A volatile view of CO2 from atop Kīlauea's magma chamber

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On cool, still mornings at the top of Kīlauea, visitors looking across the summit caldera can see a palpable example of the Earth breathing. Wisps of steamy water vapor drift above thousands of cracks and fissures present in and around Halema`uma`u and elsewhere on the caldera floor.

A volatile view of CO2 from atop Kīlauea's magma chamber...

Summit caldera panorama taken at sunrise during winter's solstice.
December 21, 2005.

(Public domain.)

This dreamy spectacle belies what is happening just a few miles away, at Pu`u`O`o vent, where a half a million cubic meters (yards) of lava are coursing through lava tubes, and over a thousand tons of noxious sulfur dioxide gas (SO2) is released each day that Kīlauea's eruption continues. People living in Hawai`i are familiar with the volatile nuisance posed by the smoggy mixture of SO2 and small acidic particles, locally called vog.

Also present atop the summit magma chamber, but undetected by our casual observer standing at the edge of Kīlauea's caldera, is another gaseous exhalation we are lately becoming more mindful of: carbon dioxide (CO2). Magma rising from the depths of Kīlauea, where confining pressures are great (many thousands of pounds per square inch) releases trapped carbon dioxide as the molten rock approaches the surface and the pressure drops. On a daily basis, Kīlauea usually emits about the same amount of carbon dioxide as a medium-sized coal-fired power plant on the mainland.

But instead of exhausting gases from a several-hundred-foot tall smokestack like a power plant, Kīlauea vents its CO2 through the vents, fissures, and fumaroles on the caldera floor, forming the pastoral scene we described earlier. Scientists from HVO quantify the total amount of carbon dioxide emitted by Kīlauea by using sensitive instruments to measure the excess CO2 in the volcanic gas plume crossing Crater Rim Drive downwind of these vents.

For several years, Kīlauea's CO2 emissions were steady at about 8,500 tons per day, but beginning in 2004, the measured emission rate doubled, then nearly tripled in 2005. In fact, CO2 emissions are currently continuing to be very high.

The effects of the increased CO2 emissions go virtually undetected by those of us present at the ground surface. Carbon dioxide is clear, colorless, and nearly odorless, unlike the milky sight and acrid smell of vog. And while high concentrations of CO2 can be harmful to humans, there is an abundant amount of clean, oxygen-rich air above ground level, especially when Hawai`i's brisk trade winds blow.

The story below ground level can be quite different, though. In the first half of 2005, CO2 concentrations present in an underground seismic instrument vault near Halema`uma`u exceeded levels safe for humans nearly half the days, owing to the tripling of carbon dioxide emissions. In comparison, in 2003, a year that had lower emission rates, only a handful of such "bad air" days occurred.

Continuous gas monitoring in this space has shown that carbon dioxide gas-release events often occur on a short time scale. One day recently, air quality within and just outside the vault was acceptable at 8:30 a.m., but by 2:00 p.m., the CO2 concentration had increased tenfold, exceeding healthy levels. By 4:30 P.M., conditions had returned to background values.

A recent survey of a lava tube "cave" located within Kīlauea's summit caldera showed that CO2 concentrations can vary widely in space as well as in time. These tubes have numerous cracks on their floors that act as infiltration points for gases escaping from Kīlauea's summit magma chamber just a few thousand meters below. During the survey, the concentration of CO2 measured in gases coming through some of these cracks exceeded safe levels, even though overall CO2 concentration within this particular tube were acceptable. With the unsteady mixing of tube air with above-ground air, hazardous levels of CO2 can build, especially when brisk trade winds are absent.

In addition, the odorless nature of CO2 and its tendency to pool in low-lying places make it an insidious hazard for people wishing to enter summit lava tubes, and the National Park Service has wisely closed them to casual entry. The park also now requires that those applying for a permit to enter lava tubes take extra precautions, including wearing personal CO2 monitors.

So for now, it is best to enjoy the serene beauty of Kīlauea's summit caldera from an above-ground perspective and be mindful of hazards that lie beneath the surface.

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Volcano Activity Update

Activity at the summit of Kīlauea Volcano has remained at a moderate level. Frequent earthquakes continue beneath the upper east rift zone of Kīlauea, between Lua Manu and Pauahi Craters. Inflation of the summit caldera continues at the accelerated rate started on January 12.

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater and on the southwest side of the cone. Lava continues to flow through the PKK lava tube from its source on the flank of Pu`u `O`o to the ocean, with occasional surface flows breaking out of the tube. In the past week, surface flows were intermittently active at the 2,300-ft elevation and on the coastal plain, 6 km (3.7 mi) from the end of Chain of Craters Road.

As of February 23, lava is entering the ocean at East Lae`apuki, in Hawai`i Volcanoes National Park. The active lava bench continues to grow following the major collapse of November 28 and is now approximately 800 m (2,600 feet) long by 200 m (660 feet) wide. Access to the ocean entry and the surrounding area remains closed, due to significant hazards. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

Eight earthquakes beneath Hawai`i Island were reported felt within the past week. On February 16, five quakes were reported: a magnitude-2.8 at 5:42 a.m., located 5 km (3 miles) south of Volcano at a depth of 2 km (1 mile); magnitude-2.7 at 6:22 a.m., also located 5 km (3 miles) south of Volcano at a depth of 4 km (2 miles); magnitude-2.9 at 6:23 a.m., located 4 km (3 miles) south of Volcano at a depth of 4 km (2 miles); magnitude-3.8 at 11:35 a.m., located 17 km (11 miles) northwest of Kailua at a depth of 45 km (28 miles); and magnitude-4.6 at 3:22 p.m., located 10 km (6 miles) northwest of Ka`ena Point at a depth of 10 km (6 miles). On February 17, two earthquakes were felt: a magnitude 2.9 at 1:32 a.m., located 3 km (2 miles) south of Kīlauea's summit at a depth of 3 km (2 miles); and magnitude 2.8 at 12:06 p.m., located 10 km (6 miles) south-southwest of Honoka`a at a depth of 24 km (15 miles). Lastly, on February 21, a magnitude 2.5 quake was felt at 2:59 a.m., located 5 km (3 miles) west of Waimea at a depth of 11 km (7 miles).

Mauna Loa is not erupting. During the past week, earthquake activity remained low beneath the volcano's summit. Inflation continues, but at a rate that has slowed since early October 2005.