Steam clouds have continuously bellowed from Augustine since Saturday, but surprisingly little ash has fallen and only two observations have detected ash on the peninsula, according to geologists monitoring the volcano.
“It’s pretty interesting that we’ve had this sustained eruption since Saturday, but very little ash fall,” said Kristi Wallace, a geologist with the U.S. Geological Survey.
The ash being emitted may be so fine that most of it is riding winds past Alaska communities and the ash that is falling may be escaping detection because it is falling within snow, Wallace said.
Particularly fine ash particles travel long distances before they fall to the ground.
“Sometimes around the world,” Wallace said. “They just keep circulating and become more diffuse.”
However, there may be more ash falling than is being detected if it is falling in the form of snowflakes. Sometimes particles of falling ash collect moisture and initiate the formation of snowflakes.
“The ash would be acting as a nucleus,” Wallace said.
If the ash is falling as snow it might escape detection unless the snow is collected and melted to find the ash that was embedded within the snowflakes.
Another possible explanation may be that the steam clouds bellowing from Augustine contain low concentrations of ash.
“Every steam event has some ash in it, but what we don’t know is the concentration of the ash in it,” said Carvin Scott, a science officer at the National Oceanic and Atmospheric Administration’s National Weather Service.
The continuous plume coming from the volcano is the result of a sustained low-level eruption and is likely to contain less ash than a high-intensity explosion, said Wallace. However, the sustained eruption that has been emitting a steady plume since Saturday was punctuated by two high-intensity blasts Sunday that should have contributed more ash to the plume.
Two independent reports made to the Alaska Volcano Observatory indicated ash had been detected in two places on the peninsula on Monday.
In Hope, an observer reported seeing, smelling and tasting ash in the air and in Kasilof an observer reported trace amounts of ashfall at the airport.
Ash was likely dusting the ground at Cape Douglas, a virtually uninhabited area about 30 miles south of the volcano, the National Weather Service said Tuesday. It canceled ash advisories for the Susitna Valley, north of the volcano, and the western peninsula several dozen miles to the east.
Sometimes the ash may be detectable in the air, but not on the ground, said Wallace.
“It looks like a haze, as if there were a forest fire,” she said.
The unbroken plume that has been drifting from Augustine since Saturday has been lingering at about 13,000 feet.
But the two high-intensity explosions that punctuated the continuous low-level eruption Sunday sent plumes more than 25,000 feet into the air and possibly as high as 50,000 feet, according to radar and pilot reports received by the AVO.
The AVO maintains close contact with the Federal Aviation Association and warns the agency whenever plumes reach more than 20,000 feet into the atmosphere, Wallace said. Most flight altitudes range from 30,000 to 35,000 feet.
Dozens of flights canceled by ash from erupting Augustine Volcano returned to the skies on Tuesday. Alaska Airlines had grounded 36 flights to and from Anchorage on Monday and Era Aviation had canceled five flights to Kodiak Island, about 80 miles south of the volcano.
“We have not made any cancellations tonight, but we continue to monitor the situation and may need to make additional flight changes as conditions change,” said Amanda Tobin, spokeswoman for Alaska Airlines.
The altitude of the plume and speed and direction of the wind at that altitude must be determined in order to predict where the plume is moving and when it will arrive. But making these determinations is no easy task, Scott said.
“It’s a very complex problem and it’s not anything that anyone does on a regular basis,” Scott said “Basically what we’re trying to do here is just capture the edge of the cloud.”
The direction and speeds of the winds moving through the atmosphere change depending on the altitude at which it is being measured, Scott said.
And depending on how stable the atmosphere is, a plume may rise like a balloon being pushed out of water or fall like a lead sinker, said Scott.
Predictions are challenging, to say the least, particularly since few U.S. meteorologists have had experience trying to forecast the movement of volcanic plumes through the atmosphere, Scott said.
“There are so many unknowns,” he said. “(There are) a lot of firsts up here for us.”
Jeannette J. Lee, an Associated Press writer in Anchorage ,contributed to this story.
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