Image credit: Ethan Hein/Flickr
The lightning observed during the eruption of Mt. Redoubt in 2009, researchers have determined, is an entirely new variety. Using radio antennas, scientists noticed that the bolts were shorter, lasting only a few milliseconds, and much more frequent than typical lightning.Love Lightning? Thunderstorms: The Dark and Stormy Drama (Slideshow)
Stephen McNutt, a volcano seismologist at the University of Alaska Fairbanks's Geophysical Institute, became interested in lightning during the 1992 Mt. Spurr eruption. While studying the seismic data from that event, he noticed strange spikes in the records. He explains that:
The seismometers were actually picking up lightning strikes...I knew that I had to reach out to the physicists studying lightning.
He teamed up with Ronald Thomas, a physicist and electrical engineer, and Sonja Behnke, a graduate student in atmospheric science. The group formulated a research plan and started waiting for the next eruption.
The Mount Redoubt Eruption
On January 30, 2009, seismologists observed an increase in activity surrounding the volcano and issued a warning that eruption was imminent. McNutt and his team mobilized but it wasn't until March 22 that Mt. Redoubt finally erupted. Though the impact fell short of history's greatest eruptions, it still managed to send ash as high as 65,000 feet into the air.
Certainly, the event was significant enough to provide McNutt and his team with data.
Measuring Volcanic Lightning
To measure the lightning, researchers deployed four Lightning Mapping Arrays prior to the eruption. Behnke explained that the arrays are "basically an old TV antenna set to pick up channel 3— the same frequency that lightning radiates from." They set the arrays 50 miles away from the volcano, on the other side of Cook Inlet. Thomas explained that they couldn't "put the LMAs on the volcano because the volcano is basically in a wilderness area and the stations need power and internet to function."
Even from 50 miles away the arrays were able to capture an astonishing amount of data. During the eruption, Thomas commented:
We're getting all the data we hoped to get and a lot more...absolutely, the quality and quantity of the data will allow us to better understand the electrical charge structure inside a volcanic plume.
Mt. Redoubt's major eruptions lasted more than a week. After that, though the volcano continues to be active even today, it was time to return to the lab to analyze the data.
Understanding Dry Lightning
Typically, lightning occurs when falling ice or rain polarizes particles in clouds. Positively and negatively charged particles separate and collect in groups of similar charge. A lightning bolt occurs when these charges are equalized.
Dry lightning is caused by the save convective forces created by a thunderstorm, without the need of precipitation and cumulonimbus clouds. Usually, dry lightning is observed during wildfires but it can occur anytime cold air moves over super-heated ground, like that created by a volcano.
Volcanic lightning, then, is a form of dry lightning. But what makes the lightning observed by McNutt and his team unique?
Defining a New Type of Lightning
The research team believes the lightning that occurred during the Mt. Redoubt eruption can be classified as a new type because of the frequency of the bolts and their duration. Thomas commented that "we saw lots of lightning—20 to 30 minutes of lighting...even more lightning than we would typically see during a major thunderstorm."
At the moment the eruption started, there were these sparks of lightning coming from the vent of Redoubt that only lasted 1 to 2 milliseconds.
He then added that "this was a different kind of lighting that we have never seen before."
What this research means for the future of volcanology and meteorology is not yet clear but there is one thing that everyone, scientists and residents alike, agree on: The Mt. Redoubt eruption was "the most spectacular lightning display that they have ever seen."
Love Lightning? Thunderstorms: The Dark and Stormy Drama (Slideshow)
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Could Volcanic Eruptions Slow Climate Change?
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Read more about lightning:
Using the "Flash" from Lightning To Predict Deadly Floods
What to Do If Your Tree is Struck By Lightning
How to Stay Safe During a Thunderstorm
More information from How Stuff Works:
How Volcanoes Work
How Lightning Works