Yellowstone National Park North Entrance Road
LOCATION: Yellowstone National Park
In June 2022, a severe rain-on-snow flooding event washed out significant portions of the Yellowstone North Entrance Road along the Gardner River and the Northeast Entrance Corridor, completely disrupting road access to the park entrances and the town of Cooke City, MT. This flooding event was the effect of heavy rains falling on a snowpack that persisted unseasonably late into June. The runoff initiated upland and upstream in the Beartooth mountains, and the flooding and damage were severe downstream in Yellowstone National Park and Gardiner, MT. BGC was engaged by Western Federal Lands Highway Division to support Yellowstone National Park to rapidly respond to the disaster to document and map damage, new landslides, and road washouts, a necessary initial step to obtain federal funding for resilient repair efforts.
In conjunction with Western Federal Lands and Jacobs Engineering, BGC is performing a geotechnical investigation to support alignment relocation studies for the North Entrance corridor from Gardiner, Montana to Mammoth, Wyoming. The proposed new alignment areas are known for numerous landslides, earthflows, and hosts the popular tourist attraction, “Slide Lake.” During the last glaciation in the Yellowstone region, the Gardner River canyon was buried under >1km-thick glacial ice that incised deeply into mountainous terrain comprising weak pyroclastic volcanic deposits >1.2 km thick atop Cretaceous marine shale bedrock. Starting approximately 12,000 years ago, the thick alpine ice began rapidly melting. Within a thousand years, the once massive glaciers receded ~80 km upstream and completely disappeared in the early Holocene.
In the project area in Gardner River valley, the rapid glacial recession left behind deeply incised canyons with over-steepened cliffs made of bentonitic shales with slippery fat clays overlain by mountainous piles of ashy volcaniclastic debris ejected by the Yellowstone hot spot magmatism, with topographic head gravitationally collapsing these relatively weak mountains into numerous creeping earthflows crossing the potential new road alignments.
In support of the North Entrance Road alignment feasibility study, BGC performed geologic mapping and site reconnaissance to assess recent flooding damage, landslide morphology, proposed road alignment options, and low-impact remote helicopter-supported geotechnical drilling investigations in the environmentally sensitive National Park.
BGC, in conjunction with Yellowstone National Park, Jacobs Engineering, and Western Federal Lands Highways Division is performing the following for the Yellowstone North Entrance Road Project:
- Digital geospatial data management with Cambio platform for visualization of data from InSAR, LiDAR Change Detection, proposed road alignments, and real-time borehole monitoring instrumentation (SAAs, VWPs)
- Helicopter and track-rig geotechnical borehole drilling
- Geomorphic digital terrain analysis and field mapping
- Geological mapping
- Detailed landslide characterization and mapping