Māhukona

Māhukona, a submerged shield volcano on the northwestern flank of Hawaiʻi Island, is considered the oldest volcano involved in building the island, predating Kohala and Mauna Kea. Now entirely underwater, it once rose about 800 feet above sea level and had a broad form with a summit caldera and a westward rift zone; an eastern rift zone was likely buried by younger volcanoes. Its main shield-building phase ended about 470,000 years ago, and submerged coral reef and slope features mark former shorelines, indicating that it sank below the sea between about 435,000 and 365,000 years ago. Exploration in 2001 helped investigate this early volcanic history.