Flat-topped seamount. Such undersea mountains are found throughout the abyssal plains of major ocean basins, and most of them are covered by an appreciable depth of water, sediment, and ancient coral. They are believed to have started as volcanic cones formed near mid-oceanic ridges or other hot spots, in relatively shallow water, and to have been truncated by wave action as their tops emerged above the surface. As they are transported away from the ridge or other birthplace, the ocean crust ages, cools, and sinks along with the seamounts on top.
Summary Article: guyot
From The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide