Statewide Landslide Information Database for Oregon (SLIDO)
What Is SLIDO?
Landslide in the Columbia River Gorge (ODOT, 2021a).
Introduction
The Statewide Landslide Information Database for Oregon, or SLIDO, is a compilation of landslide hazard data (inventory and susceptibility) in Oregon, compiled by the Oregon Department of Geology and Mineral Industries (DOGAMI). Many parts of Oregon have not yet been mapped in detail and thus the level of detail ranges from nearly complete information to very poor information. Regardless, the database contains the best available information statewide. GIS users can download and stream data and an interactive map is provided for users without GIS software.
Updates to SLIDO
SLIDO release 1 was published in 2008 and was a compilation of readily available previously published mapped landslides or landslide inventories. Before 2008, landslides were not mapped using high-resolution, lidar-based topography and therefore are considered in need of modern mapping (Burns, 2007). Since 2008, DOGAMI has continuously updated SLIDO through replacement of the older data with new modern detailed mapping following our published protocol in Special Paper 42 (Burns and Madin, 2009).
Current Version
SLIDO-4.2 is the current version, released in October 2020. Updates will continue in the future as new data are created and published. SLIDO-4.2 contains 53,311 landslide polygons from 359 studies, 14,326 historical landslide point locations, and 72 detailed studies. Click HERE to connect to the SLIDO website.
Table of Contents
This story map is designed to help users learn about landslides in the state of Oregon. You can click on one of the tabs at the top of the page to navigate directly to that section. Here is a brief explanation of the contents in each of the tabbed sections:
- Landslides in Oregon. This section defines a landslide and the difference between landslide inventory, susceptibility, and risk.
- Creating Landslide Maps. This section explains how the data in SLIDO are created.
- Quality and Availability. This section describes the variation of landslide data quality and availability throughout the state.
- Landslide Maps. This section allows users to explore statewide SLIDO data.
- Additional Resources. This section provides additional resources for learning about landslides in your area and learning how to prepare for potential landslides.
Landslides in Oregon
Landslide Inventory, Susceptibility, and Risk
There are many natural hazards that occur in Oregon and landslides are one of the most widespread and damaging in the state. To reduce losses from future landslides, areas that slid in the past must first be inventoried. This is a very similar process to reducing losses from other hazards. For example, forecasting future flooding is based on past events. Once the inventory of past events is cataloged, areas of lower or higher potential of landslides happening in the future - called susceptibility - can be modeled. After landslide inventory and susceptibility have been identified, the risk of landslides to people and infrastructure can be quantified and mitigation projects can be prioritized and implemented.
Question: What is the difference between landslide inventory and landslide susceptibility?
What Is a Landslide?
The general term “landslide” refers to a range of mass movements, including rock falls, debris flows, earth slides, and other mass movements (Varnes, 1978). Different types of landslides have different frequencies of movements, triggering conditions, speed, and depth, and very different resulting hazards. Landslides in Oregon are commonly caused by:
- intense rainfall
- rapid snowmelt
- freeze/thaw cycles
- earthquakes
- volcanic eruptions
- humans (grading, water, vegetation)
- a combination of the above
What Types of Landslides Are There in Oregon?
Landslides in Oregon can be classified into four different types of movement:
- Slides: landslides with a discrete failure surface. Most common where weak soil overlays rock or along weak plans within the rock mass. The main modes of slides are Translational and Rotational.
- Flows: mixtures of relatively high concentrations of water with soil, rock, and/or debris that have become a slurry and commonly move rapidly downslope. Examples are channelized debris flows and earth flows.
- Spreads: extension and subsidence of commonly cohesive materials overlying liquefied layers. These typically occur during an earthquake.
- Topples/Falls: rapid, nearly vertical movement of masses of material such as rocks or boulders. These usually occur in exposed areas of near-vertical soil and rock.
The graphic below provides an image and further description for each of the common landslide types in Oregon.
Types of landslides found in Oregon (Highland, 2004).
Landslide on OR Highway 41 (ODOT, 2021b).
Primary image: Landslide on OR Highway 42 (ODOT, 2021c).
Why Worry About Past Landslides?
Landslides can move repeatedly over time. Sometimes a portion of a landslide will reactivate; other times the entire landslide will reactivate. Some landslides, such as channelized debris flows, will reoccur in the same channel over and over because the conditions in the channel are suitable for this type of landslide. Therefore, existing landslides are part of the overall landslide hazard puzzle. Existing landslides are used to calibrate susceptibility models and are very commonly used as part of susceptibility maps.
What Is Susceptibility?
