LANDSLIDE MAPPING IN NORTH DAKOTA: A COMPLETE 1:24,000-SCALE DATASET AND FUTURE MAPPING ENDEAVORS

Since 2003, the North Dakota Geological Survey (NDGS) has undertaken a meticulous mapping effort, successfully delineating over 60,000 landslides at a scale of 1:24,000. Initially, this mapping was reliant on aerial photographs from the 1950s and 1960s, viewed in stereopair, and early satellite imagery (Phase 1). However, since 2017, the NDGS has transitioned to using LiDAR data and updated all 1,464 maps (Phase 2). The comprehensive landslide mapping at a scale of 1:24,000 has been successfully completed for the entire state of North Dakota during Phase 2. Although spatially comprehensive, Phase 2 maps lack temporal data associated with landslides, leading to an incomplete understanding of areas' susceptibility. To overcome this limitation, the North Dakota Department of Water Resources has now acquired statewide LiDAR data at the QL3 Quality Level and is in the process of obtaining repeat coverage at the higher QL2 Quality Level. The time interval between the two coverages typically spans 8 to 10 years. By conducting a comparison of elevation data from these two datasets, NDGS geologists can discern changes that occurred on the land surface during that timeframe, thereby gaining crucial insights into recent landslide activity. This vertical displacement method is applicable in regions where multiple LiDAR datasets are available. It enables the identification of areas of landslides that have experienced more recent movement, thereby introducing temporal data as a significant component of Phase 3 of the NDGS landslide mapping program. The implementation of this approach has resulted in the identification of over 5,000 "active" landslide areas to date. The inclusion of temporal data has proven to be invaluable in evaluating infrastructure vulnerabilities, including those related to proposed pipeline corridors, roadway impacts, and the stability of potential earthen dams. For example, in the spring of 2022, the northeastern region of North Dakota experienced heavy snowmelt and rainfall, which posed a severe threat to dams in the area. NDGS observations revealed recent slope failures (within the last 10 years) near the Bourbanis, Hanks Corner, Olga, Olson, and Senator Young Dams, offering critical information for risk assessment and potential mitigation efforts in collaboration with other government agencies.