There are three main types of submarine volcanoes, including those at spreading centers, subduction zones, and hotspot volcanoes.
At spreading centers, where two tectonic plates move apart from one another, basalt lava can rise out from beneath the seafloor. The basalt flows at these locations often have a distinctive “pillow” shape, but can also appear smooth depending on the speed and viscosity of the flow.
Submarine volcanoes also occur at subduction zones, where two tectonic plates collide, and one is pushed underneath the other and re-melted. The primary rock here is andesite, which produces a lava with high viscosity and high gas content. This lava is associated with very violent eruptions, though much of their explosiveness is dampened by the depths at which they occur.
The third type of volcano is a hot spot volcano. These occur as a consequence of a magma plume rising through the Earth’s crust overlying an area of melting in the Earth’s mantle. These eruptions often lead to chains of volcanic islands and seamounts that are older with increased distance from the surface location of the rising magma plume.