Fire-scarred landscapes here in Montana carry a risk of mudslides. It’s something staffers with the National Weather Service are keeping a close eye on, as they monitor conditions and weigh whether to issue advisories and warnings.
“Mudslides are caused when you get excessive rainfall, you get rapid snowmelt, or both,” said Dan Zumpfe, with the National Weather Service branch in Missoula.
Zumpfe used the Lolo Creek Complex Fire as an example of how fire can burn terrain on steep slopes and leave behind the risk for slides.
“What we try to do after a fire like that is send out hydrologists and other people from our office to assess the risk and put some limits on, so, for example, if you're looking at the Lolo Complex, and a thunderstorm is expected to produce an inch of rain in the next hour, that would be a big red flag,” said Zumpfe.
Zumfe says some of the most vulnerable residences are along Lolo Creek, between steep hills.
“Look for where the trees used to be, because the trees like to be in ground that's not made of a lot of rocks,” said Zumpfe.
Zumfe explains snowmelt can play a large part in causing landslides, though most of the low elevation snowmelt is already completely melted off at this point. The remaining snowmelt, if it runs off rapidly, can create problems.
“Some years we've had the melt off occur so quickly that it destabilizes soil, and we've seen entire roadways washed out by a mudslide that didn't occur with any rain,” said Zumpfe.
Experts with the Weather Service are urging folks to stay aware. If heavy rain occurs, residents should avoid burn scars. Even without rain, they’ll want to monitor any changing conditions in the soil.