Debris flow

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 (roughly 2000 kilograms per cubic meter), but owing to widespread sediment liquefaction caused by high pore-fluid pressures, they can flow almost as fluidly as water.[2] 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 (i.e., 1 cubic kilometer). As a result of their high sediment concentrations and mobility, debris flows can be very destructive.

Notable debris-flow disasters of the twentieth century involved more than 20,000 fatalities in Armero, Colombia in 1985 and tens of thousands in Vargas State, Venezuela in 1999.

Debris flow channel, Ladakh, NW Indian Himalaya
Debris flow channel with deposits left after 2010 storms in Ladakh, NW Indian Himalaya. Note coarse bouldery levees on both sides of the channel, and poorly sorted rocks on the channel floor.
Debris flow scars
Scars formed by debris flow in Ventura, greater Los Angeles during the winter of 1983. The photograph was taken within several months of the debris flows occurring.[1]

Features and behavior

Debris flows have volumetric sediment concentrations exceeding about 40 to 50%, and the remainder of a flow's volume consists of water. By definition, “debris” includes sediment grains with diverse shapes and sizes, commonly ranging from microscopic clay particles to great boulders. Media reports often use the term mudflow to describe debris flows, but true mudflows are composed mostly of grains smaller than sand. On Earth's land surface, mudflows are far less common than debris flows. However, underwater mudflows are prevalent on submarine continental margins, where they may spawn turbidity currents. Debris flows in forested regions can contain large quantities of woody debris such as logs and tree stumps. Sediment-rich water floods with solid concentrations ranging from about 10 to 40% behave somewhat differently from debris flows and are known as hyperconcentrated floods.[3] Normal stream flows contain even lower concentrations of sediment.

Debris flows can be triggered by intense rainfall or snowmelt, by dam-break or glacial outburst floods, or by landsliding that may or may not be associated with intense rain. In all cases the chief conditions required for debris flow initiation include the presence of slopes steeper than about 25 degrees, the availability of abundant loose sediment, soil, or weathered rock, and sufficient water to bring this loose material to a state of almost complete saturation. Debris flows can be more frequent following forest and brush fires, as experience in southern California demonstrates. They pose a significant hazard in many steep, mountainous areas, and have received particular attention in Japan, China, Taiwan, USA, Canada, New Zealand, the Philippines, the European Alps, Russia, and Kazakhstan. In Japan a large debris flow or landslide is called yamatsunami (山津波), literally mountain tsunami.

DebrisFlowDepositRestingSpringsPass
Ancient debris flow deposit, Resting Springs Pass, California.

Debris flows are accelerated downhill by gravity and tend to follow steep mountain channels that debouche onto alluvial fans or floodplains. The front, or 'head' of a debris-flow surge often contains an abundance of coarse material such as boulders and logs that impart a great deal of friction. Trailing behind the high-friction flow head is a lower-friction, mostly liquefied flow body that contains a higher percentage of sand, silt and clay. These fine sediments help retain high pore-fluid pressures that enhance debris-flow mobility. In some cases the flow body is followed by a more watery tail that transitions into a hyperconcentrated stream flow. Debris flows tend to move in a series of pulses, or discrete surges, wherein each pulse or surge has a distinctive head, body and tail.

Debris flow deposit, Ladakh, NW Indian Himalaya (2)
Another debris flow in Ladakh, triggered by storms in 2010. Note poor sorting and levees. Steep source catchment is visible in background.

Debris-flow deposits are readily recognizable in the field. They make up significant percentages of many alluvial fans and debris cones along steep mountain fronts. Fully exposed deposits commonly have lobate forms with boulder-rich snouts, and the lateral margins of debris-flow deposits and paths are commonly marked by the presence of boulder-rich lateral levees. These natural levees form when relatively mobile, liquefied, fine-grained debris in the body of debris flows shoulders aside coarse, high-friction debris that collects in debris-flow heads as a consequence of grain-size segregation (a familiar phenomenon in granular mechanics). Lateral levees can confine the paths of ensuing debris flows, and the presence of older levees provides some idea of the magnitudes of previous debris flows in a particular area. Through dating of trees growing on such deposits, the approximate frequency of destructive debris flows can be estimated. This is important information for land development in areas where debris flows are common. Ancient debris-flow deposits that are exposed only in outcrops are more difficult to recognize, but are commonly typified by juxtaposition of grains with greatly differing shapes and sizes. This poor sorting of sediment grains distinguishes debris-flow deposits from most water-laid sediments.

