January 26, 2006

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

Revolution in thinking about Kilauea's explosions comes to HVO: Part 2

Map showing areas covered by fallout from 4 explosions at Kilauea. This map is a work in progress, and the question marks indicate areas where more observations are needed.

The past five years, especially the past 18 months, have seen profound changes in the way HVO scientists view Last week's Volcano Watch highlighted the recent discovery that Kilauea is capable of exploding debris into the westerly jet stream, which then transports the fallout into areas where people live.

What drives such powerful explosions? Around 1,000-1,200 years ago, the largest explosion brought up rocks several kilometers (miles) from the volcano's depths. This explosion was likely caused by rapid expansion of carbon dioxide bubbles within Kilauea's deep plumbing system. Were the Keanakako`i explosions also driven by CO₂? What is the interplay between gas from the magma and steam from groundwater? These and other questions will take time to answer.

Will HVO know that a major explosion is coming? The jury is out on this important question. Until we have sound ideas of what causes such explosions, we won't really know what to look for. Most likely, everything will be theoretical until a big one takes place and monitoring data analyzed after the fact.

Small explosions, more numerous than the larger ones, may be driven by groundwater. They may happen when the floor of Halema`uma`u or of the caldera drops down to about the level of the water table, more than 500 m (1,600 feet) deep. Such a drop would serve as a warning that explosions, dangerous to people in the summit but less so in outlying areas, could occur.

Kilauea erupts explosively about as often as does Mount St. Helens, though explosions produce less tephra than do those from St. Helens. But you don't need much ash to foul water catchments and make life miserable for those living in fallout areas.

Volcanic ash taken in by jet engines may cause engine failure or deterioration in performance, and it may severely abrade windows and any forward-facing surfaces. As of 2000, seven encounters of commercial aircraft with ash caused in-flight loss of engine power that led to near-crashes. Once thought to be a problem only around the Pacific margin, the new findings for Kilauea indicate an aircraft-safety issue here in Hawai`i during powerful explosions.

These findings were partly responsible for elevating Kilauea to the top of the list, prepared by the USGS in 2005, of the most threatening volcanoes in the nation (http://www.usgs.gov/newsroom/article.asp?ID=699).

The discoveries of the explosive potential of Kilauea came from tough, boots-on-the-ground geologic field work. Faced with the power that new technology brings, field work is going out of style in some circles these days; but without it, we would still be in the dark about Kilauea's explosive past. Every volcano has secrets to tell that can be discovered only by hands-on study of the earth.

Activity update

During the past week, Kilauea Volcano has shown a bit more activity at the summit. The number of earthquakes located beneath Kilauea increased to moderate levels. Inflation of the summit caldera accelerated starting January 12, shallow earthquake activity increased beneath Puhimau crater starting January 14, followed by a flurry of shallow earthquakes centered about 2.5 km west of Namakani Paio campground west of the Kilauea summit caldera starting on January 22.

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 scattered surface flows breaking out of the tube. In the past week, the largest flows were active intermittently above the pali from the 1,900-ft to 1,725-ft elevation and just above the coastal plain near the 200-ft elevation. Surface flows on the pali are visible at night (weather permitting) from the end of Chain of Craters Road.

As of January 25, lava is entering the ocean at East Lae`apuki, in Hawai`i Volcanoes National Park. The active lava bench continues to regrow following the major collapse of November 28. 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 seven earthquakes beneath Hawai`i Island reported felt within the past week. A magnitude-2.7 earthquake occurred at 5:06 a.m. on Friday, January 20, and was located 6 km (4 miles) northwest of Pahala at a depth of 8 km (5 miles); it was felt in Pahala. The other six felt earthquakes were part of the Namakani Paio earthquake flurry described above. The largest was a magnitude-3.4 earthquake that occurred at 3:21 a.m. on Monday, January 23, at a depth of 3 km (2 miles). Many of these earthquakes were felt around the Kilauea summit area.

Mauna Loa is not erupting. During the past week, the count of earthquakes located beneath the volcano remains at low levels. Inflation continues, but at a slower rate since early October 2005.

Visit our web site (hvo.wr.usgs.gov) for daily volcano updates and nearly real-time Hawai`i earthquake information.