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.
Mauna Kea
Mauna Kea is the only Hawaiian volcano with distinct evidence of glaciation. Similar deposits probably existed on Mauna Loa, but have been covered by later lava flows. Despite Hawaii's tropical location, during several past ice ages a drop of a degree in temperature allowed snow to remain at the mountain's summit through summer, triggering the formation of an ice cap. There are three episodes of glaciation that have been recorded from the last 180,000 years: the "Pōhakuloa" (180–130 ka), "Wāihu" (80–60 ka) and "Mākanaka" (40–13 ka) series. These have extensively sculpted the summit, depositing moraines and a circular ring of till and gravel along the mountain's upper flanks. Subglacial eruptions built cinder cones during the Mākanaka glaciation, most of which were heavily gouged by glacial action. The most recent cones were built between 9000 and 4500 years ago, atop the glacial deposits, although one study indicates that the last eruption may have been around 3600 years ago.