Debris-flow source areas are often associated with steep gullies, and debris-flow deposits are usually indicated by the presence of debris fans at the mouths of gullies. Fires that denude slopes of vegetation intensify the susceptibility of slopes to debris flows. Debris avalanche: This is a variety of very rapid to extremely rapid debris flow. The slope material liquefies and runs out, forming a bowl or depression at the head.
The flow itself is elongate and usually occurs in fine-grained materials or clay-bearing rocks on moderate slopes and under saturated conditions. However, dry flows of granular material are also possible. Mudflow: A mudflow is an earthflow consisting of material that is wet enough to flow rapidly and that contains at least 50 percent sand-, silt-, and clay-sized particles.
Creep: Creep is the imperceptibly slow, steady, downward movement of slope-forming soil or rock. Movement is caused by shear stress sufficient to produce permanent deformation, but too small to produce shear failure.
There are generally three types of creep: 1 seasonal, where movement is within the depth of soil affected by seasonal changes in soil moisture and soil temperature; 2 continuous, where shear stress continuously exceeds the strength of the material; and 3 progressive, where slopes are reaching the point of failure as other types of mass movements. Creep is indicated by curved tree trunks, bent fences or retaining walls, tilted poles or fences, and small soil ripples or ridges.
Lateral Spreads: Lateral spreads are distinctive because they usually occur on very gentle slopes or flat terrain. The dominant mode of movement is lateral extension accompanied by shear or tensile fractures.
The failure is caused by liquefaction, the process whereby saturated, loose, cohesionless sediments usually sands and silts are transformed from a solid into a liquefied state. Failure is usually triggered by rapid ground motion, such as that experienced during an earthquake, but can also be artificially induced. When coherent material, either bedrock or soil, rests on materials that liquefy, the upper units may undergo fracturing and extension and may then subside, translate, rotate, disintegrate, or liquefy and flow.
Lateral spreading in fine-grained materials on shallow slopes is usually progressive. The failure starts suddenly in a small area and spreads rapidly. Often the initial failure is a slump, but in some materials movement occurs for no apparent reason. Combination of two or more of the above types is known as a complex landslide. The two major types of slides are rotational slides and translational slides. Although there are multiple types of causes of landslides, the three that cause most of the damaging landslides around the world are these:.
Landslide Mitigation — How to Reduce the Effects of Landslides: Vulnerability to landslide hazards is a function of location, type of human activity, use, and frequency of landslide events. The effects of landslides on people and structures can be lessened by total avoidance of landslide hazard areas or by restricting, prohibiting, or imposing conditions on hazard-zone activity. Local governments can reduce landslide effects through land-use policies and regulations.
Individuals can reduce their exposure to hazards by educating themselves on the past hazard history of a site and by making inquiries to planning and engineering departments of local governments.
They can also obtain the professional services of an engineering geologist, a geotechnical engineer, or a civil engineer, who can properly evaluate the hazard potential of a site, built or unbuilt. The hazard from landslides can be reduced by avoiding construction on steep slopes and existing landslides, or by stabilizing the slopes. Stability increases when groundwater is prevented from rising in the landslide mass by 1 covering the landslide with an impermeable membrane, 2 directing surface water away from the landslide, 3 draining groundwater away from the landslide, and 4 minimizing surface irrigation.
An advisory may include general statements about rainfall conditions that can lead to debris-flow activity, and list precautions to be taken in the event of heavy rainfall. People in, or planning to travel through, a watch area should check preparedness and stay informed about developing weather patterns.
Flash Flood Watches can be put into effect for as long as 12 hours, while heavy rains move into and across the area. A warning can also be issued as a result of torrential rains, a dam failure or snow thaw. GRAVITY — The natural force of attraction exerted by a celestial body, such as Earth, upon objects at or near its surface, tending to draw them toward the center of the body. Click Here to see if there are any active warnings in your area. Get a ground assessment of your property.
Landslides occur where they have before, and in identifiable hazard locations. Ask for information on landslides in your area, specific information on areas vulnerable to landslides, and request a professional referral for a very detailed site analysis of your property, and corrective measures you can take, if necessary.
