Landslides are a common chronic problem in Oregon, especially in places with or near moderate to steep slopes, during times of heavy precipitation, and during earthquakes. Landslides can also be catastrophic.
Geologists define landslides as the downslope movement of rock, soil, or related debris. Different types of landslides are composed of different materials, such as rock, sand, clay, and water and the proportions of these materials will dictate how fast a landslide moves and how much area it will cover.
To learn more about landslides in Oregon, read our Landslide Fact Sheet.
To learn more about debris flows, a dangerous type of fast moving, destructive landslide, click here.
Although landslides are propelled by gravity, they can be triggered by other natural geologic events or human activity. Volcanic eruptions and earthquakes can initiate earth movement on a grand scale. A variety of debris flows called “lahars”—a mixture of volcanic ash and water— are specific to volcanic activity and are often the major hazard experienced in a volcanic episode. Although earthquakes can initiate debris flows, the major causes of landslides in the northwest are continuous rains that saturate soils.
Landslides can also be the direct consequence of human activity. Seemingly insignificant modifications of surface flow and drainage may induce landslides. In an urban setting, improper drainage is most often the factor when a landslide occurs.
Many unstable, landslide prone areas can be recognized. Tip-offs include scarps, tilted and bent (“gun-stocked”) trees, wetlands and standing water, irregular and hummocky ground topography, and oversteepened slopes with a thick soil cover. The technology of spotting landslides by use of aerial photography and new laser based terrain mapping called lidar is helping DOGAMI develop much more accurate and detailed maps of areas with existing landslides and we are now able to create landslide susceptibility maps, that is, maps that that show where we think different types of landslides may occur in the future.
You can learn more about mapping landslides with lidar
DOGAMI Landslide Mapping
In 1998, following the deadly landslides that occurred during the storms of 1996, a task force formed by the State Legislature to look at the problem of landslides in Oregon, presented its results. You can read the report here from the Joint Interim Task Force On Landslides and Public Safety.
For additional background, you can read the Report to the Seventy-first Legislative Assembly on the Implementation of 1999 Senate Bill 12 Relating to Public Safety and Rapidly Moving Landslides
In 2006 and 2007, the Oregon Department of Geology hosted two conferences in Portland to discuss the status of landslide mitigation and preparation in the state:
Landslide Symposium 2007
Landslide Forum 2006
DOGAMI is part of a new multi-agency coalition:
OLRRT - Oregon Landslide Emergency Risk Reduction Team.
SLIDO Interactive Map
Access the SLIDO Interactive Map here
The Statewide Landslide Information Database for Oregon (SLIDO) is compilation of landslides in Oregon that have been identified on published maps. The interactive map lets you view information on location, type, and other attributes related to identified landslides in Oregon.