The infrasound signal from a draining lava lake: the exceptional recordings from Halema`uma`u, Kīlauea volcano in April and May 2018
Abstract
Kīlauea volcano's Halema`uma`u crater hosted a large lava lake for almost a decade through early 2018. Between 24-27 April, the lava lake overtopped the vent rim several times and flowed onto the crater floor. Then, just days later the lava level in the lake began to recede. It dropped out of sight and deflation of the summit and continued descent of the lava surface was inferred from Kīlauea summit tiltmeter records. This lava draining event was recorded by both a permanent, 4 element array operated by HVO at 4 km SSE of the vent and a temporary, 4 element array 800 m N of the lava lake. During normal lava lake activity, the infrasound was dominated by 0.5 Hz tremor-like signals associated with spattering activity at the surface of the lake. This same spattering activity produced seismic tremor. As the lava lake began to recede, the nature of both the seismic and infrasound tremor changed markedly. Beginning on 6 May, infrasound peak pressures increased 40-60 dB at both arrays at frequencies between 0.4 and 1 Hz. By 8 May, there was a change in peak frequency likely due to the increasing length of the conduit above this descending lava free surface. By 10 May, the infrasound returned to levels recorded prior to 6 May. Seismic tremor at stations near the summit showed a similar increase on 6 May but remained elevated as the lava level continued to drop. Seismic tremor did not decrease until after the first of many large explosive events from the summit on 16 May. Our preliminary interpretation of the increase in infrasound is that the pressure drop associated with lava lake descent promoted vigorous outgassing and resulted in the much louder infrasound source. This is broadly consistent with SO2 emission rates. This may have been enhanced by conduit resonance. It is likely that after 10 May, the conduit became partially blocked by rockfall, which muffled subsequent emissions. It was not until the explosive eruptions began that the infrasound again reached levels comparable to those on 6-8 May. We compare the variable frequency content of the infrasound to models of conduit resonance and employ the SO2 and seismic data to aid interpretation of the variable infrasound loudness. The observations from a diverse set of instruments will provide an improved understanding of volcanic infrasound and the role of the conduit in shaping the recorded signals.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.V43J0303W
- Keywords:
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- 8499 General or miscellaneous;
- VOLCANOLOGY