Landslide susceptibility maps show areas of future landslide potential (usually low, moderate, high). The zones are relative to each other. They do not indicate a landslide is imminent, but rather where landslides are more or less likely to occur.
Primary image: U.S. Ready, 2021.
Landslide Risk in Oregon
Many parts of Oregon are highly susceptible to landslides, which can pose significant threats to people and infrastructure, particularly in the portions of the state with moderate to steep slopes. As population growth expands and development on landslide-susceptible terrain increases, greater damage and losses are likely to result.
Venn diagram illustrating how risk is the intersection of people and assets and natural hazards.
The greatest risk from landslides is to life. Fatal landslides are rare but do occur in Oregon. They are most commonly associated with channelized debris flows because these slides can move very fast and travel very far. Most of Oregon’s landslide damage has been associated with severe winter storms, where landslide losses can exceed $100 million in direct damage, as occurred in an event in February 1996 (Wang and others, 2002). However, landslides are a chronic hazard in Oregon and annual average maintenance and repair costs for landslides exceed $1.5 million (Burns and others, 2017). Landslides induced by earthquake shaking are also likely in many parts of Oregon, and losses associated with sliding in moderate-to-large earthquakes are likely to be significant.
ODOT image of a landslide over an Oregon highway (ODOT, 2018).
Primary image: Landslides in the Columbia River Gorge (ODOT 2021d).
Creating Landslide Maps
How Are Landslide Inventory and Susceptibility Maps Created?
The methods DOGAMI uses for identifying areas of landslide hazard include creating an inventory of existing landslides and using this inventory to produce maps of various types of landslide susceptibility. This section will explain the differences between landslide inventories and landslide susceptibility maps and give examples of each.
Landslide Inventory
The initial step in landslide hazard identification is to create a landslide inventory, or a catalog of past (historic and prehistoric) landslides. DOGAMI follows Special Paper 42 (Burns and Madin, 2009), "Protocol for Inventory Mapping of Landslide Deposits from Light Detection and Ranging (LIDAR) Imagery." The method results in two kinds of data: spatial data and tabular data. Spatial data are data that can be mapped; tabular data are descriptive data, usually in text or numeric form, stored in rows and columns in a database and linked to spatial data. The method also generates 25 attributes about each landslide. One example is whether the landslide occurred within the last 150 years (historic) or long ago (prehistoric). Another example is if it is deep or shallow, as defined as a landslide with a failure surface of greater or less than 15 feet below ground. The diagram below shows the parts of a typical landslide.
Diagram showing the parts of a typical landslide (Highland, 2004).
Landslide Inventory Map
Landslide inventory includes deposit polygons (including debris flow fans and talus extent), scarp polygons (outlines of the head scarp and flanks), and scarp polylines (uppermost extent of the head scarp).
The legend below explains the symbology for the map on the left.
The map on the left includes the Providence Park Landslide and Zoo Landslide near downtown Portland, Oregon. Click on the first button below to view the area without the landslide inventory. Click on the middle button to add back in the area's full landslide inventory to the map. Click on the last button to view historic landslide points only.
Detailed Landslide Susceptibility
Detailed landslide susceptibility maps are created by combining a landslide inventory with a model. Different models are needed for different types of landslides. For example, shallow and deep landslide susceptibility maps use different models that result in different parts of the landscape being identified as susceptible to different landslide types. Other examples include channelized debris flows and rockfall. The diagram below shows differences between shallow [left] and deep [right] susceptibility.
Diagram showing the difference between deep [right] and shallow [left] landslides (Burns and others, 2012).
Landslide Susceptibility Map
The map on the left shows examples of both deep and shallow landslide susceptibility mapping. Shallow landslide susceptibility identifies areas with potential for future shallow landsliding. It is most commonly the movement of a relatively thin layer of slope material, typically on steep slopes, with a shallow failure surface (<15 feet) (Burns and others, 2012). Deep landslide susceptibility identifies areas with potential for future deep landsliding. Deep landslides are most commonly associated with factors within the bedrock geology, such as a contact between units or weak bedding surfaces (Burns and Mickelson, 2016).
The legend below shows the detailed landslide susceptibility symbology for the map on the left.
Click on a specific button below to view an example of one of the landslide susceptibility types in the map on the left.
Generalized Statewide Landslide Susceptibility Overview
The map on the left shows a coarse-grained, small-scale (1:500,000) landslide susceptibility dataset of the entire state of Oregon and is for use at a regional scale. This dataset is in raster format at a 32-foot (10-meter) resolution (Burns and Others, 2016). The generalized statewide landslide susceptibility map may be used if the more detailed deep and shallow susceptibility maps are unavailable.
The legend below shows the statewide landslide susceptibility symbology for the map on the left.
