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Encyclopedia > Mass wasting

Mass wasting, also known as mass movement or slope movement, is the geomorphic process by which soil, regolith, and rock move downslope under the force of gravity. Types of mass wasting include creep, slides, flows, topples, and falls, each with their own characteristic features, and take place over timescales from seconds to years. Mass wasting occurs on both terrestrial and submarine slopes, and has been observed on Earth, Mars, and Venus. Image File history File linksMetadata Download high-resolution version (1402x1000, 1583 KB) Source: Pflatsch Description: Hangrutsch an der Sanna nach dem Hochwasser 2005; aufgenommen von Pflatsch, am 25. ... Surface of the Earth Geomorphology is the study of landforms, including their origin and evolution, and the processes that shape them. ... Loess field in Germany Surface-water-gley developed in glacial till, Northern Ireland Technically, soil forms the pedosphere: the interface between the lithosphere (rocky part of the planet) and the biosphere, atmosphere, and hydrosphere. ... Regolith (Greek: blanket rock) is a layer of loose, heterogeneous material covering solid rock. ... “Rock” redirects here. ... Gravity is a force of attraction that acts between bodies that have mass. ... This article is about Earth as a planet. ... Adjectives: Martian Atmosphere Surface pressure: 0. ... Adjectives: Venusian or (rarely) Cytherean Atmosphere Surface pressure: 9. ...


When the gravitational force acting on a slope exceeds its resisting force, slope failure (mass wasting) occurs. The slope material's strength and cohesion and the amount of internal friction between material help maintain the slope's stability and are known collectively as the slope's shear strength. The steepest angle that a cohesionless slope can maintain without losing its stability is known as its angle of repose. When a slope possesses this angle, its shear strength perfectly counterbalances the force of gravity acting upon it. Mercury sticks together because of the cohesive forces. ... Shear strength in reference to soil is a term used to describe the maximum strength of soil at which point significant plastic deformation or yielding occurs due to an applied shear stress. ... The angle of repose, also referred to as angle of friction, is an engineering property of granular materials. ...


Mass wasting may occur at a very slow rate, particularly in areas that are very dry or those areas that receive sufficient rainfall such that vegetation has stabilised the surface. It may also occur at very high speed, such as in rock slides or landslides, with disastrous consequences, both immediate and delayed, e.g., resulting from the formation of landslide dams. This entry refers to the geological term landslide. ... A landslide dam is a natural damming of a river by some kind of mass wasting: landslide, debris flow, or rock avalanche. ...


Factors that change the potential of mass wasting include: change in slope angle; weakening of material by weathering; increased water content; changes in vegetation cover; and overloading. Weathering is the decomposition of rocks, soils and their minerals through direct contact with the Earths atmosphere. ... Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants, and is, by far, the most abundant biotic element of the biosphere. ...

Contents

Types of mass movement

Types of mass movement are distinguished based on how the soil, regolith or rock moves downslope as a whole.


Creep

Downhill creep is a long term process. The combination of small movements of soil or rock in different directions over time are directed by gravity gradually downslope. The steeper the slope, the faster the creep. The creep makes trees and other shrubs curve to reach the sun light. These often trigger land slides because the dirt underneath is not very strong. The trees most of the time die out because of lack of water and sun, and these rarely happen in wet climates. Caused by freezing then thawing, or hot then cold temperature, it causes surface soils to move up then down, inching it's way towards the bottom of the slope. This happens at a rate that is not noticeable to the naked eye. The slow prgoression of rock and other debris down a low grade slope; it can also refer to slow deformation of such materials as a result of prolonged pressure and stress. ...


Landslides

Where the mass movement has a well-defined zone or plane of sliding, it is called a landslide. This includes rock slides, slumps and sturzstroms. This article is about geological phenomenon. ... This entry refers to the geological term landslide. ... The slump that destroyed Thistle, Utah, by creating an earthen dam that flooded the area Slump is a form of mass wasting event that occurs when loosely consolidated materials or rock layers move a short distance down a slope. ... A sturzstrom is a rare, unique type of landslide. ...


It is also one of the common classification of mass wasting.


Flows

Movement of soil and regolith that more resembles fluid behavior is called a flow. These include avalanches, mudflows, debris flows, earth flow, solifluction, lahars and sturzstroms. Water, air and ice are often involved in enabling fluidlike motion of the material. The toe of an avalanche in Alaskas Kenai Fjords. ... A mudflow or mudslide is the most rapid (up to 80 km/h) and fluid type of downhill mass wasting. ... Scars formed by debris flow in great Los Angeles during the winter of 1968-1969. ... An earthflow (earth flow) is a downslope viscous flow of a sheet or stream of water-saturated material moving under the pull of gravity. ... Solifluction, also known as soil fluction, is a type of mass wasting where waterlogged sediment slowly moves downslope over impermeable material. ... A lahar is a mixture of rock, mud, and water that flows down from a volcano (or occasionally other mountains), typically along a river valley. ... A sturzstrom is a rare, unique type of landslide. ...


Topples

Topples are instances when blocks of rock pivot and fall away from a slope.


Falls

A fall, including rockfall, is where regolith cascades down a slope, but is not of sufficient volume or viscosity to behave as a flow. Falls are promoted in rocks which are characterised by presence of vertical cracks. Falls are a result of undercutting of water as well as undercutting of waves. This rockfall saved the underneath soil from further erosion, resulting in a hoodoo. ...


Triggers of mass wasting

Soil and regolith remain on a hillslope only while the gravitational forces are unable to overcome the frictional forces keeping the material in place (see Slope stability). Factors that reduce the frictional resistance relative to the downslope forces, and thus initiate slope movement, can include: Figure 1: Simple slope slip section The field of slope stability encompasses the analysis of static and dynamic stability of slopes of earth and rock-fill dams, slopes of other types of embankments, excavated slopes, and natural slopes in soil and soft rock. ...

  • seismic shaking
  • increased overburden from structures
  • increased soil moisture
  • reduction of roots holding the soil to bedrock
  • undercutting of the slope by excavation or erosion
  • weathering by frost heave
  • bioturbation

The term archaeological excavation has a double meaning. ... Frost heaving (or frost heave) occurs when soil expands and contracts due to freezing and thawing. ... In oceanography and limnology, the displacement and mixing of sediment particles by benthic fauna (animals) or flora (plants) is termed bioturbation. ...

References

  • Monroe, Wicander (2005). The Changing Earth: Exploring Geology and Evolution. Thomson Brooks/Cole. ISBN 0-495-01020-0. 
  • Selby, M.J. (1993). Hillslope Materials and Processes, 2e. Oxford University Press. ISBN 0-19-874183-9. 

External links

Wikimedia Commons has media related to:
landslide
  • Mass Wasting

  Results from FactBites:
 
Mass wasting - Wikipedia, the free encyclopedia (462 words)
Mass wasting, also known as mass movement or slope movement, is the geomorphic process by which soil, regolith, and rock move downslope under the force of gravity.
Mass wasting occurs on terrestrial and submarine slopes, and has been observed on Earth and Mars.
Mass wasting may occur at a very slow rate, particularly in areas that are very dry or those areas that receive sufficient rainfall such that vegetation has stabilised the surface.
Geology300 with Terry J. Boroughs: Mass Wasting and Groundwater Systems Homework (2397 words)
Mass wasting is the down slope movement of earth materials moving under the influence of gravity.
Rapid mass wasting means that the earth materials move an appreciable distance over the time span of a human life.
A mass movement of rock material and soil largely as one or more units along planes of weakness at the base of or within the rock material.
  More results at FactBites »

 
 

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