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25-536: The Cheekye Fan is a large landslide feature in southwestern British Columbia , Canada , at the head of Howe Sound . It formed by collapse on the west flank of the volcano Mount Garibaldi , which was constructed over a glacier during the Late Pleistocene period. This article about a location on the Coast of British Columbia , Canada is a stub . You can help Misplaced Pages by expanding it . This article about

50-430: A chaotic landscape marked by dozens of small hills and closed depressions. If the landslide deposit is thick enough, it may dam streams to form lakes. These lakes may eventually drain catastrophically to create floods and lahars downstream. Landslides that remove a large portion of a volcanic cone may abruptly decrease pressure on shallow magmatic and hydrothermal systems, which can generate explosions ranging from

75-702: A collapse of Anak Krakatoa . The waves struck about 313 km (194 mi) of coastline with various heights, killing at least 373 people and damaging many buildings. [REDACTED]  This article incorporates public domain material from websites or documents of the United States Geological Survey . Hummock In geology , a hummock is a small knoll or mound above ground. They are typically less than 15 meters (50 ft) in height and tend to appear in groups or fields. Large landslide avalanches that typically occur in volcanic areas are responsible for formation of hummocks. From

100-618: A depth roughly equal to the hummock’s height. This has been explained by some as the result of convection processes whereby warmer soil and water at depth expands, becomes less dense and rises, while gravity forces denser soil downwards. Circulation has also been explained as driven solely by density of soil material and not temperature induced density changes. This is the most widely accepted explanation of cryogenic hummock genesis. Irregularities in preexisting ground conditions (differences in grain size, ground temperature, moisture conditions of vegetation) cause surface downwards freezing during

125-515: A human lifetime) they are an ideal landform to monitor for medium range environmental change. There are several explanations of earth hummock formation. Hummocks may form as a result of clasts migrating to the surface through frost push and pull mechanisms. As the clasts rise they push up on the ground above forming bulging mounds. Cryogenic hummocks are found covered in vegetation in Taiga and Boreal forests. They are also known as active hummocks due to

150-585: A pore fluid that is viscous and contains fine sediment. The largest landslides from volcanoes are called sector or edifice collapses. Prehistoric sector collapses are preserved in the geological record in the form of debris avalanche deposits and collapse scars. Debris avalanche deposits can be found up to 20 km (12 mi) from the site of collapse. Collapse scars are also an indicator of sector collapse and are often described as " amphitheatre " or " horseshoe " shaped. Such collapse scars, open at one end, have long been noted in many volcanic regions around

175-550: A small steam explosion to large steam and magma-driven directed blasts. These result in tephra and ash fall hazards for surrounding areas. Large horseshoe-shaped craters formed by landslides at volcanoes will likely direct subsequent lava flows, pyroclastic flows or lahars toward its breached opening if the primary eruptive vent is located within these deep craters. The collapse of island or coastal volcanoes from giant landslides can generate tsunamis that could potentially devastate large areas of coastal land. Historically,

200-638: A specific Canadian geological feature is a stub . You can help Misplaced Pages by expanding it . Volcanic landslide All volcanic edifices are susceptible to landslides , particularly stratovolcanoes and shield volcanoes where landslides are important processes. Volcanic landslides range in size from less than 1 km (0.24 cu mi) to more than 100 km (24 cu mi). The largest volcanic landslides on Earth occur from submarine volcanoes and are several times larger than those that occur on land. Submarine landslides with volumes of 100–150 km (24–36 cu mi) have occurred in

225-456: Is adequate moisture to fuel cryogenic processes. Cryogenic earth hummocks appear in a variety of cold-ground environments, making the story of their genesis complex. Geologists recognize that hummocks may be polygenetic and form by a combination of forces that are yet to be well understood. Recent research on cryogenic hummocks has focused on their role as environmental indicators. Because hummocks can both form and disintegrate rapidly (well within

250-417: Is rich in silt , the primary make up of these mounds is volcanic ash. A clear display of layers of volcanic ash is observed within these Thufurs amidst other organic matter. Hummock excavation normally reveals a disturbed soil profile, often with irregular streaks of organic matter or other colorations suggesting fluidity at some point in the past. The disturbance, a form of cryoturbation , often extends to

275-645: The Canary Islands within the last 43 million years, but the largest submarine landslides could have been up to 900 km (220 cu mi) in volume. Massive submarine landslides have also taken place in the Hawaiian Islands over the last several million years, the largest of which constitute significant portions of the islands from which they originated. Smaller landslides have also been identified at volcanoes on Mars and Venus . Martian landslides reach lengths of 90 km (56 mi) and more while

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300-409: The amphitheater has been filled in by later volcanic activity and all that remains are the hummocks. Debris avalanche blocks are identifiable because they keep their internal stratigraphy . The blocks simply break off the mountain and slide down, completely intact, identifiable because they differ from the surrounding landscape. The volume and height of hummocks is mostly dependent on their location;