Types

Other geological flows that can be described as debris flows are typically given more specific names. These include:

Lahar

A lahar is a debris flow related in some way to volcanic activity, either directly as a result of an eruption, or indirectly by the collapse of loose material on the flanks of a volcano. A variety of phenomena may trigger a lahar, including melting of glacial ice, intense rainfall on loose pyroclastic material, or the outburst of a lake that was previously dammed by pyroclastic or glacial sediments. The word lahar is of Indonesian origin, but is now routinely used by geologists worldwide to describe volcanogenic debris flows. Nearly all of Earth's largest, most destructive debris flows are lahars that originate on volcanoes. An example is the lahar that inundated the city of Armero, Colombia.

Jökulhlaup

A jökulhlaup is a glacial outburst flood. Jökulhlaup is an Icelandic word, and in Iceland many glacial outburst floods are triggered by sub-glacial volcanic eruptions. (Iceland sits atop the Mid-Atlantic Ridge, which is formed by a chain of mostly submarine volcanoes). Elsewhere, a more common cause of jökulhlaups is the breaching of ice-dammed or moraine-dammed lakes. Such breaching events are often caused by the sudden calving of glacier ice into a lake, which then causes a displacement wave to breach a moraine or ice dam. Downvalley of the breach point, a jökulhlaup may increase greatly in size through entrainment of loose sediment from the valley through which it travels. Ample entrainment can enable the flood to transform to a debris flow. Travel distances may exceed 100 km.

Theories and models of debris flows

Numerous different approaches have been used to model debris-flow properties, kinematics, and dynamics. Some are listed here.

  • Rheologically based models that apply to mud flows treat debris flows as single-phase homogeneous materials (Examples include: Bingham, viscoplastic, Bagnold-type dilatant fluid, thixotropic, etc.)
  • Dam break wave, e.g. Hunt,[4] Chanson et al.[5]
  • Roll wave, e.g., Takahashi,[6] Davies[7]
  • Progressive wave[8]
  • A type of translating rock dam[9]

Two-phase

The mixture theory, originally proposed by Iverson[2] and later adopted and modified by others, treats debris flows as two-phase solid-fluid mixtures.

In real two-phase (debris) mass flows there exists a strong coupling between the solid and the fluid momentum transfer, where the solid's normal stress is reduced by buoyancy, which in turn diminishes the frictional resistance, enhances the pressure gradient, and reduces the drag on the solid component. Buoyancy is an important aspect of two-phase debris flow, because it enhances flow mobility (longer travel distances) by reducing the frictional resistance in the mixture. Buoyancy is present as long as there is fluid in the mixture.[10] It reduces the solid normal stress, solid lateral normal stresses, and the basal shear stress (thus, frictional resistance) by a factor (), where is the density ratio between the fluid and the solid phases. The effect is substantial when the density ratio () is large (e.g., in the natural debris flow).

If the flow is neutrally buoyant, i.e., , (see, e.g., Bagnold,[11] 1954) the debris mass is fluidized and moves longer travel distances. This can happen in highly viscous natural debris flows.[12] For neutrally buoyant flows, Coulomb friction disappears, the lateral solid pressure gradient vanishes, the drag coefficient is zero, and the basal slope effect on the solid phase also vanishes. In this limiting case, the only remaining solid force is due to gravity, and thus the force associated with buoyancy. Under these conditions of hydrodynamic support of the particles by the fluid, the debris mass is fully fluidized (or lubricated) and moves very economically, promoting long travel distances. Compared to buoyant flow, the neutrally buoyant flow shows completely different behaviour. For the latter case, the solid and fluid phases move together, the debris bulk mass is fluidized, the front moves substantially farther, the tail lags behind, and the overall flow height is also reduced. When , the flow does not experience any buoyancy effect. Then the effective frictional shear stress for the solid phase is that of pure granular flow. In this case the force due to the pressure gradient is altered, the drag is high and the effect of the virtual mass disappears in the solid momentum. All this leads to slowing down the motion.

