Mud and debris covered the road at milepost 23 on the Haines Highway on Sunday. (Photo by Lynn Cambpell)

Southeast Alaska had a very dry September. Heavy rains returned to the region this month, triggering a large mudslide on the Haines Highway over the weekend. Now the Alaska Earthquake Center says seismic activity may have also played a role.

State road crews spent most of Sunday clearing mud and debris along a four-mile stretch of the Haines Highway that kept the road closed until early evening.

Department of Transportation spokeswoman Aurah Landau said the two main slides were in places crews are familiar with.

“19 mile and 23 mile have a history of sliding,” Landau said. “There’s maybe a couple times a year that the material comes down over the road. ” 

She said Sunday’s largest slide was roughly 100 feet long and up to 8 feet deep.

“In this case, especially at the 23 mile slide, it was like soupy jello that they were shoving off the road.”

The cleanup is estimated to cost the state $200,000 to $400,000.

When it comes to mudslides, wet weather is usually the culprit. Three inches of rain were recorded by the National Weather Service at the U.S.-Canada border post 20 miles from the slide.

Federal meteorologist Joel Curtis said the steep slopes above the Haines Highway can only absorb so much rainwater.

“Once you start soaking them in real good and they become completely saturated, clearly that adds more weight to the system and is also some lubricant that allows it to move,” Curtis said.

But there’s evidence of another force at work.

A 3.6 magnitude earthquake centered about 12 miles from the slides was recorded at 7:04 a.m. Sunday. The first report of the highway mudslide came just 25 minutes later.

Seismologist Natalia Rupert at the UAF Alaska Earthquake Center reasoned the two could be linked. She told KHNS that the small quake likely provided that extra push that saw tons of mud, rock and earth tumble down and blanket parts of the highway.

So between the heavy rain, the steep terrain, and a small temblor, Sunday saw the perfect storm for a slide on the Haines Highway.

DOT can’t stop material from coming down the hillside above the Haines Highway. That is just part of the geology of the area. However, Landau said that DOT plans to make improvements to the stretch of highway between milepost 19 and 23 to help minimize the effect of the slides.