Volcano Watch — "COSPEC" helps observatory scientists study volcanic pollution and processes

Discussions of volcanic air pollution from Kīlauea frequently start out with a conversation about the large amount of sulfur dioxide gas (SO₂) that bubbles out of the volcano and is converted in air to the tiny acidic sulfate particles that form vog (volcanic smog). Dissolved gases like SO₂ are a crucial driving force for eruptive activity too, so that understanding their role in Hawaiian volcanism attendantly important. 

How is it that scientists from the U.S. Geological Survey's Hawaiian Volcano Observatory are able to measure the amount of this gas with the choking odor that accounts for less than 2 kilograms (4.4 lbs.) per metric tonne (2,200 lbs.) of magma? Fortunately we don't have to saw up rocks and analyze the gas in them. Usually we don't even have to get close enough to get smelly-we use a remote technique that involves "looking" at the gas coming from the volcano.

The sulfur dioxide correlation spectrometer, or COSPEC, is an instrument developed in Canada during the 1960s to measure pollution from power plant smokestacks. About the size of a small suitcase, the machine itself is a simple-minded but cleverly designed electronic eye that can only "see" sulfur dioxide, a gas having a unique color spectrum that is invisible to the human eye. The more SO₂ present, the stronger the color intensity seen by the COSPEC. The instrument can both discern SO₂ from other gases and quantify how much SO₂ is present, as well.

At the summit of Kīlauea, we mount the COSPEC in the passenger seat of one of our vehicles with the instrument directed vertically skyward. We then start our measurements by driving at a constant speed around Kīlauea caldera on Crater Rim Drive. Meanwhile the northeasterly tradewinds blow the relatively constant stream of gases released from Halema`uma`u straight across the road. As we drive beneath the gas plume, our upward-looking instrument dutifully records the burden (total amount) of SO₂ in the air directly above us.

We cross underneath the plume a number of times to get an average burden of SO₂. The process is a bit like wading back and forth across a stream, measuring how deep the water is each time. One way to determine how much water is flowing through a stream, is to find out how deep the water is, how wide the stream is, and how fast it's flowing. Similarly, we can figure out how much SO₂ is flowing out of Halema`uma`u if we measure how "deep" the SO₂ is (the burden) and how fast the SO₂ stream is flowing (the wind speed), so we continuously monitor windspeed at the observatory. We make a similar set of measurements down the Chain of Craters road to measure the SO₂ released from the east rift zone, including Pu`u `O`o. Combining the summit and east rift SO₂ numbers results in an estimate of the total amount of SO₂ flowing out of the volcano. The results are remarkable.

On an average day of eruption, the summit caldera of Kīlauea releases between 90 and 150 metric tonnes of SO₂. The combined emissions from the summit and east rift zone typically average around 2,000 tonnes per day. Since the fall of 1997, the values have sometimes exceeded 4,000 tonnes. For comparison, no single power plant in the U.S. emits more than 700 tonnes of SO₂ per day.

Since COSPEC SO₂ measurements at Kīlauea began in the 1970's, they have helped us monitor the eruption and improve our understanding of volcanic processes. Thomas Jaggar, founder of HVO, said it well: "The observatory worker who has lived a quarter of a century with Hawaiian lavas frothing in action cannot fail to realize that gas chemistry is the heart of the volcano magma problem."

Volcano Activity Update

The east rift zone eruption of Kīlauea Volcano from the Pu`u `O`o vent continued during the past week. Seismic recordings indicate that activity at the vent is sporadic with "gas-pistoning" occurring. Lava is primarily confined to a network of tubes from the vent to the coast, but surface flows were also observed upslope of the ocean entry areas at Waha`ula and Kamokuna. The public is again reminded that these two areas are extremely dangerous. The National Park Service has restricted access to them because of frequent explosions that accompany collapses of the growing lava bench.

There were two earthquakes reported felt in the past week. A resident of Mauna Loa Estates subdivision reported feeling an earthquake early in the morning of June 21. The 2:21 a.m. earthquake had a magnitude of 4.2 and was located 27 km (16.2 mi) south of Kīlauea summit at a depth of 41.8 km (25.1 mi). An earthquake at 3:08 a.m. on Thursday, June 25 awakened a resident of Wood Valley. The magnitude 3.3 earthquake was located 5 km (3 mi) northwest of Pahala at a depth of 8.7 km (5.2 mi).