Hawaii’s Mauna Loa is the largest active volcano on Earth. The shield volcano rises gradually from sea level to 4,169 meters (13,678 feet). The flanks of the mountain extend another 5 kilometers (3 miles) below the surface, and the massive volcano pushes Earth’s crust down another 8 kilometers. Overall, Mauna Loa’s summit stands about 17,000 meters (56,000 feet) above its base. For comparison, Mount Everest stands 8,848 meters (29,029 feet) above sea level.
Though it has been quiet during recent decades, Mauna Loa has a long history of volcanic activity. Geologists estimate that the hotspot that feeds Mauna Loa first started to erupt about one million to 700,000 years ago. After underwater eruptions built up a seamount for hundreds of thousands of years, lava emerged above the Pacific surface about 400,000 years ago.
On average, Mauna Loa has erupted roughly every six years for the past 3,000 years. The most detailed eruption records are available for the past few centuries. Eruptions usually begin in the summit caldera with lava flowing down one of the volcano’s two rift zones: the Northeast Rift Zone and the Southwest Rift Zone. The rift zones are chains of craters and fissures that extend from the summit to the sea.