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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. B11, 2522, doi:10.1029/2002JB002101, 2003

Very long period oscillations of Mount Erebus Volcano

R. Aster

Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA

S. Mah

Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA

P. Kyle

Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA
New Mexico Bureau of Geology and Mineral Resources, Socorro, New Mexico, USA

W. McIntosh

Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA
New Mexico Bureau of Geology and Mineral Resources, Socorro, New Mexico, USA

N. Dunbar

New Mexico Bureau of Geology and Mineral Resources, Socorro, New Mexico, USA

J. Johnson

Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, Hawaii, USA

M. Ruiz

Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA

S. McNamara

Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA

Abstract

The exposed top of the conduit system at Mount Erebus Volcano, Ross Island, Antarctica, is a convecting lava (magma) lake hosting Strombolian eruptions caused by the explosive decompression of large (up to 5 m radius) gas slugs. Short-period (SP; f ≥1 Hz) seismoacoustic eruption seismograms are accompanied by oscillatory very long period (VLP) signals observed in the near field by broadband seismometers 0.7 to 2.5 km from the lava lake. A variable VLP onset, preceding eruptions by several seconds, is followed by a repeatable VLP coda that persists for several minutes until the lava lake recovers to its preeruptive level. VLP signals are dominated by distinct decaying nonharmonic modes, the largest at periods of 20.7, 11.3, and 7.8 s, with respective source Q values of approximately 11, 18, and 4. Particle motions indicate a temporally evolving source producing increasingly vertical posteruptive displacements as the signal decays. VLP scalar moments, up to ∼5×10¹¹ N m, exceed SP moments by an order of magnitude or more, suggesting distinct, though genetically related, SP and VLP source mechanisms. We conclude that VLP signals arise from excitation of a quasi-linear resonator that is intimately associated with the conduit system and is excited by gravity and inertial forces associated with gas slug ascent, eruption, and magma recharge. VLP signal stability across hundreds of eruptions spanning 5 years, the persistence of the lava lake, and the rapid posteruptive lava lake recovery indicate a stable near-summit magma reservoir and VLP source process.

Received 17 July 2002; accepted 12 August 2003; published 12 November 2003.

Index Terms: 4544 Oceanography: Physical: Internal and inertial waves; 7280 Seismology: Volcano seismology (8419); 8414 Volcanology: Eruption mechanisms; 8419 Volcanology: Eruption monitoring (7280).

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Citation: Aster, R., S. Mah, P. Kyle, W. McIntosh, N. Dunbar, J. Johnson, M. Ruiz, and S. McNamara (2003), Very long period oscillations of Mount Erebus Volcano, J. Geophys. Res., 108(B11), 2522, doi:10.1029/2002JB002101.

Copyright 2003 by the American Geophysical Union.