The Alaska Division of Geological & Geophysical Surveys completed a comprehensive landslide hazard assessment for the city, the division reported in a Dec. 11 press release.
The hazard assessment created a map and database of historical and prehistoric slope failures, maps of shallow and deep-seated landslide susceptibility, and a map of simulated debris flow runouts for the City of Homer and neighboring Kachemak.
The full report was composed by J. Barrett Salisbury, a geologic hazards geologist based out of Fairbanks. Salisbury is a partner in the Alaska arm of the National Tsunami Hazard Mitigation Program and is the current chair of the Alaska Seismic Hazards Safety Commission, according to the Alaska Division of Geological and Geophysical Surveys (https://dggs.alaska.gov/) .
The results are intended to educate officials and the public regarding locations of potential slope failure hazards, provide a basis for regional long-term planning and resilience and to inform the City of Homers’ update of their comprehensive plan, the press release said.
Acting City Manager Julie Engebretsen said in the release that she was pleased for the access to much-needed Federal Emergency Management Agency funds for Homer. Though Engebretsen did not provide any more direct quotes to the Homer News she referred to an article from the New York Times describing how other communities in the state of Alaska including Sitka, Haines, Wrangell and Ketchikan are doing to use the landscape mapping for potential landslides. The Oct. 21 article is titled, “Scientists are mapping landslides in Alaska. Some homeowners don’t want to know.”
“Our Planning Commission and City Council will use the new lidar data and landslide susceptibility report as resources while we work on slope stability issues in the coming years,” she said.
The intention for the maps produced in the study is not predict slope failures but demonstrate where landslides have occurred in the past and when increased geotechnical investigations might be suggested for areas targeted for development.
The abstract for the project defines how slope safety is determined by incorporating landslide inventory data, geotechnical soil properties, and lidar-derived topographic slope.
Sheet maps are included with the study that show slope failure in several different time frames in different color coding: pre-1952; 1975 to mid-1980s; mid-1990s to 2000; 2000 to 2012; and 2012 to 2016. The full document and map links are available online at https://dggs.alaska.gov/webpubs/dggs/ri/text/ri2024_003.pdf.
