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A mudflow or mud flow is a form of mass wasting involving "very rapid to extremely rapid surging flow"of debris that has become partially or fully liquified by the addition of significant amounts of water to the source material.
Mudflows contain a significant proportion of clay, which makes them more fluid than debris flows; thus, they are able to travel farther and across lower slope angles. Both types are generally mixtures of various kinds of materials of different sizes, which are typically sorted by size upon deposition.
Mudflows are often called mudslides, a term applied indiscriminately by the mass media to a variety of mass wasting events.Mudflows often start as slides, becoming flows as water is entrained along the flow path; such events are often called flow slides.
Other types of mudflows include lahars (involving fine-grained pyroclastic deposits on the flanks of volcanoes) and jökulhlaups (outbursts from under glaciers or icecaps).
A statutory definition of "flood-related mudslide" appears in the United States' National Flood Insurance Act of 1968, as amended, codified at 42 USC Sections 4001 and following.
Heavy rainfall, snowmelt, or high levels of groundwater flowing through cracked bedrock may trigger a movement of soil or sediments. Floods and debris flows may also occur when strong rains on hill or mountain slopes cause extensive erosion and/or what is known as "channel scour". The 2006 Sidoarjo mud flow may have been caused by rogue drilling.
Some broad mudflows are rather viscous and therefore slow; others begin very quickly and continue like an avalanche. If large enough, they can devastate villages and countrysides. They are composed of at least 50% silt and clay-sized materials and up to 30% water. Mudflows are common even in the hills around Los Angeles, California, where they have destroyed many homes built on hillsides without sufficient support after fires destroy vegetation holding the land.
The point where a muddy material begins to flow depends on its grain size and the water content. Fine grainy material or soil has a smaller friction angle than a coarse sediment or a debris flow, but falling rock pieces can trigger a material flow, too.
On December 14, 1999 in Vargas, Venezuela, a mudflow known as The Vargas tragedy significantly altered more than 60 kilometers (37 mi) of the coastline. It was triggered by heavy rainfall and caused estimated damages of US$1.79 to US$3.5 billion, killed between 10,000 and 30,000 people, forced 85,000 people to evacuate, and led to the complete collapse of the state's infrastructure.
Landslide is a more general term than mudflow. It refers to the gravity-driven failure and subsequent movement downslope of any types of surface movement of soil, rock, or other debris. The term incorporates earth slides, rock falls, debris flows, and mudslides, amongst other categories of hillslope mass movements.They do not have to be as fluid as a mudflow.
Mudflows can be caused by unusually heavy rains or a sudden thaw. They consist mainly of mud and water plus fragments of rock and other debris, so they often behave like floods. They can move houses off their foundations or bury a place within minutes because of incredibly strong currents.
When a mudflow occurs it is given four named areas, the 'main scarp', in bigger mudflows the 'upper and lower shelves' and the 'toe'. The main scarp will be the original area of incidence, the toe is the last affected area(s). The upper and lower shelves are located wherever there is a large dip (due to mountain or natural drop) in the mudflow's path. A mudflow can have many shelves.
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The world's largest historic landslide (in terms of volume) occurred during the 1980 eruption of Mount St. Helens, a volcano in the Cascade Mountain Range in the State of Washington, USA. The volume of material displaced was 2.8 km3 (0.67 cu mi). Directly in the path of the huge mudflow was Spirit Lake. Normally a chilly 5 °C (41 °F), the lahar instantly raised the temperature to near 38 °C (100 °F). Today the bottom of Spirit Lake is 100 ft (30 m) above the original surface, and it has two and a half times more surface area than it did before the eruption.
The world's largest known prehistoric terrestrial landslide took place in southwestern Iran, and is named the Saidmarreh landslide. The landslide was on the Kabir Kuh anticline at 33.0°N, 47.65°E. The landslide had a volume of about 20 km3 (4.8 cu mi), a depth of 300 m (980 ft), a travel distance of 14 km (8.7 mi), and a width of 5 km (3.1 mi). This means that about 50 billion tons of rock moved in this single event.
