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.
Geology of the United States
The State of Hawaii consists of a chain of islands, or archipelago. The archipelago developed as the Pacific plate moved slowly northwestward over a hotspot in the Earth's mantle at a rate of approximately per million years. Thus, the southeast island (Hawaii) is volcanically active whereas the islands on the northwest end of the archipelago are older and typically smaller, due to longer exposure to erosion. The age of the archipelago has been estimated using potassium-argon dating methods. From this study and others, it is estimated that the northwestern most island, the Kure Atoll, is the oldest at approximately 28 million years (Ma); while Hawaii, is approximately 0.4 Ma (400,000 years). The only active volcanism in the last 200 years has been on Hawaii and on the submerged but growing volcano to the extreme southeast, Loihi.