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HAWAII Mauna Kea 7 ½’ quadrangle: Mauna Kea, HI Hawaii County Mauna Kea State Park
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Volcanic 13, 796 ft (4, 205 m) |
| Bedrock: Laupahoehoe Volcanics |
Quaternary (Holocene) |
| Rough aa lava flows, and cinder cones with vesicular lapilli, ash and bombs cover the summit area of Mauna Kea. The lava is aphyric, dense, medium to dark gray hawaiite, with rare olivine or plagioclase phenocrysts, and benmoreite, with biotite and brown apatite phenocrysts. The highest point is a cone, Puu Wekiu, but four other cones are nearly as high. Mauna Kea is only 35 meters higher than the nearby active shield volcano, Mauna Loa.
Volcanism at Mauna Kea may have started about one million years ago, but most of the mountain above sea level was formed by eruptions from 200,000 to 65,000 years ago, building a shield volcano made up of tholeiitic alkali basalt (the Hamakua Volcanics). The younger Laupahoehoe Volcanics at the summit are composed of a more viscous lava than tholeiitic basalt, and they form a relatively small part of the mountain’s bulk. They erupted both before, during and after Pleistocene glaciation, from 65,000 to 4,000 years ago, filling the summit caldera and forming several large cinder cones. For a discussion of all the volcanic highpoints, see http://www.unh.edu/esci/volcanic_highpoints03.pdf. Surficial Geology: Pleistocene glacial till, 40,000 to 13,000 years old, is overlain by the four volcanic cones at the summit. The Hawaiian name means "white mountain" because of the snow cap which still appears on the summit each winter. Mauna Loa also gets snow, but its shield shape does not allow the summit to be seen from the coast, whereas the top of Mauna Kea is steeper and clearly visible. Soil Series: Cinders with no significant soil horizons.
Selected References: Wolfe, E.W., W.S. Wise, and G.B. Darymple, 1997, Geology and petrology of Mauna Kea volcano, Hawaii - - A study of post shield volcanism: U.S. Geological Survey Professional Paper 1557.
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