Click on the top button below to view an example of the statewide landslide susceptibility map. Note the difference in detail between the shallow and deep susceptibility datasets and the statewide susceptibility dataset.
Quality and Availability
This section explores the detail, completeness, and accuracy of the landslide inventory and susceptibility datasets included in SLIDO.
Exploring Landslides in Oregon
Within SLIDO, the original studies vary widely in location, scale, scope, and focus. This variety is reflected in a wide range of accuracy, detail, and completeness with which landslide hazards are mapped. Important factors that can affect the quality include:
- Original mapping scale: In general, the original mapping scale can be thought of as a proxy for level of detail. For example, a map created at a statewide scale will not capture features like landslides, which are most commonly seen at a local, or zoomed in, scale.
- Original mapping purpose: This factor can be thought of as the scope of the mapping. For example, a mapping project focused on bedrock and groundwater may mostly ignore surficial features like landslides.
- Information and technology available at the time of mapping: Technology has been rapidly increasing our ability to map landslide hazards, specifically in the last 20 years. For example, a mapping project completed in the 1970s or 80s would not have used computers, GIS, orthophotography, or lidar-derived topography, and thus many landslides would have been missed. Burns (2007) concluded that in Oregon, lidar must be used for a complete and detailed landslide inventory.
- Background of and interpretation by original mapper: Geologists with proficiency in engineering geology, geomorphology, and hazards backgrounds may make more specialized maps with detailed hazards information than others without that type of specialized training.
Primary image: Landslide in the Columbia River Gorge (ODOT, 2021e).
Landslide Inventory Quality
The original landslide inventory studies were conducted at various scales, for various purposes, and by authors with various levels of expertise in identifying landslides and various tools for identification. Therefore, the level of detail, completeness, and accuracy of the data varies greatly across the state. There are three levels of landslide inventory quality in Oregon: State, Regional, Local, where local is highest quality and state is the lowest. The map of Oregon at right shows the the accuracy, detail, and completeness of mapped landslide inventories throughout the state.
The legend below explains the mapping quality symbology for the map on the right.
Landslide Susceptibility Quality
Landslide susceptibility data come in two levels of detail: state, and local, where local is highest quality and state is the lowest, similar to the landslide inventory. The map of Oregon at right shows the the accuracy, detail, and completeness of mapped landslide susceptibility zones throughout the state.
The legend below explains the mapping quality symbology for the map on the right.
Future Updating Procedure
SLIDO is mostly commonly updated when DOGAMI publishes a new dataset that contains landslide inventory or susceptibility.
Historic points and data published by authors outside DOGAMI are commonly updated annually or biannually.
To keep track of updates, we use a primary release number such as the current release 4, along with a decimal number identifying the update, such as 4.2. When we apply major updates to the database, a new primary release number (e.g., 5.0) is assigned.
Primary image: Landslides in the Columbia River Gorge (ODOT, 2021f).
Map Limitations
SLIDO was created by compiling the best landslide inventory data available. However, several limitations are worth noting.
- Although every effort was made to ensure that database entries 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 limited in terms of scale.
- The database is from original sources. Data from these sources vary in scale, original purpose of mapping, available tools at the time of mapping, and background and interpretation by original mapper.
- DOGAMI neither collected nor analyzed any new data to create this database. It is a compilation of mostly previously published data.
Primary image: Landslide in the Columbia River Gorge (ODOT, 2021g).
Landslide Maps
The map on the left allows you to explore all of the SLIDO datasets: inventory, historic landslide points, shallow and deep susceptibility, and statewide susceptibility. Be aware, the map may draw slower, depending on internet connection speeds.
Navigation
To zoom to an area of interest, use the Zoom Buttons (lower left, + or - ) or hover over the area and use your mouse roller.
To find a specific area of interest, type the address or place name into the Search Window (upper left, spyglass).
To zoom to the full, statewide extent, click on the Home Button (lower left, house icon).
Turn Datasets On and Off
To access the legend and turn datasets on and off, click on the Legend Button (upper left, three stacked diamonds) and the legend window will open. The datasets are organized into "Susceptibility Datasets" and "Inventory Datasets." You can turn a group or individual dataset on or off by clicking its adjacent check box. Click and drag the legend window to place it around the map.
View Map at Full Screen
To view the map at full screen, click on the Open Live Content Button (upper right, box with NE-pointing arrow). This will open the map in a new tab, without the sidebar.
The legend below shows the landslide inventory and detailed and regional landslide susceptibility symbology for the map on the left.
Additional Resources
This section provides links to websites or documents that provide additional information about channelized debris flows, landslide warnings, preparing for landslides, and continued landslide mapping in Oregon.
