Analysis of a large moist landslide, Lost River Range, Idaho, U.S.A.

Abstract

This paper describes the regional geology, dimensions, morphology, sedimentology, and age relations of the Holocene "Carlson landslide," a large moist landslide composed of basalt breccia located on the eastern margin of the Lost River Range, Idaho. These data are combined to deduce the factors that prompted the slope failure, the kinematics of initiation, travel, and stopping of the landslide, as well as its postemplacement degradation. The landslide is compared with other terrestrial mass movements on the basis of morphology, sedimentology, log(volume) versus fall height –runout length (H/L) relations and estimated Bingham plastic yield strength. Morphology and sedimentology distinguish dry landslides from moist and water-saturated deposits. However, moist and water-saturated landslides plot well within the log(volume) versus H/L envelope for dry terrestrial landslides and exhibit overlapping ranges of estimated Bingham plastic yield strength values with dry landslides, indicating that moist and water-saturated landslides must travel much like dry rock avalanches of similar volume. Thus the mechanism(s) responsible for causing anomalous runout in large dry landslides could operate in moist and water-saturated landslides as well. Morphological comparison of the Carlson landslide with lobate martian landslides suggests a role for water in the martian landslides. Key words: landslides, debris flows, long runout, morphology, water, Mars.