Volcanoes which have submerged beneath the surface of the sea are termed seamounts.

Here's a breakdown:

* Seamount: An isolated underwater mountain rising from the ocean floor that does not reach the water's surface. They are often formed by extinct volcanoes.

* Guyot: A flat-topped seamount. The flat top is often the result of erosion by waves when the volcano was closer to the surface.

It's important to note that not all underwater mountains are volcanoes. Some are formed by other geological processes, like tectonic uplift.