Abstract

Known evidence of glaciation in the tropical mid-Pacific is restricted to the upper, slopes of Mauna Kea, the highest of five massive shield volcanoes comprising the island of Hawaii (Fig. 1). Mauna Kea was built largely during Pleistocene time but has experienced minor eruptive activity during Holocene time, the last occurring about 3,600 to 5,000 yr ago. Glaciers do not exist on the mountain today, for the snowline currently lies above the summit (4,206 m). However, during the last several glacial ages, the volcano supported a succession of small ice caps, as evidenced by widespread glacial landforms and numerous stratigraphic sections on the upper slopes. Eruptions occurred intermittently during late Pleistocene time, for both lava flows and tephra layers of this age are intercalated with sheets of glacial drift. Most lava flows and associated pyroclastic cones lying within the limits of former ice caps can be related stratigraphically to the glacial deposits, thereby affording a basis for relative dating of volcanic and glacial events. Furthermore, certain distinctive volcanic landforms and deposits, which in Hawaii apparently are unique to the upper slopes of Mauna Kea, provide striking evidence of subglacial eruptions. Such volcanic units offer a direct basis for obtaining radiometric ages of several episodes of ice-cap glaciation.

Although a number of observations on the geology of Mauna Kea were reported following the earliest recorded ascent in 1823, the first systematic study of the volcano was made by Stearns and Macdonald (1946) as part of a broader investigation on the geology of the island. The rocks of Mauna Kea were subdivided into two major units, the Hamakua and Laupahoehoe volcanic series (Fig. 2), and their distribution was mapped at a scale of 1:125,000. Shorter contributions on various aspects of the geology, petrology, chronology, and geophysics of the volcano have appeared subsequently (Doell and Cox, 1965; Funkhouser and others, 1968; Kinoshita and others, 1963; Macdonald, 1945, 1949a, 1949b, 1968; Macdonald and Abbott, 1970; Mc-Dougall, 1969; McDougall and Swanson, 1972; Malahoff and Woollard, 1966, 1968). In addition, reports bearing on Holocene volcanism, tephrochronology, and evidence of a buried summit caldera have resulted from the present investigation (Porter, 1971, 1972a, 1972b, 1973).

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