Volcano Watch — Waiting for the pause that refreshes

What do Kīlauea Volcano's eruption and Hilo's 7:30 a.m. traffic have in common? For one thing, lots of stops and starts. The stops and starts in the eruption at Kīlauea are the by now familiar pauses; the stops and starts in busy Hilo traffic might be referred to in more colorful terms.

The latest pause in Kīlauea's ongoing eruption occurred just over a week ago and was brief. The pause started late on Wednesday, August 23, and ended Saturday, August 26. This was the first Y2K pause but the 30th of the current eruptive episode, which began in February 1997. Eruptive pauses can be short, lasting only a few hours, or long, lasting days or even tens of days. For avid local volcano viewers and once-in-a-lifetime visitors, a pause can be a frustrating experience, since lava stops flowing completely, and there is little, if anything, to see that is red and molten. However, for residents and visitors who are acutely aware of air quality, a pause can be a refreshing experience.

Since the current eruption began in 1983, Kīlauea has released a total of around 8 million tons of toxic sulfur dioxide gas (SO₂)—enough to fill 400,000 Goodyear blimps or 350 billion party balloons. This gas, which reacts in the atmosphere to form sulfuric acid and other aerosols, is the principle gas responsible for the formation of volcanic smog (vog). At Kīlauea, the amount of sulfur dioxide gas released is directly proportional to the amount of lava erupted. Therefore, when the lava eruption rate declines, there is generally a decrease in the amount of SO₂ discharged.

During a long pause, the amount of SO₂ released from the eruption site is usually drastically reduced. For example, during a 25-day break in the eruption in early 1997, so little SO₂ was being emitted that it could not be detected downwind of the eruption site using our standard measurement techniques. This abrupt decrease in gas confirmed that, in addition to the absence of lava at the surface, magma had also withdrawn from beneath Pu`u `O`o.

Several months later, SO₂ emissions were still only around half their typical value, reflecting the sluggish start-up of the eruption. During this delightful three-month period of very low SO₂ emissions, Kona residents reported the return of the clear air that was the norm before 1986, when the eruption became continuous. Residents who had moved off-island to escape the hazy Kona air quality inquired whether the improved conditions were likely to continue and it might be time to move back. The respite was brief however, and as the lava production came up to full volume, so did the SO₂ emissions, and thereby the air pollution problem.

During brief pauses, SO₂ emissions may decline somewhat but not stop altogether. During the most recent event, measurements showed that the amount of SO₂ released during the pause was still around two-thirds of what we had measured prior to the pause. Although no active lava was flowing, residual degassing of cooling lava, tubes, the vent areas, and shallow magma beneath Pu`u 'O`o continued. It can take many days for all of the gas to escape from the material remaining in the system, so a brief pause may give little chance for chronic volcanic air pollution, such as that in Kona, to clear.

Close to the emission sources, it may also be difficult to detect that a decrease in SO₂ has occurred. Under steady trade wind conditions, a compact plume of the residual SO₂ from the inactive eruption site can cross the Chain of Craters Road in Hawai`i Volcanoes National Park, 9 km (5.5 miles) from the emission source. This plume is concentrated enough so that a person would still experience the pungent smell, taste and ensuing watery eyes associated with SO₂ exposure. Although the latest pause in Kīlauea's ongoing eruption was brief, an extended "pause that refreshes" may lie in the future.

Volcano Activity Update

The eruption of Kīlauea Volcano continues, following a brief pause last week. Lava flows started up late on the 26th, with breakouts occurring from the lava tube at the 2,300-ft elevation, 1.5 km (0.9 mi) southeast of Pu`u `O`o cone. By mid-week, flows had extended about 2 km (1.2 mi) downslope. It appears that the tube is blocked below the 2,300-ft level, and new tubes will have to form before lava once again reaches the ocean. This can be a slow process, so it may be several weeks or longer before lava is visible on the coastal plain. In the meantime, volcano-watchers may see bright glow at night from the new surface flows above the pali.

There were no felt earthquakes on the island during the past week.