Mass Movement

11 Key excerpts on "Mass Movement"

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  Introduction to Process Geomorphology

  • Vijay K. Sharma(Author)
  • 2010(Publication Date)
  • CRC Press

    (Publisher)

  81 4 Mass Movement Mass Movement refers to the activity of downslope movement of competent and incompetent earth materials alike when they become unstable under stress . This instability, called slope failure , can be affected in different degrees and types of movement that depend on certain aspects of geology, climate, topography, hydrol-ogy, and other environmental stress conditions, including human activities. Slope failure can be surficial or deep-seated along shear planes, and localized or regional in nature. It can likewise be imperceptibly slow to rapid, involving the transfer of microscopic fractions through to mega-sized detritus down the slope, and subsid-ence. The movement can similarly be independent of or assisted by moisture and air as mediums of transport in the deforming mass. Seismic and volcanic activities are other stress-producing events that directly impact on slope failure at local and regional scales. The stress of diverse human activities on the environment also vari-ously manifests in many different forms of the instability of the earth materials on slopes. The Mass Movement activity thus can have many causes. It is also complex and diverse in nature. The Mass Movement term is often interchangeably used with mass wasting ; however, that additionally connotes the failure of a unit mass of slope-forming material as in creep or slide. CAUSES Every slope experiences a gravity-controlled shear stress , the magnitude of which increases with slope inclination and unit weight of slope-forming material. In gen-eral, at-a-site slope instability depends on the balance of opposing forces of shear stress and shear resistance of the slope-forming earth materials. The slope becomes unstable and deforms when the shear stress due to external causes, internal causes, or both exceeds the shear resistance of the earth materials (Terzaghi, 1950; Hansen, 1984).

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  Principles and Dynamics of the Critical Zone

  • (Author)
  • 2015(Publication Date)
  • Elsevier

    (Publisher)

  National Research Council, 2001 , p. 89). The zone extends from the top of the canopy to the bottom of the groundwater aquifer. Mass Movement, one of the main processes of the Critical Zone in areas that have varying elevations connected by slopes, represents complex hydrologic, atmospheric, cryogenic, soil-geomorphic, and biogeochemical feedbacks in response to climatic, tectonic, and anthropogenic forcing at a range of spatial and temporal scales. Mass Movement occurs in all climatic regions and plays a major role in the sustainability of terrestrial life and environment.

  Processes of Mass Movement are the dominant modes of mobilization (i.e., erosion), transport, and deposition of materials in the Critical Zone. Mass Movement is the result of a variety of geomorphic, geologic, and hydrologic factors, which predispose hillslopes towards instability. Events such as earthquakes, intense rainfalls, and snowmelt trigger various types of Mass Movement, which yield a large amount of mass (i.e., sediment) from the hillslopes and play a significant role in the modification of the hillslope by transporting mass from a slope to the base below. The velocity of movement of slope material downslope ranges from extremely slow or imperceptible to extremely rapid movement (5 m/s). The sediment transported by these processes moves downslope and is deposited along valley floors, in lakes, along floodplains, or into oceans by fluvial, glacial, and/or anthropogenic processes. The volume of debris mobilized by Mass Movement depends on a combination of the spatial distribution and frequency of triggering events, the number of failures triggered in a given event, the probability distribution of mass-movement volume for such a triggering event, and the flux of the debris from Mass Movement into the channel network.

  The study of Mass Movement is one of the major interests among geomorphologists and engineers. Literature on Mass Movement exists from the beginning of the nineteenth century (Hubbard, 1908 ; Van Horn, 1909 ; Sharpe, 1938 ) to recent (Brunsden, 1993 ; Shroder et al., 2011 ; Roering, 2012

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  Planetary Surface Processes

  • H. Jay Melosh(Author)
  • 2011(Publication Date)
  • Cambridge University Press

    (Publisher)

  319 8 Slopes and Mass Movement Imagine a landmass upon which no rain falls, no rivers flow, no glaciers form, no waves beat, no winds blow. Let chemical and mechanical disin- tegration disrupt the rocks, and gravity exert its downward pull. On such a landmass earth and rock will move ceaselessly from higher to lower levels, slopes will soften, relief will fade. Given time enough, the whole will be reduced to a featureless plane of disintegrated rock debris. Douglas Johnson, foreword to the book Landslides and Related Phenomena by C. F. S. Sharpe, 1937 In the summer of 1935 young C. F. S. Sharpe undertook an excellent adventure. Having acquired a car, he drove 16 000 miles through 28 American states and 3 Canadian prov- inces. His quest was unusual: He was out to demonstrate that Mass Movement of debris over the Earth’s surface is an important geological process. After he returned he wrote up his observations in a book (Sharpe, 1938) that forms the basis of our modern understanding of gravity-driven mass motions for the evolution of the Earth’s landscape. The current era of space exploration has greatly broadened the reach of the processes he described: Mass motion is important on bodies ranging from tiny asteroids and comets only a few kilom- eters in diameter up to the largest moons and planets. Its action has been observed on every solid body in the Solar System. 8.1 Soil creep The mantle of loose debris on slopes everywhere in the Solar System is slowly creeping downhill. This insidious motion is usually too slow to appreciate on human timescales, but the evidence is there for anyone who will look. On Earth, gravestones and old fence posts gradually tilt downhill. Linear trails of fragments lead downslope from distinctive rock outcrops and steep stream banks are gradually overridden by thick sheets of soil that often include intact mats of vegetation and trees.

