Abstract
Active landslides throughout the states and territories of the United States result in extensive property loss and 25–50 deaths per year. The U.S. Geological Survey (USGS) has a long history of detailed examination of landslides since the work of Howe (1909) in the San Juan Mountains of Colorado. In the last four decades, landslide inventory maps and landslide hazard maps have depicted landslides of different ages, identified fresh landslide scarps, and indicated the direction of landslide movement for different regions of the states of Colorado, California, and Pennsylvania. Probability-based methods improve landslide hazards assessments. Rainstorms, earthquakes, wildfires, and volcanic eruptions can trigger landslides. Improvements in remote sensing of rainfall make it possible to issue landslide advisories and warnings for vulnerable areas. From 1986 to 1995, the USGS issued hazard warnings based on rainfall in the San Francisco Bay area. USGS workers also identified rainfall thresholds triggering landslides in Puerto Rico, Hawaii, Washington, and the Blue Ridge Mountains of central Virginia. Detailed on-site monitoring of landslides near highways in California and Colorado aided transportation officials. The USGS developed a comprehensive, multi-sector, and multi-agency strategy to mitigate landslide hazards nationwide. This study formed the foundation of the National Landslide Hazards Mitigation Strategy. The USGS, in partnership with the U.S. National Weather Service and the State of California, began to develop a real-time warning system for landslides from wildfires in Southern California as a pilot study in 2005.
