Subglacial Eruptions Research Articles

Quaternary Stratigraphy and Chronology of Mauna Kea, Hawaii: A 380,000-yr Record of Mid-Pacific Volcanism and Ice-Cap Glaciation

Research Article| July 01, 1979 Quaternary Stratigraphy and Chronology of Mauna Kea, Hawaii: A 380,000-yr Record of Mid-Pacific Volcanism and Ice-Cap Glaciation Stephen C. Porter Stephen C. Porter 1Department of Geological Sciences and Quaternary Research Center, University of Washington, Seattle. Washington 98195 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1979) 90 (7_Part_II): 980–1093. https://doi.org/10.1130/GSAB-P2-90-980 Article history received: 21 Jun 1976 rev-recd: 20 Feb 1979 accepted: 05 Mar 1979 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Stephen C. Porter; Quaternary Stratigraphy and Chronology of Mauna Kea, Hawaii: A 380,000-yr Record of Mid-Pacific Volcanism and Ice-Cap Glaciation. GSA Bulletin 1979;; 90 (7_Part_II): 980–1093. doi: https://doi.org/10.1130/GSAB-P2-90-980 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search 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). This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Quaternary stratigraphy and chronology of Mauna Kea, Hawaii: A 380,000-yr record of mid-Pacific volcanism and ice-cap glaciation: Summary

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).

About deep-sea volcanism

Hyoclastites mainly result from underwater comminution of molten basalts initially explosively erupted out of the sea-floor and instantaneously pulverized by closely succeeding phreatic explosion (s). Many sea-mounts probably never were the alleged volcanic islands, later sea-level eroded into truncated cones and eventually drowned several km down, they are claimed to be. They are here considered as submarine polygenic volcanoes, the shape of which is congenital. Their building up probably started by accumulation of numberless flows of basalt, quietly poured out from a long-lived central vent; when this lava-volcano's crater, so progressively carried higher and higher, reached depths where explosive phenomena became possible because of lowered hydrostatic pressure, magmatic explosions occurred due to violent release of primitively dissolved (or combined) gases. Shattering of lava, 1∘) increases by several orders of magnitude lava's surface to volume ratios, so allowing huge quantities of super-heated steam to be engendered; 2∘) this super-heated steam trapped below the lava-lumps, as well as in their numberless holes, immediately explodes and comminutes the primary lavalumps; 3∘) so other super-heated steam is produced and further steam explosions are resumed in confined room until almost all the primitive heat content of the magma is transformed into kinetic energy and the lava is comminuted into glassy, ashy, hyaloclastites. This process also works above fissural eruptions. The difference is that fissural volcanoes, contrarily to large central ones, are usually monogenic (i. e. delivering one eruption only through the same vent instead of numberless ones for polygenic volcanoes). Linear effusive eruptions also produce quietly flowing basaltic flows but — because being monogenic — they cannot build up big, and eventually steep, reliefs as polygenic volcanoes do. When not poured over steep slopes where pillowlavas develop, submarine flows are characterized by 1∘) the lack of any scoriaceous, more or less thick, upper part (or jacket), and 2∘) a regular pavingstone-like surface, each polygon of which being the upper face of short prisms similar to ordinary columnar prismation, but one or two orders of magnitude shorter. As for central volcanoes, explosive activity along submarine fissures produces huge quantities of hyaloclastites, but these cannot be heaped up into steep ridges, as happens for subglacial eruptions, because sea-currents spread them far and wide.

Discussion

Sir E dward B ailey said that the paper concerned one of the most important subjects of present-day geological research. A reassessment was required wherever acid rock veined basic, etc. Discussion had been proceeding on these lines for a number of years. Analogies had been drawn between basic magma entering acid magma, and basic magma entering the sea. In some cases fuller analogy was afforded by the subglacial eruptions of Iceland, with their pillow-lavas, their melted ice, and their floods. Dr Doris Reynolds had drawn attention to this sort of thing in a paper on Slieve Gullion in 1937. The A uthors agreed with Sir Edward Bailey that a reassessment was indeed required of the time-relations and genesis whenever acid and basic rocks were intimately associated. They would like to acknowledge the important contributions that Sir Edward had made on the subject of acid-basic relationships. The analogy with subglacial eruptions mentioned by Sir Edward was in fact very close; it was a few days after having studied the products of a subglacial eruption in south-east Iceland that two of the authors reinterpreted the Austurhorn net-veined complex, so impressed were they by the similarities between the basic pillows, whole and broken, in each. Dr J. F. D ewey said that the authors had presented excellent examples of contacts indicating the simultaneous intrusion and eruption of acid and basic magmas. The speaker had observed similar relationships in Lower Palaeozoic volcanic sequences in Ireland and North Wales. The Crogenen granophyre, south of the Mawddach estuary in Merionethshire,