guyot

A guyot, also known as a tablemount, is a flat-topped seamount. Guyots show evidence of having been above the surface with gradual subsidence through stages from fringed reefed mountain, coral atoll, and finally a flat topped submerged mountain. Guyots are very commonly found in the Pacific Ocean, and are considered to be extinct volcanoes. The Emperor Seamounts are an excellent example of an entire volcanic chain undergoing this process and contain many guyots among their other examples.
See more at Wikipedia.org...

Noun
1. a seamount of volcanic origin (especially in the Pacific Ocean)
(hypernym) seamount

A seamount, the top of which has been flattened by weathering, wave action, or stream erosion.

GUYOT