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What caused the mysterious haze over Alaska’s Bristol Bay?

Ben Anderson
NASA photo

Many Alaskans may have looked to the heavens on Election Day, perhaps hoping for a sign of whom to vote for or an explanation of why their preferred candidate lost. But what they probably didn't see is a haze of dust that hovered, high in the upper atmosphere, over Alaska’s Bristol Bay region and the Gulf of Alaska for two days last week.

And while satellite imagery from NASA captured the dusty cloud apparently migrating in an easterly direction, what’s less clear is where the haze came from -- and what, exactly, it was.

According to a report from NASA’s Goddard Space Flight Center, the mystery cloud appeared on Nov. 6 over the Alaska Peninsula and the waters of Bristol Bay, then was noted again by satellite the next day, this time over the Gulf of Alaska and the Prince William Sound region.

The dusty cloud was observed by the Earth-observing Aqua satellite operated by NASA.

Because it was perched so high in the atmosphere, the dust didn’t raise air-quality concerns for the regions. According to Brian Hagenbuch, who works with the aviation weather division of the Alaska National Weather Service, it didn’t merit any aviation alerts, either.

The explanation for the dust is tricky: There are numerous possible explanations, and some of these are explored by NASA in trying to nail down the dust’s origin.

One prospect is glacial or river sediment, originating when glacial melt slows as Alaska cools in the fall. As the runoff from glaciers slows, so too do the levels of riverbanks. That exposes fine sediment -- known as “glacial flour” -- from glacial erosion. Wind can then pick up glacial flour and easily carry it into the air. An example of this can be seen in the concentration of wind in the picture taken over the Gulf of Alaska, blowing out from the Copper River delta.

But NASA says the Bristol Bay debris is more difficult to explain. NASA earth scientist Santiago Gassó speculated that the cloud over southwest Alaka may have a more-distant source than locally-grown glacial sediment.

“It might be pollution and dust from China,” he said in the NASA roundup of the observation. Another NASA satellite photo shows the extensive pollution that hangs over China this time of year.

Other possible explanations? Smoke from a tundra fire, unusual this time of year, that began near Dillingham in early November and was still burning at the time the photo was taken.

One possibility that Hagenbuch, with the National Weather Service in Alaska, ruled out for certain was ash from volcanic activity. Only about a week prior, the agency issued a  “Significant Meteorological Event” warning to pilots when ash from the 100-year-old Novarupta volcano -- the biggest eruption of the 20th century -- was lifted into the air and drifted over to Kodiak Island in the Gulf of Alaska.

“(The Nov. 6 dust cloud) was completely unrelated to that other warning about ash,” Hagenbuch said. “There was no reason to suspect it had anything to do with volcanic activity or anything like that.”

For his part, Hagenbuch had a couple of other possible explanations for the recent mystery cloud, also from distant sources. He said that debris kicked up in the deserts of central Russia can occasionally make its way to the sky above Alaska. Smoke from wildfires can also drift Alaska’s way, but Hagenbuch noted that such fires in that region are also unusual this late in the year.

Contact Ben Anderson at ben(at)alaskadispatch.com