When a volcano surfaces just above sea level, erosion from waves can create a plateau called a guyot, that eventually sinks below sea level. Guyots sinks as a result of both erosion and the tectonic plates that the ocean floor rests on slowly moving apart.
Since guyots are created from volcanoes, it should not be surprising that most guyots are found in the Pacific ocean. The top plateau of most guyots span at least 200 meters across. Guyots can be identified from the fossils of sea life that lived in nearby waters when the volcano was above sea level. Certain shallow-water sea life would not be found so far from the shore unless other shallow water was at one time present.