Natural Disaster || Landslide
A landslide, also known as a landslide, is a form of large-scale wastage that involves a variety of grassroots activities, such as rocks, deep failure of slopes and shallow rubble stow. Landslides can occur underwater, called submarine landslides, coastal and onshore environments. Although the action of gravity is the primary driving force for landslides, there are other contributing factors affecting the original slope stability. Typically, pre-conditional factors create specific subsurface conditions that cause the area / slope to fail, while actual landslides often require triggers before they are released. Landslides are not to be confused with the flow of sludge, a type of mass flowing very rapidly that has been partially or completely liquefied by the addition of significant amounts of water to the source material.
Causes
Momias Landslide, in the Mamiece neighborhood of Baro Portugu Urbano, Ponce, Puerto Rico, which is buried in more than 100 homes, was caused by widespread accumulation of rain and, according to some sources, lightning.
Landslides occur when the slope changes from a steady to an unstable state. A change in slope stability can be caused by many factors, acting simultaneously or singly. Natural causes of landslides include:
· loss or absence of vertical vegetative structure, soil nutrients, and soil structure (e.g. after a wildfire - a fire in forests lasting for 3–4 days)
Landslides are aggravated by human activities, such as
· construction, agricultural or forestry activities (logging) which change the amount of water infiltrating the soil.
Types
Debris flow
Slope materials that become saturated with water may develop in debris flows or soil flows. Rocks and muds can result in picking up weathered trees, houses and cars, thus causing bridges and tributaries to flood its way.
Debris flows are often mistaken for flash floods, but they are completely separate processes.
Flowing mud-debris in Alpine areas causes severe damage to structures and infrastructure and often claims human life. Muddy-debris flow can begin as a result of slope-related factors and shallow landslides can cause damage to stream beds, resulting in intermittent water blockages. As impoundment fails, a "domino effect" can be created, leading to a significant increase in the amount of flow mass, which picks up debris in the stream channel. Solid-liquid mixtures 2,000 kg / m 3 (120 lb / cubic ft) and 14 m / s (46 ft / sec) and Chirley and Luino, 1998; Arattano, 2003). These processes typically cause severe road disruption at first, not only due to roadway accumulations (ranging from several cubic meters to hundreds of cubic meters), but in some cases bridges or roadways crossing the bridges, or the railway as a whole. Is removed in kind. The disadvantage usually derives from a general diminution of the flow of sludge-debris: in alpine valleys, for example, bridges are often destroyed by the impact force of the flow, as their duration is usually only limited by the discharge of water. Is calculated for. For a small basin in the Italian Alps (area 1.76 km2 (0.68 sq mi)) affected by the flow of debris, Cherl and Luino (1998) reported peak discharge of 750 m3 / s (26,000 cu ft / s) for the section located Guessed. In the middle of the main channel. At the same cross section, the maximum telescopic water discharge (by HEC-1), was 19 m3 / s (670 q ft / sec), which is approximately 40 times lower than the debris flow calculated.
Earthflows
Earth flows are downslope, viscous flows of saturated, fine-grained material, which grow slower at any speed. Typically, they can accelerate from 0.17 to 20 km / h (0.1 to 12.4 mph). Although they are mudflow-like, they tend to run more slowly and are covered by solids flowing from within. They differ from fluid flows which are more intense. Soil, fine sand and silt, and fine-grained, pyroclastic materials are all susceptible to the edges of the earth. The velocity of the earthflow all depends on the amount of water in the flow: if there is more water content in the flow, the higher the velocity.
These flows typically begin when the pore increases the pressure to a larger size mass until the weight of the material is sufficiently lowered so that the internal shear strength of the material is significantly reduced. This creates a bulging lobe that moves with a slow, rolling motion. As these lobes expand, the drainage of the mass increases and the margin dries up, reducing the overall velocity of flow. The flow becomes thicker due to this process. The bulbous variety of Earthlocks is not that spectacular, but they are much more common than their rapid counterparts. They develop a dysfunction on their head and usually arise from slippery at the source.
Earthflow is very high during periods of high rainfall, which saturates the ground and adds water to the slope material. Cracks develop during the movement of materials such as soil that cause infiltration into the Earth's water. The water then increases the pore-water pressure and decreases the shear strength of the material.
