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Volcano Watch — In Every Volcanic Paradise, a Little Vog Must Fall

August 14, 2008

Locally, the term "vog" has become a household word, with a rash of media articles and even a respectable Wikipedia entry online. After 25 years of nearly continuous eruption on Kīlauea's east rift zone and over six months of increased gas emissions from Kīlauea's summit, most Hawai`i Island residents and many visitors are well acquainted with this volcanic air pollution.

Area with vog.

The new vent in Halema`uma`u Crater at the summit of Kīlauea Volcano has created additional challenges for communities in the Ka`u and Kona districts with regard to air quality. During trade winds, which blow 90 percent of the time during the summer months, Pahala, Na`alehu, Ocean View, and other downwind communities are plagued by high concentrations of both sulfur dioxide (SO2) gas and their associated sulfate particles. Communities farther from the volcano, such as those on the Kona coast, are affected predominantly by particles.

The very worst vog days are frequently characterized by exceedences of EPA regulatory standards for SO2 gas and particulate matter. For these pollutants, 24-hour health standards have been set to protect the general population. For SO2 gas there is also a short-term standard meant to protect visibility, property, vegetation, and animals.

Since the new activity at Halema`uma`u began, the EPA standards for SO2 have been exceeded on numerous occasions in Pahala, and for particulate matter they have been exceeded in both Pahala and South Kona. The Pahala air quality monitoring station, which was installed in August 2007, only measured exceedence of SO2 standards after the opening of the Halema`uma`u vent in March 2008. Exceedence data are available at

An air quality monitoring site located at the Hawaiian Volcano Observatory (HVO), less than 2 km (1.2 mi) from the vent, offers an interesting perspective. When trade winds are interrupted, gas emissions from the summit and east rift zone are blown toward this station. Data show that, over the past 7 years, the 24-hour health standard was exceeded 1-9 times per year--on average just a handful of days. However, during the first half of 2008, the standard at this site has been exceeded 21 times.

Preliminary data also show that 2008 HVO wind patterns are consistent with those of previous years. This suggests that the larger number of SO2 events is due to the increase in SO2 emissions from Halema`uma`u, rather than to an increase in non-trade wind days.

The total output of SO2 gas from Kīlauea has increased by about 50 percent since the gas vent at Halema`uma`u appeared. Emissions from the summit jumped from a long-term average of about 200 t/d to the current 500-1000 t/d--an increase of 250-500 percent. Pu`u `Ō `ō, on Kīlauea's east rift zone, is still the predominant source of SO2 emissions, but the relative impact of summit emissions has increased significantly.

During prevailing trade winds, the east rift gas plume is generally blown out to sea, where it is dispersed and diluted before being carried back onshore to impact downwind communities. The Halema`uma`u plume remains onshore and is generally blown through the Ka`u desert to directly affect downwind communities.

During trade wind disruptions, which occur as much as 50 percent of the time during winter months, air quality in windward Hawai`i deteriorates. Communities on the east side of the island will continue to be impacted by the east rift plume as they have been for the past two decades. Communities close to the Halema`uma`u vent and to the north, like Kulani Prison, will most strongly experience the additional impact of the summit plume on these days.

Although Kīlauea's dynamic past suggests that the current situation could change suddenly, there is no indication that the summit eruption will end in the near future. Hawai`i residents are practiced at preparing for natural hazards, such as lava flows, tsunami, floods, and earthquakes. Learning about vog and how it can affect specific areas will help individuals adjust their activities to minimize their exposure to volcanic air pollution. For more information, see the new Frequently Asked Questions about Air Quality in Hawai`i at the USGS-HVO Web site.


Volcano Activity Update

Kīlauea Volcano continues to be active. A vent in Halema`uma`u Crater is erupting elevated amounts of SO2 gas and very small amounts of ash. Resulting high concentrations of SO2 in downwind air have closed the south part of Kīlauea caldera and produced occasional air quality alerts in more distant areas, such as Pahala and communities adjacent to Hawai`i Volcanoes National Park, during kona wind periods. There have been several small ash-emission events, lasting only minutes, in the last week. These are preceded by small seismic events and are probably caused by tiny rock falls within the vent.

Pu`u `Ō`ō continues to produce sulfur dioxide at even higher rates than the vent in Halema`uma`u Crater. Trade winds tend to pool these emissions along the West Hawai`i coast, while Kona winds blow these emissions into communities to the north, such as Mountain View, Volcano, and Hilo. Incandescence continues to be observed at night inside Pu`u `Ō`ō and suggests minor activity from vents within the crater.

Lava continues to erupt from fissure D of the July 21, 2007,eruption and flows toward the ocean through a well-established lava tube. A deformation event at Kīlauea's summit, starting on Tuesday, August 5, choked off the supply of lava to the east rift zone eruption site for several days. The Waikupanaha ocean entry had died by Wednesday, August 6 and the lava tube was observed to be empty on Thursday, August 7. Inflation began at the summit on the afternoon of Friday, August 8, resuming the lava supply to the east rift zone. On Saturday, August 9, lava began to overflow from the Thanksgiving Eve Breakout (TEB) vent and reenter the tube system. Breakouts were observed on the morning of Sunday, August 10, at the top of Royal Gardens subdivision and on the coastal plain. The largest of these coastal plain breakouts created a new short-lived ocean entry west of the main Waikupanaha entry and sent a minor flow into a kipuka on the east margin of the flow field. The coastal plain breakouts, and the new western ocean entry, were inactive by Wednesday, August 13. The main Waikupanaha entry reactivated on Sunday, August 10, resuming its characteristic littoral explosions and vigorous plume.

Be aware that lava deltas could collapse at any time, potentially generating large explosions. This may be especially true during times of rapidly changing lava supply conditions, as have been seen lately. Do not venture onto the lava deltas. Even the intervening beaches are susceptible to large waves generated during delta collapse; avoid these beaches. In addition, steam plumes rising from ocean entries are highly acidic and laced with glass particles. For viewing hours at the coast, check the Civil Defense Web site or call 961-8093 for viewing hours.

Mauna Loa is not erupting. One earthquake was located beneath the summit this past week. Continuing extension between locations spanning the summit indicates slow inflation of the volcano.

Three earthquakes beneath Hawai`i Island were reported felt within the past week. A magnitude-3.0 earthquake occurred at 10:48 p.m. H.s.t., on Saturday, August 9, 2008, and was located 8 km (5 miles) southwest of Waiki`i, at a depth of 17 km (10 miles). A magnitude-2.5 earthquake occurred at 9:43 p.m. on Sunday, August 10, and was located 17 km (11 miles) west of Kawaihae at a depth of 11 km (7 miles). A magnitude-3.0 earthquake occurred at 1:01 a.m. on Wednesday, August 13, and was located 33 km (20 miles) northwest of Wai`anae, O`ahu, at a depth of 16 km (10 miles).

Visit our Web site for daily Kīlauea eruption updates, a summary of volcanic events over the past year, and nearly real-time Hawai`i earthquake information. Kīlauea daily update summaries are also available by phone at (808) 967-8862. Questions can be emailed to skip past bottom navigational bar