Pre-Historic Landslides on the Southeast Flank of the Uinta Mountains, Utah: Character and Causes of Slope Failure

More than 100 landslides have been mapped along the southeast flank of the Uinta Mountains. Large landslide deposits are up to 4.6 kilometers long and have an area of approximately 5-9 km². Landslide types include multiple and successive rock slumps, debris slumps and debris flows. Most landslides have a main head scarp in the Bishop Conglomerate and the large landslides have many minor scarps. Multiple slump blocks are manifest by repeated transverse ridges and trenches in the head area of some landslides. Most body and toe areas are deeply incised by gully erosion (up to 91 meters deep) and drainages are well developed with little ponding. Detailed mapping of the large landslides shows that the deposits are an accumulation of successive slope failures that have continually eroded the landscape over time. Many landslides in the area appear to be inactive and dormant but slopes may continue to fail particularly if landslides are disturbed. A Geographic Information System (GIS) was used to analyse slope failing factors and the main factor that seems to have contributed to slope failure is the presence of abundant shale-rich, weak bedrock capped with the thick and fairly resistant Bishop Conglomerate. Slopes are further destabilized as water percolates down through the porous Bishop Conglomerate. Eventually the water meets underlying shale-rich bedrock where it is channelled near this contact until it emerges as springs. This groundwater flow likely reduces shear strength of the shale-rich substrate and of some of the finer grained layers in the Bishop Conglomerate. Other important slope failure factors include the removal of easily erodable Mesozoic shales from beneath the more-resistant Bishop Conglomerate, headward gully erosion, bedrock dip and slope aspect.

Name thesis:degree_name

MS

Grantor dc:publisher

Brigham Young University - Provo

Author dc:creator

• Bradfield, Todd D.

• landslide
• GIS
• uinta mountain
• bishop conglomerate
• slope failing analysis
• slump
• Geology

Language dc:language

English

Repository record dc:identifier

https://scholarsarchive.byu.edu/etd/1038

OAI identifier oai:identifier

oai:scholarsarchive.byu.edu:etd-2037