Volcano Watch — Volcanoes are a part of the "breathing" of the Earth

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One evening a couple of weeks ago, the summit of Kilauea began to deform at an impressive rate. Although the ground tilt and associated tremor caused by magma moving beneath the caldera was not humanly perceptible, sensitive instruments let us know that something unusual was up.

A couple of hours later, those of us here at HVO who study volcanic gases were found carefully picking our way back to the trailhead from our favorite Halemaumau sampling sites through the dark and murk of a near white-out. Our goal for the rest of the evening was to analyze the gas samples we collected, looking for, among other things, a possible change in the amount of carbon dioxide emitted from Kilauea by comparing these results with those of the previous day.

Carbon dioxide, CO2, is the gas we exhale and the gas that bubbles out of soda, beer, and even champagne when it's uncorked. It's also at the heart of the global warming debate.

Although nearly tasteless and odorless at low concentration, atmospheric CO2 monitoring was long ago recognized as a purposeful way to watch the Earth "breathe." In the late 1950s, researchers began doing just that. They chose Hawai`i to site the instrumentation, because the island's remote location was devoid of large local forms of pollution that might bias the data.

Forty-three years later, Mauna Loa Observatory, part of the Department of Commerce, hosts the longest continuous atmospheric CO2 database on the planet. Great care has been taken to ensure that the data are globally representative.

No matter where you stand on the global warming issue, one particular conclusion from these data is irresistible: Carbon dioxide levels in the atmosphere have increased over 15 percent since 1958. This "modern" database can be combined with studies of CO2 trapped in polar ice cores, where CO2 concentrations are literally frozen in time. Together, the data suggest that although concentrations ranged widely during 400,000 years of ice core record, the recent high levels of atmospheric CO2 are unprecedented.

The ice core data show that CO2 has been part of the atmosphere for at least the last 400,000 years, and studies in Hawai'i and elsewhere indicate that volcanoes played a profound role in the formation of Earth's atmosphere during the previous 4-plus billion years. Visualize Kilauea's magma chamber as a leaky balloon being filled from below. The material entering the balloon is a bubbly mixture of magma and gas coming up a narrow pipe-shaped conduit from the earth's mantle.

The pressure at the depth of the mantle is enormous, more than 28 million kilograms per square meter (40,000 pounds per square inch), owing to the weight of solid and liquid rock resting upon it. It's like being at the bottom of a swimming pool, only the pool is 10,000 meters (33,000 feet) instead of 4 meters (13 feet) deep, and it's filled with dense liquid rock instead of merely water. As magma ascends from the mantle and enters the chamber "balloon," pressure becomes lower because the chamber is centered a scant 4 km (2.5 miles) beneath the summit of the volcano. This lower pressure allows some of the gas, notably CO2, to bubble out in the same way uncorking a champagne bottle does.

Much of the buoyant CO2 floats to the top of the chamber and leaks out through the roof, escaping to the atmosphere through surface vents and fumaroles-more than 8,000 tonnes each day. The magma, however, almost continuously leaks out through the side and is currently being erupted at Pu`u `O`o. Sudden changes of magma supply or eruption rate, or of plumbing, such as those detected two weeks ago, accompany pressure changes within the chamber.

On a good day, those of us who study gases record these events as more or less spectacular changes in gas emissions. Although our sampling results from two weeks ago were of the less spectacular variety, these and other studies have taught us much about how volcanoes work. They have enhanced our understanding of how emissions from a very active volcano contribute to the breathing of the earth.

Volcano Activity Update

Eruptive activity of Kilauea Volcano continued unabated and effusively at the Pu`u `O`o vent during the past week. Lava extruded sporadically from several vents in the crater of Pu`u `O`o as well as from the Episode 55 pit and Puka Nui, two small craters at the southwest base of the cone. Bright glow persists over the "rootless" shield area, where short flows emanate from overflows of the perched ponds and from leaks at the base of the shields. No surface flows were observed on Pulama pali or on the fan at the base of the pali. There are no ocean entries.

One earthquake was reported felt during the week ending on April 18. A resident of Leilani Estates subdivision felt a magnitude-2.7 shock at 10:32 a.m. on April 16. The earthquake was located about 3 km (1.8 miles) northeast of Pu`ulena Crater at a very shallow depth.