The roiling, sulfurous ash blasting from Mount Augustine during last winter’s eruptions triggered “spectacular lightning,” offering Alaska volcanologists the most detailed glimpse ever of one of the Earth’s most elusive electrical phenomena.
And watching for such a “dirty thunderstorm” over Alaska’s volcanoes may be one more trick to monitor eruptions and keep the lid on hazards that threaten aircraft and communities, according to University of Alaska Fairbanks researchers Steve McNutt, Guy Tytgat and Edward Clark.
An article describing the findings, “Electrical activity during the 2006 Mt. Augustine volcanic eruptions,” appeared Feb. 23 in the prestigious journal of Science.
Although the immense build-up of static electricity during volcanic eruptions has long been known to produce lightning inside ash clouds, scientists have rarely measured the discharges.
“Volcanic lightning continues to be poorly understood, because there are few direct scientific observations of the phenomena,” wrote Ron Thomas of Langmuir Laboratory in New Mexico, McNutt and seven co-authors.
But after volcanologists at the Alaska Volcano Observatory saw lightning during eruptions on Jan. 11 and 13 of 2006, two electromagnetic lightning detectors were installed in Homer about 60 miles across lower Cook Inlet from the volcano.
Augustine, a stunning 4,134-foot storybook cone in lower Cook Inlet, is one of the most active volcanoes in the world. It has erupted at least 16 times in the past 200 years, including events in 1986, 1988, 1998 and 2006. An avalanche in the late 1800s may have triggered a tsunami in Kachemak Bay.
Within a two days of the installation, Augustine exploded again with four big eruptions overnight between Jan. 27 to Jan. 28.
“Although not observed visually because of stormy weather, the data showed that the first and largest of the eruptions produced a spectacular lightning sequence,” the scientists wrote.
The lightning monitors detected an extraordinary event: continuous radiation and bursts of lightning within the rock and ash as it rushed upward from the vent.
New, small dome on Augustine on 1/16/06.
Yellow/orange in steam is caused by volcanic gases.
Game McGimsey / AVO-USGS
About three minutes after the main explosion, another 300 lightning discharges zapped from the ash plume drifting south from the summit of the volcano. One of the last strikes lasted 650 milliseconds and extended more than 13 miles.
“The discharges undoubtedly occurred within the volcano’s plume,” the scientists wrote.
After analyzing the data, the scientists concluded that the lightning occurred in two phases. In a process that had never been documented before, the first series of zapping bolts occurred because the ash and rock and other debris emerged from the volcano’s throat already loaded with a high positive electrical charge.
The second phase continued inside the plume that drifted downwind — a swirling cloud of grit, ash, water vapor and fumes. It appeared to be producing its own lightning as it went.
“Volcanoes are known to release copious amounts of water,” the scientists wrote, “and may behave as ‘dirty’ thunderstorms.”
Eastern flank of Augustine Volcano on 11/4/06.
A steam plume extends north from the summit.
Jennifer Adleman / AVO-USGS
Scientists and meteorologists already use lightning detectors to pinpoint thunderstorms and “strikes” that might cause forest fires across Alaska in the spring and summer. But these results suggest that detectors might also offer another way to monitor ash eruptions of volcanoes, according to McNutt, a UAF research professor of geophysics at UAF and staff seismologist at the observatory.
As a result of this research, AVO staffers hope to install a simple lightning detector on Mount Cleveland this summer, a 5,676-foot cone on an Aleutian Island about 940 miles southwest of Anchorage. It’s been restless for months.
Working with the UAF scientists was a research team who designed and built the instruments with technical support from Tytgat and Clark. From the Langmuir Laboratory at New Mexico Tech were lead author Ron Thomas joined by P.R. Krehbiel, W. Rison, H.E. Edens, G.D. Aulich and W.P. Winn.