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Explosive eruptions at the summit of Mauna Loa: Lithology, modeling, and dating

By
Frank A. Trusdell
Frank A. Trusdell
U.S. Geological Survey, Hawaii Volcanoes National Park, Hawaii 96718, USA
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Jefferson D.G. Hungerford
Jefferson D.G. Hungerford
National Park Service, Yellowstone National Park, Wyoming 82190, USA
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John O. Stone
John O. Stone
Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195, USA
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Keith Fifield
Keith Fifield
Department of Nuclear Physics, Australia National University, Canberra, ACT 200, Australia
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Kaitlin McCann
Kaitlin McCann
GZA GeoEnvironmental, Inc., Philadelphia, Pennsylvania 19102, USA
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Harold Wershow
Harold Wershow
Physical Sciences Department, Everett Community College, Everett, Washington 98201, USA
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Shikma Zaarur
Shikma Zaarur
Institute of Earth Sciences, Hebrew University, Jerusalem 9190401, Israel
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Melissa Dimeo Boyd
Melissa Dimeo Boyd
Yeh and Associates, Denver, Colorado 80211, USA
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Publication history
24 January 201819 September 2018

ABSTRACT

Near Moku‘āweoweo, Mauna Loa’s summit caldera, there are three fans of explosive deposits. The fans, located to the west, northwest, and east, are strongly arcuate in map view. Along ‘Āinapō Trail, 2.8–3.5 km southeast of the caldera, there are several small kīpuka that expose a fourth explosive deposit. Although these explosive deposits have been known for some time, no study bearing on the nature of the explosive activity that formed them has been done. By analyzing cosmogenic exposure age data and the physical properties of the debris fans—lithology, size distributions, and clast dispersal—we conclude that the lithic deposits are the result of five separate phreatic events. The lithic ejecta consist of fragments of ponded lavas, pāhoehoe, gabbroic xenoliths, and “bread-crust” fragments. The exposure ages indicate that the explosive deposit on the west caldera rim was erupted 868 ± 57 yr B.P.; for the northwest fan, the age determination is 829 ± 51 yr B.P.; and on the east rim, ejecta deposits are younger, with ages of 150 ± 20 and 220 ± 20 yr B.P. Lavas underlying these deposits have exposure ages of 960–1020 yr B.P., consistent with the stratigraphy. Near ‘Āinapō Trail, the explosive deposit is much older, overlain by flows dated with a pooled mean age of 1507 ± 19 yr B.P. From the cosmogenic dating, we have three reliable and unambiguous dates. At a much earlier time, a fourth explosive eruption created the ‘Āinapō Trail deposit. We conclude there were at least five explosive episodes around the summit caldera. These deposits, along with recent work done on Kīlauea’s explosive activity, further discredit the notion that Hawaiian volcanoes are strictly effusive in nature. The evidence from the summit of Mauna Loa indicates that it, too, has erupted explosively in recent history.

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Contents

GSA Special Papers

Field Volcanology: A Tribute to the Distinguished Career of Don Swanson

Geological Society of America
Volume
538
ISBN electronic:
9780813795386

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