The seamount is about two-thirds of a mile high (1.1 kilometers), researchers said. Seamounts, rocky leftovers from extinct, underwater volcanoes, are found on ocean floors around the world. The newly discovered seamount is about 186 miles (300 km) southeast of Jarvis Island, an uninhabited island in a relatively unexplored part of the South Pacific Ocean, experts said. "These seamounts are very common, but we don't know about them, because most of the places that we go out and map have never been mapped before," James Gardner, a University of New Hampshire research professor who works at the university's NOAA Center for Coastal and Ocean Mapping/Joint Hydrographic Center, said in a statement.