Almaty1921 Sel Malaya Almatinka
Almaty, Kazakhstan, after the catastrophic debris flow of 1921. A number of facilities, including the Medeu Dam, have been built since to prevent flows of this kind from reaching the city.[13]

Damage prevention

In order to prevent debris flows reaching property and people, a debris basin may be constructed. Debris basins are designed to protect soil and water resources or to prevent downstream damage. Such constructions are considered to be a last resort because they are expensive to construct and require commitment to annual maintenance.[14]

In popular culture

In 1989, as part of his large-scale piece David Gordon's United States, and later, in 1999, as part of Autobiography of a Liar, choreographer David Gordon brought together the music of Harry Partch and the words of John McPhee from The Control of Nature, read by Norma Fire, in a dance titled "Debris Flow", a "harrowing taped narrative of a family's ordeal in a massive L.A. mudslide..."[15][16]

See also

References

Notes

  1. ^ D.M. Morton, R.M. Alvarez, and R.H. Campbell. "PRELIMINARY SOIL-SLIP SUSCEPTIBILITY MAPS, SOUTHWESTERN CALIFORNIA" (Open-File Report OF 03-17 USGS 2003)
  2. ^ a b Iverson, R.M., 1997, The physics of debris flows, Reviews of Geophysics, 35(3): 245–296.
  3. ^ Pierson, Thomas C. Distinguishing between debris flows and floods from field evidence in small watersheds. US Department of the Interior, US Geological Survey, 2005.
  4. ^ Hunt,B. (1982). "Asymptotic Solution for Dam-Break Problems." Jl of Hyd. Div., Proceedings, ASCE, Vol. 108, No. HY1, pp. 115–126.
  5. ^ Hubert Chanson, Sebastien Jarny & Philippe Coussot (2006). "Dam Break Wave of Thixotropic Fluid". Journal of Hydraulic Engineering, ASCE. 132 (3): 280–293. doi:10.1061/(ASCE)0733-9429(2006)132:3(280).
  6. ^ Takahashi, T., 1981. Debris flow, Annu. Rev. Fluid Mech., 13, 57–77.
  7. ^ Davies,T.R.H. 1986. Large debris flows: a macro-viscous problem. Acta Mechanica, 63, 161–178.
  8. ^ Hungr,O. 2000. Analysis of debris flow surges using the theory of uniformly progressive flow. Earth Surface Processes and Landforms, 25, 483–495
  9. ^ Coleman, P. F., 1993. A new explanation for debris flow surge phenomena (abstract), Eos Trans. AGU, 74(16), Spring Meet. Suppl., 154.
  10. ^ E. B., Pitman; L. Le (2005). "A two-fluid model for avalanche and debris flows". Philosophical Transactions of the Royal Society A. 363: 1573–1602. Bibcode:2005RSPTA.363.1573P. doi:10.1098/rsta.2005.1596.
  11. ^ R. A. Bagnold (1954). "Experiments on a gravity-free dispersion of large solid spheres in a Newtonian fluid under shear". Proceedings of the Royal Society A. 225: 49–63. Bibcode:1954RSPSA.225...49B. doi:10.1098/rspa.1954.0186.
  12. ^ B. W., McArdell & P. Bartelt, J. Kowalski (2007). "Field observations of basal forces and fluid pore pressure in a debris flow". Geophys. Res. Lett. 34. Bibcode:2007GeoRL..34.7406M. doi:10.1029/2006GL029183.
  13. ^ Jakob, Matthias; Hungr, Oldrich (2005). "Debris-flow hazards and related phenomena". Debris-Flow Hazards and Related Phenomena. Springer: 38–39. Bibcode:2005dfhr.book.....J. ISBN 3-540-20726-0
  14. ^ "Debris Basins". U.S. Fish & Wildlife Service. Retrieved 30 January 2013.
  15. ^ Tobias, Tobi. "Dance: Burning the Flag" New York (November 20, 1989), p.116
  16. ^ Jowitt, Deborah. "Rush Forward. Look Back." Village Voice (December 21, 1999)

