ANCHORAGE — 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 canceled 41 flights within the state Monday, and 28 more 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.

Cpl. Barrett Taylor saw ash falling at 1:30 a.m. Monday.

“It was raining ash for a little bit,” Taylor said. “It turned everything black, the rooftops, the fuel tanks, homes.”

The community has put out a health advisory to stay inside until Wednesday. He’s hoping strong wind or rain will sweep some of it away.

“I actually saw an eagle land on the grass today, and as he landed, a big pile of ash came up and flew away. It’s still there,” he said.

Pat Walsh, a wildlife biologist for the Togiak National Wildlife Refuge, saw ash 25 miles west of Dillingham as a gray haze as he tracked wolves from the air in the refuge. He could also see traces of ash in fresh wolf tracks and in the snow.

“It looks like dirty snow,” he said.

Tisha Christensen, a health aide at the clinic in Port Heiden, said gray ash mixed with snow fell Monday night in the community on the Bering Sea side of the Alaska Peninsula.

It affected her 8-year-old son, who has asthma but tried going to school Tuesday.

“He didn’t even make it a half hour and had to come home and have a nebulizer treatment,” she said.

Only trace amounts of ash had been reported from Pavlof eruptions since 1996.

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