Volcano Watch — Volcano unrest spurs increased monitoring in Alaska and HAWII

Mount Spurr, an ice- and snow-covered volcano about 125 km (80 miles) west of Anchorage, has grown restless in recent months. AVO scientists first noticed the unrest in early July, when hundreds of small earthquakes occurred deep beneath Mount Spurr's summit.

Since the current unrest began, aerial reconnaissance revealed a circular melt pit in the summit ice cap, suggesting the presence of volcanic heat. Moreover, sensitive gas monitoring instruments detected a volcanic gas plume consisting of carbon dioxide and hydrogen sulfide. The increased seismicity, heat, and volcanic gas emissions most likely indicate that new magma has risen into Mount Spurr.

Not all magmatic intrusions lead to eruptions, however. At this point, it is impossible to determine whether the current intrusion into Mount Spurr will culminate in an eruption, just as we cannot be certain that the current swelling and deep seismicity at Mauna Loa will lead to an eruption in the near future.

If the activity at these volcanoes is leading to eruptions, we expect to observe distinct increases in the number and size of earthquakes, especially in the number of shallow earthquakes. During the past month, we have detected numerous earthquakes beneath Mauna Loa, but they are extremely deep - about 50 km (30 miles) beneath the summit.

Other changes we can expect as an eruption becomes imminent are increases in the volume of volcanic gas emissions and in the rates of ground deformation. When magma rises into a volcano, it causes the earth's crust to swell. This swelling is usually very small, only in the most extreme cases visible by eye. However, Global Positioning System (GPS) receivers and electronic tiltmeters can track the ground deformation caused by the migration of magma.

Since the beginning of the current reinflation of Mauna Loa in 2002, we have added nine continuously recording GPS stations and two electronic tiltmeters to our monitoring network. We've also upgraded the seismic network on the volcano and performed baseline measurements of gas emissions.

At Mount Spurr, AVO scientists will race the onset of winter to add instrumentation over the next several weeks to increase their monitoring capabilities. Five new seismometers will be added, which will improve earthquake locations and provide better records of volcanic tremor. Three or four new continuous GPS receivers will be installed on the volcano's flanks. Gas emissions will also be monitored on a regular schedule of overflights as long as the current unrest continues (and Alaskan daylight permits).

While the major hazard posed by Mauna Loa volcano is lava flow inundation, the most significant hazard from Mount Spurr is volcanic ash.

The only two historical eruptions of Mount Spurr, in 1953 and 1992, were from Crater Peak vent on the south flank of the volcano. These eruptions were relatively small, but violent. In 1992, volcanic ash blanketed south-central Alaska and forced the closure of Anchorage International Airport for 20 hours. The effects were felt well beyond Alaska as the ash cloud drifted across the continental U.S. and Canada, shutting down airports in the northeast and midwest two days after the eruption.

Indeed, the hazards of volcanic ash to aviation are a major concern at AVO. The north Pacific air routes connecting Alaska to the far east carry more than 10,000 people per day over one of the most active volcanic areas in the world. Alaska has over 100 volcanoes and over 40 of these have been active in historic time!

A new fact sheet about Alaskan volcanoes and AVO's terrific work of mitigating the hazards associated with them is available online at http://pubs.usgs.gov/fs/2004/3084. More information about the current status of Mount Spurr can also be found at AVO's web.

We don't envy our AVO colleagues the daunting task of monitoring this vast region, nor the weather they have to endure to do it!

Volcano Activity Update

Eruptive activity at Pu`u `O`o continues. In the past week no flows were active on the coastal plain. Surface-flow activity is concentrated on the upper reaches of the PKK (Kuhio) flow, above Pulama pali. Broad fans of pahoehoe have spread from the lava tube in this area. Lava in the Banana flow, which breaks out of the Mother's Day lava tube a short distance above Pulama pali, fed an `a`a flow on Pulama pali earlier this week. Lava has not entered the ocean since August 5.

No earthquakes were reported felt on the island for the week ending August 18.

Mauna Loa is not erupting. The summit region continues to inflate slowly. Seismic activity was notably high for the fourth week in a row, with 80 earthquakes recorded in the summit area. Most of the earthquakes are the long-period type and located deep, about 40 km (23 miles) or more.