Seward Highway rockslides increase in frequency, trigger Alaska DOT emergency measures

Rocks, mud and trees slid onto the Seward Highway near Mile 105 in 2017. (Alaska Department of Transportation photo)

Rockslides in the mountains south of Anchorage, like one that shut down the Seward Highway on Monday, have occurred more often in the year since a magnitude 7.1 earthquake shook the region.

Coupled with an ever-warming climate and more frequent freeze-thaw cycles, that has caused an increase in rockslide activity that, at times, has the Department of Transportation conducting round-the-clock patrols.

“It is a safe highway,” said DOT spokesperson Shannon McCarthy. “We are not happy with the rate of debris coming down either.”

The department is doing a couple different things in the short term to mitigate risks to motorists on the only highway to the Kenai Peninsula, mostly on a stretch from miles 104 to 114, roughly from the town of Indian to Potter’s Marsh.

“When we see these kind of high winds and heavy rains, we actually have our, our heavy equipment operators are actually patrolling the area. That’s why we were able to close the highway so quickly (Monday),” McCarthy said. “So there’s that, and we’re actually going to be doing some emergency work in the next weeks or months to bring down some additional areas that we’re not happy with that we don’t think are long-term, you know, stable.”

The emergency work could include bolting rocks in place or installing mesh around them. In some cases, McCarthy said, workers might also need to rappel down to problem areas and use a kind of long pry bar to proactively bring down debris. She said there is also the longer-term possibility of blasting back into some of the cliffs to make the highway farther away from potential slides.

In the meantime, state geologists are keeping a close eye on the mountains as the emergency rockslide work ramps up.

“It’s a concern in that the rock will come down but you can’t really predict will it be a month from now or will it be five years from now,” McCarthy said. “I mean it’s one of those things if you can see the mechanics and you know it’s on the way, that’s probably a pretty good time to strike.”

According to the DOT, there will be intermittent partial or full highway closures to remove debris Wednesday, but the schedule for when the emergency work will be done, or dates of any associated highway closures, remain to be determined.