presentation on mass wasting

MassMovements/Wasting

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Group members

Hassaan Ameer Umer Shahid Zain Ahmed Muhammad Bilal Rathor Haider Sikandar Zohaib Naseer Faizan Sabir

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Contents Introduction Effects Controls of mass wasting Causes of mass wasting Classification Types of mass wasting Preventions Destruction by Mass Wasting Conclusion Reference

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Mass Wasting

“It is downslope movement of masses of bedrock, rock debris, regolith or soil, under the direct

influence of gravity”

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Mass Wasting

The downslope transfer of material through the direct action of gravity

Component of erosion and transport of sediment Follows weathering, which weakens and breaks the rock

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Effects Of Mass Wasting

The combined effects of mass wasting and running water produce

stream valleys, which are the most common and conspicuous of

Earth’s landforms.

If streams alone were responsible for creating the valleys in which

they flow, the valleys would be very narrow features.

Most river valleys are much wider than they are deep, is a strong

indication of the significance of mass-wasting processes in

supplying material to streams.

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Effects of Mass Wasting Mass movements affect the following elements of the

environment The topography of the earth's surface, particularly the

morphologies of mountain and valley systems, both on the continents and on the ocean floors

The character/quality of rivers and streams and groundwater flow

The forests that cover much of the earth's sub-aerial surface

Habitats of natural wildlife that exist on the earth's surface, including its rivers, lakes, and oceans.

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MASS WASTING

SLUMP NEAR BISMARCK,N.d

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Changes In Slopes

If Mass wasting is to occur, there must be slopes from which rock, soil, and regolith can move down

Earth’s mountain building and volcanic processes that produce these slopes through sporadic changes in the elevations of landmasses and the ocean floor.

If dynamic internal processes did not continually produce regions having higher elevations, the system that moves debris to lower elevations would gradually slow and eventually cease.

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Most rapid and spectacular mass-wasting events occur in areas of rugged, geologically young mountains. Newly formed mountains are rapidly eroded by rivers and glaciers into regions characterized by steep and unstable slopes. It is in such settings that massive destructive landslides.

Through time, steep and rugged mountain slopes give way to gentler, more subdued terrain. Thus, as a landscape ages, massive and rapid mass-wasting processes give way to smaller, less dramatic downslope movements.

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Controls of Mass Wasting

Gravity Angle of repose Water Time Type of material Climate Vegetation

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Role of Gravity

Gravity causes the downward movement of rock body

If gravity pull is greater than resistive force then body will move downward

AA

AA

RR

RR13

Forces due to gravity Two opposing forces determine

whether the body will remain stationary or will move. These two forces are shear stress and shear strength.

Shear Stress force acting to cause movement of a

body parallel to the slope. There are two components of gravity:

(a) Perpendicular component (acts at right angles to the slope)

(b) Tangental component (acts parallel to the slope)

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Forces due to gravity As the slope becomes steeper, the

tangental component of gravity increases relative to the perpendicular component and the shear stress becomes larger.

Shear Strength internal resistance of the body to

movement. This internal resistance includes:

(a) frictional resistance (b) cohesion between particles (c) binding action of plant roots

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Angle of repose

Steepest angle at which material remains stable Depends upon

Particle size Particle shape Moisture Content

Angle varies from 25 to 40 degrees Larger and more angular particles maintain steepest

angle Small and round particles do not maintain steep angle

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Moisture effecting angle of repose

Moisture also increases the angle of repose of sediments

A small amount of moisture between sand grains will bind them together due to surface tension. Surface tension is the attractive force between molecules at a surface

Too much water will results in particles moving freely over one another and therefore dramatically reduces the angle of repose.

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Role of Water

Sedimentary rocks commonly have porosities of 10 - 30%

If pore spaces fill with water, the weight of the material is increased substantially, creating instability

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Role of Time

Physical and chemical weathering can weaken slope materials decreasing resisting force. This causes the rock to become very weak and mass wasting occurs

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Role of Earth Materials

Weak rocks(sedimentary) will weather quickly than hard rocks(igneous, metamorphic)

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Role of Climate

Climate plays a vital role in weathering of material

Climate influences the amount and timing of water in the form of rain or snow

Influences type and amount of vegetation

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Role of Vegetation

Plant roots provide a strong interlocking network to hold unconsolidated rocks and sediment

Vegetation removes moisture from the soil

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ROLE OF TREES IN STABILITY

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Causes Of IntstabilityFactors that either weaken cohesion forces or increase

downslope force1. Heavy rainfall 2. Over-steepening of the slope3. Slope Modification4. Ground vibrations5. Expansion/contraction cycles of soil/regolith

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Heavy Rainfall

Addition of water in soil Lubricates the material

(decreases cohesion) Adds weight (increases

downslope force) Increases pore pressure

(increases downslope force and decreases cohesion)

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Over-steepening of the Slope

Can be human-induced or by natural processes – increases the downslope force.

Stream undercutting a valley wall (headward erosion, bank erosion, etc.).

Waves cutting cliffs on a shoreline. Construction of roads, buildings, homes

etc.

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Slope ModificationRemoval of Vegetation

Roots of plants and trees hold regolith together

Plants and trees remove water from the soil

Removal decrease cohesive force

Building of structures decrease in cohesive force

or increase downslope force due to added weight will cause movement

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Ground Vibrations

Earthquakes – triggers the rock and initiates its movement

Human induced – blasting for construction, large equipment, etc.