The largest known of all prehistoric landslides was an enormous submarine landslide that disintegrated 60,000 years ago and produced the longest flow of sand and mud yet documented on Earth. The massive submarine flow travelled 1,500 km (930 mi) – the distance from London to Rome.[ citation needed ]
By volume, the largest submarine landslide (the Agulhas slide off South Africa) occurred approximately 2.6 million years ago. The volume of the slide was 20,000 km3 (4,800 cu mi).
The area most generally recognized as being at risk of a dangerous mudflow are:
The term landslide or less frequently, landslip, refers to several forms of mass wasting that include a wide range of ground movements, such as rockfalls, deep-seated slope failures, mudflows, and debris flows. Landslides occur in a variety of environments, characterized by either steep or gentle slope gradients, from mountain ranges to coastal cliffs or even underwater, in which case they are called submarine landslides. Gravity is the primary driving force for a landslide to occur, but there are other factors affecting slope stability that produce specific conditions that make a slope prone to failure. In many cases, the landslide is triggered by a specific event, although this is not always identifiable.
A lahar is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a river valley.
The geology of the Lassen volcanic area presents a record of sedimentation and volcanic activity in the area in and around Lassen Volcanic National Park in Northern California, U.S. The park is located in the southernmost part of the Cascade Mountain Range in the Pacific Northwest region of the United States. Pacific Oceanic tectonic plates have plunged below the North American Plate in this part of North America for hundreds of millions of years. Heat from these subducting plates has fed scores of volcanoes in California, Oregon, Washington and British Columbia over at least the past 30 million years and is also responsible for activities in the Lassen volcanic area.
A geologic hazard is one of several types of adverse geologic conditions capable of causing damage or loss of property and life. These hazards consist of sudden phenomena and slow phenomena:
Mass wasting, also known as slope movement or mass movement, is the geomorphic process by which soil, sand, regolith, and rock move downslope typically as a solid, continuous or discontinuous mass, largely under the force of gravity, frequently with characteristics of a flow as in debris flows and mudflows. Types of mass wasting include creep, slides, flows, topples, and falls, each with its own characteristic features, and taking place over timescales from seconds to hundreds of years. Mass wasting occurs on both terrestrial and submarine slopes, and has been observed on Earth, Mars, Venus, and Jupiter's moon Io.
A rockslide is a type of landslide caused by rock failure in which part of the bedding plane of failure passes through compacted rock and material collapses en masse and not in individual blocks. While a landslide occurs when loose dirt or sediment falls down a slope, a rockslide occurs only when solid rocks are transported down slope. The rocks tumble downhill, loosening other rocks on their way and smashing everything in their path. Fast-flowing rock slides or debris slides behave similarly to snow avalanches, and are often referred to as rock avalanches or debris avalanches.
On February 17, 2006, a massive rock slide-debris avalanche occurred in the Philippine province of Southern Leyte, causing widespread damage and loss of life. The deadly landslide followed a 10-day period of heavy rain and a minor earthquake. The official death toll was 1,126.
Debris flows are geological phenomena in which water-laden masses of soil and fragmented rock rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. They generally have bulk densities comparable to those of rock avalanches and other types of landslides, but owing to widespread sediment liquefaction caused by high pore-fluid pressures, they can flow almost as fluidly as water. Debris flows descending steep channels commonly attain speeds that surpass 10 m/s (36 km/h), although some large flows can reach speeds that are much greater. Debris flows with volumes ranging up to about 100,000 cubic meters occur frequently in mountainous regions worldwide. The largest prehistoric flows have had volumes exceeding 1 billion cubic meters. As a result of their high sediment concentrations and mobility, debris flows can be very destructive.
The Kolka–Karmadon rock-ice slide occurred on the northern slope of the Mount Kazbek massif in North Ossetia–Alania on the 20 of September 2002, following a partial collapse of the Kolka Glacier. It started on the north-northeast wall of Dzhimarai-Khokh, 4,780 m (15,680 ft) above sea level, and seriously affected the valley of Genaldon and Karmadon. The resulting avalanche and mudflow killed 125 people. While this type of avalanche is not uncommon this particular event is considered extraordinary because of several aspects.
