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Landslide hazards in Oregon

Landslide Hazards in Oregon fact sheet (1266 KB PDF)

Learn more about debris flow warnings

Homeowner's Guide to Landslides, produced by Portland State University (PDF)

Did You See It? -- report a landslide to the USGS and view reported landslides

SLIDO landslide map interface Interactive
Oregon Landslides Map
(SLIDO)

More lidar-based landslide mapping:

DOGAMI Fact Sheet: Understanding Landslide Deposit Maps

IMS-22, GIS overview map of potential rapidly moving landslide hazards in western Oregon, by R. J. Hofmeister, D.J. Miller, K. A. Mills, J. C. Hinkle and A. E. Beier, 2002.
Full publication includes short explanatory text and GIS files for landslides hazards in Benton, Clackamas, Clatsop, Columbia, Coos, Curry, Douglas, Hood River, Jackson, Josephine, Lane, Lincoln, Linn, Marion, Multnomah, Polk, Tillamook, Washington, and Yamhill counties.


New maps reveal landslides using lidar-based imaging

thumbnails of plates from IMS-32, Lake Oswego quadrangle

IMS-35, Landslide inventory maps of the Linnton quadrangle, Multnomah and Washington Counties, Oregon | order | preview plates

IMS-34, Landslide inventory maps of the Beaverton quadrangle, Washington County, Oregon | order | preview plates

IMS-34 and IMS-35 include: SP-42 coverSpecial Paper 42, Protocol for Inventory Mapping of Landslide Deposits from Light Detection and Ranging (Lidar) Imagery, by William J. Burns and Ian P. Madin

- for more information on the protocol, contact Bill Burns

We hear a lot about landslides in Oregon, especially in the rainy season and most especially in western Oregon where steep slopes and wet, water saturated soils mix together to make the earth move.

What can you do about landslides before and during an intense storm? Click here for some helpful tips.

Geologists define landslides as the downslope movement of rock, soil, or related debris. Geologists use the term “mass movement” to describe a great variety of different landslides, such as rock fall, creep, slump, mudflow, earth flow, debris flow, and debris avalanche, but in most mass movement events, water plays a pivotal role by assisting in the loosening and lubricating of rock and soil surfaces to help begin the earth moving. 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.

In December of 2007, a powerful debris flow roared down a steep drainage near the town of Clatskanie, destroying home and businesses and closing Highway 30. Oregon Department of Geology landslide specialist Bill Burns visited the site and put together this presentation:

first slide of presentation showing house engulfed by debris flow material
Woodson Debris Flow - December 2007
PDF of PowerPoint presentation (1.7 MB)

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 (Light Detection and Ranging) is helping the Oregon Department of Geology 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 here.

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


The U.S. Geological Survey has also put together information on landslides that you can view and/or download:

USGS Fact Sheets on Landslides and Debris Flows:
2004 FS 2004-3072 Landslide types and processes
2000 FS 071-00 Landslide Hazards
1997 FS 176-97 Debris-Flow Hazards in the United States




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