MAPPING LANDSLIDE AND ROCK FALL HAZARDS IN YELLOWSTONE NATIONAL PARK USING THE UNSTABLE SLOPE MANAGEMENT PROGRAM’S SLOPE ASSESSMENT MOBILE APPLICATION

As a flagship park of the National Park Service (NPS), Yellowstone had over 4 million visitors in 2017, the second highest visitation for this park ever recorded. As vehicle traffic continues to increase, it is critical that slopes along transportation corridors in Yellowstone are monitored and managed efficiently and effectively so the NPS can provide suitable access within the park.

To help address this need, a team of students from Western Carolina University have assessed landslide and rockfall hazards in Yellowstone, focusing primarily on threats to infrastructure including roads, parking lots, and buildings. The NPS Unstable Slope Management Program (USMP) protocol was used to assess slopes along key road corridors in the park between the West Entrance and the North Entrance, including the Old Faithful corridor. These corridors were prioritized by the NPS due to the high traffic volume throughout the visitation season.

For each corridor, general slope and road characteristics (e.g., slope height, slope angle, frequency of movement, structural conditions, material catchment effectiveness), as well as specific slope hazard and risk factor ratings were recorded using the USMP mobile application. These data were used to calculate a total score defining the slope rating category: good (<200 points), fair (200-400 points), or poor (>400 points). Observations and ratings were uploaded in near-real time to the NPS USMP database. Slope rating category and documentation were then reviewed in the field and in the database for consistency before finalizing slope ratings.

A total of 198 slopes (~85 miles) were rated during two months of fieldwork in summer 2018. Of these, 165 were identified as rockfall hazards (e.g. planar, wedge, toppling, raveling/undermining, rock avalanche, differential erosion, or other), and 33 were characterized as landslide hazards (e.g. translational, rotational, debris flow, shallow slump, erosional failure). Among rockfalls, 34 were classified as poor, 123 were classified as fair, and 8 were classified as good. For landslides, 8 were rated as poor, while the remaining 25 were rated as fair. Observations and results reported through the national USMP database will allow the NPS to plan management of unstable slopes of greatest concern at Yellowstone.