The behavior of the landslide is usually measured by an extensometer, an inclinometer, or GPS (global positioning system). This equipment measures some points or along the lines; it is difficult to measure the whole landslide area. Sometimes radar is used to see deep into the landslide.
There are several methods to measure the displacement of a landslide surface: optical, ultrasonic, magnetic, and more recently laser scanners have been used instead. All these methods have their advantages and disadvantages. Optical measurement techniques include dial gauges, total stations, and scanning laser beams. Dial gauges are mechanical devices that use needles to measure depth by turning a dial. Total stations are computerized systems that measure distances by sending out infrared light that is reflected back from objects before falling on them. Scanning laser beams work like the light beams in a CD player but they are focused with great precision onto small areas of the ground. They can measure very small changes in distance over time (i.e., displacement) down to 0.01 mm.
Landslide monitoring programs should include measurements of mass loss due to erosion, mass gain due to accretion, and surface displacement. Mass loss due to erosion can be estimated from changes in elevation or depth of a channel bed or valley floor. Mass gain due to accretion can be estimated from changes in slope angle or curvature.
Scientists have created slope stability models to evaluate the danger locally in order to anticipate landslides. NASA has just developed a prototype method for mapping landslide threats throughout the world using satellite data of rainfall, land cover, and other surface characteristics. The agency plans to use this tool on future Earth-observing missions.
Landslides are dangerous natural disasters that can take many forms. A mass movement of earth caused by pressure from ice or rock breaking away from a mountain side is called an avalanche. When earth moves because of human activity such as mining or deforestation, it is known as soil displacement. The term landslide also includes mudflows and pyroclastic flows. These are different types of volcanic debris carried by rivers or overland surfaces toward the sea. Volcanic debris is usually accompanied by hot gas, dust, and small amounts of lava.
Landslides occur when surface conditions cause earth to become unstable. If sufficient force is applied to it, even very solid earth will fail under certain conditions. The most common form of failure is through rupture, which means that part of the ground breaks away and falls into another layer or depression. This may be followed by further ruptures and more complete slides. Landslides can bury buildings, destroy bridges, and kill people. They are a major concern in areas where gold mining or forestry activities cause destabilization of soil surfaces.
A landslide occurs when a pile of rock, rubble, or dirt slides down a hill. Landslides are a sort of "mass wasting," which refers to any downward-slope movement of soil and rock caused by gravity. Earthquake shaking and other reasons can potentially cause underwater landslides. Loose soil on slopes may appear stable but actually be about to slide down into the valley below. These areas are called "loose moraines." The term "moraine" comes from the French word for "marshland," because these features often form along the edge of a glacier before it melts back down toward the sea.
Landslides can be either slow-moving (stages) or fast-moving (avalanches). Slow-moving landslides occur when an area of land at the foot of a mountain becomes unstable due to natural causes (ageing of the earth's surface) or human activity (logging, mining, farming), causing a portion of the land to collapse. As this happens, the material falls down the side of the mountain forming a long, winding path. These paths can be as long as 100 miles! Fast-moving landslides occur when an entire section of a mountain face collapses, usually due to heavy rain or ice melting away under the weight of many tons of rock. These collisions can happen very suddenly, with the sound of thunder followed by a loud roar. They can destroy everything in their path!
The movement of rock, soil, or debris down a sloping area of terrain is referred to as a landslide. Rain, earthquakes, volcanoes, and other elements that make the slope unstable produce landslides. The size of a landslide is usually measured by the volume of material that moves. Small volumes of material that do not cover much distance may be described as small slides, while large volumes that travel a long distance are called landslides. A slide that covers an area larger than 100 acres (40 hectares) is called a flood landslide.
Landslides can be either natural or caused by human activity. Natural landslides are often triggered by precipitation that washes away earth's surface layers, causing the soil beneath it to collapse. Examples include mudflows after heavy rains or snowmelt from mountainous areas. Human-caused landslides are usually the result of construction on steep slopes without adequate protection against erosion or degradation of stabilizing soil features. Common causes of human-caed landslides include road building and maintenance, timber harvesting, mining activities, drainage system construction, and even lawn mowing!
Landslides can be very dangerous if they occur in remote areas where people might not know about them. They can also be dangerous if they block roads or drainages, causing floods or accidents. Landslides can be prevented to some degree through proper land use management.
The phrase "landslide" refers to five different types of slope movement: falls, topples, slides, spreads, and flows. A fall is the sudden release of energy when an object moves from a high place to a lower one. An example would be if a tree fell over on its side. A topple is similar to a fall in that it is the sudden release of energy when an object loses its balance and falls over, but it does not have to be caused by an external force. For example, if a heavy object such as a boulder sits on an unstable surface like sand or gravel, then it could tip over without anyone being there. A third type of slope movement is a slide. With this type of movement, large quantities of soil or rock move down the slope slowly. Examples of slides include a river bank collapsing under the weight of water flowing over it or a glacier moving across the ground very slowly.
The fourth type of slope movement is a spread. With this type of movement, the area above the sliding portion of the slope is also moved down, but not as far or as fast as the sliding portion. An example of a spread movement is when a person standing on ice hears something behind them and turns around to see what caused the sound.
Mass wasting can occur as a single large slide or as a series of smaller slides that build up speed and force as they go.
Landslides can be natural occurrences related to geology (such as avalanches) or man-made disasters such as those caused by deforestation or road construction. Natural landslides can also be called "mudflows" or "muddy floods."
The term "landslide" usually implies damage or risk of damage to buildings and infrastructure, but this depends on how you use the word. A moving block of stone could strike another object without causing damage if it hits with no more than its surface area. For example, if a boulder is rolling down a slope and comes to a stop before it reaches the end of the slope then there has been no damage done to anything because none of the surface area of the boulder was in contact with anything solid.
However, if that same boulder were to roll over a person then damage would have been done because body parts would have made contact with the ground.