The Mount Meager massif is a group of volcanic peaks in the Pacific Ranges of the Coast Mountains in southwestern British Columbia, Canada. Part of the Cascade Volcanic Arc of western North America, it is located 150 km (93 mi) north of Vancouver at the northern end of the Pemberton Valley and reaches a maximum elevation of 2,680 m (8,790 ft). The massif is capped by several eroded volcanic edifices, including lava domes, volcanic plugs and overlapping piles of lava flows; these form at least six major summits including Mount Meager which is the second highest of the massif.
There have been known various classifications of landslides and other types of mass wasting.
An earthflow is a downslope viscous flow of fine-grained materials that have been saturated with water and moves under the pull of gravity. It is an intermediate type of mass wasting that is between downhill creep and mudflow. The types of materials that are susceptible to earthflows are clay, fine sand and silt, and fine-grained pyroclastic material.
The Medeu Mudflow Control Dam is a dam across the Medeu Valley south-east of Almaty, Kazakhstan, designed to protect the city from devastating debris flows.
Kautz Creek is a tributary of the Nisqually River, flowing from the Kautz Glacier, with its watershed in the Mount Rainier National Park of Washington. It drains southwest from Mount Rainier for about 6 miles (9.7 km) before it joins the Nisqually River near Mount Rainier Highway. It is notable for being a severe flooding hazard due to the volume of summer glacier melt and its frequently changing course. The 400-foot (120 m) Kautz Creek Falls on the headwaters of the creek was formed by the retreat of the Kautz Glacier in the past 50 years.
A volcanic hazard is the probability that a volcanic eruption or related geophysical event will occur in a given geographic area and within a specified window of time. The risk that can be associated with a volcanic hazard depends on the proximity and vulnerability of an asset or a population of people near to where a volcanic event might occur.
A major landslide occurred 4 miles (6.4 km) east of Oso, Washington, United States, on March 22, 2014, at 10:37 a.m. local time. A portion of an unstable hill collapsed, sending mud and debris to the south across the North Fork of the Stillaguamish River, engulfing a rural neighborhood, and covering an area of approximately 1 square mile (2.6 km2). Forty-three people were killed and 49 homes and other structures destroyed.
The Bridge for Kids is a proposed bridge across the Carbon River in Orting, Washington, about a mile upstream of where it joins the Puyallup River. It would provide an emergency evacuation route for school children to escape a future lahar flow from Mount Rainier, consisting of an up to 10-meter (33 ft) high flood of mud, rock and boulders. As of 2016, the $40 million bridge was still in the planning phase.
The West Salt Creek landslide occurred on the evening of May 25, 2014 near Collbran, Colorado, along the north side of the Grand Mesa, about 30 miles (48 km) east of Grand Junction. It was the largest landslide in Colorado's history.
A series of mudflows occurred in Southern California in early January 2018, particularly affecting areas northwest of Los Angeles in Santa Barbara County. The incident was responsible for 23 deaths, although the bodies of two victims were not found. Approximately 163 people were hospitalized with various injuries, including four in critical condition. The disaster occurred one month after a series of major wildfires. The conflagrations devastated steep slopes, which caused loss of vegetation and destabilization of the soil and greatly facilitated subsequent mudflows. The mudflows caused at least $177 million in property damage, and cost at least $7 million in emergency responses and another $43 million to clean up.
The 2010 Mount Meager landslide was a large catastrophic debris avalanche that occurred in southwestern British Columbia, Canada, on August 6 at 3:27 a.m. PDT (UTC-7). More than 45,000,000 m3 (1.6×109 cu ft) of debris slid down Mount Meager, temporarily blocking Meager Creek and destroying local bridges, roads and equipment. It was one of the largest landslides in Canadian history and one of over 20 landslides to have occurred from the Mount Meager massif in the last 10,000 years.