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  The Changing Earth

  Exploring Geology and Evolution

  • James Monroe, Reed Wicander(Authors)
  • 2014(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  This terrible tragedy illustrates how geology affects all of our lives. The underlying causes of the mudslides in Brazil can be found anywhere in the world. In fact, worldwide, land-slides (a general term for Mass Movements of Earth materi-als) cause an average of 7,500 deaths and approximately $25 billion in damages per year. In the United States, landslides result in 25 to 50 deaths per year and damages exceeding $2 billion annually. By being able to recognize and under-stand how landslides occur and what the results may be, we can find ways to reduce hazards and minimize damage in terms of both human life and property damage. Mass wasting (also called Mass Movement ) is defined as the downslope movement of material under the direct influence of gravity. Most types of mass wasting are aided by weathering and usually involve surficial material. The material moves at rates ranging from almost imperceptible, as in the case of creep, to extremely fast, as in a rockfall or slide. Although water can play an important role, the relentless pull of gravity is the major force behind mass wasting. 11.2 Factors That Influence Mass Wasting Mass wasting is an important geologic process that can occur at any time and almost any place. Although all major landslides have natural causes, many smaller ones are the result of human activity and could have been prevented or their damage minimized. When the gravitational force acting on a slope exceeds its resisting force, slope failure (mass wasting) occurs. The resisting forces that help maintain slope stability include the slope material’s strength and cohesion, the amount of internal friction between grains, and any external support of the slope ( ❚ Figure 11.1). These factors collectively define a slope’s shear strength .

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  Geological Hazards

  Their Assessment, Avoidance and Mitigation

  • Fred G. Bell(Author)
  • 1999(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 4 Mass Movements

  4.1 Soil creep and valley bulging

  Mass Movements on slopes can range in magnitude from soil creep on the one hand to instantaneous and colossal landslides on the other. Sharpe (1938) defined creep as the slow downslope movement of superficial rock or soil debris, which is usually imperceptible except by observations of long duration. Walker et al. (1987) suggested that creep could be regarded as Mass Movement that occurs at less than 0.06 m per year. Creep is a more or less continuous process and a distinctly surface phenomenon. It occurs on slopes with gradients somewhat in excess of the angle of repose of the material involved. Like landslip, its principal cause is gravity, although it may be influenced by seasonal changes in temperature, and by swelling and shrinkage in surface rocks. Other factors that contribute towards creep include interstitial rain washing, ice crystals heaving stones and particles during frost, and the wedging action of rootlets. The liberation of stored strain energy in the weathered zone, particularly of overconsolidated clays with strong diagenetic bonds, is another contributory cause of creep (Bjerrum, 1967). Although creep movement is exceedingly slow, there are occasions on record when it has carried structures with it.

  Evidence of soil creep may be found on almost every soil-covered slope. For example, it occurs in the form of small terracettes, downslope tilting of poles, the curving downslope of trees and soil accumulation on the uphill sides of walls. Indeed, walls may be displaced or broken, and sometimes roads may be moved out of alignment. The rate of movement depends not only on climatic conditions and the angle of slope but also on the soil type and parent material.

  Talus (scree) creep occurs wherever a steep talus exists. Its movement is quickest and slowest in cold and arid regions, respectively.

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  Physical Geology

  The Science of Earth

  • Charles Fletcher(Author)
  • 2017(Publication Date)
  • Wiley

    (Publisher)

