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.
Tamu Massif
The Tamu Massif was formed about 145 million years ago during the Late Jurassic to Early Cretaceous period over a relatively short period of time (a few million years) and then became extinct. If confirmed, the suggestion that it could be a single volcano would make the Tamu Massif the largest known volcano on Earth, dwarfing the current record-holder, Mauna Loa on the Hawaiian Islands. Tamu's rounded dome extends over an area of , totaling more than , many times larger than Mauna Loa, which has an area of , and about half the area of the Martian volcano Olympus Mons. The entire mass of Tamu consists of basalt. Its slopes are very gradual, ranging from less than half a degree to one degree near its summit. While the Shatsky Rise oceanic plateau is comparable in size to California or Japan, Tamu Massif, which is the plateau's oldest and largest edifice, is comparable in size to New Mexico or Britain and Ireland together.