why and how Material on surface of Earth move

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Mass Wasting
Submitted by: Umer Shahid 01-161151-106
Zain Ahmed 01-161151-108
Hassaan Amir 01-161142-
Haider Sikander 01-161142-
Faizan Sabir 01-161142-103
Muhammad Bilal Rathor 01-161142-
Zohaib Naseer 01-161151-109
Submitted to: Sir Anwar Maqsood
Submission date: 09-12-2015
Class: 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

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

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downward. There are two opposing forces which determine whether the body will remain
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 Repose
It 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.
 Water
Water 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.
 Time
With 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 material
Weak 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.
 Climate
Climate 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 Modification
Modifying 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.

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 Ground vibrations
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 material
Mass 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 movement
Mass 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 Motion
There 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:
 Slump
A 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 underlying layer of rock.

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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