Landslides, also known as landslips, are several forms of mass wasting that may 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.
Geomorphology is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or near Earth's surface. Geomorphologists seek to understand why landscapes look the way they do, to understand landform and terrain history and dynamics and to predict changes through a combination of field observations, physical experiments and numerical modeling. Geomorphologists work within disciplines such as physical geography, geology, geodesy, engineering geology, archaeology, climatology, and geotechnical engineering. This broad base of interests contributes to many research styles and interests within the field.
A glacial erratic is glacially deposited rock differing from the type of rock native to the area in which it rests. Erratics, which take their name from the Latin word errare, are carried by glacial ice, often over distances of hundreds of kilometres. Erratics can range in size from pebbles to large boulders such as Big Rock in Alberta.
Mass wasting, also known as mass movement, is a general term for the movement of rock or soil down slopes under the force of gravity. It differs from other processes of erosion in that the debris transported by mass wasting is not entrained in a moving medium, such as water, wind, or ice. Types of mass wasting include creep, solifluction, rockfalls, debris flows, and landslides, 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, Jupiter's moons Io, and on many other bodies in the Solar System.
A rockfall or rock-fall is a quantity/sheets of rock that has fallen freely from a cliff face. The term is also used for collapse of rock from roof or walls of mine or quarry workings. "A rockfall is a fragment of rock detached by sliding, toppling, or falling, that falls along a vertical or sub-vertical cliff, proceeds down slope by bouncing and flying along ballistic trajectories or by rolling on talus or debris slopes."
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. Note that a rockslide is similar to an avalanche because they are both slides of debris that can bury a piece of land. 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.
A mudflow, also known as mudslide or mud flow, is a form of mass wasting involving fast-moving flow of debris and dirt that has become liquified by the addition of water. Such flows can move at speeds ranging from 3 meters/minute to 5 meters/second. Mudflows contain a significant proportion of clay, which makes them more fluid than debris flows, allowing them to travel farther and across lower slope angles. Both types of flow are generally mixtures of particles with a wide range of sizes, which typically become sorted by size upon deposition.
Rock glaciers are distinctive geomorphological landforms, consisting either of angular rock debris frozen in interstitial ice, former "true" glaciers overlain by a layer of talus, or something in-between. Rock glaciers are normally found at high latitudes and/or elevations, and may extend outward and downslope from talus cones, glaciers or terminal moraines of glaciers.
On 17 February 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.
There have been known various classifications of landslides. Broad definitions include forms of mass movement that narrower definitions exclude. For example, the McGraw-Hill Encyclopedia of Science and Technology distinguishes the following types of landslides:
Umhausen is a municipality in the Imst district of state of Tyrol in western Austria. It and is located 17 km southeast of Imst at the Ötztaler Ache in the Ötztal. It has 3078 inhabitants.
Submarine landslides are marine landslides that transport sediment across the continental shelf and into the deep ocean. A submarine landslide is initiated when the downwards driving stress exceeds the resisting stress of the seafloor slope material, causing movements along one or more concave to planar rupture surfaces. Submarine landslides take place in a variety of different settings, including planes as low as 1°, and can cause significant damage to both life and property. Recent advances have been made in understanding the nature and processes of submarine landslides through the use of sidescan sonar and other seafloor mapping technology.
In April and May 1991, two consecutive rockslides occurred from a cliff above the town of Randa in the Matter valley of Switzerland. The rockslides released a cumulative volume of approximately 30 million cubic meters of debris, with each of the rockslide stages occurring over several hours. Slide debris buried key regional transportation lines including the road and railway leading to Zermatt, and dammed the Mattervispa river which eventually flooded a portion of the town of Randa upstream. There were no fatalities resulting from either of the rockslide events, though livestock, farmhouses and holiday homes were destroyed.
A landslide occurred at about 5:38 am local time on 24 June 2017 in Diexi Town, Mao County, Sichuan Province in south-western China. It destroyed 40 homes in Xinmo Village and killed 10 people, with a further 73 people missing, as of 27 June. A second smaller landslide at around 17:19 pm impeded rescue efforts.
Mount Cayley is an eroded but potentially active stratovolcano in the Pacific Ranges of southwestern British Columbia, Canada. Located 45 km (28 mi) north of Squamish and 24 km (15 mi) west of Whistler, the volcano resides on the edge of the Powder Mountain Icefield. It consists of massif that towers over the Cheakamus and Squamish river valleys. All major summits have elevations greater than 2,000 m (6,600 ft), Mount Cayley being the highest at 2,385 m (7,825 ft). The surrounding area has been inhabited by indigenous peoples for more than 7,000 years while geothermal exploration has taken place there for the last four decades.
The 1970 Huascarán Debris Avalanche occurred on May 31, 1970, when a debris avalanche and mudflow triggered by the Ancash earthquake destroyed the Peruvian town of Yungay and ten nearby villages, leaving up to 30,000 people dead. It is the deadliest avalanche or glacier-related disaster in history, and the third or fourth most deadly landslide-related disaster of the 20th century, after the Haiyuan landslides (China), the Armero tragedy (Colombia) and by some estimates the Khait landslide (Tajikistan).
The Gemmi Fault or Gemmi Pass Fault is a geologic fault in Switzerland. It lies close to the Gemmi Pass at Leukerbad and is a strike-slip fault. This fault is at least 2.6 kilometres (1.6 mi) long and shows evidence of Holocene movement; several landslides and traces of early Holocene earthquakes found in Swiss lakes may correlate to movements along the Gemmi Fault.
The area of Oeschinen Lake and Kander river valley in Switzerland have been subject of multiple large landslides during the Holocene. Both the number and timing of landslides is controversial, with the most recent estimates stating that the large Kander landslide occurred about 3,210 years ago and the smaller Oeschinen Lake landslide 2,300 years ago. Both may have been caused by earthquakes, and the latter landslide generated the Oeschinen Lake. More recent landslides have occurred, and unstable rock masses occur in the landslide area.
The Tsergo Ri landslide was a prehistoric landslide in the Nepalese Himalaya, which took place around 51,000±13,000 years ago, during the Last Glacial Period. During the collapse, a mass of rock of about 10–15 cubic kilometres (2.4–3.6 cu mi) detached from a previous mountain or ridge and descended with a speed of about 450 kilometres per hour (120 m/s); later, glaciers eroded almost the entire landslide mass. Previously weakened rocks may have contributed to the collapse, which was probably started by an earthquake.
