Underwater Volcanoes

Discover that most volcanic activity on Earth is out of sight underwater.

About Underwater Volcanoes

Much of Earth's volcanic activity occurs beneath the oceans. Mid-ocean ridges continuously create new oceanic crust, while isolated submarine volcanoes can grow into seamounts and sometimes islands.

Visual learning: These pages use real volcanic landscape and eruption photographs from Wikimedia Commons. Final image URLs should be browser-tested before deployment.

Kilauea Lava — Kilauea LavaLava at Kilauea shows molten rock reaching Earth's surface.

Mount St. Helens — Mount St. HelensMount St. Helens is a famous Cascade volcano shaped by explosive eruptions.

Mauna Loa — Mauna LoaMauna Loa is one of the largest active volcanoes on Earth.

Volcanic Crater — Volcanic CraterVolcanic craters form around vents where material reaches the surface.

Mid-Ocean Ridges

Mid-ocean ridges are long underwater mountain chains.

Seamounts

Seamounts are underwater volcanic mountains.

Pillow Lava

Lava erupted underwater can cool into rounded pillow-shaped forms.

Hydrothermal Vents

Seawater circulates through hot ocean crust and returns carrying dissolved minerals.

Island Building

Long-lived submarine volcanoes can build ocean islands.

Observation

Studying underwater eruptions is difficult.

Hazards

Submarine eruptions can create local hazards.

New Crust

Ocean ridges create huge amounts of new volcanic rock.

Mid-Ocean Ridges

Tectonic plates separate there and magma rises to form new crust.

Seamounts

Some grow high enough to become islands, while others remain permanently submerged.

Pillow Lava

Cold seawater chills the outside rapidly while lava continues moving inside.

Hydrothermal Vents

Vent ecosystems can support organisms using chemical energy rather than sunlight.

Island Building

Hawaii is part of a volcanic chain formed as the Pacific Plate moved over a hot spot.

Observation

Research ships, sonar, remotely operated vehicles, seafloor sensors, and satellites help scientists detect changes.

Hazards

Ash, floating pumice, gas, water displacement, and seafloor landslides can affect ships and coasts.

New Crust

This crust slowly moves away from the ridge as plate tectonics continues.