Debris landslide
A debris slide is a type of slide, which consists of a disordered motion of debris mixed with rocks, soil and water and / or ice. They usually originate from the saturation of thick vegetation slopes, resulting in an inconsistent mixture of wood, small vegetation, and other debris. Debris avalanches differ from debris slides because their movement is much more rapid. This is usually a consequence of low cohesion or high water content and usually stator slopes.
Steep coastal rocks can be caused by devastating debris avalanches. These are common on submerged ridges of ocean island volcanoes such as the Hawaiian Islands and Cape Verde Islands. This type of slug was a sloga landslide.
Movement
Debris slides generally start with big rocks that start at the top of the slide and begin to break apart as they slide towards the bottom. This is much slower than a debris avalanche. Debris avalanches are very fast and the entire mass seems to liquefy as it slides down the slope. This is caused by a combination of saturated material, and steep slopes. As the debris moves down the slope it generally follows stream channels leaving a v-shaped scar as it moves down the hill. This differs from the more U-shaped scar of a slump. Debris avalanches can also travel well past the foot of the slope due to their tremendous speed.
Sturzstrom
A sturzstrom is a rare, poorly understood type of landslide, typically with a long run-out. Often very large, these slides are unusually mobile, flowing very far over a low angle, flat, or even slightly uphill terrain.
Shallow landslide
Hotel Limon in Lake Garda. A portion of a hill of Devonian shale was removed to form a road, forming a steep slope. The upper block broke apart along a bed plane and slid down the hill, leading to a mound of rock at the foot of the slide.
Landslides in which the slippery surface lies within the soil mantle or seasoned bedrock (usually from a few decimeters to a few meters depth) is called a shallow landslide. These usually include debris slides, debris flows and road cut-slope failures. Landslides occurring in the form of large large blocks of rock are called gradual gradients.
The shallow landslides can often occur in areas with slopes with high permeable soils above low permeable soils. The less permeable, bottom soil gets trapped in shallow water, the higher permeable soil creates the higher water pressure in the top soil. As the top soil is filled with water and becomes heavy, the slopes can be very unstable and slide on the soil with less permeable bottom. It is said to have a slope with silt and sand and its soil as the lowest soil. During an intense rain, the bedrest will trap the rain in the top soil of silt and sand. As the topsoil becomes saturated and heavy, it may begin to slide over the bedrake and form shallow landslides. R. H. Campbell did a study on shallow landslides on Santa Cruz Island California. He notes that if permeability decreases with depth, a water table may develop in the soil during times of intense rainfall. When pore water pressures are sufficient to reduce the effective normal stress to a critical level, failure occurs.
Deep-seated landslide
Deep-seated landslide on a mountain in Sehara, Kihō, Japan caused by torrential rain of Tropical Storm Talas
Landslides in which the sliding surface is mostly deeply located below the maximum rooting depth of trees (typically to depths greater than ten meters). Deep-seated landslides usually involve deep regolith, weathered rock, and/or bedrock and include large slope failure associated with translational, rotational, or complex movement. This type of landslides are potentially occur in an tectonic active region like Zagros Mountain in Iran. These typically move slowly, only several meters per year, but occasionally move faster. They tend to be larger than shallow landslides and form along a plane of weakness such as a fault or bedding plane. They can be visually identified by concave scarps at the top and steep areas at the toe.
Causing tsunamis
Landslides that occur undersea, or have an impact on water, can generate tsunamis. Massive landslides can also generate megatsunamis, which are usually hundreds of meters high. In 1958, one such tsunami occurred in Lituya Bay in Alaska.
Related phenomena
· An avalanche, similar in mechanism to a landslide, involves a large amount of ice, snow and rock falling quickly down the side of a mountain.
· A pyroclastic flow is caused by a collapsing cloud of hot ash, gas and rocks from a volcanic explosion that moves rapidly down an erupting volcano.
Landslide prediction mapping
Landslide hazard analysis and mapping can provide useful information for catastrophic loss reduction, and assist in the development of guidelines for sustainable land use planning. The analysis is used to identify the factors that are related to landslides, estimate the relative contribution of factors causing slope failures, establish a relation between the factors and landslides, and to predict the landslide hazard in the future based on such a relationship. The factors that have been used for landslide hazard analysis can usually be grouped into geomorphology, geology, land use/land cover, and hydrogeology. Since many factors are considered for landslide hazard mapping, GIS is an appropriate tool because it has functions of collection, storage, manipulation, display, and analysis of large amounts of spatially referenced data which can be handled fast and effectively.Cardenas reported evidence on the exhaustive use of GIS in conjunction of uncertainty modelling tools for landslide mapping. Remote sensing techniques are also highly employed for landslide hazard assessment and analysis. Before and after aerial photographs and satellite imagery are used to gather landslide characteristics, like distribution and classification, and factors like slope, lithology, and land use/land cover to be used to help predict future events. Before and after imagery also helps to reveal how the landscape changed after an event, what may have triggered the landslide, and shows the process of regeneration and recovery.
