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In hilly areas with humid climates, landslides are among the most problematic natural hazard risk a property owner faces. Living on a landslide is equivalent to living on an active fault or in a floodplain: the land will move or a flood will occur, but it's not possible to predict when these events will happen. Unlike flood or earthquake damage, however, landslide damage is not easily insurable. Therefore, understanding the landslide risk on your property and how to mitigate it becomes an important responsibility of land ownership.
During the winter of 1996-97, there were over 9,000 reported landslides in Oregon. The vast majority of those were located west of the Cascade Mountain Range. In Clackamas County, 970 landslides occurred between 1964 and 2009. While many of these landslides can be directly attributed to the heavy winter rains, there are other causes that should be considered as well. Human activities such as excavation or placement of fill on slopes, broken irrigation systems and large piles of wet yard debris can be triggers. Additionally, earthquakes, freeze/thaw cycles and rapid snow melt are known contributing factors.
In an effort to help communities and their residents better understand landslides and become better prepared to manage landslide risk, the Oregon Department of Geology and Mineral Industries (DOGAMI) recently completed an extensive inventory, mapping and data analysis of local landslides and landslide susceptibility across the landscape.
The information below provides a brief explanation of some of the products produced by DOGAMI in the course of their landslide analysis. Additionally, links to the relevant studies, informational fact sheets and various landslide maps are provided.
In 2005, DOGAMI began a collaborative landslide research program with the U.S. Geological Survey (USGS) Landslide Hazards Program to identify and understand landslides in Oregon. Using high-resolution Lidar mapping technology and following a strict protocol, DOGAMI set out to complete an inventory and develop maps of existing historic and prehistoric landslides throughout the state.
In December of 2013, DOGAMI released a landslide susceptibility report and accompanying maps that are expected to aid land use and emergency planners in northwestern Clackamas County and could help make area communities safer.