Mauna Kea
Mauna Kea ( or , ) is a dormant volcano on the island of Hawaii. Its peak is above sea level, making it the highest point in the state of Hawaii. Most of the mountain is under water, and when measured from its oceanic base, Mauna Kea is the tallest mountain in the world measuring over . Mauna Kea is about a million years old, and has thus passed the most active shield stage of life hundreds of thousands of years ago. In its current post-shield state, its lava is more viscous, resulting in a steeper profile. Late volcanism has also given it a much rougher appearance than its neighboring volcanoes due to construction of cinder cones, decentralization of its rift zones, glaciation on its peak, and weathering by the prevailing trade winds. Mauna Kea last erupted 6,000 to 4,000 years ago and is now considered dormant. The peak is only about higher than its more massive neighbor, Mauna Loa.
Māhukona
Māhukona is a submerged shield volcano on the northwestern flank of the Island of Hawaii. 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.
This makes Māhukona the oldest volcano to build Hawaii island, compared to Kohala to the east and Hualālai to the southeast. The Monterey Bay Aquarium Research Institute investigated the area with a remotely controlled submarine in 2001.