325-528: The flanks of mountains, especially volcanoes. These events are fast-moving, gravity-driven currents of saturated debris that do not necessarily include juvenile material. Debris avalanche deposits are characterized by the debris-avalanche block (hummocks) and the debris-avalanche matrix. Debris avalanches are diagnosed for landscapes where the volcano has an amphitheater at the source with hummocky terrain downhill. In some cases, such as Mount Shasta in California,

350-435: The freeze and thaw cycle of the ice lenses that continually occur within the organic layers of their mounds. The freezing of ice lenses is what causes the mounds to rise. When the ice lenses thaw during a forest fire, the mounds collapse until they freeze again. Thufurs are small sized hummocks typically found in climates like that of Iceland. They prefer areas with seasonal freezing and maritime climates. While their sediment

375-407: The hummocks further modify to break up or merge to form larger structures. It is difficult to make generalizations about hummocks because of the diversity in their morphology and sedimentology. An extremely irregular surface may be called hummocky . An ice hummock is a boss or rounded knoll of ice rising above the general level of an ice-field. Hummocky ice is caused by slow and unequal pressure in

400-422: The initiation of the landslide to the final formation, hummocks can be characterized by their evolution, spatial distribution, and internal structure. As the movement of landslide begins, the extension faulting results in formation of hummocks with smaller ones at the front of the landslide and larger ones in the back. The size of the hummocks is dependent on their position in the initial mass. As this mass spreads,

425-500: The largest Venusian landslides extend only about 50 km (31 mi). The most dramatic landslide deposits on Venus occur beneath the slopes of volcanoes. Since erosion rates on Venus are much lower than those on Earth due to the lack of water on the surface, landslides are an important mechanism in wearing down mountain regions on Venus. The rounded hills of the complexly deformed tessera , or tile-like, terrain on Venus have probably been modified by numerous landslides. At volcanoes,

450-453: The main body of the packed ice, and by unequal structure and temperature at a later period. Hummocks in the shape of low ridges of drier peat moss typically form part of the structure of certain types of raised bog , such as plateau , kermi , palsa or string bog . The hummocks alternate with shallow wet depressions or flarks . Swamp hummocks are mounds typically initiated as fallen trunks or branches covered with moss and rising above

475-627: The most deadly volcanic landslide occurred in 1792 when sliding debris from Mount Mayuyama in Japan slammed into the Ariake Sea and generated a tsunami that reached the opposite shore and killed nearly 15,000 people. The sector collapse of Ritter Island in 1888 generated a tsunami with runups of up to 15 m (49 ft) that caused damage more than 700 km (430 mi) away and killed anywhere between 500 and 3,000 people on neighbouring islands. A landslide originating from Devastation Glacier on

500-706: The southern flank of the Mount Meager massif in British Columbia , Canada, buried and killed a group of four geologists at the confluence of Devastation Creek and Meager Creek in July 1975. In 1979, a landslide from the Indonesian volcano Iliwerung produced 9 m-high (30 ft) waves that killed more than 500 people. In December 2018, another landslide-induced tsunami took place in Indonesia's Sunda Strait following

525-975: The swamp floor. The low-lying areas between hummocks are called hollows. A related term, used in the Southeastern United States , is " hammock ". Cryogenic earth hummocks go by various names; in North America they are known as earth hummocks ; the Icelandic term þúfa/thúfa (pl. þúfur/thúfur ) is also used to describe them in Greenland and Iceland, and the Finnish term pounu (pl. pounut ) in Fennoscandia . These cold climate landforms appear in regions of permafrost and seasonally frozen ground. They usually develop in fine-grained soils with light to moderate vegetation in areas of low relief where there

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550-656: The term landslide is commonly used for slope movements with shear and displacement in a relatively narrow zone. They can be in the form of debris avalanches , debris flows , slumps and rockfalls . A debris avalanche is a sudden, very rapid flow of rock and soil in response to gravity. It is a common middle stage in the transformation of a cohesive debris flow from a landslide or rockslide. Debris avalanches may be restricted to grain flows or granular flows, in which flow mechanics are governed by particle interactions involving friction and collision. Debris flows, in contrast, owe much of their behaviour to excess pore-water pressure and

575-423: The volcano flank while sector collapses are large enough to involve the volcano summit. The smaller size of a flank collapse indicates that there need be no repose time before another flank collapse occurs, and hence they can be treated as random events. Several conditions can trigger landslides at volcanoes: Large landslides from volcanoes often bury valleys with tens to hundreds of metres of rock debris, forming

600-434: The winter to spread unevenly. Encroaching frost exerted increasing pressure on the adjacent unfrozen soil. Trapped between the freezing surface soils and the buried permafrost layer the soil material is forced upwards into hummocks. While this is currently the most commonly accepted hypothesis, there is still only limited evidence of this happening. Debris avalanches are caused by sudden collapses of large volumes of rock from

625-433: The world. The largest volcanic island sector collapse in historic times took place in 1888 when Ritter Island collapsed off the northern coast of Papua New Guinea . Edifice reconstruction generally must occur before a second sector collapse. Flank collapses are much smaller than sector collapses, but they may also yield far-reaching debris flows. Flank collapses differ from sector collapses in that they only involve

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