October 24, 1997

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

The fall Vog season opens with symposia

Recently, fall "vog season" returned to east Hawai`i, ushered in with phone calls to the U.S. Geological Survey's Hawaiian Volcano Observatory (HVO). Residents from Hamakua to Volcano have called us with concerns about what has been some of the worst regional air quality of the year.

No, Virginia, there's really not an official vog season for east Hawai`i, but, this is the time of year when our northeasterly tradewinds become interrupted. This winter's air may be worse than normal for east Hawai`i, as El Nino is expected to cause more frequent tradewind disruptions. During the summer months, especially, the prevailing trades help sweep the vog produced by Kilauea away from east Hawai`i, and to the chagrin of the other half of the county, toward the leeward side of the island.

The several-day break in the tradewinds caused two exceedences of the Environmental Protection Agency's (EPA) primary standard for irritating sulfur dioxide gas in Hawai`i Volcanoes National Park (HVNP). This is a standard that EPA established to protect human health. Basically, the standard says that the level of sulfur dioxide in the air should not exceed a certain concentration (0.139 parts per million), averaged over a 24-hour period, more than once each calendar year. A single exceedence was already recorded earlier this year, and about 70 exceedences have been measured during the past 10 years in HVNP.

During the two recent exceedences on October 10 and 12, motorists from Glenwood to Volcano turned on headlights at mid-morning in order to be seen by others on the highway. In the National Park, a group of 30 or so students trudged down the trail, covering their noses and mouths with shirts and bandannas, making them look like a pack of bank-robbers-in-training. Elsewhere, Maui County issued a "no burn" ban in order to preserve what was left of their air quality; vog was wafted to the northwestward, obscuring views of Kaho`olawe, and Lana`i, on its way toward Oahu. Residents on Maui and the Big Island complained about runny noses, burning eyes, headaches, and a general lack of energy.

These scenes are in stark contrast to the respiratory relief felt island-wide during an eruptive hiatus that began on February 1 of this year. Although the eruption started up again on February 24, sulfur dioxide emission rates from Kilauea remained low until the beginning of June when they recovered to a more "normal" amount of around 2,000 metric tons per day.

The sulfur dioxide released from Kilauea is converted in moist air to a mist of sulfuric acid and other sulfates which, along with the gas, comprise the hazy form of pollution we know as vog. Normally, the amount of sulfur dioxide produced by Kilauea is fairly constant, but in late August the emission rate doubled over a period of three weeks before returning to normal. These emission rates are measured by HVO staff as part of our regular program for monitoring Kilauea's activity.

Speaking of vog, those who are interested in learning more about this part of every day Big Island life are invited to attend one of two Vog and Laze Symposia, to be presented by the Center for the Study of Active Volcanoes (CSAV).

The first symposium will be held on November 8 at the University of Hawai`i at Hilo Campus Center, Room 306-307; the second will be held in Kona on November 22 at the Kona Surf Hotel in the Kamehameha Ballroom.

Both symposia begin at 9 a.m., with presentations by scientists and medical professionals, who will discuss the sources of vog and laze, their compositions, and their impacts on the community. An informal discussion and resource booths will also be featured. These free-admission symposia are sponsored by a grant from the Federal Emergency Management Agency. For additional information, call 974-7631.

Kilauea Eruption Status--October 24, 1997

The past week started with vigorous eruptive activity within Pu`u `O`o Crater. Lava topped both the east and west rims on several occasions, and bursts of spatter up to 60 meters (200 ft) high were observed. The crater overflows decreased the volume of lava entering the tube system, and the ocean entry volume was estimated to be only 10% of normal. By the end of the week, activity returned to normal, and copious amounts of lava resumed flowing through the network of tubes down to the seacoast. The molten rock enters the ocean at two locations - Waha`ula and Kamokuna. On Sunday night at 6:48 p.m., residents living near Pu`u `O`o reported hearing a booming noise coming from the vent. The HVO seismic station closest to the vent detected the acoustic event, which is interpreted to be caused by a rapid discharge of gas.

Recent Big Island Earthquakes

Late Sunday night at 9:57 p.m., residents of Pa`auilo, Ahualoa, and Waimea reported feeling an earthquake. The location of the magnitude-3.8 earthquake was 5 km (3 mi) west of Laupahoehoe at a depth of 18 km (10.8 mi). A magnitude-3.4 earthquake was felt on Thursday morning at 6:38 a.m. by a visitor at the Volcano House. The epicenter was 10 km (6 mi) southeast of the summit of Kilauea Volcano at a depth of 3.1 km (1.9 mi).