- Also called:
- Mass Wasting
- Related Topics:
- settlement
mass movement
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What is mass movement in geology?
In geology, mass movement refers to the bulk movements of soil and rock debris down slopes due to gravity or the sinking of the Earth’s surface. It includes mass wasting processes and the sinking of confined areas of the Earth’s ground surface and plays a role in landform alteration.
Several factors can cause mass movements, including the presence of debris cover on slopes, the structure of rocks, removal of vegetation, increased slope steepness, earthquake tremors, and flowing ground water. These factors often combine with climatic factors like precipitation and frost activity.
Types of mass movements include rockfalls, creep, landslides, slumps, earthflows, mudflows, debris flows, avalanches, solifluction, subsidence, and settlement.
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What causes mass movement to occur?
Mass movements, or the bulk movements of soil and rock debris down slopes due to gravity, are influenced by several factors. These include weathering, the character and structure of rocks, removal of vegetation, increased slope steepness, earthquake tremors, and flowing ground water. Climatic factors such as precipitation and frost activity can combine with slope conditions to cause mass movement.
Different types of mass movements include:
* Rockfalls
* Creep
* Landslides
* Slump
* Earthflow
* Mudflow
* Debris flow or avalanche
* Solifluction
* Subsidence
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What are the main types of mass movement?
Mass movements, also known as mass wasting, involve the downslope transport of soil and rock debris due to gravity. These movements are often influenced by factors such as slope steepness, water content, vegetation cover, and seismic activity.
The main types of mass movement are:
* Falls Abrupt movements and free fall of loosened blocks of solid rock.
* Creep The almost imperceptible downslope movement of surficial soil particles and rock debris.
* Landslides Downslope movements of bedrock and other debris caused by the separation of a slope section along a plane of least resistance or slip surface.
* Slump The separation of a mass along a concave head scarp, moving down a curved slip surface and accumulating at the slope’s foot.
* Flows A type of landslide in which the distribution of particle velocities resembles that of a viscous fluid.
* Spreads The complex lateral movement of relatively coherent earth materials resting on a weaker substrate that is subject to liquefaction or plastic flow.
* Toppling Rotation of a mass of rock, debris, or earth outward from a steep slope face.
* Solifluction The downslope movement of moisture-saturated surficial material over frozen substratum material, occurring in sub-Arctic regions during seasonal periods of surface thaw.
* Subsidence Relatively rapid sinking mass movements involving a roof collapse or breakdown of a subsurface cavity such as a cave.
* Settlement Gradual sinking mass movements that occur through consolidation of soil and rock by the squeezing or removal of fluids from the pore spaces, and by the collapse of the grain structure.3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How does gravity affect mass movement?
Mass movement, also known as mass wasting, is the movement of soil and rock down slopes due to gravity. Gravity is the primary force that induces this movement. Several factors can influence mass movement, including the slope's steepness, the presence of water, the type of rock and soil, and the vegetation cover. These elements can affect the stability of the slope and, when combined with gravity, can result in various types of mass movements such as landslides, rockfalls, and creep.
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What role does water play in mass movement events?
Water plays a significant role in mass movement events by increasing shear stress and reducing the shear strength of slope materials. Saturation from rainfall adds weight to the soil, and reduces friction between particles. This can trigger various types of mass movements, including landslides, mudflows, and soil creep. Additionally, water can cause liquefaction in certain soils, leading to spreads, where coherent blocks of earth move over a weaker, saturated substrate.
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How can mass movement impact people and the environment?
Mass movements, such as landslides, are geological phenomena that involve the downslope movement of soil and rock due to gravity. These movements can significantly impact both people and the environment.
Mass movements can destroy infrastructure, endanger lives, and displace communities. Economically, they can disrupt transportation, damage property, and affect agriculture. Environmentally, mass movements can alter landscapes, causing deforestation, soil erosion, and habitat loss. They can also affect water quality by increasing sedimentation in rivers and streams.
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mass movement, bulk movements of soil and rock debris down slopes in response to the pull of gravity, or the rapid or gradual sinking of the Earth’s ground surface in a predominantly vertical direction. Formerly, the term mass wasting referred to a variety of processes by which large masses of crustal materials are moved by gravity from one place to another. More recently, the term mass movement has been substituted to include mass wasting processes and the sinking of confined areas of the Earth’s ground surface. Mass movements on slopes and sinking mass movements are often aided by water and the significance of both types is the part each plays in the alteration of landforms.
The variety of downslope mass movements reflects the diversity of factors that are responsible for their origin. Such factors include: weathering or erosional debris cover on slopes, which is usually liable to mass movement; the character and structure of rocks, such as resistant permeable beds prone to sliding because of underlying impermeable rocks; the removal of the vegetation cover, which increases the slope’s susceptibility to mass movement by reducing its stability; artificial or natural increases in the slope’s steepness, which will usually induce mass movement; earthquake tremors, which affect the slope equilibrium and increase the likelihood of mass movement; and flowing ground water, which exerts pressure on soil particles and impairs slope stability. These factors affecting slope conditions will often combine with climatic factors such as precipitation and frost activity to produce downslope mass movement.
The types of mass movements caused by the above factors include: the abrupt movement and free fall of loosened blocks of solid rock, known as rockfalls; several types of almost imperceptible downslope movement of surficial soil particles and rock debris, collectively called creep; the subsurface creep of rock material, known as bulging: the multiplicity of downslope movements of bedrock and other debris caused by the separation of a slope section along a plane of least resistance or slip surface, collectively called landslides; the separation of a mass along a concave head scarp, moving down a curved slip surface and accumulating at the slope’s foot, known as a slump; the saturation of debris and weathered material by rainfall in the upper section of a slope or valley, increasing the weight of the debris and causing a slow downslope movement, called an earthflow; a rapidly moving earthflow possessing a higher water content, known as a mudflow; a fast-moving earthflow in a mountainous region, called a debris flow or avalanche; and the downslope movement of moisture-saturated surficial material, known as solifluction, over frozen substratum material, occurring in sub-Arctic regions during seasonal periods of surface thaw.
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Sinking mass movements occur in relatively rapid fashion, known as subsidence, and in a gradual manner, called settlement. Subsidence involves a roof collapse or breakdown of a subsurface cavity such as a cave. Extensive subsidence is evident in areas where coal, salt, and metalliferous ores are mined. Marine erosion sometimes causes the roof collapse of sea caves. Regions of karst topography will exhibit widespread subsidence in the form of sinkholes caused by underground drainage. Other types of subsidence caused by underground solutions have been found in chalk, gypsum, anhydrite, halite (salt), and loess terrains. The melting of ground ice also contributes to subsidence such as the formation of glacial kettles and depressions following the seasonal surface thaw of perennially frozen land. The chemical decomposition of subsurface rocks and ores is also a cause of subsidence. Another form of subsidence is the steep-walled depression, known as a volcanic sink, formed following the withdrawal of magma from below the ground surface.
The gradual settlement of confined areas of earth material occurs through consolidation of soil and rock by the squeezing or removal of fluids from the pore spaces, and by the collapse of the grain structure. The most widespread cause of consolidation is by surface loading such as the continued deposition of sediments in sea and lake beds or by loads imposed on land by glacial ice sheets or outwash deposits. Human-made structures also cause surface loading, consolidation, and settlement. Consolidation is also caused by the lowering of the ground water table. The extraction of pressurized water or oil from deep beneath the surface will cause a collapse of the pore spaces and consolidation of rock material. Grain structure collapse usually occurs from the wetting of rock materials such as clays and sands, which causes the structure of the grains to shift and settle in a more compact and dense configuration.