A rock ‘the size of a small car’ fell on the Seward Highway this week — and slides there are getting more frequent.

It was almost completely dark along the Seward Highway when rocks began raining down across the road Monday night in five places along Turnagain Arm south of Anchorage.

"You’re right up against the rock and you can’t see if it’s going to come down on you,” said Ellen Prigge Sheehan, who was headed into Anchorage from her Kenai home.

Prigge Sheehan said she was prepared to brave the treacherous weather — heavy winds and rain pounded the Kenai Peninsula and just south of Anchorage throughout the day — but she hadn’t considered a rock slide could hamper her trip.

But just after 4 p.m. she saw a line of taillights ahead of her. Then, she said, she noticed the rocks and debris spread across the highway.

Shannon McCarthy, a spokeswoman for the Alaska Department of Transportation, said five rock slides hit that stretch of highway Monday night. The area has seen a significant uptick in rock slides during the last year and officials may take emergency action to prevent more slides throughout the rest of the season, she said.

Rocks and debris toppled from the cliffs first at Mile 111, near McHugh Creek, and fell across the highway, blocking the northbound lane and causing officials to temporarily shut down the whole highway.

During the next hour, four more rock slides fell in the next five miles of the highway. One of the rocks was “the size of a small car,” McCarthy said.

The highway completely reopened by Tuesday at 7 a.m., although traffic was restrained to one lane overnight. Piles of debris and rocks were visible alongside the highway Tuesday.

On average, 6,800 drivers travel that section of road each day, although McCarthy said the numbers are often much higher in summer. The Seward Highway is the only road connecting Anchorage to the Kenai Peninsula.

It’s unusual to have so many slides happen simultaneously, McCarthy said, but the heavy winds and rain Monday contributed to the chaos. The National Weather Service recorded a gust of 113 mph Monday morning near McHugh Creek.

“That heavy wind can really push any of these fractures to the point where they’re going to fall,” she said.

Unstable weather patterns this winter — including repeated freezing and thawing — have also exacerbated the situation, McCarthy said. Anchorage set numerous warm-weather records throughout October and November before finally hitting single-digit temperatures close to December. Warm southeast winds pushed into the region this week, causing temperatures to rise again rapidly and melt much of the sitting ice and snow.

“What can happen is that as things freeze up they’re a little bit more stable,” McCarthy said.

State transportation planners identified the Turnagain Arm stretch as a problem area even before the 7.1 earthquake hit the region in November of 2018, but McCarthy said the “mechanical shakeup” loosened and fractured rocks, causing them to fall more frequently since.

“We’re not happy with that uptick. ... We have rock slides in other parts of the state ... but the difference is this area seems to be shedding a lot of rocks in the last 12 months and we have higher traffic counts and that creates conflicts," she said.

[Related: The quake made rocks rain down on the Seward Highway. Even before then, DOT was planning fixes.]

The transportation department identified seven areas from miles 104 to 114 — basically Indian Valley to the Potter weigh station — as the most unstable areas and began looking at ways to prevent the falling rocks about five years ago. McCarthy said there have only been a handful of injuries caused during the rock slides in recent years, but she considers that too many.

Geologists surveyed the area last summer for safety improvements and McCarthy said bids for construction are expected to open this June. Crews will manually remove some of the riskiest chunks of rock, secure other portions with large bolts and install mesh to capture smaller portions of rock or landslides.

McCarthy said the Monday night slides may have prompted emergency work this winter, although it was too early to tell how extensive it could be. Crews will continue cleaning up debris and rocks from the Monday night storms as the week continues.

Cheyenne Marshall, who commutes to Anchorage from Girdwood nearly every day, said she looks forward to repairs on the highway. She said she felt grateful her children were not in the car with her Monday night as she waited to pass through the landslide zones.

“I’m just super glad no one was hurt.”