Mass Wasting

Submitted by: Umer Shahid 01-161151-106Zain Ahmed 01-161151-108Hassaan Amir 01-161142-Haider Sikander 01-161142-Faizan Sabir 01-161142-103Muhammad Bilal Rathor 01-161142-Zohaib Naseer 01-161151-109

Submitted to: Sir Anwar MaqsoodSubmission date: 09-12-2015Class: Geophysics 2-A

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Contents

Abstract ………………………………………………………………………..3

Introduction…………………………………………………………………….4

Effects………………………………………………………………………….4

Controls of mass wasting……………………………………………….……...5

Causes of mass wasting………………………………………………………...8

Classification of mass wasting…………………………………………………9

Types of mass wasting………………………………………………………...11

Preventions…………………………………………………………………….14

Destruction by Mass Wasting………………………………………………….14

Conclusion……………………………………………………………………..15

Reference……………………………………………………………………....15

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Abstract

Mass wasting is a natural phenomenon in which earth’s material move down the slope under the direct influence of gravity. Mass wasting is responsible for all the landforms which exist on the face of earth. Landforms such as mountain river valleys, steep slopes of mountains, slopes of land and submarine surface etc. are all due to this. Heavy rainfalls and earthquakes are the main causes due to which these movements starts but steep slopes and removal of vegetation also plays a vital role in triggering the movement of earth’s material. Although it is a natural phenomenon but humans activities from last two centuries are also responsible for it. It is classified into different types depending upon the type of movement the exhibit, the material they carry and the rate at which the move. The most common form of mass wasting is Slump in which earth’s material move as a unit on a curved surface. The most rapid and destructive type of mass movement are rockslide and mudflows which are responsible for millions of life and destroying billions worth of property. Different techniques and methods are now used all across the world in order to prevent these disasters.

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Introduction

Mass wasting, also known as slope movement or mass movement, is the geomorphic process

by which soil, sand, regolith, and rock move downslope as a mass, under the force of gravity.

Process of mass wasting initiates when weathering (physical and chemical) and other processes

weakens the rock material and it falls apart. When the gravitational force acting on the material

overcomes the resistive forces of the material that work to keep it in its place, it causes the

material to move downslope. It is also largely affected by water and moisture because it helps the

weathering process and water in streams acts as career of material. It can be very fast or very

slow depending upon its type and factors which affects it. It can be caused by both human and

natural phenomenon.

Types of mass wasting include creep, slides, flows, and falls, each with its own characteristic

features, and taking place over timescales from seconds to years. Mass wasting occurs on both

land and submarine slopes, and it has been observed not only on Earth but also on Mars, Venus,

and Jupiter's moon.

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,

ground vibrations and expansion/contraction or freezing/thawing of material.

Effects of Mass Wasting

Mass wasting is responsible for morphological process taking places on the earth. Although mass

wasting results in shaping the earth but also effects vegetation, humans and other species. It has

caused many destruction to buildings, vegetation, humans and animals.

Mass wasting produces different landforms on the earth not only on land but also in sub-marine

slopes. The combined effects of mass wasting and running water produces 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. Water

bodies erodes and breaks off the anchoring material by continuously striking with it. When the

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anchoring material is removed the upper material starts to move downward. Then this material is

further carried away by streams and other water channels. As most of the river valleys are much

wider than they are deep, it is a strong indication of the significance of mass-wasting processes

in supplying material to streams and shaping the landforms.

Mass wasting also changes the slopes of the mountains and elevated area. It occurs when there

are 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. 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. 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. Slopes in sub-marine are also shaped by mass wasting.

During the movement of material, new material is deposited on the old one, which effects the

vegetation and living beings. When mass wasting occurs at large scale it deposit thick layers of

material on the forest, crops, buildings, roads etc. which causes destruction. So the living beings

has to adjust in order to avoid the damages caused by mass wasting.

Controls of Mass Wasting

There are factors which controls the process of mass wasting. These factors decides the type of

mass wasting which is occurring or will occur. Following are the factors which controls the mass

wasting: Gravity, Angle of repose, Water, Time, Type of material, Climate, Vegetation.

