By: R. E. Giraud
Movement of the Heather Drive landslide in late-August 2001 forced homeowners to evacuate their houses and suffer significant economic loss. Preliminary loss estimates indicate that landslide-related losses exceed $1 million. The landside is a reactivation of a prehistoric landslide in lacustrine silt and clay of the Lake Bonneville Weber River delta on a north-facing slope above South Fork Kays Creek. Landslide movement impacted six houses; three were moved off the landslide and three were demolished due to landslide-related damage. The landslide movement history indicates a gradual reactivation followed by relatively rapid movement and an abrupt stop. The majority of landslide movement occurred between August 20 and 29, 2001.
The landslide surface is relatively undeformed indicating movement of a relatively intact mass. Landslide movement resulted in a main scarp ranging up to 9.5 feet high, and a minimum of 7.1 feet of northward displacement of the lower landslide and 4.1 feet of toe displacement into the creek restricting the flow in South Fork Kays Creek. The exact cause(s) of landslide movement in 2001 is unknown, but observations indicate that movement likely started in 1997 or 1998 when other nearby landslides reactivated. No documented changes in slope configuration or ground-water conditions preceded accelerated movement in 2001. The landslide apparently moved intermittently or at an extremely slow to very slow rate since at least 1998, perhaps until the slip surface developed and shear strengths along the slip surface were reduced sufficiently to allow accelerated movement in late-August 2001. Future movement could enlarge the landslide, placing additional houses, Heather Drive and underlying utilities, and South Fork Kays Creek at risk. The Utah Geological Survey recommends continued landslide monitoring and a geotechnical-engineering slope-stability investigation to determine the conditions under which future movement may occur and the risk posed to nearby houses, Heather Drive and underlying utilities, and flow in the creek.
Pages: 22 p.
Location: Davis County
Media Type: Paper Publication