Volcano Infrasound Event – VIE150503
Prepared by: ISLA
Source: Rock fall into Halemaˋumaˋu lava lake
Location: 19.404365° N, 155.280515° W
Origin Time: Reported time ~23:21 05/03/2015 UTC
IS Arrays: AIND, AHUD, and MENE
REDVOX: iPhone6 with iTestMic, unit 1000000007.
Data Quality: Good at MENE, some wind noise at AHUD and AIND.
Part of the crater rim wall just below the Halemaˋumaˋu overlook failed and fell into the lava lake around 1:21 PM HT of 3 May 2015. The failure triggered a brief explosive event which was recorded on the HVO/UH infrasound network, as well as an iPhone6 with the REDVOX Infrasound Recorder. The explosion was also captured by several HVO webcams.
A rockfall and associated explosive event occurred on 3 May 2015 at ~23:21 UTC in the Halemaˋumaˋu crater. This event was reported by HVO (appendix A) and was well recorded by webcams and infrasound stations around the crater (Figure 1). According to the HVO Daily Update on May 4, a portion of the wall of Halemaˋumaˋu crater collapsed and impacted the lava lake (which was at or near the rim of the overlook crater at the time). This rockfall then triggered a small explosive event.
The current Hawaii Island infrasound network consists of five arrays, two outside of Kailua-Kona, and three around Kilauea Volcano. MENE (UH) is located in the village of Volcano and is has a range of 7 km and heading of 250 degrees to Halemaˋumaˋu crater. AHUD (HVO) is located within Hawaii Volcanoes National park and has a range of 4 km and a heading of 335 degrees to Halemaˋumaˋu crater. AIND (HVO) is located on the flank of Mauna Loa with a range of 19 km and a heading of 78 degrees to Halemaˋumaˋu crater. All three infrasound arrays detected the event. In addition, a specially-configured iPhone6 at HVO also captured the infrasound signature at a range of 2 km and heading of 156 degrees.
The University of Hawaii Infrasound Lab (ISLA) runs several automated processes for real-time analyses of infrasound data streams. Figure 2 is one of the automatic spectral and array processing products. The raw infrasound data were reanalyzed to prepare this report.
ISLA uses Progressive Multi-Channel Correlation (PMCC) for array processing. By using the expected signal heading and estimated arrival time, the detections from this event can be isolated from other coherent detections at the array (Figures 3-5).
ISLA uses the array processing results at each site to verify the source location. This method makes no assumptions about the time, location, or range of the signal, and only considers intersecting heading projections and the sound speed. The result of that association is shown in Figure 6.
The signal-to-noise ratios were substantially improved by beamforming along the heading angle and the application of the Infrasonic Energy, Nth Octave (INFERNO) algorithm (Figures 7-9).
Spectral analysis was also performed on data collected by an iPhone6 running the REDVOX Recorder App designed to turn Apple iOS into infrasound recording systems. During the time of this event there was a single iPhone 6 recording at the HVO overlook. The data were recorded on the internal hard drive, and were recovered on 6 May. Spectral and INFERNO signal-to-noise analysis were performed on these data (Figures 10 and 11), as well as the barometer data recorded by the iPhone6 (Figure 12).
The iPhone6 was replaced with unit 1000000008 on 6 May 2015, and is streaming live infrasound data via wifi, with cell as a communication backup system. Prototype ubiquitous system data products can be viewed at ubq2s.isla.hawaii.edu.
-M. Garces, A. Perttu, & B. Williams
Mahalos to F. Trusdell for hosting MENE, to W. Thelen for his encouragement and constructive collaborations, and to L. Lee for comms support.