ANCHORAGE — The largest volcanic eruption of the 20th Century created a 40-square mile desert known as the Valley of 10,000 Smokes on the Alaska Peninsula. More than a century later, ash from the event is still creating a hazard.

Scientists from the Alaska Volcano Observatory will set up equipment next week to monitor clouds of ash that are regularly blown across Shelikof Strait toward Kodiak Island and the Gulf of Alaska, said U.S. Geological Survey geologist Kristi Wallace. The ash creates a hazard for aircraft and possibly for humans, she said.

“For as long as we know, probably over the last 100 years, ash on the surface in the Valley of 10,000 Smokes over in Katmai has been re-suspended during the fall and springtime during times when it’s snow-free conditions, dry surface conditions, and very high northwesterly winds,” Wallace said.

The ash came from the Novarupta-Katmai eruption in June 1912. According to the USGS, three explosive episodes spanning 60 hours deposited 4 cubic miles of fallout near Mount Katmai. Vegetation has never returned to the Valley of 10,000 Smokes and the site is now part of Katmai National Park.

Ash deposits in some valleys are still more than 600 feet deep. When strong winds blow, the ash kicks up in such large volumes, it’s detected from space and can be mistaken for a new volcanic eruption.

“In satellite imagery, they look for all intents and purposes like an eruption cloud,” Wallace said.

That makes jet airline pilots nervous. If ash reaches 20,000 feet, it’s considered a major threat to trans-continental aircraft because it can shut down a jet engine.

Ash from Katmai typically has been observed at 5,000 to 11,000 feet, Wallace said, which can cause abrasion issues for the windshields and engines of smaller aircraft.

There’s also a potential threat to breathing.

“We want to understand whether or not there’s a public health hazard associated with these fallout events in terms of air quality,” Wallace said.

Particulate finer than 10 microns can be inhaled and a danger to the elderly and small children. Research ties fine particulate to heart attacks, decreased lung function and premature death in people with heart or lung disease.

Geologists have taken samples in the past when ash has been deposited on Kodiak roofs but don’t have a good understanding of how much particulate is swirling in the air.

Observatory scientists on Tuesday will install particulate-measuring instruments in the city of Kodiak of the east side of the island and in Larsen Bay on the west side. The devices will collect ash samples to determine whether they contain fine particulate and how much is crossing the roughly 80 miles to communities.

“This is going to give us a little more quantitative information,” Wallace said.