon State researchers predict Axial Seamount will erupt in mid-to-late 2026 based on seafloor inflation rates. The caldera floor has risen 10 cm past its pre-2015 level, with roughly 20 cm more to go before reaching the estimated eruption threshold. Four cabled bottom pressure recorders monitor every millimeter. If the prediction holds, this will be the third successfully forecast eruption at Axial — an extraordinary achievement in volcanology. Located 1,410 meters deep, the eruption poses no tsunami risk.
Ahyi Seamount — Monitoring After 2025 Unrest
Discolored water plumes were observed over Ahyi Seamount through January 9, 2026. No unrest has been observed since, but USGS continues monitoring. At just 50 meters depth, a major eruption here could produce hazardous steam and ash emissions visible from Farallon de Pajaros island, 20 km north.
Kikai Caldera — Submarine Supervolcano Recharging
A March 2026 Kobe University study confirmed that the submarine Kikai Caldera south of Japan is recharging with new magma at 8.2 km³ per millennium. The original Akahoya eruption (~5,300 BCE) was the most destructive of the last 10,000 years. Our caldera guide covers the full story.
7 Notable Underwater Volcanoes
Each links to its full VolcanoDB profile with eruption timeline, coordinates, and monitoring data.
The most intensively monitored underwater volcano on Earth. Located 480 km off Oregon on the Juan de Fuca Ridge, Axial erupted in 1998, 2011, and 2015 — each time successfully forecast by Oregon State researchers using seafloor pressure sensors. The next eruption is predicted for mid-to-late 2026, and the caldera floor has already inflated 10 cm past its pre-2015 level. Four cabled bottom pressure recorders track every millimeter of uplift in real time.
The January 15, 2022 eruption was the largest atmospheric explosion recorded by modern instruments. The blast sent an ash column 58 km into the stratosphere, injected the equivalent of 58,000 Olympic swimming pools of water vapor, and generated a shockwave that circled the globe four times. The pressure wave was detected by weather stations from New Zealand to Switzerland. Maximum tsunami height: 22 meters on Tofua Island. Despite the explosive power, only 4 deaths were recorded, thanks in part to Tonga's early warning systems.
A submarine stratovolcano in the Mariana Arc, Ahyi sits just 50 meters below the surface and has erupted 13 times in our records. Its most recent activity was in 2025 — satellite images showed plumes of discolored water. USGS monitors Ahyi because a shallow eruption could produce tsunamis threatening Guam and the Northern Mariana Islands, 350 km away.
Known as Rejo te Kvachi ('Kavachi's Oven') by locals, this is the most active submarine volcano in the southwestern Pacific. It's erupted 20 times in our records and has repeatedly built temporary islands that erode away within months. In 2022, NASA satellite imagery revealed sharks swimming inside the active crater — earning it the nickname 'Sharkcano.' The summit sits just 20 meters below sea level.
The Caribbean's most active submarine volcano, 180 meters below the surface north of Grenada. It's erupted 15 times since its discovery in 1939 and poses a genuine tsunami risk — an underwater flank collapse or major eruption could send waves toward Grenada, the Grenadines, and nearby islands. A 5 km exclusion zone has been in place since 2001 because shallow eruptions reduce water density enough to sink ships.
This Japanese submarine volcano created a temporary island in August 2021 that was visible from space. The island lasted only a few months before wave erosion destroyed it, but pumice from the eruption drifted across the Pacific for thousands of kilometers, washing up on beaches in Okinawa and disrupting shipping. Located in the Ogasawara (Bonin) Islands, it's erupted 20 times in our records.
One of the most active volcanoes in the Kermadec Arc south of Tonga. Its summit fluctuates in height by tens of meters — ocean-bottom instruments have recorded the seamount growing 18 meters in just 5 days, then collapsing again. This cycle of growth and collapse has been repeating since at least 1998, making Monowai a natural laboratory for studying volcanic deformation in real time.
When Underwater Volcanoes Build New Islands
Submarine volcanoes occasionally build new land. Some islands persist; others wash away within months. It's one of the most dramatic demonstrations of geology in real time.
Surtsey, Iceland (1963-1967): The textbook example. Surtsey erupted from the seafloor south of Iceland, building a 2.7 km² island in four years. It's been a UNESCO World Heritage Site since 2008, designated as a pristine natural laboratory for studying ecological succession — scientists track how life colonizes raw volcanic rock. Only approved researchers can visit.
Nishinoshima, Japan (2013-present): This tiny volcanic island 1,000 km south of Tokyo started growing dramatically in 2013 and hasn't really stopped. Multiple eruption phases through 2020 expanded the island to over 4 km² — 12 times its original size. It's essentially building a new volcanic island in real time, visible via satellite.
Home Reef, Tonga (2006, 2022, 2025): This submarine volcano has created temporary islands at least three times. The 2022 island covered ~8,000 m² — visible in satellite imagery — before ocean waves eroded it away. Home Reef sits in the Tonga volcanic arc, one of the most volcanically active regions in the Pacific Ring of Fire.
Dangers of Underwater Volcanoes
Deep submarine eruptions are harmless to humans. But shallow ones can be genuinely dangerous — and in ways that land volcanoes aren't.
Tsunamis
The biggest threat. Submarine eruptions generate tsunamis through explosion blasts, flank collapses, and caldera collapses. Hunga Tonga's 2022 eruption sent a 22-meter wave onto nearby islands. Anak Krakatau's 2018 flank collapse killed 437 people with a tsunami that arrived with no warning. The Caribbean's Kick 'em Jenny poses an ongoing tsunami threat to Grenada and neighboring islands.