Further reading

External links

Agglomerate

Agglomerate (from the Latin agglomerare meaning "to form into a ball") is a coarse accumulation of large blocks of volcanic material that contains at least 75% bombs. Volcanic bombs differ from volcanic blocks in that their shape records fluidal surfaces: they may, for example, have ropy, cauliform, scoriaceous, or folded, chilled margins and spindle, spatter, ribbon, ragged, or amoeboid shapes. Globular masses of lava may have been shot from the crater at a time when partly molten lava was exposed, and was frequently shattered by sudden outbursts of steam. These bombs were viscous at the moment of ejection and by rotation in the air acquired their shape. They are commonly 1 to 2 feet (30 to 60 cm) in diameter, but specimens as large as 12 feet (3.7 m) have been observed. There is less variety in their composition at any one volcanic centre than in the case of the lithic blocks, and their composition indicates the type of magma being erupted.

Agglomerates are typically found near volcanic vents and within volcanic conduits, where they may be associated with pyroclastic or intrusive volcanic breccias. Older (pre-1970) publications, particularly in Scotland, referred to any coarse-grained volcaniclastic rock as 'agglomerate', which led to debris flow deposits, talus deposits and other types of breccia being mistaken for vents. Agglomerates are typically poorly sorted, may contain a fine ash or tuff matrix and vary from matrix to clast support. They may be monolithologic or heterolithic, and may contain some blocks of various igneous rocks. There are various differences between agglomerates and ordinary ash beds or tuffs. Agglomerates are coarser and less frequently well-bedded. Agglomerates can be non-welded or welded, such as coarse basaltic 'spatter'. They typically form proximally during Strombolian eruptions, and are common at strongly peralkaline volcanoes. Some large agglomerate deposits are deposited from pyroclastic density currents during explosive caldera-forming eruptions, such as at Santorini, Taal, and Campi Flegrei. They may be massive to crudely bedded, and can attain great thicknesses.

Crystalline masses of a different kind occur in some numbers in certain agglomerates. They consist of volcanic minerals very much the same as those formed in the lava, but exhibiting certain peculiarities which indicate that they have formed slowly under pressure at considerable depths. They bear a resemblance to plutonic igneous rocks, but are more correctly to be regarded as agglomerations of crystals formed within the liquid lava as it slowly rose towards the surface, and at a subsequent period cast out by violent steam explosions. The sanidinites of the Eifel belong to this group. At Vesuvius, Ascension, St Vincent and many other volcanoes, they form a considerable part of the coarser ash-beds. Their commonest minerals are olivine, anorthite, hornblende, augite, biotite and leucite.

Comet Falls

Comet Falls is a tall waterfall located on Van Trump Creek in Pierce County, Washington. The falls are thought to be the best in the Mount Rainier region.

Diamictite

Diamictite ( ; from Ancient Greek δια (dia-): through and µεικτός (meiktós): mixed) is a type of lithified sedimentary rock that consists of nonsorted to poorly sorted terrigenous sediment containing particles that range in size from clay to boulders, suspended in a matrix of mudstone or sandstone. The term was coined by Richard Foster Flint and others as a purely descriptive term, devoid of any reference to a particular origin. Some geologists restrict the usage to nonsorted or poorly sorted conglomerate or breccia that consists of sparse, terrigenous gravel suspended in either a mud or sand matrix.Unlithified diamictite is referred to as diamicton.

The term diamictite is often applied to nonsorted or poorly sorted, lithified glacial deposits such as glacial tillite, and diamictites are often mistakenly interpreted as having an essentially glacial origin (see Snowball Earth). The most common origin for diamictites, however, is deposition by submarine mass flows like turbidites and olistostromes in tectonically active areas, and they can be produced in a wide range of other geological conditions. Possible origins include:

glacial origin

meltwater flow deposition

unsorted moraine glacial till

basal melt-out

ice rafted sediments deposited by melting icebergs or disintegrating ice sheets (dropstones)

volcanic origin

lahars

lahar mass flows entering the ocean

marine origin

debris flow

turbiditic olistostromes

mixing of sediments by submarine landslides

tectonic origin

fault gouge

erosional origin

regolith, in the form of a debris flow

other mass wasting events

extraterrestrial origin

impact breccia

Euripus Mons

Euripus Mons is a mountain on the planet Mars. The name Euripus Mons is a classical albedo name. It has a diameter of 91 kilometres (57 mi). This was approved by International Astronomical Union in 2003. It is just east of Hellas Basin and is surrounded by debris flow.