  In many other countries, losses tend to be even higher due to irresponsible land-use practices and building codes that ignore geologic hazards. Driven by gravity, the mass wasting process, which pulls regolith down a hillside or cliff, is shown in Figure 16.1. Prevention Through Avoidance Mountain building, weathering, and erosion are perpetually altering the slope of the land. And inevitably, gravity drags loose and unstable accumulations of rock and sediment down- hill. But mass wasting is not a single phenomenon; it occurs in several variations (discussed in the next section), from the instantaneous event that trapped Jenny on the beach to longer and slower processes that shift soil and regolith to the base of slopes over the course of years, decades, and centuries. However, all mass wasting events can be hazardous to humans when we, or our communities and infrastructure, are in the path of these events. Mass wasting is another example of a geologic hazard that is best dealt with simply by avoiding it. We can counteract the threat posed by mass wasting by first, learning to recognize the characteristics of an unstable slope The process by which gravity pulls soil, debris, sediment, and broken rock (collectively known as regolith) down a hillside or cliff is called mass wasting. And the best way to convey the force of this phenomenon is with a true story. LO 16.1 Define mass wasting. USGS FIGURE 16.1 Mass wasting is defined as the movement of rock and soil down a slope under the force of gravity. Human activity caused this landslide. List three human activities that might be responsible for mass wasting of this magnitude. Mass Wasting Is the Movement of Rock and Soil Down a Slope Under the Force of Gravity 499 and second, electing not to build or engage in other activities there.

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  Introduction to Physical Geology

  • Charles Fletcher, Dan Gibson, Kevin Ansdell(Authors)
  • 2014(Publication Date)
  • Wiley

    (Publisher)

  Over the past century, the world’s population has grown enormously, and many people now live in places that were formerly considered too dangerous or risky. As buildable land becomes scarce, communities are expanding into environments that are exposed to mass wasting and other geologic hazards, turning them into neighbourhoods. The best way to manage mass- wasting hazards is to know the characteristics of a hazardous slope and avoid building there. Doing this is called “hazard avoidance.” Avoidance is the most effective and inexpensive approach to managing geologic hazards. LET’S REVIEW “GEOLOGY IN OUR LIVES” STUDY GUIDE 18-1 Mass wasting is the movement of rock and soil down a slope due to the force of gravity. • According to Natural Resources Canada, in a typical year, land- slides cause $200 million to $400 million in damage. They have accounted for approximately 600 human fatalities in recorded Canadian history. In many other countries, the toll is higher due to poor land-use practices and building codes that ignore geo- logic hazards. • Regolith consists of soil, debris, sediment, and broken rock. Mass wasting is the movement of regolith down a slope due to the force of gravity. Mass wasting is an example of a geologic hazard that is best avoided by learning to recognize the signs of an unstable slope and not building or engaging in any sort of unsafe activity there. This policy is called avoidance. • The world’s population has grown tremendously, and people now live in places that formerly were considered too dangerous or risky. We not only live in dangerous places, we alter them and unintentionally make them more dangerous. 18-2 Creep, solifluction, and slumping are common types of mass wasting. • Most canyons and valleys have been formed by a combination of glacial and stream erosion and mass wasting. • Soil creep is the slow downslope migration of soil under the influ- ence of gravity. Creep occurs over periods ranging from months to centuries.

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  Geology

  Earth in Perspective

  • Reed Wicander, James Monroe, Reed Wicander(Authors)
  • 2019(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Rapid Mass Movements involve a visible movement of material. Such movements usually occur quite suddenly, and the material moves quickly downslope. Rapid mass move- ments are potentially dangerous and frequently result in loss of life and property damage. Most rapid Mass Movements occur on relatively steep slopes and can involve rock, soil, or debris. Slow Mass Movements advance at an imperceptible rate and are usually detectable only by the effects of their movement, such as tilted trees and power poles or cracked foundations. Although rapid Mass Movements are more dramatic, slow Mass Movements are responsible for the downslope transport of a much greater volume of weath- ered material. Falls Rockfalls are a common type of extremely rapid Mass Movement in which rocks of any size may fall through the air ( ●FIGURE 10.7). Rockfalls occur along steep can- yons, cliffs, and road cuts, and they build up accumu- lations of loose rocks and rock fragments at their base called talus. ● FIGURE 10.6 Landslide Triggered by Heavy Rains, La Conchita, California La Conchita, California, is located at the base of a steep-sloped terrace. Heavy rains and irriga- tion of an avocado orchard (visible at the top of the terrace) contributed to the landslide that destroyed nine homes in 1995. Ten years later (2005), similar factors caused another massive landslide in the same area. Photograph by R.L. Schuster, U.S. Geological Survey rapid Mass Movement Any kind of mass wasting that involves a visible downslope displacement of material. slow Mass Movement Mass Movement that advances at an imperceptible rate and is usually detectable only by the effects of its movement. rockfall A type of extremely fast mass wasting in which rocks fall through the air. Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).

