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What makes hydromagmatic eruptions violent? Some insights from the Keanakāko'i Ash, Kı̄lauea Volcano, Hawai'i

Journal of Volcanology and Geothermal Research

By:
, , , , and
DOI: 10.1016/j.jvolgeores.2004.05.015

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Abstract

Volcanic eruptions at the summit of Ki??ilauea volcano, Hawai'i, are of two dramatically contrasting types: (1) benign lava flows and lava fountains; and (2) violent, mostly prehistoric eruptions that dispersed tephra over hundreds of square kilometers. The violence of the latter eruptions has been attributed to mixing of water and magma within a wet summit caldera; however, magma injection into water at other volcanoes does not consistently produce widespread tephras. To identify other factors that may have contributed to the violence of these eruptions, we sampled tephra from the Keanaka??ko'i Ash, the most recent large hydromagmatic deposit, and measured vesicularity, bubble-number density and dissolved volatile content of juvenile matrix glass to constrain magma ascent rate and degree of degassing at the time of quenching. Bubble-number densities (9 ?? 104- 1 ?? 107 cm-3) of tephra fragments exceed those of most historically erupted Ki??lauean tephras (3 ?? 103-1.8 ?? 105 cm-3), and suggest exceptionally high magma effusion rates. Dissolved sulfur (average = 330 ppm) and water (0.15-0.45 wt.%) concentrations exceed equilibrium-saturation values at 1 atm pressure (100-150 ppm and ???0.09%, respectively), suggesting that clasts quenched before equilibrating to atmospheric pressure. We interpret these results to suggest rapid magma injection into a wet crater, perhaps similar to continuous-uprush jets at Surtsey. Estimates of Reynolds number suggest that the erupting magma was turbulent and would have mixed with surrounding water in vortices ranging downward in size to centimeters. Such fine-scale mixing would have ensured rapid heat exchange and extensive magma fragmentation, maximizing the violence of these eruptions.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
What makes hydromagmatic eruptions violent? Some insights from the Keanakāko'i Ash, Kı̄lauea Volcano, Hawai'i
Series title:
Journal of Volcanology and Geothermal Research
DOI:
10.1016/j.jvolgeores.2004.05.015
Volume
137
Issue:
1-3 SPEC. ISS.
Year Published:
2004
Language:
English
Publisher:
Elsevier
Description:
17 p.
First page:
15
Last page:
31
Online Only (Y/N):
N
Additional Online Files(Y/N):
N