Tamu Massif is an extinct submarine shield volcano in the northwest Pacific Ocean, with the characteristics of a hybrid between a mid-ocean ridge and a shield volcano. On 5 September 2013, researchers announced that it could be a single volcano which, if corroborated, would make Tamu Massif the largest known volcano on Earth. Tamu Massif is located in the Shatsky Rise about 1,600 km (990 mi) east of Japan. The volcano, which comprises the entire Shatsky Rise, covers an area of about 553,000 square kilometres (214,000 sq mi), making Tamu Massif the largest known volcano in the solar system, in terms of surface area. Its summit is about 1,980 m (6,500 ft) below the surface of the ocean, and its base extends to about 6.4 km (4.0 mi) deep. The volcano is about 4,460 metres (14,620 ft) tall.
William Sager, a marine geophysicist from the Department of Earth and Atmospheric Sciences at the University of Houston, began studying the volcano in about 1993 at the Texas A&M College of Geosciences. According to Sager and his team, Tamu Massif is “the biggest single shield volcano ever discovered on Earth”. Other igneous features on the planet are larger, such as the Ontong Java Plateau, but it has not yet been determined if they are indeed just one volcano or rather complexes of several volcanoes.