Question

What evidence do geologists have that volcanoes occur on the ocean floor?

Answer 1

Sonar studies of the sea floor, submersible subs and the fact the some eventually make it to the surface.

Explanation:

Sonar studies are very useful in mapping the topography of the sea floor and submarine volcanoes can usually be detected by this method. Manned or unmanned submersible submarines and provide confirming evidence of under sea volcanoes,

Finally, many volcanoes on the sea floor eventually poke above the sea floor to reveal their presence. This can happen in a dramatic scene where usual amounts of water vapour and volcanic ash gets thrown into the atmosphere.