THE WEST SALT CREEK ROCK AVALANCHE: A HIGHLY MOBILE, COMPLEX LANDSLIDE IN WESTERN COLORADO
High-resolution imagery and digital-topographic data from Unmanned Aerial Vehicle (UAV) and LiDAR acquisitions are being used as base materials for ongoing, 1:1000-scale field mapping of landslide geology and structures. This mapping shows that most of the avalanche is composed of rotated, broken, and brecciated Eocene Green River Formation; and basalt-rich, Quaternary colluvium and/or landslide deposits. The basalt-rich deposits formed distinct flow bands on the surface of the avalanche. The chronological sequence of movement was complex, with at least 5 phases: a debris flow; the catastrophic, high-energy rock avalanche, including the rotational rock slide; movement of the hummock-rich, central core of the avalanche deposit; a second debris flow; and ongoing movement of the upper central core. Ongoing potential threats to downstream residents include: the catastrophic failure of the rock slide block, a large failure upslope from the headscarp, a rapid release of water from the lake, and rapid or slow movement of the avalanche deposit. Ongoing instrumental monitoring provides near real-time information on these threats.