Volcano Watch — Aloha e na makani `olu`olu; we welcome the return of the tradewinds

The spate of kona winds that brought the vog "home for the holidays" in December abated early last week. Undoubtedly, residents of the Hilo and Puna districts and parts of Ka`u on the Big Island had lighter hearts due to the clean air, just in time for Valentine's Day.

Those of us who work at the observatory were relieved, too, partly because we could all breathe a bit easier, since fume from Halemaumau and Pu`u `O`o was no longer blowing into the observatory or our homes. HVO's scientists were also glad to be able to measure sulfur dioxide (SO₂) gas emissions from the vents again. This is a task that is important for monitoring the eruption but is difficult or impossible when trade winds are absent.

We measure these emissions by driving underneath Kīlauea's volcanic plumes with a vertically directed spectrometer strapped to the side of a field vehicle. When trade winds blow, plumes from the summit and rift emission sources are opportunely blown across Crater Rim Drive and Chain of Craters Road, respectively, where they are easily quantified. When sluggish southerly or multi-directional winds take the place of the trades, the summit and rift emissions form a smeared plume that can not be accurately measured, but which often creates a pollution problem for nearby areas.

During December and January, we heard numerous complaints from residents and visitors who reported such symptoms as headache, itchy eyes, and breathing discomfort. During this period, due to the lack of trades, we could not measure the SO₂ emission rate. This measure describes the amount of gas released over time and is often expressed in tonnes of SO₂ emitted per day. However, other types of instruments did record high concentrations of this noxious gas, commonly reported in parts per million (ppm). As an example, the "recipe" for 10 ppm SO₂ is 10 parts of SO₂ mixed with 999,990 parts of air.

To further understand the difference between emission rate and concentration, we can look back to a time when bars in Hawai`i were full of smokers. We can consider the emission rate of the bar to be the amount of smoke produced in the bar over a business day. The concentration is the amount of smoke in the room at a particular time that bar patrons will experience during their visit.

Similarly, high concentrations of irritating SO₂ gas are experienced at, and near, Kīlauea when slow southerly winds blow the stagnant fume into populated areas. This can, and does, affect our respiratory comfort, but the true gauge of production from the volcano is expressed by the emission rate. At the summit of Kīlauea, about 100 tonnes of SO₂ are emitted per day. Much more SO₂ comes from the Pu`u `O`o vent, which has averaged about 1,500 tonnes per day for the past several years. This emission rate increases commensurately with activity of the volcano.

The return of the trade winds last week was welcomed by those who live and work in east Hawai'i. On February 7, the first day we were able to measure SO₂ emission rates again, we found that they had nearly doubled since our last measurements in December. During the next three days, they climbed to over 3,000 tonnes per day, a level we haven't seen since 2002.

This period of high SO₂ emission rate corresponded to an increase in activity at the eruption site. The spatter from several cones within Pu`u `O`o crater increased, and the East Pond Vent produced a small lava flow for the first time in more than 6 months. Activity at vents outside the crater increased, as well. Dome fountains were photographed by a time-lapse camera located on the south flank of Pu`u `O`o, and the vigor of spattering from one of these vents was sufficient to destroy a seismic monitoring station located nearby.

In keeping with the ups and downs of living and working on an active volcano, we regret the loss of the monitoring equipment. However, we celebrate the return of the trade winds as we breathe more easily and measure Kīlauea's gas emission rates.

Volcano Activity Update

Eruptive activity at Pu`u `O`o continues. At least five of the vents inside Pu`u `O`o crater have been spattering frequently since February 1, producing bright glow from the crater on clear nights. On the night of February 10, spattering activity inside the crater escalated, and one vent, on the eastern end of the crater, produced a small fan of Pāhoehoe on the crater floor. The same night, the MLK vent, at the southwest base of the cone, erupted a flow that extended 500 m from the vent. The heightened activity diminished by the morning of February 11.

The PKK flow continues to host substantial breakouts from the 2,300-ft elevation to the coastal plain. Lava is entering the ocean at both West Highcastle and at Ka`ili`ili. The closest activity to the end of Chain of Craters Road, in Hawai`i Volcanoes National Park, is at West Highcastle, 2.6 km (1.6 mi) from the ranger shed. Expect a 1-to-1.5-hour walk each way and remember to bring lots of water. Stay well back from the sea cliff, regardless of whether there is an active ocean entry or not. Heed the National Park warning signs.

During the week ending February 17, four earthquakes were felt on Hawai`i Island. The first earthquake, at 3:28 a.m. on February 10, was a magnitude-3.1 located at a depth of 30 km (19 miles) about 9 km (5 miles) north of Honaunau that was felt in Captain Cook. A pair of earthquakes occurred 68 seconds apart just before 5 p.m. on Valentine's Day, February 14. They had magnitudes of 2.4 and 3.1, and occurred at depths of a little more than 1 km (0.6 miles), and were located between Kīlauea summit and Volcano. A magnitude-3.0 earthquake occurred at 8:05 a.m. on February 17 and was located at a depth of only a few hundred meters (feet) in the same area as the previous pair. These three earthquakes were felt within the National Park housing and Volcano.

These felt Kīlauea earthquakes are part of a swarm beneath Kīlauea summit that started in mid-January. The swarm accompanies accelerated inflation of Kīlauea summit, increasing from 8 cm/yr (3 inches/yr) to over 40 cm/yr (15 inches/yr).

Mauna Loa is not erupting. The summit region continues to inflate. Since July 2004, the rate of inflation and number of deep earthquakes has increased. Mauna Loa caldera is widening at an average rate of 6 cm/yr (2 inches/yr) while the flanks are widening at a faster rate of 20 cm/yr (8 inches/yr). Weekly earthquake counts have varied from 5 to over 150 in the last half of 2004 but have been less than 10 since the beginning of 2005. During the week ending February 16, six earthquakes were recorded beneath the summit area. Nearly all are 30 km (18 mi) or more deep, and most are the long-period type, with magnitudes less than 3.