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Expansion/Contraction CyclesMovement of material due to

Wetting and drying cycles Freeze-thaw cycles

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Classification of Mass Wasting

Type of Material Bedrock - Rock Unconsolidated material - Debris

Soil Regolith Sediment

Rate of movementFast moving, which are calculated in km/hr E.g. Rock avalanches moving up to speed of 200 km/hr Slow moving, which are calculated in mm/yr or cm/yr E.g. creep

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Classification of Mass Wasting Type of Motion

Fall Fall – free-fall of detached particles, slope steep

enough that material falls to base

SlideSlide – material remains cohesive and moves along a

well-defined surface

FlowFlow – material moves downslope as a viscous flow

(most are saturated with water)

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Fall It is the free fall of

material of any size It fall directly to the base

of the slope or move in a series of leaps and bounds over other rocks along the way

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Slides Slide occurring on a planar surface or on a slip plane Slide occurring along a curved slip plane

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FlowFlow Lahar flowing at surface

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Types of Mass Wasting

Slump Rockslide Mudflow (Lahar, Debris Flow) Earthflow Creep Permafrost & Solifluction

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Slump Downward slipping (slide) of a

mass of rock or unconsolidated material moving as a unit

Rock or unconsolidated material move in a curved path

Does not move very fast or far away

May be single or multiple blocks Caused by overloading, excess of

water, over steeping, removal of anchoring material

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Slump (a type of slide) Indicators:

Scarp

earthflow

Anchoring material

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Rockslide Sliding of blocks of bed rock along a defined

slippage plane

Sudden, rapid and destructive movement

Takes place where rock strata are

inclined(steep slopes), joints or fracture exist

parallel to slope, underlying layer is thin

layer of clay or river cut the anchoring

material

Can be triggered by rain falls or ground

vibration

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Mudflow

Rapid movement of debris containing large amount of water Water get mixes with rock debris, soil or regolith and forms a mud

which flow downward stream or mountain Characteristic of semiarid mountainous area Caused when snow melts quickly creating a flood or cloud burst

rapidly

Mudflow is of two types: Lahar Debris Flow

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Lahar WHEN debris flows

composed mostly of volcanic materials on the flanks of volcanoes are called lahars.

Unstable layers of ash and debris becomes saturated with water

They can occur either during an eruption or when a volcano is quiet. They cause mass destruction of land and life.

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Debris Flow

Mixture of rocks debris or soil

& water

Moves as a viscous fluid

Common after heavy rains

Rapid movement – up to 50

km/hr, the more water present

the faster the rate of movement

Common in semi-arid regions

and along volcanoes (lahars)

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Earthflow

A type of debris flow, generally move slower

Forms on hillside humid areas as a result of excessive rainfall

Water saturates the clay-rich regolith and material break away and flow a short distance downslope

Speed of earthflow vary from few meters per hour to several meters per minutes

Can remain active over periods of years

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CreepCreep

Gradual downslope movement of soil or regolith– mm/yr

Expansion/contraction, freezing/thawing or wetting/drying cycles play a key role

Process so slow one cannot observe it in action

Enhanced by burrowing organisms, periods of prolonged rains or snow,

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Permafrost

Layer of permanently frozen ground, known as permafrost, occurs where summers are too cool to melt more than a shallow surface layer

It refers to the permanently frozen ground that occurs in climates in which annual air temperature is low enough to maintain a continuous surface temperature below 0֯C

Depth to which water freezes exceeds the depth of summer thawing

The water in soil underlining does not melt

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Solifluction

Special type of creep Occurs in regions underlain by

permafrost (permanently frozen, water-bearing ground)

During warm periods top portion (active layer) thaws and becomes saturated

Melt waters are unable to percolate into permafrost layer below

Saturated (active) layer flows over frozen layers

It can occur on slopes as gentle as 2-3 degree

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SOLIFLUCTION

In mat of vegetation Solifluction move downward in well-defined lobes or overriding folds

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MASS WASTING PREVENTION

Move material from the top to the toe.

Build barriers.

Build retaining walls.

Drain the slope.

Plant vegetation.

Prevent flooding.

Prevent undercutting.

Don’t over-steepen slope.

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RETAINING WALLS55

Destruction caused by mass wasting56

year Location Type Fatalities1916 Italy, Austria Landslide 10,0001920 China Earthquake triggered landslide 200,0001945 Japan Flood triggered landslide 1,2001949 USSR Earthquake triggered landslide 12,000-20,0001954 Austria Landslide 2001962 Peru Landslide 4,000-5,0001963 Italy Landslide 2,0001970 Peru Earthquake related debris avalanche 70,0001985 Columbia Mudflow related to volcanic eruption 23,0001987 Ecuador Earthquake related landslide 1,000

1998 Nicaragua Debris avalanche and mudflow tirggered by heavy rains during Hurricane Mitch ~2,000

2001 El Salvador Earthquake-induced landslide 585

2006 Philippines Rain triggered debris avalanche >11002009 Taiwan Typhoon Marakot triggered landslide 3972010 Gansu, China Rain triggered mud flows 12872013 Northern India Heavy rain triggered landslides 5700

Conclusion

Mass wasting is the movement of earth material under influence of gravity

It is responsible for shaping the earth and forming different land forms

It causes destruction to humans beings if it occurs in living areas

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References

Monroe, Wicander (2005). The Changing Earth: Exploring Geology and Evolution. Thomson Brooks/Cole.

Tarbuck, E.J.; Lutgens, F.K. (1998), Earth, an introduction to Physical Geology (6th ed.)

Easterbrook, D. J. (1999), Surfaces Processes and Landforms (2nd ed.)

http://www.britannica.com/science http://www.study.com/academy

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presentation on mass wasting

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