Māhukona is a submerged shield volcano on the northwestern flank of the Island of Hawaiʻi. A drowned coral reef at about 3,770 feet (-1,150 m) below sea level and a major break in slope at about 4,400 feet (-1,340 m) below sea level represent old shorelines. The summit of the shield volcano was once 800 feet (250 m) above sea level. It has now subsided below sea level. A roughly circular caldera marks the summit of Māhukona. A prominent rift zone extends to the west. A second rift zone probably extended to the east but has been buried by younger volcanoes. The main shield-building stage of volcanism ended about 470,000 years ago. The summit of the shield volcano subsided below sea level between 435,000 and 365,000 years ago.