Using satellite imagery in combination with GIS and on-the-ground studies, it is possible to generate maps of likely occurrences of future landslides.Such maps should show the locations of previous events as well as clearly indicate the probable locations of future events. In general, to predict landslides, one must assume that their occurrence is determined by certain geologic factors, and that future landslides will occur under the same conditions as past events. Therefore, it is necessary to establish a relationship between the geomorphologic conditions in which the past events took place and the expected future conditions.
Natural disasters are a dramatic example of people living in conflict with the environment. Early predictions and warnings are essential for the reduction of property damage and loss of life. Because landslides occur frequently and can represent some of the most destructive forces on earth, it is imperative to have a good understanding as to what causes them and how people can either help prevent them from occurring or simply avoid them when they do occur. Sustainable land management and development is also an essential key to reducing the negative impacts felt by landslides.
A Wireline extensometer monitoring slope displacement and transmitting data remotely via radio or Wi-Fi. In situ or strategically deployed extensometers may be used to provide early warning of a potential landslide.
GIS offers a superior method for landslide analysis because it allows one to capture, store, manipulate, analyze, and display large amounts of data quickly and effectively. Because so many variables are involved, it is important to be able to overlay the many layers of data to develop a full and accurate portrayal of what is taking place on the Earth's surface. Researchers need to know which variables are the most important factors that trigger landslides in any given location. Using GIS, extremely detailed maps can be generated to show past events and likely future events which have the potential to save lives, property, and money.
Global landslide risks
Prehistoric landslides
· Storegga Slide, some 8000 years ago off the western coast of Norway. Caused massive tsunamis in Doggerland and other countries connected to the North Sea. A total volume of 3,500 km3 (840 cu mi) debris was involved; comparable to a 34 m (112 ft) thick area the size of Iceland. The landslide is thought to be among the largest in history.
· Landslide which moved Heart Mountain to its current location, the largest continental landslide discovered so far. In the 48 million years since the slide occurred, erosion has removed most of the portion of the slide.
· Flims Rockslide, ca. 12 km3 (2.9 cu mi), Switzerland, some 10000 years ago in post-glacial Pleistocene/Holocene, the largest so far described in the alps and on dry land that can be easily identified in a modestly eroded state.
· The landslide around 200 BC which formed Lake Waikaremoana on the North Island of New Zealand, where a large block of the Ngamoko Range slid and dammed a gorge of Waikaretaheke River, forming a natural reservoir up to 256 metres (840 ft) deep.
· The Manang-Braga rock avalanche/debris flow may have formed Marsyangdi Valley in the Annapurna Region, Nepal, during an interstadial period belonging to the last glacial period. Over 15 km3 of material are estimated to have been moved in the single event, making it one of the largest continental landslides.
· A massive slope failure 60 km north of Kathmandu, involving an estimated 10–15 km3. Prior to this landslide the mountain may have been the world’s 15th mountain above 8000m.
Historical landslides
· Monte Toc landslide (260 million cubic metres, 9.2 billion cubic feet) falling into the Vajont Dam basin in Italy, causing a megatsunami and about 2000 deaths, on October 9, 1963
· Hope Slide landslide (46 million cubic metres, 1.6 billion cubic feet) near Hope, British Columbia on January 9, 1965.
· Vargas mudslides, due to heavy rains in Vargas State, Venezuela, in December, 1999, causing tens of thousands of deaths.
Extraterrestrial landslides
Before and after radar images of a landslide on Venus. In the center of the image on the right, the new landslide, a bright, flow-like area, can be seen extending to the left of a bright fracture. 1990 image.
Evidence of past landslides has been detected on many bodies in the solar system, but since most observations are made by probes that only observe for a limited time and most bodies in the solar system appear to be geologically inactive not many landslides are known to have happened in recent times. Both Venus and Mars have been subject to long-term mapping by orbiting satellites, and examples of landslides have been observed on both.
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