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Spokane, Washington  Est. May 19, 1883
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Weathercatch: How distant volcanic eruption triggered a shockwave in Inland Northwest

This map from the National Weather Service in Spokane charts the atmospheric shockwave as it zips east from Western Washington across Montana to North Dakota.  (National Weather Service Spokane)
This map from the National Weather Service in Spokane charts the atmospheric shockwave as it zips east from Western Washington across Montana to North Dakota. (National Weather Service Spokane)
By Nic Loyd and Linda Weiford For The Spokesman-Review

The blast from the recent eruption of the underwater Hunga Tonga volcano produced surging ocean waves, which wasn’t a surprise. But the atmospheric waves that shot around the globe in less than 24 hours – including here in the Inland Northwest – that was a surprise.

The powerful shock wave that rippled through the atmosphere after the volcano’s explosive eruption on Jan. 15 in a remote part of the Pacific Ocean “was one of the most extraordinary ever detected,” Corwin Wright, atmospheric physicist at the University of Bath in England told the New York Times.

Barometers at numerous weather stations, including here in Spokane, recorded a rapid fluctuation in air pressure as the massive shock wave radiated outward across the world, traveling nearly as fast as the speed of sound. During a shock wave, air pressure jumps as air molecules are quickly compressed and then sharply drops before returning to normal.

On Jan. 16, the National Weather Service in Spokane wrote this in a Facebook post: “Although we didn’t get any tsunami activity in the Inland Northwest we did see an interesting atmospheric phenomena triggered by yesterday’s (Jan. 15) strong volcanic blast from the Tongan volcano.” The agency also displayed a fascinating map that we’ve included with this column. As you can see, it charts the shock wave’s arrival to the town of Hoquiam located on Washington’s coast and its movement through the Inland Northwest and on to Fargo, North Dakota.

When the atmospheric wave arrived in the Inland Northwest about 4 a.m. on Jan. 15, within seconds of each other, barometers at airports in Spokane, Lewiston, Pullman-Moscow and Coeur d’Alene recorded air pressure fluctuations. As the wave traveled east, it took 23 minutes to reach Helena, which is 265 miles from Spokane as the crow flies and an hour to reach Fargo, another 614 miles away.

How did a shock wave produced by the eruption of an isolated undersea volcano travel so far and wide?

First and foremost, it was an extremely explosive eruption that created a thick plume of ash, steam and gas that shot upward to roughly 100,000 feet or 19 miles – three times the altitude at which commercial jets fly. Such a powerful force entering three different layers of the atmosphere was able to move a vast amount of air at once. This created an atmospheric wave, similar to a liquid wave that ripples outward after a stone is thrown into a pond. Meteorologists and weather enthusiasts alike watched with intrigue as pressure readings from their professional and home weather stations jumped up and down between 1-2 millibars.

The eruption also triggered seven hours of lightning strikes caused by static discharge occurring inside the towering plume.

At least three people were killed in the Pacific island nation of Tonga and dozens more were left homeless. Even so, it’s a wonder that the devastation wasn’t more widespread. Now that the ash has been cleared from the main airport’s runway, governments from various countries are sending flights to deliver water, food and other supplies.

Back in the Spokane area, after this week’s back-to-back days of mostly dry conditions with areas of fog and low-hanging clouds, barometric pressure variability is the result of normal weather conditions, not a shock wave caused by a volcanic eruption. A pattern change looks likely for the start of February, when we could see a little rain, snow and cooler temperatures.

Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek. Contact: ldweiford@gmail.com

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