An unusual flat-topped seamount is called a Guyot.
View page
it means either a flat topped submarine mountain or a flat
topped seamount.
View page
A guyot is a flat-topped sea mount
View page
We'd call the underwater geographic feature thus described a tablemount or guyot. It's a seamount, which is an underwater mountain, with a flat or platform top.
View page
A guyot, also known as a tablemount, is a flat-topped seamount. It was named after the Swiss-American geographer and geologist Arnold Henry Guyot. The term was coined around 1946 by Harry Hammond Hess. Guyots are most commonly found in the Pacific Ocean.