Pretty Rocks Landslide
Section last updated: April 2, 2019
Pretty Rocks Landslide Comparison (September 2018 vs April 2019)
The eastern landslide scarp through the road on September 29, 2018. The road was last graded on September 14th and closed to most vehicle traffic on September 19th. The photo below was taken six months later in the same location. NPS Photo
The eastern landslide scarp through the road on 3/22/2019. Survey rod held by park employee is 6.5 feet (2.0 m) tall and is placed near center-line of the road. Note employees had recently shoveled dirty snow in foreground to aid in measuring the scarp. NPS Photo
Igloo Debris Slide
On September 30th and October 18th 2018, the Igloo Debris Slide partially blocked the Denali Park Road. In each event, the Denali road crew cleared approximately 500 cubic yards (450 m3) from the roadway within a few hours. Like the 2013 event, 12’ (4 m) blocks of ice-rich, unconsolidated debris slid on the same or similar unfrozen clay layer. 2013 and 2018 both experienced unusually mild fall weather. Such weather further thaws permafrost, which decreases cohesion and increases pore water pressure. Therefore, this combination of processes can cause and trigger landslides. As more permafrost has thawed and the slide has continued to move, the area of the slide has increased. Several smaller events have filled the road ditch since September 30th.
In late October 2013, road maintenance staff discovered that a 600’ (180 m)-long, 110’ (35 m)-wide debris slide had blocked the park road near Mile 38.