Landslides
The very nature of natural hazards means that they have the potential to impact a majority of Americans every year.
Landslide Hazards
USGS science provides part of the foundation for emergency preparedness whenever and wherever disaster strikes. Recent concerns related to slope stability after the State Route Landslide near Oso, Washington, forced the closure of the U. Summary statistics derived from the frequency—area distribution FAD of inventories of triggered landslides allows for direct comparison of landslides triggered by one event e.
The use of preevent and postevent digital elevation models DEMs to estimate the volume of rock avalanches on glaciers is complicated by ablation of ice before and after the rock avalanche, scour of material during rock avalanche emplacement, and postevent ablation and compaction of the rock avalanche deposit. We present a model to account for Geological Survey Landslide Hazards Program that collects and distributes all forms of information related to landslides. The NLIC is designed to serve landslide researchers, geotechnical practitioners engaged in landslide stabilization, and anyone else concerned in any way with landslide education, hazard, safety, and mitigation.
Every state in the US has a geoscience agency and most have some landslide information. What was the most expensive landslide to fix in the United States?
Landslide Hazards
The landslide occurred during the spring of , when unseasonably warm weather caused rapid snowmelt to saturate the slope. It also flowed across the Spanish Fork River, forming a dam. The impounded river water inundated the small town of Thistle. The inhabitants of the town of Thistle, directly upstream from the landslide, were evacuated as the lake began to flood the town, and within a day the town was completely covered with water.
Populations downstream from the dam were at risk because of the possible overtopping of the landslide by the lake. This could cause a catastrophic outburst of the dam with a massive flood downstream. Eventually, a drain system was engineered to drain the lake and avert the potential disaster. How many deaths result from landslides? An average of between 25 and 50 people are killed by landslides each year in the United States. The worldwide death toll per year due to landslides is in the thousands.
Most landslide fatalities are from rock fall, debris-flows, or volcanic debris flows. What should I know about wildfires and debris flows? Wild land fires are inevitable in the western United States. Expansion of human development into forested areas has created a situation where wildfires can adversely affect lives and property, as can the flooding and landslides that occur in the aftermath of the fires. There is a need to develop tools and methods to identify and quantify the potential hazards posed by landslides produced from burned watersheds.
Post-fire landslide hazards include fast-moving, highly destructive debris flows that can occur in the years immediately after wildfires in response to high intensity rainfall events, and those flows that are generated over longer time periods accompanied by root decay and loss of soil strength. Post-fire debris flows are particularly hazardous because they can occur with little warning, can exert great impulsive loads on objects in their paths, and can strip vegetation, block drainage ways, damage structures, and endanger human life. Wildfires could potentially result in the destabilization of pre-existing deep-seated landslides over long time periods.
How do landslides cause tsunamis? Tsunamis are large, potentially deadly and destructive sea waves, most of which are formed as a result of submarine earthquakes. They may also result from the eruption or collapse of island or coastal volcanoes and the formation of giant landslides on marine margins. These landslides, in turn, are often triggered by earthquakes.
Tsunamis can be generated on impact as a rapidly moving landslide mass enters the water or as water displaces behind and ahead of a rapidly moving underwater landslide. What are some examples of landslides that have caused tsunamis?
The Alaska earthquake caused deaths in Alaska alone, with of those due to tsunamis generated by tectonic uplift of the sea floor, and by localized subareal and submarine landslides. The earthquake shaking caused at least 5 local slide-generated tsunamis within minutes after the shaking began. An eyewitness account of the tsunami caused by the movement and landslides of the Alaska earthquake.
Research in the Canary Islands concludes that there have been at least five massive volcano landslides that occurred in the past, and that similar large events may occur in the future. Giant landslides have the potential of generating large tsunami waves at close and also very great distances and would have the potential to devastate large areas of coastal land as far away as the eastern seaboard of North America. Rock falls and rock avalanches in coastal inlets, such as those that have occurred in the past at Tidal Inlet, Glacier Bay National Park, Alaska, have the potential to cause regional tsunamis that pose a hazard to coastal ecosystems and human settlements.
On July 9, , a magnitude M 7. The landslide generated a wave that ran up m on the opposite shore and sent a m high wave through Lituya Bay, sinking two of three fishing boats and killing two persons. How soon does the danger of landslides end after the rain stops? Residents near mountain slopes, canyons, and landslide prone areas should stay alert even after heavy rain subsides. Areas that have been burned by recent wildfires are highly susceptible to debris-flow activity that can be triggered by significantly less rainfall than that which triggers debris flows from unburned hill slopes.
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What was the biggest landslide in the world? The volume of material was 2. What was the biggest prehistoric landslide? The landslide is located on the Kabir Kuh anticline in Southwest Iran at 33 degrees north latitude, The landslide has a volume of about 20 cubic kilometers, a depth of m, a travel distance of 14 km and a width of 5 km. This means that about 50 billion tons of rock moved in this single event! Types of Landslides Rotational slide: This is a slide in which the surface of rupture is curved concavely upward and the slide movement is roughly rotational about an axis that is parallel to the ground surface and transverse across the slide.
Landslide mitigation and prevention
In this type of slide, the landslide mass moves along a roughly planar surface with little rotation or backward tilting. Falls are abrupt movements of masses of geologic materials, such as rocks and boulders, that become detached from steep slopes or cliffs. Separation occurs along discontinuities such as fractures, joints, and bedding planes, and movement occurs by free-fall, bouncing, and rolling. Falls are strongly influenced by gravity, mechanical weathering, and the presence of interstitial water.
Toppling failures are distinguished by the forward rotation of a unit or units about some pivotal point, below or low in the unit, under the actions of gravity and forces exerted by adjacent units or by fluids in cracks. A debris flow is a form of rapid mass movement in which a combination of loose soil, rock, organic matter, air, and water mobilize as a slurry that flows downslope. Debris flows are commonly caused by intense surface-water flow, due to heavy precipitation or rapid snowmelt, that erodes and mobilizes loose soil or rock on steep slopes. Debris flows also commonly mobilize from other types of landslides that occur on steep slopes, are nearly saturated, and consist of a large proportion of silt- and sand-sized material.
Over the next two days, many people in Northwestern Oregon, the Portland Metro area, parts of the Gorge, and portions of the Hood River Valley need to be on alert for landslides. The specific areas impacted are the central and northern coast, the Coast Range, the central Willamette Valley, the greater Portland metro area, the central and western Columbia River Gorge, and the upper Hood River Valley.
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The NWS warns that heavy rain can trigger landslides and debris flows in steep terrain, and that they move faster than a person can run. The risk is even higher in burn areas. Landslides can carry heavy and destructive objects like boulders and logs, and areas below steep slopes and near the mouths of canyons may present a serious risk to people, structures and roads. If your home, work, or route is in a watch area, here are some important safety tips from the NWS:. Track the flood watch by radio, TV, weather radio or online. If told to evacuate, do so immediately.
Unusual sounds might indicate moving debris, such as trees cracking or boulders knocking together.