PORCUPINE CREEK LANDSLIDE, ALPINE, WY

This study focuses on two aspects of the Porcupine Creek Landslide – possible triggers and current morphology. Drone imagery and climate data were collected to analyze the impacts of water saturation, surface morphology, and seasonal snowpack.

The landslide, discovered early in February 2018, blocked approximately a quarter mile of road and built an earthen dam across the Greys River. A 4.3 m (14 ft) deep lake formed upstream of the slide; downstream areas were closed due to concerns of a catastrophic dam breach and subsequent flooding.

Landslide lithology consists of unconsolidated sediment, including clay and silt deposited in past landslide and glacial events. Underlying bedrock (lower Cretaceous volcanic mudstone, shale, sandstone and clastic limestone) dip toward the river at approximately 20° creating optimal slip planes which contribute to landslide hazards. Morphology was analyzed using 2 cm resolution, drone-collected imagery mosaicked and processed using Pix4D and GIS to create a 3D model. The model can be used to document future slide movement.

Possible triggers of the Porcupine Creek Landslide include a 3.5-3.7 Mw earthquake which occurred Feb 1, 2018, weight added from winter snowpack, and precipitation in months preceding the event, particularly late fall rains. Underlying geology, steepness of canyon walls, and the river suggest that Greys River Canyon is prone to landslides. Studying possible triggers for the Porcupine Creek Landslide can help plan for and mitigate future incidents in the canyon.