# Volcano Watch - Volcanic gas measurements on Mauna Loa are an expanded challenge

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Several recent Volcano Watch articles have discussed the difficult nature of making specific eruption predictions about Mauna Loa, the largest volcano on Earth. One way to decrease the difficulty is to monitor many different behaviors of the volcano. In addition to monitoring seismic and ground deformation changes, we also measure the gases coming out of Mauna Loa.

Mauna Loa's summit caldera, Mokuaweoweo, is capable of easily holding all of Waikiki. In addition, the part of Mauna Loa above sea level stretches over 75 miles (120 km), from Hawaiʻian Ocean View Estates on the southern end of the island, to Hilo town on the east side.

All eruptions since 1843 have started in the summit caldera, with activity migrating to either of the rift zones, and some eruptions producing flows that quickly reach the sea. Over a dozen eruptive vents below the rift zones on Mauna Loa's flanks, including several submarine vents, show that activity can occur over an even wider area.

With Mauna Loa's footprint of 2,035 square miles (5,271 km) comprising over 50 percent of the Big Island, monitoring this volcano is a huge task. After all, "Mauna Loa" is a Hawaiʻian place name that literally means "Long Mountain"-a clear understatement.

One way we monitor changes in eruptive activity at Mauna Loa's younger sibling, Kīlauea, is by studying the release of gases trapped in the magma. At Kīlauea, gases escape primarily from the summit caldera and from Puu Oo vent on the east rift zone.

A network of National Park roads makes monitoring gas release fairly straightforward for Kīlauea. Using instruments mounted in our field vehicle, we measure the quantity of gas blowing across Crater Rim Drive at the top of the volcano, and across Chain of Craters Road, lower down on the east rift zone. Within 20 minutes of leaving the observatory, we can also sample volcanic gas vents located at the rim of Halemaumau pit crater, Pele's home. Kīlauea is a volcanic gas enthusiast's delight.

In contrast, Mauna Loa's summit caldera and rift zone degassing sites are remote and widely spaced. Consequently, studying these emissions is much more challenging. We recently completed a field campaign for the long mountain by loading our gas-measuring equipment into a helicopter and flying these instruments along Mauna Loa's degassing locations. With the GPS recording our three-dimensional position each second of the flight, we collected data for carbon dioxide and sulfur dioxide gases escaping from vents along the southwest and northeast rift zones, as well as from the summit caldera fissures and cones.

The data collected during these field measurements show that gases escaping from vents in Mokuaweoweo and along the northeast rift are dominated by carbon dioxide, with little or no sulfur gas. Emissions from the upper southwest rift zone around the 3350 meter (11,000 foot) elevation are conversely mostly sulfur dioxide, with a small amount of carbon dioxide detected recently, as well. These results are subtly different from those of an earlier campaign carried out at the end of August, but taken by themselves, do not indicate a huge change in the volcano's activity.

In addition to these campaign-style studies, additional continuous monitoring equipment for carbon dioxide, sulfur dioxide, and vent temperature will be installed in the next several months. These instruments, to be located in the summit caldera, will transmit data back to HVO by radio every 10 minutes. Since all eruptions of Mauna Loa since 1843 have begun at the summit, instruments within Mokuaweoweo are expected to detect early changes in the shallow magma-gas system. Colleagues at the Mauna Loa Climate and Diagnostics Laboratory, operated by the National Oceanic and Atmospheric Administration (NOAA), are also monitoring gases escaping from caldera vents by looking at emissions carried past their instruments in the night-time downslope winds.

Mauna Loa continues to present all the challenges expected of a huge volcano whose summit rises over 17 km (56,000 feet) above a buried seafloor depressed by its weight. By incorporating gas geochemistry measures with real-time monitoring of seismic and ground surface changes, we hope to produce the best ongoing assessment of activity beneath the long mountain.

### Volcano Activity Update

Eruptive activity at Puu Oo continues. Spatter cones in the crater of Puu Oo glow brightly on clear nights but have not produced any lava flows for several months. The MLK vent area, at the southwest base of the cone, intermittently erupts small Pāhoehoe flows that stack up close to the vent.

The PKK flow continues to host scattered breakouts from above the top of Pulama pali to the coastal plain. Lava is not entering the ocean. As of December 29, breakouts were active on the coastal plain, about 600 m (660 yd) inland of the shore at Laeapuki. The area of breakouts is about 3.2 km (2 mi) from the end of the pavement on Chain of Craters Road in Hawaii Volcanoes National Park. Expect a two-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 December 28, four earthquakes were felt on our Big Island. The first three (reported last week) occurred at 7:07, 7:29, and 8:27 a.m. on December 22, about 5 km (3 miles) south of Kīlauea summit, at a depth of 2.9 to 4.2 km (1.8 to 2.6 miles). They were felt primarily in the Volcano area. The initial shock had a magnitude of 4.0, and the two later shocks had magnitudes of 2.1 and 2.4.

A magnitude 3.3 quake was felt at the Hawaiʻian Volcano Observatory at 8:05 p.m. on December 25 by one of our loyal seismologists. It was located 19 km (12 miles) south of Hilo at a depth of 25 km (15 miles).

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. Weekly earthquake counts have varied from 5 to over 150. During the week ending December 28, 128 earthquakes were recorded beneath the summit area. This is a slight decrease from the past week. Nearly all are 30 km (18 mi) or more deep and are the long-period type, with magnitudes less than 3.