1. Anatomy of a landslide

2. Erosional Phases
No erosion
Rapid Erosion
Slow Erosion

3. No erosion Can last seconds to decades
Volume of deposit increases as upstream sediments are trapped
Debris dams are more likely to form and persist with large amounts of woody debris

4. Rapid erosion
Incision through sediment occurs during the development of new channels
Downcutting may be limited by bedrock or coarse armoring material supplied by landslide
Rough estimate of material moved during this phase = length of channel affected x channel width x depth of deposit
Phase ends when channel geometry is equilibrated to upstream water and sediment discharge

5. Slow erosion Sediment is supplied primarily by bank erosion
Supply rate is a function of flood occurrence, channel shifting and the establishment of bank vegetation

6. Significance of landslides
Sediment input affects riparian habitat
Infilling of Salmon redd’s
Gravel recruitment
Societal impacts
Damage to infrastructure
Potentially lethal

7. The 1983 Thistle landslide at Thistle, Utah-This landslide began moving in the spring of 1983 in response to groundwater buildup from heavy rains the previous September and the melting of deep snowpack for the winter of Within a few weeks the landslide dammed the Spanish Fork River, obliterating U.S. Highway 6 and the main line of the Denver and Rio Grande Western Railroad. The town of Thistle was inundated under the floodwaters rising behind the landslide dam. Total costs (direct and indirect) incurred by this landslide exceeded $400 million, the most costly single landslide event in U.S. history.