Ship sinking (reduced buoyancy)
Shallow submarine eruptions release vast quantities of volcanic gas into the water, reducing its density. A ship floating above an erupting submarine volcano can lose buoyancy and sink. This is why Kick 'em Jenny has a 5 km exclusion zone for all marine traffic. Pumice rafts from eruptions also clog engine intakes and damage hulls.
Climate effects
The 2022 Hunga Tonga eruption injected an estimated 146 million tonnes of water vapor into the stratosphere — equivalent to 10% of the stratosphere's normal water content. Water vapor is a greenhouse gas, and researchers estimate this injection could temporarily warm global surface temperatures by ~0.035°C for several years. Most submarine eruptions are too deep to affect the atmosphere, but the big shallow ones can.
Where Submarine Volcanoes Form
Submarine volcanoes cluster in three main tectonic settings:
Mid-ocean ridges (most activity): The 65,000 km ridge system where plates diverge produces more lava than all land volcanoes combined. The Mid-Atlantic Ridge, East Pacific Rise, and Juan de Fuca Ridge (where Axial Seamount sits) are the main segments. These eruptions are deep, quiet, and create new ocean floor. For more on this process, see our divergent volcanoes guide.
Subduction zone arcs: Where oceanic plates dive beneath other plates, volcanic arcs form — and many of those arc volcanoes are submarine. The Tonga-Kermadec Arc, Mariana Arc, and Izu-Bonin Arc all have dozens of active submarine volcanoes. These tend to be shallower and more explosive than ridge volcanoes.
Hotspots: The Hawaiian chain includes Loihi Seamount, currently building a new island 975 meters below the surface southeast of the Big Island. At current growth rates, Loihi could break the surface in 10,000-100,000 years. Not exactly urgent, but a reminder that island building is an ongoing process.
Submarine Volcanoes by Region
Where we track the most submarine volcanoes, based on our database of 114:
Region / Country
Count
Key Areas
United States
23
Mariana Arc, Hawaii, Alaska
Undersea Features
16
Mid-ocean ridges
New Zealand
13
Kermadec Arc
Tonga
13
Tonga-Kermadec Arc
Japan
13
Izu-Bonin-Mariana Arc
France
6
Kerguelen, Réunion
Solomon Islands
4
Southwest Pacific
Italy
3
Mediterranean
The US count is high because American territorial waters span the Mariana Arc (including Ahyi), Hawaii, and Alaska's Aleutian Islands. "Undersea Features" refers to volcanoes on mid-ocean ridges that don't fall within any nation's EEZ.
How Scientists Monitor Underwater Volcanoes
You can't put a seismometer on a seamount the way you'd instrument Mount St. Helens. Monitoring submarine volcanoes requires specialized tools:
Hydrophones: Underwater microphones detect the acoustic signatures of eruptions, even from thousands of kilometers away. The NOAA Vents Program uses hydrophone arrays across the Pacific to detect submarine eruptions that no one would otherwise know about.
Seafloor pressure recorders: The gold standard for eruption forecasting. At Axial Seamount, four cabled bottom pressure recorders measure caldera floor uplift in real time, transmitted via the OOI Regional Cabled Array to shore. This is how Oregon State researchers predicted the 2015 eruption — and how they're calling mid-to-late 2026 for the next one.
Satellite detection: Discolored water, pumice rafts, and steam plumes from shallow eruptions are visible in satellite imagery. NASA's MODIS and Sentinel-2 satellites have detected activity at Kavachi, Ahyi, Home Reef, and Fukutoku-Oka-no-Ba within hours of surface expressions appearing.
ROVs and AUVs: Remotely operated and autonomous underwater vehicles can survey eruption sites, sample lava flows, and map bathymetry. They're expensive and weather-dependent, but they've provided some of the most spectacular underwater eruption footage ever captured.
Explore All 114 Submarine Volcanoes on Our Map
Find underwater volcanoes by region, depth, and eruption history
Scientists estimate over 1 million submarine volcanoes exist on the ocean floor, but only a small fraction have been mapped. Our database tracks 114 with confirmed eruption data from the Smithsonian Global Volcanism Program. The vast majority remain undiscovered — we've mapped more of the Moon's surface than the deep ocean floor.
Can underwater volcanoes cause tsunamis?
Yes. Submarine volcanic eruptions can trigger tsunamis through several mechanisms: explosive eruption blasts (like Hunga Tonga-Hunga Ha'apai in 2022, which generated 22-meter waves), underwater flank collapses, and caldera collapses that displace massive volumes of water. Kick 'em Jenny in the Caribbean maintains a 5 km exclusion zone partly because of tsunami risk.
What was the biggest underwater volcanic eruption?
The January 2022 eruption of Hunga Tonga-Hunga Ha'apai in Tonga was the largest atmospheric explosion recorded by modern instruments. The blast column reached 58 km — the highest eruption plume ever documented — and the shockwave circled the globe four times. The submarine Kuwae eruption around 1452 CE in Vanuatu may have been even larger, with some researchers arguing it was comparable to the 1815 Tambora eruption.
What percentage of volcanoes are underwater?
By estimated count, about 75-80% of all volcanic activity on Earth occurs underwater, mostly along the 65,000 km mid-ocean ridge system. In our tracked database of 1,740 volcanoes, 114 (7%) are submarine — a fraction of the true total because most deep-ocean eruptions are never detected.
Can you see an underwater volcano erupt?
Shallow submarine eruptions (less than 200-300 meters deep) often break the surface as Surtseyan eruptions — dramatic jets of steam, ash, and lava fragments. Kavachi in the Solomon Islands and Fukutoku-Oka-no-Ba in Japan regularly produce visible surface eruptions. Deep eruptions (below 1,000m) are invisible from the surface because water pressure suppresses explosive activity — lava simply oozes out as pillow basalt on the seafloor.