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  Natural Hazards and Disasters

  • Donald Hyndman, David Hyndman(Authors)
  • 2016(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Rockfalls can be triggered by strong earthquakes, passing trains, slope undercutting, and blasting during min- ing (Case in Point: A Rockfall Triggered by Blasting—Frank Slide, Alberta, 1903, p. 214). Types of Downslope Movement Landslides and other downslope movements are generally classified on the basis of material type, movement type, and rate of movement. Materials are classified into categories of blocks of solid bedrock; debris of various sizes mostly coarser than 2 mm; and earth or soil mostly finer than 2 mm. Water plays a major role in many of these, especially those involving smaller-size particles. Rates of downslope movements are highly variable, even for individual mechanisms of movement. Rates depend on many factors, including slope steepness, grain size, water content, thickness of the moving mass, clay mineral type, and amount of clay. Table 8-1 provides approximate move- ment rates. Styles of movement include falls from cliffs, topples, slides, lateral spreads, and flows. Note that any of them can involve rock, debris, or soil. A continuous range of characteristics exists between most of these types of materials and styles of movement, and one type often transforms into another as it Table 8-1 Typical Velocities for Various Types of Downslope Movement VELOCITY (CM/S) RATES TYPE OF MOVEMENT 10 5 =100,000 cm/s 1km/s 10 4 = 100 m/s = 360 km/h (race car speed) Extremely rapid 10 3 = 10 m/s = 36 km/h Rockfalls and debris avalanches (dry) 10 2 = 1 m/s = 3.6 km/h (walking speed) Very rapid 10 1 = 10 cm/s 10 0 = 1 cm/s Rapid Debris flows (wet) and mudflows (water-saturated) 10 −1 = 6 cm/min.

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  Landslides and Their Control

  • Q. Záruba, V. Mencl(Authors)
  • 2014(Publication Date)
  • Elsevier Science

    (Publisher)

  Chapter 2 FACTORS CAUSING Mass MovementS It is of primary importance to recognize the conditions that cause slopes to become unstable and the factors that trigger the movement. Susceptibility to sliding is deter-mined by the geological structure of the slope, the lithology of the rocks, hydrogeo-logical conditions and the stage of morphological development of the area. Only an accurate diagnosis makes it possible to appreciate the extent of the danger and to propose effective remedial measures. The great variety of slope movements reflects the diversity of factors that may disturb slope stability. The most important of these are as follows: (1) Changes in the slope gradient: These may be caused by natural or artificial influences (e.g. by the undermining of the foot of a slope by stream erosion, or by excavations). Exceptionally, the angle of the slope is steepened as a result of tectonic processes, such as subsidence or uplift. An increase in slope gradient produces a change in the internal stress of the rock mass and equilibrium conditions are disturbed by the increase of shear stress. (2) Changes in the slope height as a result of vertical erosion or excavation work. The deepening of a valley relieves lateral stress and this in turn leads to the loosening of rocks in the slope and the formation of fissures parallel to the slope surface. The penetration of rain water is thus facilitated. (3) Overloading by embankments, fills and spoil heaps. This produces an increase in shear stress and an increase in the pore-water pressure in clayey soils, which results in decreased shear strength. The more rapid the loading, the more dangerous it is. (4) Shocks and vibrations. Tremors produced by earthquakes, large-scale explo-sions and machine vibrations affect the equilibrium of slopes on account of the temporary changes of stress that are caused by oscillations of different frequencies.

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  Geomorphology: The Research Frontier and Beyond

  Proceedings of the 24th Binghamton Symposium in Geomorphology, August 25, 1993

  • J.D. Vitek, J.R. Giardino(Authors)
  • 2013(Publication Date)
  • Elsevier Science

    (Publisher)

  Geomorphology, 7 (1993) 85-128 85 Elsevier Science Publishers B.V., Amsterdam Mass Movement; the research frontier and beyond: a geomorphological approach Denys Brunsden Department of Geography, King's College, London, UK (Received January 29, 1993; accepted March 25, 1993) To boldly go where no man has been before (Star Trek). Introduction The instructions given to the authors of this special issue were: Within the realm of your speciality, provide a brief perspective of the par-adigms in use which contribute to the position of the research frontier. Then 'star-gaze'! Where are we going? Where do we need to go? What will be the focus of the speciality in the future and what techniques etc., will help expand the research frontier? Be outrageous!! It is proposed to meet this request by dis-cussing for each subject: reality — what do we do now? certainty — what will we do in the near future? and speculation — what may happen in the twenty-first century? Following Dury (1978), reality is the current geomorphologi-cal capital on which we may build, certainty means what will happen if present trends fulfill their promise and speculation is the prospect for the future. The value of that depends on the degree to which the mind is unfettered from what is probable to what is possible. In the conclusion it is intended to treat the brief with ambiguity and express a degree of outrage. The field discussed is Mass Movement but this will be limited to selected geomorphologi-cal aspects of the subject. This is an interdisci-plinary field which greatly benefits from co-operation between geology, geomorphology, geophysics, hydrology and soil mechanics. This also means that it is easy to possess an imper-fect understanding of the individual disci-plines. In the present case, for example, a de-gree of uncertainty about advanced soil mechanics, groundwater hydrology and geo-physics is acknowledged.

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