Geologists Continue To Study Cause Behind Massive Denali National Park Landslide

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The Igloo Creek Slide in Denali National Park. NPS photo.

Geologists are continuing to search for the cause behind a massive landslide at Denali National Park and Preserve that had blocked the park road near Mile 38 in late October.

The slide, which coverd approximately 200 feet of the road in depths of up to 35 feet, was released from a point 500 feet above the road and flowed south below the road, according to park officials.

Blocks of permafrost-frozen, unconsolidated debris as thick as 15’ and the size of a small cabin had slid on a slippery, unfrozen clay that acted as the failure plane. With winter snows held off by unseasonably warm weather, the Denali road crew managed to clear the road of debris after considerable effort.

The trigger for the slide remains unknown. Ground, aerial, and satellite imagery of the site in the years and months before to the event indicate that a small slide had previously occurred here, groundwater seeped from the area, and the ground was beginning to move slightly.

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The Igloo Creek Slide from above. NPS photo.

In the days preceding discovery of the slide, the area was experiencing temperatures that fluctuated near the freezing point. Therefore, the forces associated with the expansion of ice during the repeated freezing and thawing of water near the surface may have triggered the slide. Alternatively, we also know that a thick layer of permafrost slid on an unfrozen layer of clay.

How safe travel will be along the Denali Park Road in the spring is being reviewed by park staff, as additional slides are possible.

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The human perspective of the slide. NPS photo.

"In the spring, when the ground thaws, additional activity at the Igloo Debris Slide can be expected. A ditch to capture these materials has been excavated," a park release said. "If deemed necessary, Denali National Park staff will institute additional protective measures with the assistance of the Federal Highways Administration. Denali staff has already begun the process of analyzing other sections of the Park Road for similar problems so that potential hazards can be mitigated."