| Description | Spatial | Attributes |
One of the primary chronic and most devastating geologic hazards in Oregon is landslides. Average annual repair costs for landslides in Oregon exceed $10 million and severe winter storm losses can exceed $100 million (Wang and others, 2002). As population growth continues to expand and development into increased landslide susceptible terrain occurs, greater losses are likely to result (Figure 1). In order to begin reducing losses from landslides, large-scale endeavors are necessary at all community levels from state government to individual family homes. One successful way to reduce losses from landslides is through pre-disaster mitigation, which can be performed at many scales from statewide to local. To begin pre-disaster mitigation of landslides, the landslide hazard must be located (Figure 1). Once the hazard is located the population and infrastructure vulnerable to the hazards can be identified and the risk mitigated. In order to improve our understanding of the landslide hazard in Oregon and to create a statewide base level of landslide data, this database of mapped landslides, the Statewide Landslide Information Database of Oregon (SLIDO) was created. The four main objectives of this study were 1) identify previously mapped landslide deposits statewide, 2) improve the understanding of landslide hazards throughout Oregon, 3) improve the abilities of communities to begin effective landslide management and risk reduction activities, and 4) recommend future improvements and updates to the database. The resulting database includes more than 15,000 landslide and landslide related features (polygons) extracted from 257 published and non-published studies. The original studies vary widely in scale, scope and focus which is reflected in a wide range in the accuracy, detail and completeness with which landslides are mapped.
In order to improve our understanding of the landslide hazard in Oregon and to create a statewide base level of landslide data, this database of mapped landslides, the Statewide Landslide Information Database of Oregon (SLIDO) was created. The four main objectives of this study were 1) identify previously mapped landslide deposits statewide, 2) improve the understanding of landslide hazards throughout Oregon, 3) improve the abilities of communities to begin effective landslide management and risk reduction activities, and 4) recommend future improvements and updates to the database.
The resulting database includes more than 15,000 landslide and landslide related features (polygons) extracted from 257 published and non-published studies. The original studies vary widely in scale, scope and focus which is reflected in a wide range in the accuracy, detail and completeness with which landslides are mapped. SLIDO was created through the compilation of the best data available. Several limitations are worth noting, and underscore that any hazard map is generally useful for regional applications but should not be used as an alternative to site-specific studies in critical areas. 1. Although it every effort was made to ensure that digitization and database entry were accurate and complete, no effort was made to verify the original data on which the compilation is based. Geologic data in the less populated eastern portions of the state were particularly limited in terms of scale, for example the 1:500,000 scale geologic map of the state was used in some locations. 2. As previously discussed, the developed database is from original sources that vary in scale, original purpose of mapping, available tools at the time of mapping, and background and interpretation by original mapper. These factors all affect the level of detail and accuracy of the landslides. 4. We neither collected, nor analyzed any new data to create this map. Therefore, this database is a snapshot view of the current data. Results of a recent study by DOGAMI and USGS geologists in a small study area in the Portland Hills (60 km2) found roughly 200 landslides using a LIDAR derived high resolution DEM (Table 3). The same area also has roughly 300 mapped landslide points in the 1996-1997 storm event inventories. SLIDO release-1 has roughly 50 landslides located in this same area, roughly 10 of which are from 1:24,000 scale geologic maps and roughly 40 from landslide specific mapping done in the 70's. Since this area (the small study area in the Portland Hills) of SLIDO release-1 was compiled from geologic mapping done at a relatively small scale, and other mapping performed specifically to locate landslides, the area is likely one of the areas that should be considered to have higher accuracy with regard to landslides. The number of landslides in SLIDO release-1 within this small study area, compared to the LIDAR mapping would be roughly 25%. Therefore, this percentage (~25%) should be considered an upper value of accuracy of SLIDO release-1 for most areas, except for the previously mentioned new landslide specific mapping (Lincoln County Coast and City of Oregon City) recently completed by DOGAMI. In conclusion, most of SLIDO release-1 should be considered to have located between 0% - 25% of the actual landslides at any location.