GravityGravity is the main cause due to which the rock body or material moves downward. If there is no

gravity the material will not be able to move downslope. Gravity pulls the every object have

mass towards the center of the earth. If gravity pull is greater than resistive force then body will

move downward. There are two opposing forces which determine whether the body will remain

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stationary or will move. These two forces are shear stress (caused by gravity) and shear

strength (internal resistance).

Shear Stress

This force is produced by gravity which 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)

As the slope becomes steeper, the tangental component of gravity

increases relative to the perpendicular component and the shear stress

becomes larger.

Shear Strength

This force is the internal resistance of the body to movement. It does not

allow the movement of the body. Factors which affect this force are :

(a) Frictional resistance

(b) Cohesion between particles

(c) Binding action of plant roots

Angle of ReposeIt is the steepest angle at which material remains stable on slope. If

we pour sand out of bucket onto the ground it will create a pile,

which will have a certain angle with the ground. This angle is

known as angle of repose. Every particle has its own angle of repose

depending upon its size, particle shape, moisture Content. Larger

and more angular particles maintain steepest angle while on other

hand small and round particles do not maintain steep angle. Angle

of repose varies from 25 to 40 degrees depending upon the material.

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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.

WaterWater plays a vital role in the movement of the material from one place to another. It reduces the

resistance and cohesion present between the two materials, which causes the materials to start

movement. Water can both increase the risk of mass wasting and decrease the risk, depending on

how much water is present Sedimentary rocks commonly have porosities of 10 - 30%. If pore

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

When sudden floods come from melting of snow or burst of cloud all the debris and

unconsolidated material present on slopes get mixed with water and creates a mudflow moving

downslope.

TimeWith the passage of time even the hard and resistant rocks becomes weak due to weathering and

other processes and they fall apart from each other and causes movement of rock debris or

regolith from one place to another

Type of materialWeak rocks like sedimentary rocks are weak and not very resistant to weathering as compare to

hard rocks like igneous and metamorphic. So they will break off quickly aiding the material for

the mass wasting.

ClimateClimate also plays a vital role in weathering of material. Climate influences the amount and

timing of water in the form of rain or snow. It also influences type and amount of vegetation

which will grow in any area. In dry areas mass wasting will occur less than the areas where rain

falls in a large amount.

Vegetation

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Vegetation and trees has a very important role in reducing the mass wasting because roots of

plants and trees hold the ground firmly and stops the erosion of soil. If trees and plants are

removed then the soil will erode easily and will aid in mass wasting.

Causes of mass wasting

Mass wasting initiates by both natural and human phenomenon. These Factors weaken cohesion

forces or increase downslope force which causes mass movement. Following are the causes of

mass wasting: Heavy rainfall, Over-steepening of the slope, Slope Modification, Ground

vibrations, Expansion/contraction cycles of soil/regolith

Heavy rainfall

Water is one of the most important factor that play a role in erosion and triggering mass wasting.

Water from heavy rainfalls can saturate the soil/regolith which will add weight to material. It

also act as a lubricant so mass wasting occurs more in tropic regions.

Over-steepening of the slope

Over-steepening of slopes can trigger the movement of material. Sometimes human activities

gives gravity an edge by cutting a slope too steep during road construction along the side of a

mountain. When there is increased slope steepness, gravity has an easier time pulling rock, soil

and debris down. Humans are not the only culprit that can lead to mass wasting due to slope

steepness. Nature can also play a role, especially along streams and coastlines where water or

waves can erode rock and soil and steepen the slopes.

Slope ModificationModifying the slope in such way that it decrease the cohesive force can also lead to mass

wasting. Removal of Vegetation can aid soil for movement because roots of plants and trees hold

regolith together. Plants and trees remove water from the soil which decrease lubrication and

increase cohesive forces. If we remove trees it will do the opposite. Building of structures which

add considerable weight to material below which will cause movement.

