# Volcano Watch — Hualālai is Third Most Active Volcano in Hawaii

October 1, 2009

The West Hawaii Today issue for September 11, 2009, contained a letter to the editor titled "Hualālai is a real and present threat." The writer's main point was that "Hualālai is the 'secret in the closet' that nobody wants to talk about," that Hualālai is under-monitored, and that, should Hualālai erupt, there is no evacuation plan.

The letter writer's concerns about Hualālai were valid, but he was not aware of HVO's current efforts and plans to improve the monitoring of Hualālai. We hope to shed some light on recent and future activities planned for Hualālai.

Hualālai is the third most active volcano on Hawaii Island behind Kīlauea and Mauna Loa, according to the Hawaiian Volcano Observatory's (HVO) Web site, and attained national ranking of "High Threat" for active volcanoes in the U.S..

In the ranking, there were 37 volcanoes nation-wide that were highest-priority targets for improved monitoring; Kīlauea and Mauna Loa were included in this group. Furthermore, 21 additional volcanoes were found to be under-monitored and were regarded high priority for improved monitoring; Hualālai is in this group.

What is the basis for this ranking? Hualālai has erupted three times in the last 1,000 years, the most recent eruption occurring in 1801. An intense and damaging seismic swarm in 1929 marked a failed eruption. In the same interval, Mauna Loa and Kīlauea have each erupted more than 150 times, and Haleakalā has erupted at least 10 times. Hualālai was rated a higher threat than Haleakalā, due to the extent of development (airport, power station, etc.) and the larger population living on the volcano's flanks.

Is Hualālai under-monitored? In 2005, HVO and the Pacific Tsunami Warning Center (PTWC) each had one seismometer on the volcano, and bi-annual deformation surveys were conducted by our staff. With the permission of Kamehameha Schools, a continuous GPS receiver was installed near the summit in late 2006. In 2009, HVO still has one seismometer and uses two instruments operated by PTWC for eruption monitoring, and we continue the bi-annual surveys. Plans for the next two years include upgrading our seismic site and adding a new one.

We routinely scrutinize all available satellite imagery daily, including visual and thermal images to indicate any significant visual and temperature changes, or increased gas emissions. Moreover, radar scans several times each year can pinpoint any ground deformation that may be a precursor to volcanic activity. The radar scans are so sensitive that several small areas of subsidence were detected after the October 15, 2006, Kiholo earthquakes.

The conclusion from evaluating all of these data is that there have been no signs of swelling, major subsidence, temperature changes, gas emissions, or unusual seismic activity on Hualālai that would indicate volcanic activity in the near future. Nevertheless, we continue to look for any changes.

If the rankings were done today, Hualālai would be nearly fully monitored.

We agree with the letter writer that "the more people know about Hualālai, the more will be prepared." In 2004, University of Hawaii at Manoa (UHM) scientists published two studies on Kona community's perception of volcanic risk and preparedness for lava flows from Hualālai and Mauna Loa. They concluded that "current community understanding and preparedness? falls short of that required for a volcanic crisis, particularly for those eruptions with short onset and high effusion rates on steep slopes that would impact Kona in just a few hours?"

There are several reasons for the lack of understanding, but foremost may be the constant influx of new residents who haven't educated themselves about volcanic hazards. The primary mission of the U.S. Geological Survey's Hawaiian Volcano Observatory is to monitor the active volcanoes in the State of Hawaii. Through our Web site, public forums, and newspaper articles, we strive to disseminate information on the volcanoes and their hazards.

The people of Kona should know that we are keeping an eye on Hualālai and that if there are any changes (in its eruption status), we will let the public know!

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### Volcano Activity Update

Lava continues to erupt from the TEB vent, on Kīlauea's east rift zone and flow through tubes to the ocean at Waikupanaha. A deflation-inflation cycle this past week resulted in a reduction of lava supply for several days, followed by a resumption of flow on Wednesday, Sept. 30. Breakouts from the tube system started at that time, and these surface flows remain active at the top of Royal Gardens subdivision. The flows are mostly staying close to the breakout point along the east margin of the flow field.

Faint glow above the vent at Kīlauea's summit has been visible at night. A portion of the Halemaumau vent cavity collapsed on Saturday, Sept. 26, followed by the appearance of an active lava pond deep within the vent cavity on the night of Tuesday, Sept. 29. Volcanic gas emissions remain elevated, resulting in high concentrations of sulfur dioxide downwind.

Four earthquakes beneath Hawaii Island were reported felt this past week. A magnitude-2.3 earthquake occurred at 12:30 p.m., H.s.t., on Friday, September 25, 2009, beneath Kīlauea's summit at a depth of 6 km (4 miles). Two earthquakes occurred on Sunday, September 27-a magnitude-2.1 earthquake at 9:52 a.m., H.s.t., located 7 km (4.3 miles) N of Kailua at a depth of 8 km (5 miles) and a magnitude-2.3 earthquake at 10:22 p.m., H.s.t., located 7 km (4.3 miles) ENE of Honaunau at a depth of 6 km (3.7 miles). A 1.6-magnitude earthquake at 7:11 p.m. H.s.t., on Wednesday, September 30, was located 15 km (10 miles) NW of Mauna Kea's summit at a depth of 25 km (16 miles).

Visit our Web site for detailed Kīlauea and Mauna Loa activity updates, recent volcano photos, recent earthquakes, and more; call (808) 967-8862 for a Kīlauea activity summary; email questions to askHVO@usgs.gov.