Graded bedding

In geology, a graded bed is one characterized by a systematic change in grain or clast size from one side of the bed to the other. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones. Normally graded beds generally represent depositional environments which decrease in transport energy (rate of flow) as time passes, but these beds can also form during rapid depositional events. They are perhaps best represented in turbidite strata, where they indicate a sudden strong current that deposits heavy, coarse sediments first, with finer ones following as the current weakens. They can also form in terrestrial stream deposits.

In reverse or inverse grading the bed coarsens upwards. This type of grading is relatively uncommon but is characteristic of sediments deposited by grain flow and debris flow. It is also observed in Aeolian processes. These deposition processes are examples of granular convection.

Hyperconcentrated flow

A hyperconcentrated flow is a two-phase flowing mixture of water and sediment in a channel which has properties intermediate between fluvial flow and debris flow. Large quantities of sand may be transported throughout the flow column, but the transport of suspended and bedload sediment along the channel depends on flow turbulence and high flow velocities, and coarser sediment remains as bedload. Hyperconcentrated flows do not show the characteristics of non-Newtonian flow typical of debris flows, e.g., levees, coarsening up or matrix supported deposits.Hyperconcentrated flows may contain anywhere from 5–60 % sediment by volume. Higher concentrations tend to be characteristic of debris flows, less of normal fluvial flow.

Kinematic wave

In gravity and pressure driven fluid dynamical and geophysical mass flows such as ocean waves, avalanches, debris flows, mud flows, flash floods, etc., kinematic waves are important mathematical tools to understand the basic features of the associated wave phenomena. These waves are also applied to model the motion of highway traffic flows.

In these flows, mass and momentum equations can be combined to yield a kinematic wave equation. Depending on the flow configurations, the kinematic wave can be linear or non-linear, which depends on whether the wave celerity is a constant or a variable. Kinematic wave can be described by a simple partial differential equation with a single unknown field variable (e.g., the flow or wave height, ) in terms of the two independent variables, namely the time () and the space () with some parameters (coefficients) containing information about the physics and geometry of the flow. In general, the wave can be advecting and diffusing. However, in simple situation, the kinematic wave is mainly advecting.

Lahar

A lahar ( , from Javanese: ꦮ꧀ꦭꦲꦂ, translit. wlahar) 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.Lahars are extremely destructive: they can flow tens of metres per second (22 mph or more), they have been known to be up to 140 metres (460 ft) deep, and large flows tend to destroy any structures in their path. They have even been known to decimate entire settlements. Notable lahars include those at Mount Pinatubo and Nevado del Ruiz, the latter of which killed thousands of people and caused extensive damage to infrastructure.

Landslide

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 which produce specific conditions that make a slope prone to failure. In many cases, the landslide is triggered by a specific event (such as a heavy rainfall, an earthquake, a slope cut to build a road, and many others), although this is not always identifiable.

Landslide classification

There have been known various classifications of landslides and other types of mass wasting.

For example, the McGraw-Hill Encyclopedia of Science and Technology distinguishes the following types of landslides:

fall (by undercutting)

fall (by toppling)

slump

rockslide

earthflow

rockslide that develops into rock avalanche

Matrix-supported rock

A matrix-supported rock is a sedimentary rock of which a defined majority is the fine-grained matrix as opposed to the clasts (in the case of a conglomerate) or allochems (in the case of a limestone). For a conglomerate, a rock is considered matrix-supported when clasts constitute less than 15% of its volume. Matrix support is considered to be characteristic of debris flow deposits, in which clasts are supported within a fabric of mud as they move downstream. Wackestones and mudstones under the Dunham classification of limestones are also considered to be matrix-supported due to the predominance of micrite (as opposed to, for example, macrofossils).

Moabosaurus

Moabosaurus (meaning "Moab reptile") is a genus of turiasaurian sauropod dinosaur from the Early Cretaceous Cedar Mountain Formation of Utah, United States.

