Event Report, infrasound

Halma’uma’u Rockfall July 23, 2014

Volcanic Infrasonic Event – VIE140723

Prepared by:  ISLA
Source: Rockfall event at Halema’uma’u Crater
Location: 19°24’15.34″N 155°16’49.47″W
Origin Time: Reported around 10:00 HST 07/23/2014
IS Array: MENE, UH Infrasound network (data available through IRIS)
Data Quality: DQ is less than optimal due to sensor noise issue

A rockfall and “ash event” was reported by the National Park at Hawai’i Volcanoes National Park on 23 July 2014. The event was captured on the summit webcam (figure 1), as well as from the Jagger Museum overlook (figure 2).

Figure 1: Image of the rock fall/”ash event” recorded at the summit webcam at around 10:10 am HST. Photo courtesy of Hawaii Volcano Observatory, USGS.
Figure 1: Image of the rock fall/”ash event” recorded at the summit webcam at around 10:10 am HST. Photo courtesy of Hawaii Volcano Observatory, USGS.
Figure 2: Image of the “ash event” taken from the Jagger Museum overlook, at Hawai’i Volcanoes National Park. Photo courtesy of the Hawai’i Volcanoes National Park facebook page (NPS Photo/Nicolyn Charlot).
Figure 2: Image of the “ash event” taken from the Jagger Museum overlook, at Hawai’i Volcanoes National Park. Photo courtesy of the Hawai’i Volcanoes National Park facebook page (NPS Photo/Nicolyn Charlot).

This event was recorded at the University of Hawaii Infrasound Network site MENE located in the village of Volcano, HI. This site is located 7 km NW of Halema’uma’u. In recent days the station has mostly been recording activity from the other active vent at Kilauea volcano Pu’u O’o. This event was picked up by the ISLA, UH automated analysis system (figure 3), and then re-processed. Data quality is only “ok” due to a noise issue with one of the sensors at site MENE; however the signal was still recorded with good signal to noise.

The signal of interest (SOI) was then reprocessed manually at ISLA. The array processing was redone using Progressive Multi Channel Cross Correlation (PMCC) v. 4.15. The results of this analysis can be seen in figures 4 and 5. The results of this analysis show there was a small impulsive event before the larger impulsive event.

Figure 3: The event signal of interest (SOI) as recoded in the ISLA automated processes (circled in green).
Figure 3: The event signal of interest (SOI) as recoded in the ISLA automated processes (circled in green).
Figure 4: Results from the reprocessing of the SOI in PMCC v4.15. Note that the main SOI was preceded by another smaller impulsive event. Data in this figure are masked by correlation and azimuth due to the simultaneous signal from Pu’u O’o.
Figure 4: Results from the reprocessing of the SOI in PMCC v4.15. Note that the main SOI was preceded by another smaller impulsive event. Data in this figure are masked by correlation and azimuth due to the simultaneous signal from Pu’u O’o.
Figure 5: Radar of SOI from PMCC analysis showing detail on the back azimuth calculation. The known back azimuth to the summit is ~ 250° from the site.
Figure 5: Radar plot of SOI from PMCC analysis showing detail on the back azimuth calculation. The known back azimuth to the summit is ~ 250° from the site.

The results of the array processing were plotted in GoogleEarth in relation to the summit and the site (figure 6). The results from the PMCC v4.15 analysis result in a back azimuth that plots back to the Halema’uma’u crater.

Figure 6: Results from the array processing plotted in GoogleEarth.
Figure 6: Results from the array processing plotted in GoogleEarth.

In addition to the serious analysis, the signal was also sped up into the audio range for your listening pleasure. Enjoy!

Appendix: Reports 

HVO Eruption update 24 July 2014: […] The lava lake level was relatively steady, hovering mostly between 30 and 35 m below the Overlook crater rim. The level dropped briefly to about 40 m below the crater rim mid-morning yesterday, following a small explosive event that bombarded the closed tourist overlook at Halemaʻumaʻu with spatter. The explosion was triggered by a rockfall from the southeast wall of the Overlook crater. […]

Hawai’i Volcanoes National Park update: We’ve had a few “ash events” at Halema‘uma‘u today, probably caused by a slight rise in the height of the lava lake which then “cooks” rocks in the crater walls, causing them to collapse into the 2,000+ degree lava sloshing below. NPS youth ranger Nicolyn shared these photos from this afternoon. We’ll keep an eye on the Kīlauea status report from USGS Hawaiian Volcano Observatory and see if our hunch is right. NPS Volunteer Mark reported that a rock fall this morning (10:15 a.m. or so) caused big globs of spatter to shoot up out of the crater 100 feet!! It was over in a flash. Anyone get photos of THAT? Post them please!!! Hopefully HVO got some…we’re checking. (NPS Photo/Nicolyn Charlot)