Pretty Rocks Landslide

Denali Park Road is closed at mile 43 due to the Pretty Rocks landslide at mile 45.4. The only ways to access the parts of the park west of mile 43 are to hike around the landslide or to take a helicopter or plane. The landslide has been active for decades, but it notably sped up in 2014. A monitoring program started in 2016. The monitoring program found that the landslide caused road movement at a scale of inches per month in 2017, inches per week in 2018, inches per day in 2019, and up to 0.65 inches per hour in 2021. Road crews spread up to 100 truckloads of gravel per week to fill in the slumping road in July and August of 2021. The road was closed on August 24, 2021, because maintaining the road was no longer feasible or safe.

I took a park transit bus to East Fork at mile 43 to acquire GPS data in the new turnaround for the buses, and then walked a few miles down the road until I reached the Pretty Rocks landslide. Seeing it in person was breathtaking; geologic hazards is a topic I learned in university, but I had never seen one so devastating in person. The landslide displaced 100 yards of the full width of the road.

The landslide is probably the result of climate change in the park. Denali National Park has experienced a temperature increase of 7.7°F ± 2.0°F (4.3°C ± 1.1°C) per century.  The substrate of the Pretty Rocks landslide is a rock glacier (rocky debris with ice in the pore spaces). The landslide is still being monitored and there is a Polychrome Area Plan in place to create a bridge over it.

I had the pleasure of spending a few days in the field with Park Geologist Denny Capps and his crew, University of Alaska Fairbanks professor Dr. Louise Farquharson and her crew, and Park Archeologist Elizabeth Negrete. I helped with GPS data collection and I learned a ton about how to properly collect data in the field. It is important to monitor geohazards no matter how small, since a small problem now may become a huge one in the future.

References

https://www.nps.gov/dena/learn/nature/pretty-rocks.htm

https://www.nps.gov/dena/getinvolved/polychrome-plan.htm