Northern Minnesota wildfires burning underground

The wildfires that struck northwest Minnesota have gone underground, igniting layers of peat that could burn well into the winter.

More than 150 people were working Monday by hand, with fire trucks and with heavy equipment to try to contain the wildfire, which had grown from about 4,000 acres last week to 24,848 and was declared 30 percent contained, although it was partly burning underground, said Gil Knight, spokesman for the multiagency team working the fire north of Red Lake.

That fire, as well a 1,400-acre fire near the city of Viking, penetrated into the layer of peat that underlies much of northern Minnesota and runs 2 to 3 feet deep where the fires have been. Peat is plant material that decomposes slowly in the region's cool climate. It is often used as a domestic fuel source.

In dry conditions like this year's, the peat actually repels moisture, so fire crews have had to inject water into the ground to saturate it, in some places at a rate of 175,000 gallons per acre.

"We have to get in there and basically drown the heck out of it," Knight said.

Peat fires, which smolder instead of burning with an open flame, move laterally underground and can sometimes burst into flame on the surface.

Meanwhile, they have been melting last week's snow above them and sending steam into the air, according to DNR officials.

Peat fires can also burn in a way that weakens the ground, causing holes and pockets of ash that can trip up firefighters.

"They're difficult to deal with," Knight said.

Although the peat can repel water and snow and, if burning, cause it to evaporate, Knight said a new half inch of snow that was in Monday night's forecast would be welcome. "Any moisture is good moisture," he said.