ANCHORAGE, Alaska —An Alaska volcano kept pumping out new ash Tuesday that could threaten aircraft, but it came in smaller amounts at lower heights, according to the Alaska Volcano Observatory.

Pavlof Volcano, 625 miles southwest of Anchorage on the Alaska Peninsula, erupted Sunday. The initial eruption continued for about 17 hours and put out an ash cloud that reached 37,000 feet.

The plume blew northeast and by Tuesday had reached Canada, but Dave Schneider, a U.S. Geological Survey geophysicist at the observatory, said activity had calmed from the continuous eruptive phase.

“Over the last six to eight hours the activity is more intermittent,” he said. “There are short duration, small explosive events that are occurring, as opposed to sort of a continuous plume.”

The original ash cloud crossed Bristol Bay, spread into interior Alaska, and stretched into northern Canada, said Don Moore, meteorologist in charge of the National Weather Service Alaska Aviation Weather Unit.

“The extent of the plume is certainly greater but the concentration of the ash is becoming less,” Moore said. “The plume is becoming thinner over time.”

Volcanic ash is angular and sharp and can cause a jet engine to shut down. Alaska Airlines on Monday canceled 41 flights within the state affecting 3,000 customers heading to Fairbanks, Bethel, Kotzebue, Nome, Barrow and Deadhorse. The airline had canceled at least 14 more flights Tuesday.

The volcano in the 8,261-foot mountain is one of Alaska’s most active. It has had 40 known eruptions.

Pavlof eruptions in the past 20 years have not been as intense, but the current eruption is not unprecedented for the volcano, Schneider said.

The length of the eruption was a major factor in the size of the ash cloud, Schneider said. So were the winds and possibly the smaller size of the ash, which takes longer to fall out of the atmosphere.

The observatory took reports of ash fall, which can be hazardous to eyes, skin and breathing passages, from several communities.

USGS geologist Kristi Wallace said the most significant was in Nelson Lagoon, a village of 39 people about 55 miles northeast of the volcano. Residents reported one-eighth to two-thirds of an inch of ash.

Trace amounts of ash were reported in Dillingham, a Bristol Bay fishing community, and Port Heiden on the Alaska Peninsula.

In the past, the volcano has erupted intermittently over months or shut off abruptly.

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