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.
Kauhakō Crater
Kauhakō Crater is a volcanic crater located in Kalawao County, Hawaii, United States. The crater was formed between 230,000 and 300,000 years ago, as the result of the eruption of volcano Pu'u' 'Uao. It is located in the center of the Kalaupapa Peninsula on the island of Molokaʻi, and has a diameter of by . Lake Kauhakō, located at the bottom of the crater, has the world's greatest depth-to-surface area ratio of a lake and is the fourth deepest lake in the United States. In 2011, the lake underwent an overturning event, causing hydrogen sulfide to float to the surface of the lake and lifeforms, including shrimp and plankton, to disappear.