Most seamounts are remnants of extinct volcanoes. Typically, they are cone shaped, but often have other prominent features such as craters and linear ridges and some, called guyots, have large, flat summits. There is a broad size distribution for seamounts but to be classified as a seamount, the feature must have a vertical relief of at least 1,000 meters (3,300 feet) above the surrounding seafloor.
Seamounts are found in every world ocean basin and while it is not known precisely how many seamounts there are, they are very numerous. Based on data from satellite altimetry and bathymetric mapping data obtained from survey ships, the number of seamounts that are at least 1,000 meters high is thought to be greater than 100,000. Despite their abundance, however, less than one-tenth of a percent of the seamounts in the world have been explored.