Mass wasting, also known as mass movement,[1] 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 moon
Io, and on many other bodies in the
Solar System.
Subsidence is sometimes regarded as a form of mass wasting. A distinction is then made between mass wasting by subsidence, which involves little horizontal movement, and mass wasting by slope movement.
Rapid mass wasting events, such as landslides, can be deadly and destructive. More gradual mass wasting, such as soil creep, poses challenges to
civil engineering, as creep can deform roadways and structures and break pipelines. Mitigation methods include
slope stabilization, construction of walls, catchment dams, or other structures to contain rockfall or debris flows,
afforestation, or improved drainage of source areas.
Types
Mass wasting is a general term for any process of
erosion that is driven by
gravity and in which the transported soil and rock is not
entrained in a moving medium, such as water, wind, or ice.[2] The presence of water usually aids mass wasting, but the water is not abundant enough to be regarded as a transporting medium. Thus, the distinction between mass wasting and stream erosion lies between a
mudflow (mass wasting) and a very muddy
stream (stream erosion), without a sharp dividing line.[3] Many forms of mass wasting are recognized, each with its own characteristic features, and taking place over timescales from seconds to hundreds of years.[2]
Based on how the soil, regolith or rock moves downslope as a whole, mass movements can be broadly classified as either
creeps or
landslides.[4]Subsidence is sometimes also regarded as a form of mass wasting.[5] A distinction is then made between mass wasting by subsidence, which involves little horizontal movement,[6] and mass wasting by slope movement.[7]
Soil creep is a slow and long term mass movement. The combination of small movements of soil or rock in different directions over time is directed by gravity gradually downslope. The steeper the slope, the faster the creep. The creep makes trees and shrubs curve to maintain their perpendicularity, and they can trigger landslides if they lose their root footing. The surface soil can migrate under the influence of cycles of freezing and thawing, or hot and cold temperatures, inching its way towards the bottom of the slope forming
terracettes. Landslides are often preceded by soil creep accompanied with
soil sloughing — loose soil that falls and accumulates at the base of the steepest creep sections.[8]
Solifluction is a form of creep characteristics of arctic or alpine climates. It takes place in soil saturated with moisture that thaws during the summer months to creep downhill. It takes place on moderate slopes, relatively free of vegetation, that are underlain by
permafrost and receive a constant supply of new debris by
weathering. Solifluction affects the entire slope rather than being confined to channels and can produce terrace-like landforms or
stone rivers.[9]
A landslide, also called a landslip,[10] is a relatively rapid movement of a large mass of earth and rocks down a hill or a mountainside. Landslides can be further classified by the importance of water in the mass wasting process. In a narrow sense, landslides are rapid movement of large amounts of relatively dry debris down moderate to steep slopes. With increasing water content, the mass wasting takes the form of
debris avalanches, then
earthflows, then
mudflows. Further increase in water content produces a sheetflood, which is a form of
sheet erosion rather than mass wasting.[11]
Occurrences
On
Earth, mass wasting occurs on both terrestrial and submarine slopes.[12] Submarine mass wasting is particularly common along glaciated coastlines where glaciers are retreating and great quantities of sediments are being released. Submarine slides can transport huge volumes of sediments for hundreds of kilometers in a few hours.[13]
Mass wasting is a common phenomenon throughout the Solar System, occurring where volatile materials are lost from a
regolith. Such mass wasting has been observed on
Mars,
Io,
Triton, and possibly
Europa and
Ganymede.[14] Mass wasting also occurs in the equatorial regions of
Mars, where stopes of soft
sulfate-rich sediments are steepened by wind erosion.[15] Mass wasting on
Venus is associated with the rugged terrain of
tesserae.[16] Io shows extensive mass wasting of its volcanic mountains.[17]
Deposits and landforms
Mass wasting affects
geomorphology, most often in subtle, small-scale ways, but occasionally more spectacularly.[18]
Soil creep is rarely apparent but can produce such subtle effects as curved forest growth and tilted fences and telephone poles. It occasionally produces low scarps and shallow depressions.[19] Solifluction produced lobed or sheetlike deposits, with fairly definite edges, in which
clasts (rock fragments) are oriented perpendicular to the contours of the deposit.[20]
Rockfall can produce
talus slopes at the feet of cliffs. A more dramatic manifestation of rockfall is
rock glaciers, which form from rockfall from cliffs oversteepened by glaciers.[19]
Landslides can produce scarps and step-like small terraces.[21] Landslide deposits are poorly
sorted. Those rich in clay may show stretched clay lumps (a phenomenon called
boudinage) and zones of concentrated shear.[20]
Debris flow deposits take the form of long, narrow tracks of very poorly sorted material. These may have natural
levees at the sides of the tracks, and sometimes consist of lenses of rock fragments alternating with lenses of fine-grained earthy material.[20] Debris flows often form much of the upper slopes of
alluvial fans.[22]
Causes
Triggers for mass wasting can be divided into passive and activating (initiating) causes. Passive causes include:[23]
Rock and soil
lithology. Unconsolidated or weak debris are more susceptible to mass wasting, as are materials that lose cohesion when wetted.
