# Volcano Watch — Volcano watching at Mauna Loa is a BIG job

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Since Mauna Loa began showing signs of renewed restlessness in mid-2002, we have put a lot of effort into improving our capability for detecting the types of changes expected to herald the onset of the next eruption.

This has amounted to no small undertaking on a volcano that comprises over 50 percent of the land mass of the island of Hawaii or about 85 percent of the other islands in the state combined.

So how does a group of 20-or-so folks with the already ongoing eruption of Kīlauea cope with the challenge of better monitoring the largest active volcano on the planet? The answer lies largely in improving remote, continuous monitoring. Since 2002, we have tuned up the network of 50-plus seismometers that continuously measure minute ground-shaking, associated with magma movement, along with the computer infrastructure that ingests and performs preliminary calculations on the data. These instruments have thus far recorded several intense episodes of small earthquakes, very deep but directly beneath Mauna Loa's summit.

We have also improved our monitoring of small changes in Mauna Loa's ground surface by expanding the network of continuously recording tiltmeters and Global Positioning Satellite (GPS) receivers. The GPS data show that the summit of the volcano is inflating, indicating that magma is approaching the surface.

Another area we are working on to improve our Mauna Loa monitoring, and one that has helped us much in our studies at Kīlauea, is the study of gas release. As magma moves toward the ground surface from depth, some of the pressure caused by the overlying rock is relieved. When this happens, gas dissolved in the magma bubbles out and escapes at the ground surface through fumarolic vents and fissures. On Hawaiʻian volcanoes, this occurs primarily at the summit and along the rift zones.

To plumb the gas release aspects of Mauna Loa we measure concentration changes of a couple of principal volcanic gases, carbon dioxide and sulfur dioxide (SO2 and CO2), in the nearly invisible plume above the ground. Because of the size of the volcano, with over 200 km of rift zones alone, we have been making helicopter-based measurements by flying up the rifts and through the summit caldera, recording CO2 and SO2 concentrations and our precise GPS position, thereby creating a gas map for the volcano. By measuring every few months, we can observe changes that occur between campaigns.

The gas mapping technique provides good geographic coverage but only for the time when we're making the measurements. Our experience at other volcanoes has shown that because gases are light and mobile, gas release events at Mauna Loa could occur on a timescale too short to be recorded by the helicopter-based measurements alone.

To address this concern, we recently installed instruments within the summit caldera that continuously record sulfur dioxide and carbon dioxide concentrations in an actively degassing area located on a fissure running along the caldera's main axis. These measurements, along with vent temperature, are radioed back to HVO every 10 minutes for near real-time analysis.

This monitoring site, while it only examines gases released at this particular location, improves greatly our understanding of how Mauna Loa degasses as magma moves closer to the surface. We are currently adding another instrument, a spectrometer that will "look" down the axis of the caldera and record sulfur dioxide escaping anywhere in its view. These data, examined concurrently with other geologic and geophysical measures, are expected to further improve our tracking of Mauna Loa's eruptive progress.

It is important to carefully relate the upgraded monitoring at Mauna Loa, and the information produced by it, to our understanding of the volcano's eruptive history. This seemingly obvious statement carries with it a subtle message. The same new technology that is enabling us to better monitor Mauna Loa's progress toward eruption is producing some signals that we haven't seen before. One of our biggest new challenges is interpreting the changes that we're seeing through the lens of eruptive experiences at Mauna Loa and other volcanoes around the world.

### Volcano Activity Update

After deflating for many years, the summit of Kīlauea volcano started to inflate in the fall of 2003. The inflation has accelerated in the last few months. During the current eruption, sustained inflation similar to this has occurred only two other times; each has resulted in shifts in the eruption source area (now at Puu Oo). The current sustained inflation raises the possibility that a significant change in the behavior of the current eruption may be coming.

Eruptive activity at Puu Oo 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 near Puu Oo to the ocean, with only a few surface flows breaking out of the tube. Flows are visible intermittently on the steep slope of Pulama pali. As of October 20, lava is entering the ocean at East Laeapuki, in Hawaii Volcanoes National Park.

Small bench collapses continue to occur at the ocean entry. Large cracks cross both the old and new parts of the bench. 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.

There were two earthquakes reported felt on Hawai`i Island within the past week. A magnitude-2.6 earthquake occurred at 8:55 p.m. on Saturday, October 15, and was located 3 km (2 miles) east of Holualoa at a depth of 9 km (6 miles). Another magnitude-2.6 earthquake occurred at 12:38 p.m. on Tuesday, October 18, and was located 4 km (3 miles) southeast of Kīlauea summit at a depth of 4 km (2 miles).

Mauna Loa is not erupting. During the past week, the count of earthquakes located beneath the volcano remains at low levels. Inflation continues, but has slowed over the last month.