Mauna Loa is one of five volcanoes that form the Island of Hawaiiin the U.S. state of Hawaiʻi in the Pacific Ocean. Mauna Loa is the largest subaerial volcano in both mass and volume, and has historically been considered the largest volcano on Earth. It is an active shield volcano, with a volume estimated at approximately 18,000 cubic miles (75,000 km3. Lava eruptions from Mauna Loa are silica-poor, and very fluid; eruptions tend to be non-explosive and the volcano has relatively shallow slopes. Mauna Loa has probably been erupting for at least 700,000 years, and may have emerged above sea level about 400,000 years ago. The oldest-known dated rocks are not older than 200,000 years. The volcano's magma comes from the Hawaii hotspot, which has been responsible for the creation of the Hawaiian island chain over tens of millions of years. The slow drift of the Pacific Plate will eventually carry Mauna Loa away from the hotspot within 500,000 to one million years from now, at which point it will become extinct.