COLLECTING AND USING LANDSLIDE INVENTORY DATA IN OREGON

Landslides reflect a significant hazard throughout the state of Oregon. As with most natural hazards, a comprehensive understanding of what has happened in the past is the foundation to predicting the future. Our objective is to build on an existing landslide database developed for Oregon, making it more robust and accessible for scientific applications and risk reduction.

Prior to the digital revolution 15,093 landslide polygons were mapped and published on paper maps maintained by the Oregon Department of Geology and Mineral Industries (DOGAMI). During the last decades, staff at DOGAMI has compiled more than 12,000 historically active landslide points with movement dates ranging from 1932 to 2015. With the advent of remote sensing lidar technology, the landslide polygon database has increased to over 41,000. All of this data is located in the Statewide Landslide Information Database for Oregon (SLIDO). Many of these database entries have extensive attributes associated with them. Our current primary landslide inventory data collection methods include using lidar, serial orthophotos, and the internet. Our lidar based mapping has substantially increased our understanding of the landslide hazard in communities in Oregon. For example, 1,517 landslides were located using lidar in a typical Oregon Coast Range watershed, which previously had 176 identified landslides.

The SLIDO landslide database has permitted us and others to examine the details of why Oregon has such an extensive landslide hazard, predict areas of relative future landslide susceptibility, assess landslide risk, and will eventually help to create future probabilistic hazard maps and understand the impact from climate change. The detailed landslide polygons have enabled us to calculate area statistics, for example certain geologic units in Oregon are covered by up to 45% deep landslides. We are also in a better position today to explore the relationship between the landslides and dip direction of geologic features and the contacts between units. Combined, these data enable us to create better landslide susceptibility maps. As our understanding of the landslide hazard improves, we have also been able to perform limited risk analysis, in order to examine how the hazard may impact property and infrastructure in the future.