Ground vibrations

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Ground vibrations are also responsible for triggering the mass movement. These vibrations can

either be natural such as earthquake or human induced such as blasts etc. When ground vibrates

it initiates the movement of weakened layers of regolith or rocks

Expansion/contraction cycles of soil/regolith

Expansion/contraction cycles can be either by freezing-thawing cycle or wet-dry cycle.

In freezing of water within surface sediment on a slope causes the sediment to expand upward,

perpendicular to the slope surface. As the ice melts, gravity pulls the sediment grains downward

causing progressive down-slope movement (creep) of the upper few inches of the slope

sediment.

Clay-rich sediment expands when it is moistened, and contracts when it dries.   Over a period of

years, this expansion and contraction causes the surface sediment of a slope to creep down slope,

much like the freeze-thaw cycle described above.

Classification of Mass wasting

Different types of mass wasting are divided and classified on the basis of type of Material, type

of Motion and Rate of Movement.

Type of materialMass which is moving downslope can either be in form of Rock unit or unconsolidated material-

bedrock. When the material is Soil, Regolith or Sediments then the terms Debris, mud or earth

are used for them.

Rate of movementMass moving downward can be moving fast, which is calculated in km/hr or moving slowly,

which is calculated in mm/yr or cm/yr. Rock avalanches are one of fastest mass wasting which

can move up to speed of 200 km/hr while on other hand Creep is one of the slowest mass

wasting which only moves few inches or millimeters per hour.

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Type of MotionThere are three types of motion in which the mass can move. Following are the types of motion:

(a) Fall

In this type of motion object or rock material fall free from

detached particles. For this type of motion the slope should be

steep enough that material falls to base. A rock fall may be a

single rock or a mass of rocks, and the falling rocks can dislodge

other rocks as they collide with the cliff. At the base of most cliffs

is an accumulation of fallen material termed talus.

(b) Slide

In this motion material remains cohesive and moves along a well-defined surface, such as a

bedding plane, foliation surface,  or joint surface (joints are regularly spaced fractures in rock

that result from expansion during cooling or uplift of the rock mass). Piles of talus are common

at the base of a rock slide or debris slide.

Slide can either be transitional (Rock Slide) or rotational (Slump).

(c) Flow

In this motion the material is carried away by water bodies. Sudden floods often cause this

motion because sediments and unconsolidated material become saturated with water and starts to

move downslope. Examples of this motion are Lahar, debris flow.

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Types of Mass Wasting

Mass wasting are divided into different types depending upon the type of material, motion and

rate of movement. Following are the types of mass wasting:

SlumpA slump is a type of mass wasting that results in the sliding of coherent rock materials along a

curved surface.

A slump is referred to as a rotational slide because a

portion or block of the slope 'slides' down as it

'rotates' around an axis parallel to the slope. A slump

can occur as a single unit or as a number of slumps

grouped together, and they form when the anchoring

material of the mountain slope or hillside is eroded or

cut away. Water or waves may undercut a mountain

slope, removing the physical foundation holding up

the rocky material. Without a base, the block of

mountain slumps down. It can also be caused by

overloading, excess of water or over steeping of slope.

Slumps leave accurate scars or depressions on the hill slope known as “Scrap”. Slumps can also

be caused by human activities. For example, if a road crew cuts away the base of a mountain

slope to make room for a road, the structural stability of the slope could be weakened, resulting

in a slump. They are common along river banks and sea coasts, where erosion has under-cut the

slopes.  Heavy rains and earthquakes can also trigger slumps.

Rockslide

Rockslide is a type of mass wasting in which rock material

slide down a mountain. It is similar to a slump, but a rockslide

does not rotate as a block around an axis, like a slump. It is

more of a translational slide because it moves in a more

uniform direction along a pre-existing plane, such as an

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underlying layer of rock. It can be caused when the underlying material is unconsolidated and

overlying is consolidated. It can be triggered by vibrations or when water saturates the

underlying unconsolidated material.

It is as if the rocks were skiing down the slope and nothing is going to stop them until they reach

the bottom. And they often do reach the bottom of the slope. So, in an area that experienced a

rockslide, it's common to see a pile of rocks at the base of the slope.