Mount Meager (British Columbia)

Not to be confused with the Mount Meager massif, which is also commonly referred to as Mount Meager.Mount Meager is a mountain in the Pacific Ranges of the Coast Mountains in British Columbia, Canada. It represents the second highest peak of the Mount Meager massif, a group of coalescent stratovolcanoes in the Garibaldi Volcanic Belt.The mountain was the source of the 2010 Mount Meager landslide. On August 6, the southern 2,554 m (8,379 ft) peak of Meager collapsed in a series of major rockfalls. The rockfalls transformed into a large debris flow that dammed Meager Creek for about one day. The landslide dam was about 30 m (98 ft) high and impounded water in a temporary lake about 4 km (2.5 mi) long. The debris flow also crossed the Lillooet River downstream and wiped out a forestry road on the opposite bank of the Lillooet River. The response of emergency personnel, fearing a sudden failure of the dam on Meager Creek, was to direct residents on the Lillooet River floodplain, in the village of Pemberton 55 km (34 mi) downstream and in the Lil'wat community at Mount Currie to evacuate the area.

Mount Meager massif

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.

The Garibaldi Volcanic Belt (GVB) has a long history of eruptions and poses a threat to the surrounding region. Any volcanic hazard ranging from landslides to eruptions could pose a significant risk to humans and wildlife. Although the massif has not erupted for more than 2,000 years, it could produce a major eruption; if this were to happen, relief efforts would be quickly organized. Teams such as the Interagency Volcanic Event Notification Plan (IVENP) are prepared to notify people threatened by volcanic eruptions in Canada.

The Mount Meager massif produced the largest volcanic eruption in Canada in the last 10,000 years. About 2,400 years ago, an explosive eruption formed a volcanic crater on its northeastern flank and sent avalanches of hot ash, rock fragments and volcanic gases down the northern flank of the volcano. Evidence for more recent volcanic activity has been documented at the volcano, such as hot springs and earthquakes. The Mount Meager massif has also been the source of several large landslides in the past, including a massive debris flow in 2010 that swept down Meager Creek and the Lillooet River.

Prydz Bay

Prydz Bay is a deep embayment of Antarctica between the Lars Christensen Coast and Ingrid Christensen Coast. The Bay is at the downstream end of a giant glacial drainage systems that originates in the East Antarctic interior. The Lambert Glacier flows from Lambert Graben into the Amery Ice Shelf on the south-west side of Prydz Bay. Other major glaciers drain into the southern end of the Amery Ice Shelf at 73° S where the marine part of the system starts at the modern grounding zone.

The Amery Ice Shelf extends about 550 km north of the Lambert Glacier grounding zone and occupies a valley between 80–200 km wide. Depths to the bed beneath the Amery Ice Shelf are poorly known in detail but it is clearly over-deepened, reaching around -2500 m MSL close to the grounding zone. The Amery Ice Shelf occupies a very large U-shaped valley with exposed nunataks along the flanks reaching 1500 m in elevation and total relief as high as 3000 m.

Seaward of the Amery Ice Shelf, Prydz Bay shows bathymetry typical of glaciated margins with deeper water near the coast with a broad topographic basin, the Amery Depression that is around -700 m MSL along the front of the Amery Ice Shelf. The Amery Depression shoals gently to outer shelf banks around 100–200 m deep. The shelf break is at around 400–500 m. The western side of Prydz Bay features a broad trough crossing from the inner shelf to the shelf edge, Prydz Channel. It is around 100 km wide and is 500 m deep at the shelf break. It is a typical example of a cross-shelf glacial trough that occupy 40.2% of the area of the Antarctic continental shelf and that are formed by fast-flowing ice streams.During the late Neogene, the Lambert Glacier–Amery Ice Shelf drainage system flowed across Prydz Bay in an ice stream that reached the shelf edge and built a trough mouth fan on the upper continental slope. The fan consists mostly of debris flow deposits derived from the melting out of subglacial debris at the grounding line at the continental shelf edge. Ocean Drilling Program Site 1167 indicates that thick debris flow intervals are separated by thin mudstone horizons deposited when the ice had retreated from the shelf edge. The bulk of the trough mouth fan was deposited prior to ~780,000 years ago with as few as three debris flow intervals deposited since then.

Slide Mountain (Nevada)

Slide Mountain is a 9,702-foot (2,957 m) peak in the Carson Range near Reno, in Washoe County, Nevada. From the summit of Slide Mountain, Lake Tahoe, Washoe Lake, Carson Valley, and the city of Reno can be viewed.