Watch the patterns of storm-water drainage near your home, and note the places where runoff water converges, increasing flow in channels. These are areas to avoid during a storm. Make evacuation plans. Plan at least two evacuation routes since roads may become blocked or closed. The eruption of the Mount St. Helens volcano in the Cascade Mountain Range saw a landslide with a volume of material of 67 cubic miles. The March 22, landslide in Oso resulted in 43 deaths, with damage to approximately 50 homes and one square mile of land, rivers and infrastructure were destroyed.
How to Help Planning reduces catastrophic loss. By investing in hazard analysis and mapping to guide land-use decisions, the potential for catastrophic loss can be reduced. By using GIS in combination with satellite images, it is possible to create detailed maps that show highly probable areas for future landslides. Land use planning, including zoning certain areas as unsafe for development will not always reduce the chance of a landslide but can minimize damage.
Physical barriers can prevent damage. In cases where potential landslides could affect existing structures, physical controls can be used. Government of Puerto Rico. The Government of Puerto Rico's Portal Datos Geograficos Gubernamentales governmental geographic data portal provides a range of information on natural hazards and resources in Puerto Rico, which can be viewed in a GIS program.
The interactive map includes: Lakes, rivers, and streams Map of landslides in Wyoming. Wyoming State Geological Survey. The Wyoming State Geological Survey has produced a map of recent and historical landslide activity in Wyoming, showing the location and extent of all mapped landslides. Click here to access the WSGS landslide map. Source: Wyoming State Geological Survey. Interactive map of Washington's geology and natural resources.
Washington Division of Geology and Earth Resources. The Washington Division of Geology and Earth Resources' interactive map of Washington provides a huge variety of information on the state's geology and natural resources, including: Hazards - tsunami hazard areas, volcanoes, earthquakes, landslides, radon hazards, and likely ground responses to Interactive map of geohazards in Oregon. Oregon Department of Geology and Mineral Industries. The Oregon Department of Geology and Mineral Industries statewide geohazard viewer, HazVu, provides a way to view a range of geohazards in the state of Oregon,including: Earthquakes - active faults, historical epicenters, expected shaking, and liquefaction hazards Tsunami inundation hazard Interactive map of New Jersey's geology and natural resources.
New Jersey Department of Environmental Protection. The New Jersey Department of Environmental Protection's GeoWeb Map Viewer provides a large amount of information on New Jersey's geology, natural resources, and environmental management in interactive map form, including: Surface and bedrock geology Hazards - earthquakes, landslides, drought Interactive map of Kentucky's geology and natural resources. Kentucky Geological Survey. The Kentucky Geological Survey's interactive map provides a large amount of information on Kentucky's geology and natural resources in interactive map form, including: Surface geology Coal, oil, and gas resources Water wells and springs Hazards - sinkholes and landslides Mineral Interactive map of landslides in California.
California Geological Survey. The California Geological Survey's interactive landslide map displays landslide locations and links to detailed landslide maps and reports for select Californian regions. The type of landslide reports vary by area and include both historical and recent landslide information. Click here Previous Pause Next. Geologic maps identify landslide hazards in California. Geologic maps identify post-wildfire hazards in Colorado.
This is because debris flows can move much faster than floods in steep channel reaches and much slower than floods in low-gradient reaches. In addition, debris-flow Skip to main content.
Search Search. Landslide Hazards. Landslides Continuum of flood and debris flow characteristics. Cartoon of debris flow with red box showing location of fan deposits. Below are publications associated with this project. Year Published: The Landslide Handbook - A Guide to Understanding Landslides This handbook is intended to be a resource for people affected by landslides to acquire further knowledge, especially about the conditions that are unique to their neighborhoods and communities.
Highland, Lynn M. View Citation. Filter Total Items: 3. Chen, C. Year Published: Distinguishing between debris flows and floods from field evidence in small watersheds Post-flood indirect measurement techniques to back-calculate flood magnitude are not valid for debris flows, which commonly occur in small steep watersheds during intense rainstorms.
Pierson, Thomas C. Distinguishing between debris flows and floods from field evidence in small watersheds; ; FS; ; Pierson, Thomas C.
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