Rockslides can be some of the most dangerous forms of deformation because of the way that

large rocks are traveling quickly down slope; this large material can cause massive damage to

anything in its path.

Mudflow

Mudflow is a form of mass wasting involving "very rapid to extremely rapid flow” of debris that

has become partially or fully liquefied by the addition of water to the source material. Mudflows

can be generated in any climatic regime but are most common in arid, semiarid areas and near

volcanos. They may rush down a mountainside at speeds as great as 100 km (60 miles) per hour

and can cause great damage to life and property. Boulders as large as houses have been moved

by mudflows. Mudflows contain a significant proportion of clay, which makes them more fluid

and they are able to travel farther and across lower slope angles.

Mudflow is further divided into two types

(a) Debris flow

Debris flow is similar to Mudflow but it contain particles size greater than that of Mudflow and it

is more viscous. Both types are generally mixtures of various kinds of materials of different

sizes, which are typically sorted by size upon deposition

(b) Lahar

It is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris,

and water. The material flows down from a volcano, typically along a river valley.. Lahars are

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extremely destructive, they can flow tens of metres per second (22 mph or more), and destroy

any structures in their path.

Earthflow

An earthflow is a downslope viscous flow of fine-grained materials that have been saturated with

water, and moves under the pull of gravity. They are an intermediate type of mass wasting

between creep and mudflow. The types of materials that are susceptible to earthflows are clay,

fine sand and silt, and fine-grained pyroclastic material. When the ground materials become

saturated with enough water, they will start flowing. Its speed of earthflow depend upon the

amount of water. It can take minutes or years for the materials to move down the slope. An

earthflow may affect as few as several square meters or up to several hectares.

Creep

Creep is a very slow mass movement that goes on for years or even centuries. You can't see

creep happening but leaning fences and poles and broken retaining walls show where it has taken

place. This mass wasting is the result of freezing/thawing and wetting/drying cycles. Sediment

expands and particles are lifted up at right angles to the slope, when they freeze, get wet or are

heated up in the sun. When the sediments shrink, the particles fall straight back down. Creep

takes a long time because each particle might only move a millimeter to a few centimeters at a

time.

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. In permafrost the depth to which water freezes exceeds the depth of

summer thawing.

Solifluction

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Special type of creep which occurs in regions underlain by permafrost (permanently frozen,

water-bearing ground). During warm periods top portion (active layer) thaws and becomes

saturated, but melt water is unable to percolate into permafrost layer below. Saturated (active)

layer starts flowing over frozen layers very slowly. It can occur on slopes even as gentle as 2-3

degree.

Preventions for Mass Wasting

Although mass wasting shape the earth but at same time it is very dangerous for humans. So

some steps must be taken in order to avoid its destruction.

Move material from the top of slopes to the toe so it does not aid in during floods.

Build barriers and retaining walls to avoid down cutting of material.

Drain the slope so that water does not saturate it or lubricate it for movement.

Plant vegetation because tree roots hold soil firmly and suck up the water.

Prevent flooding by creating dams.

Prevent undercutting by making roads and other structures rightly.

Don’t over-steepen slope because it helps the material to fall easily.

Destruction by Mass Wasting

Mass wasting is responsible for destruction to not only property but also of human life. In last 14

years almost 10000 people has become victims of mass wasting.

In year 2013, heavy continuous rainfall triggered landslides in Northern India which take life of

5700 people and thousands more became homeless.

In 2010, in China rains triggered the Mudflows which caused a lot of damage to the crops and

property and almost 1300 people died by it.

In 1920, China again become victim of landslides due to earthquake. It is one of the deadliest

landslides of all time because almost 200,000 people lost their life and property worth of billions

was destroyed.

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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 is essential for the landforms and other

different process but at the same time it causes destruction to human beings. Almost all countries

has become victim of mass wasting and all these countries uses its geologists to study these

phenomenon in order to reduce damages caused by mass wasting. Geologist has succeeded a lot

to prevent these natural phenomenon but not completely because natural hazards cannot be

stopped.

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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