# Volcano Watch — HVO maintains a careful watch on Hualālai and Haleakalā

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Of the five most active volcanoes in the Hawaiian Islands, Mauna Loa and Kīlauea garner the most attention, and justifiably so.

A beautiful sunrise of the mountainside. Photo taken from the top of Hualālai volcano.

(Public domain.)

Kīlauea has been in a state of continuous eruption since 1983, and Mauna Loa, the largest volcano on Earth, frequently erupts large volumes of lava that can threaten several different communities on the Big Island.

Loihi, Hualālai, and Haleakalā comprise the other three Hawaiian volcanoes that have erupted at least once within the past several hundred years (Mauna Kea is also classified as active, but has been quiet for many thousands of years). Loihi is located beneath the sea, 20 miles off the south coast of the Big Island. It last erupted in 1998, based on seismic activity and acoustic signals recorded by the University of Hawaii's Hawaiian Undersea Geo-Observatory. But it won't pose a danger to people for at least another 10,000 years, when it will have grown tall enough to rise above the ocean.

Although eruptions are comparatively infrequent at Hualālai and Haleakalā, we should not underestimate the hazards posed by these volcanoes. Both have erupted within the past few hundred years. Hualālai, which rises above Kailua-Kona on the west side of the Big Island, was most recently active in 1801, when it erupted lava flows that destroyed several villages. Now, the Big Island's second largest city, an international airport, several resort complexes, and numerous small towns lie within reach of lava flows from Hualālai.

Recent carbon dating of lava flows from Haleakalā Volcano, on Maui, indicates that the most recent eruption of the volcano occurred about 400 years ago. Renewed activity there could affect not only people visiting the national park, but also thousands of residents who live on the flanks of the volcano.

To mitigate against hazards posed by potential eruptions at Hualālai and Haleakalā, the Hawaiian Volcano Observatory monitors activity at both sites. A critical component of this monitoring is the measurement of ground surface motion. When magma accumulates beneath a volcano, the volcano inflates, much like a balloon. By measuring this deformation, the depth and amount of magma that is causing the unrest can be estimated.

Every few years, staff from the Hawaiian Volcano Observatory travel to Maui to conduct Global Positioning System (GPS) measurements on Haleakalā. The most recent of these measurements took place in 2005. In addition, a continuously operating GPS station (maintained by our University of Hawaii at Manoa colleagues) provides around-the-clock monitoring of deformation near the volcano's summit. Thus far, no significant surface motions have been detected, so it is likely that a magma chamber is not growing beneath the mountain.

Ground deformation at Hualālai is measured, using both GPS and tilt, every other year. In addition, radar interferometry, which detects centimeter-scale deformation from space, provides monthly views of the surface of the volcano and any motion that may be occurring. Like Haleakalā, no signs of deformation have been detected at Hualālai, though HVO continues to keep a watchful eye on the volcano for signs of renewed magmatic activity. Plans for the coming year at Hualālai include additional GPS and tilt surveys, as well as the installation of a continuously operating GPS station.

While Kīlauea and Mauna Loa erupt much more frequently, maintaining a watchful eye on Hawaii's lesser known, but still dangerous, volcanoes - Hualālai and Haleakalā - is clearly important. Hoping that these volcanoes will remain quiet forever is unrealistic - we know that they will erupt again. Through continued vigilance, we should be able to detect the warning signs that will precede an eruption. In addition, we must continue to prepare our communities for future eruptions of all the active volcanoes in Hawaii, so that when such activity does occur (hopefully far in the future), these natural events do not become natural disasters.

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### Volcano Activity Update

This past week, activity levels at the summit of Kīlauea Volcano have remained at background levels. The number of earthquakes located in the summit area has slightly increased (usually less than 10 per day that are large enough to locate) with the largest number located south and west of Halemaumau. Widening of the summit caldera, indicating inflation, continues.

Eruptive activity at Puu Oo continues. On clear nights, glow is visible from several vents within the crater. Drainhole vent, in Puu Oo crater, has had several gas-pistoning events in the past week. These are, essentially, big gas-bubble bursts. Lava continues to flow through the PKK lava tube from its source on the flank of Puu Oo to the ocean at East Laeapuki. There were a few short-lived breakouts from the PKK lava tube close to the coast in the past week. These breakouts sent lava pouring over the sea cliff onto the East Laeapuki bench, but quickly stagnated. Lava also flows through an eastern branch of the PKK tube, called the Campout flow, to the ocean at East Kailiili. Both locations where lava is entering the ocean are within Hawaii Volcanoes National Park.

Access to the sea cliff near the ocean entries is closed, due to significant hazards. The recent breakouts at East Laeapuki occurred inside the closed area. The surrounding area, however, is open. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

There were three earthquakes beneath Hawaii Island reported felt within the past week, all of which were located beneath the northwest flank of Mauna Kea. A magnitude-2.6 earthquake occurred at 11:58 p.m. H.s.t. on Wednesday, September 13, a magnitude-2.4 earthquake occurred at 00:38 a.m. H.s.t. on Thursday, September 14, and a magnitude-2.5 earthquake occurred at 9:22 p.m. H.s.t. later the same day. All were located 12 km (8 miles) northeast of Waikii (southeast of Waimea) at a depth of 13 km (8 miles).

Mauna Loa is not erupting. During the past week, earthquake activity remained low beneath the volcano's summit (five earthquakes were located). Extension of distances between locations spanning the summit, indicating inflation, continues at slow rates.