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Contact: G.W. Hitchcock, 907-683-9583
DENALI PARK, Alaska: Denali National Park and Preserve is taking a close look at the condition of the Park Road, particularly the Pretty Rocks portion of Polychrome Pass, an area known for its increasing geologic activity. Movement of the Pretty Rocks landslide at mile 45.4 of the Park Road is multiplying, creating need for intensified monitoring, maintenance, and planning. The park expects an increased demand for resources during next year’s maintenance.
“We had an excellent season thanks to the tireless efforts of our road crews and the flexibility of our Joint Venture partners and the Kantishna inholders, but it is becoming apparent that movement along the Park Road is steadily increasing,” said Superintendent Don Striker. “It’s not a new problem by any means, but it is demanding more and more of our attention and resources.”
“Landslide activity has intensified along the road, especially at Pretty Rocks,” said Denny Capps, Park Geologist. “In 2018, we saw downhill movement of the Pretty Rocks landslide increase to 0.4 inches a day, which became our new norm, but starting this August we began measuring 1.5 – 2 inches a day.”
Weather is the biggest factor effecting the Park Road’s condition. While there were only three travel restrictions implemented this season, an exceptionally wet fall has had a cumulative effect on the road’s integrity. Maintenance staff noted 65 discreet incidents that required mitigation due to adverse weather. While a majority of these were handled quickly, 24 sites require continued monitoring and maintenance.
According to rainfall data the park submits to the National Weather Service, there was 19.01 inches of rainfall at Eielson Visitor Center (EVC) during the month of August. This marks the wettest month since 17.62 inches of rain fell in August 2000. On August 16, EVC experienced a record rainfall of 4.15 inches in a 24-hour period (previous record was 2.36 inches), which led to a closure that kept 300 visitors and 17 shuttles buses at the Toklat Rest Area for three hours as maintenance crews cleared a debris (mud) flow near the Polychrome Overlook.
“Rain makes soil more volatile,” said Denny Capps. “As rain falls, water pressure builds within soil increasing the likelihood that it will move downhill. The wet weather this season means we’ve seen a lot of movement along the road, particularly at Pretty Rocks.”
Despite the rainy season being over, the park won’t have a full understanding of the road’s condition until next spring. The weather this winter will play a major role in determining the road’s condition.
“The road’s stability is hugely dependent on the underlying permafrost,” said Denny Capps. “Within the Pretty Rocks landslide, a layer of ice sits approximately 30 feet beneath the surface. Our resource teams, along with contracted geotechnical experts, are currently taking core samples and monitoring conditions in this area. The ice-rich permafrost within the landslide is likely thawing. As this ice melts, it adds more water to the already saturated soils and reduces cohesion, which further increases the likelihood of downhill movement.”
“We don’t have data going back far enough to allow us to definitively attribute the slumping rate increase to climate change,” said Dave Schirokaurer, Resources Team Lead for the park, “but these increases in deformation since 2014 coincide with the last 5 years being among the warmest on record here at Denali. We’ve begun seeing a whole host of changes that are the result of winters being warmer and summers being wetter than expected.”
Each year the park, in partnership with the Federal Highways Administration, uses geotechnical equipment to collect data on the Pretty Rocks landslide. Maintenance staff uses this data to estimate crew size, project timelines, and supply (such as gravel) needs. Using current data, the park is expecting a 13-foot or greater drop in the Pretty Rocks landslide portion of the road over the coming winter. This 2020 estimate is double the actual drop experienced along the road when it was cleared this past spring, which itself was a doubling of the drop experienced in 2017. Visitors may have seen this drop of the previous road as a darker scar several feet beneath the current road at Pretty Rocks.
“The stability of next year’s road is partially dependent on how cold it gets this winter,” said Denny Capps. “Colder temperatures generally mean less snow and a more stable base; warmer temperatures generally mean a less stable base and more snow, resulting in more soil saturation and more deformation.”
“Surprisingly, a warmer winter means more work for maintenance crews,” said Ray Moore, Facility Operations Manager for the park. “More snow means crews spend more time digging out the road and then have less time to get it ready.”
“The longer we wait for the road to be cleared, the longer it is before staff can assess the road and the longer it is before maintenance crews can implement a plan to open it for the season,” said Dave Schirokauer.
The park encourages visitors to continue to plan their trips to Denali. We are not currently planning to delay the road’s opening, or to implement any travel restrictions.
“Denali National Park will be open for business and ready to greet everyone who visits us next year,” said Superintendent Striker. “We are simply acting out of an abundance of caution and a desire to be as transparent as possible with the public and our partners.”
The park is planning for a busy and compressed maintenance season next spring. The park is currently considering continuing road maintenance operations beyond September 27, allowing Kantishna inholders increased access to their properties this fall. The park is also working with its Joint Venture partners to better coordinate the required driver training and to create flexible training plans during the pre-season.
“Our primary concern is always visitor safety,” said Miriam Valentine, Team Leader for External Affairs, “but we are also aware of how the road’s condition impacts our Kantishna inholders and our tourism partners. Our partners do a lot of training and preparation prior to the season’s start, so we are working diligently with them to make sure that they have the access they need, so they can prepare for next year’s season.”
“Being aware of the problem has allowed us to prepare for a solution,” said Superintendent Striker. “We have increased our road maintenance budget, increased the size of our maintenance crews for next year, and we’ve also begun stockpiling and staging raw resources such as gravel, so these can be available no matter what happens this winter.”
The Pretty Rocks landslide is located near the midpoint of the park’s 92-mile road. This means that under any scenario, approximately half of the road will be open for travel and wildlife viewing, as will the entire front country. A majority of the park’s hiking trails will remain open, backcountry units and campgrounds will be accessible for camping, and interpretative programs will be available. The park expects that every visitor will continue to have opportunities to experience the Alaskan wilderness and stand in awe of its vast and varied landscapes.
Additional park information is available at http://www.nps.gov/dena or 907-683-9532 from 9 am to 4 pm daily. Stay connected with "DenaliNPS" on Twitter, Instagram, Facebook, YouTube, Flickr, and iTunes.
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Last updated: September 24, 2019