LARGE-SCALE LANDSLIDE ACTIVITY ACROSS VARYING LITHOLOGIES IN NORTH DAKOTA

The North Dakota Geological Survey (NDGS) has been mapping landslides for over two decades, however, it has accelerated its landslide mapping in recent years. In total, over 70,000 landslides have been mapped throughout North Dakota. Change detection utilizing repeat LiDAR collections has recently identified over 5,600 active landslides. The State of North Dakota has statewide LiDAR coverage (QL₃) and a second LiDAR coverage (QL₂) covering approximately 80% of the state. A full second coverage is anticipated to be completed in 2025. It wasn’t until recently that a second LiDAR dataset was available in the badlands of western North Dakota. This is important because this area has a high concentration of landslides and is the region of the state where the Bakken oil fields are located. The NDGS strives to work with industry to make the presence of landslides known, so oil well pads, pipelines, and roadways can be safely constructed. Due to the scale of these operations, the NDGS is routinely evaluating these areas for landslide movement identified via elevation change detection at a scale of 1:500. This makes landslide mapping a time-intensive and meticulous process; however, it results in a high-resolution product for the end user. There are two major types of large-scale landslides in the state, rotational slumps in the badlands of western North Dakota and earth flows in glacial meltwater trenches in eastern North Dakota. The northern portion of the badlands began forming roughly 600,000 years ago in western North Dakota by the erosion/downcutting of the Little Missouri River due to ice-age base level changes. This rapid erosion caused very steep slopes, resulting in tens of thousands of rotational landslides in Tertiary aged sandstones, claystones, and lignites. On the eastern side of North Dakota, Cretaceous shales play a major role in landslide issues, as seen in the Pierre Formation. The Pierre Formation most commonly presents issues in the Pembina Gorge and throughout the Sheyenne River Valley, glacial meltwater trenches that formed far more recently at the end of the last glacial period. Recent detailed mapping in these two distinct terrains offer new insights into their respective modern stabilities.