Slide Mountain is named after the repeated large landslides that occur high on the mountain's south east side. The slide areas are devoid of trees and vegetation and are covered in granite rock and decomposed granite sand. This gives the barren slopes a whitish color, and the distinctive slide zones are plainly visible from points to the southeast of the mountain in Washoe Valley.

The most recent large slide occurred on May 30, 1983. The slide ran immediately into Price Lake in a small valley half way down the mountain. The resulting slurry of granite sand, granite rock, and forest debris flowed freely down the canyon below Price Lake, and ran out on the flat floor of Washoe Valley. The debris flow severed the older US 395 highway, and partially covered the newer US 395 freeway. The slide destroyed several homes, killed one person, and injured several others. The volume of water flushed out of Price Lake was estimated to be 7 million gallons. The debris flow in the canyon was measured as 30 feet high at the bottom of the canyon, and the rock fall volume was estimated to be 1.4 million cubic yards. Slide Mountain dominates the Reno skyline, standing 5,000 feet (1,500 m) above the city just to the south of its larger neighbor Mount Rose. Several ski trails and a maintenance road lead to the summit, making the hike to the top an easy one, especially from the Mount Rose Summit Campground located on State Route 431 at the Northwest base. The "Mount Rose Ski Tahoe" resort is located on Slide mountain. This leads some to believe that the mountain itself is named Mount Rose, but Mount Rose is actually approximately 1,000 feet (300 m) higher and several miles to the northwest.

Many communications towers adorn the summit, providing television, radio, emergency responder and amateur communications service to the Reno, Carson City and Lake Tahoe areas.

Sorting (sediment)

Sorting describes the distribution of grain size of sediments, either in unconsolidated deposits or in sedimentary rocks. This should not be confused with crystallite size, which refers to the individual size of a crystal in a solid. Crystallite is the building block of a grain. Very poorly sorted indicates that the sediment sizes are mixed (large variance); whereas well sorted indicates that the sediment sizes are similar (low variance).

The terms describing sorting in sediments - very poorly sorted, poorly sorted, moderately sorted, well sorted, very well sorted - have technical definitions, and semi-quantitatively describe the amount of variance seen in particle sizes. In the field, sedimentologists use graphical charts to accurately describe the sorting of a sediment using one of these words.The degree of sorting may also indicate the energy, rate, and/or duration of deposition, as well as the transport process (river, debris flow, wind, glacier, etc.) responsible for laying down the sediment. Sorting of sediments can also be affected by reworking of the material after deposition, for instance, by winnowing.Well sorted rocks are generally porous, while poorly sorted rocks have low porosity.

Swansea, California

Swansea is a former settlement and unincorporated community in Inyo County, California. It is located 8.5 miles (14 km) south of New York Butte, at an elevation of 3,661 ft (1,116 m).Swansea was a boomtown located on the eastern shore of Owens Lake. Spawned by the success of the silver mining operations in the nearby Cerro Gordo Mines in the late 1860s, Swansea became a hub for smelting the ore and transporting the resulting ingots to Los Angeles, over 200 miles away. The smelter operated from 1869 to 1874.Swansea was named after the mining town Swansea in south Wales, from which many experienced miners emigrated to the United States.

The 1872 Lone Pine earthquake damaged the smelters and uplifted the shoreline, rendering the Swansea pier inaccessible by Owens Lake steamships. As a result, most of the smelting and transportation business moved to Keeler, approximately one mile to the south.

In the summer of 1874, a thunderstorm-induced debris flow inundated Swansea under several feet of water, rock, and sand. By then the town had been almost deserted, and the debris flow marked the end of Swansea.

As of 2007, only one building and a smelter foundation remained alongside Route 136 (about 10 miles southeast of Lone Pine). Now the community is a ghost town.

Vargas tragedy

The Vargas tragedy was a natural disaster that occurred in Vargas State, Venezuela on 14–16 December 1999, when torrential rains caused flash floods and debris flows that killed tens of thousands of people, destroyed thousands of homes, and led to the complete collapse of the state's infrastructure. According to relief workers, the neighborhood of Los Corales was buried under 3 metres (9.8 ft) of mud and a high percentage of homes were simply swept into the ocean. Entire towns including Cerro Grande and Carmen de Uria completely disappeared. As much as 10% of the population of Vargas died during the event.

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