Volcano Watch — Kīlauea's Emissions and Their Effects: It's All about Location

Since 1983, SO₂ has been emitted from two main source locations on Kīlauea: in and around Halema`uma`u Crater at the volcano's summit, and at the Pu`u `Ō `ō vent on its East Rift Zone.

Beginning in late 2007, however, summit emissions began to climb steadily and by early January 2008, they had reached their highest level in twenty years. The location of the summit emission source relative to popular visitor areas, along with an associated increase in respiratory emergency calls, resulted in the National Park Service closing roughly half of Crater Rim Drive in mid-February 2008.

Gas emissions from the summit source increased further in mid-March 2008 with the opening of a new volcanic vent just below the Halema`uma`u Overlook. Since the grand opening of this vent, summit SO₂ emissions have varied widely, but, on average, have been about 850 tonnes/day.

This amount of gas release is substantial, well above its previous average of 140 tonnes/day, yet the increased summit emissions represent only a modest change, about 30 percent of the total amount of SO₂ emitted by Kīlauea. By comparison, in 2005, the volcano's East Rift Zone emissions increased by a whopping 200 percent, but that increase didn't generate air quality standard exceedences like those produced by the recent summit activity.

The reason for this seeming disparity between changes in emission rates and corresponding changes in air quality links back to the real estate catchphrase, "location, location, location." The summit vent is closer to locations where people live and work than is the east rift vent.

Tradewinds blow roughly 90 percent of the year, and when they do, communities including Pahala, Na`alehu, and Hawaiian Ocean View Estates are directly downwind of and relatively close to the summit emission source. This proximity to Halema`uma`u was a primary factor driving the 42 exceedences of the 24-hour SO₂ air quality standard—as measured in Pahala by the Hawai'i Department of Health—since the new summit vent opened.

East Rift Zone emissions, swept along the southerly Ka`u coastline by tradewinds, are frequently brought back on shore in the lee of Kīlauea's landmass by daytime onshore breezes and further impact air quality, especially in Pahala. With a longer travel time to Pahala from Pu`u `Ō `ō than from the summit vent, east rift SO₂ emissions are more likely to be converted to particles, a factor which reasonably contributed to the 19 exceedences of Federal particle standards in Pahala since April 2008.

When the northeasterly tradewinds are absent or when Kona (southerly) winds blow, folks in the National Park, Volcano Golf Course subdivision and Volcano Village, all located immediately adjacent to the summit vent, are subjected to brief, but episodically spectacular SO₂ and particle levels.

There has been, however, some improvement in air quality. While summit emissions continue at variable but elevated, levels, East Rift Zone SO₂ emissions decreased in late 2008 and remain at about 60 percent of their previous four year average. This decrease appears to have produced some relief for downwind communities.

The number of monthly air quality standard exceedences recorded by Department of Health monitors declined by about half in 2009 for both Pahala and South Kona. It is reasonable to expect that populated areas from Kea`au to Volcano Village, which are sometimes impacted by Pu`u `Ō `ō emissions during variable or southerly winds might also experience some relief.

Despite the decrease at Pu`u `Ō `ō, the combined SO<sub>2</sub> emissions from Kīlauea's summit and East Rift Zone vents still remain high. Seasonal tradewind lapses have begun, and high gas and particle concentrations returned to Hawaii Volcanoes National Park and adjacent communities for several days this past week. These bad air days remind us that on Kīlauea "location, location, location" (summit, rift, and your location relative to these vent areas) are three things that matter greatly regarding the effects of SO<sub>2</sub> emissions on Hawai`i Island residents and visitors.

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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 mid-week deflation-inflation cycle resulted in a reduction in surface flows on the flow field that had not recovered as of Thursday, October 8.

Very faint glow above the vent at Kīlauea's summit has been visible at night, but the lava surface has receded below the view from the webcam on the rim of Halema`uma`u above the vent and is not currently visible. Volcanic gas emissions remain elevated, resulting in high concentrations of sulfur dioxide downwind.

One earthquake beneath Hawai`i Island was reported felt this past week. A magnitude-2.4 earthquake occurred at 5:32 a.m., H.s.t., on Friday, October 2, 2009, beneath Kīlauea's summit at a depth of 2 km (1.2 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.