Stratigraphy, such as thinly bedded rock or alternating beds of weak and strong or impermeable or permiable rock lithologies.
Mass wasting causes problems for
civil engineering, particularly
highway construction. It can displace roads, buildings, and other construction and can break pipelines. Historically, mitigation of landslide hazards on the
Gaillard Cut of the
Panama Canal accounted for 55,860,400 cubic meters (73,062,600 cu yd) of the 128,648,530 cubic meters (168,265,924 cu yd) of material removed while excavating the cut.[25]
^Allaby, Michael (2013). "mass movement". A dictionary of geology and earth sciences (Fourth ed.). Oxford: Oxford University Press.
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abJackson, Julia A., ed. (1997). "Mass wasting". Glossary of geology (Fourth ed.). Alexandria, Virginia: American Geological Institute.
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^Thornbury, William D. (1969). Principles of geomorphology (2d ed.). New York: Wiley. p. 36.
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^Allaby, Michael (2013). "mass-wasting". A dictionary of geology and earth sciences (Fourth ed.). Oxford: Oxford University Press.
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^Fleming, Robert W.; Varnes, David J. (1991). "Slope movements". The Heritage of Engineering Geology; the First Hundred Years: 201–218.
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10.1130/DNAG-CENT-v3.201.
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^Moore, Jeffrey M.; Mellon, Michael T.; Zent, Aaron P. (July 1996). "Mass Wasting and Ground Collapse in Terrains of Volatile-Rich Deposits as a Solar System-Wide Geological Process: The Pre-Galileo View". Icarus. 122 (1): 63–78.
Bibcode:
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^Bindschadler, D. L.; Head, J. W. (August 1988). "Diffuse scattering of radar on the surface of Venus: Origin and implications for the distribution of soils". Earth, Moon, and Planets. 42 (2): 133–149.
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^Turtle, Elizabeth P.; Keszthelyi, Laszlo P.; McEwen, Alfred S.; Radebaugh, Jani; Milazzo, Moses; Simonelli, Damon P.; Geissler, Paul; Williams, David A.; Perry, Jason; Jaeger, Windy L. (May 2004). "The final Galileo SSI observations of Io: orbits G28-I33". Icarus. 169 (1): 3–28.
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^
abcMücher, Herman; van Steijn, Henk; Kwaad, Frans (2018). "Colluvial and Mass Wasting Deposits". Interpretation of Micromorphological Features of Soils and Regoliths: 21–36.
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^Fornari, Daniel J.; Garcia, Michael O.; Tyce, Robert C.; Gallo, David G. (10 December 1988). "Morphology and structure of Loihi Seamount based on Seabeam Sonar Mapping". Journal of Geophysical Research: Solid Earth. 93 (B12): 15227–15238.
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^Carey, Steven; Ballard, Robert; Bell, Katherine L.C.; Bell, Richard J.; Connally, Patrick; Dondin, Frederic; Fuller, Sarah; Gobin, Judith; Miloslavich, Patricia; Phillips, Brennan; Roman, Chris; Seibel, Brad; Siu, Nam; Smart, Clara (November 2014). "Cold seeps associated with a submarine debris avalanche deposit at Kick'em Jenny volcano, Grenada (Lesser Antilles)". Deep Sea Research Part I: Oceanographic Research Papers. 93: 156–160.
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^De Blasio, Fabio Vittorio (2011). Introduction to the physics of landslides : lecture notes on the dynamics of mass wasting. Dordrecht. p. 280.
ISBN9789400711228.{{
cite book}}: CS1 maint: location missing publisher (
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