Guyot

A guyot, also called a tablemount, is an isolated underwater volcanic mountain, a type of seamount, with a flat top lying more than 200 meters below the sea surface. Guyots begin as volcanoes that once rose above sea level, and as the ocean crust beneath them cools and subsides over millions of years they sink deeper into the ocean, while wave erosion or coral growth near the surface flattens their summits, a flat top that persists even as the guyot continues to sink.