allaboutmasswasting-120126093137-phpapp02

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Adhish Luitel Prasil Koirala

Pranav Bhandari Zubin Raj BhandaryBegin Presentation >>>

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Definition: Geomorphic process by which soil, regolith,and rock move down slope under the force of gravity.

Mass wasting occurs on both terrestrial and submarine slopes, andhas been observed on Earth, Mars, Venus, and Jupiter's moon.

When the gravitational force acting on a slope exceeds its resistingforce, slope failure (mass wasting) occurs. The slope material'sstrength and cohesion and the amount of internal friction betweenmaterial help maintain the slope's stability and are known

collectively as the slope's shear strength. The steepest angle that acohesionless slope can maintain without losing its stability is knownas its angle of repose. When a slope possesses this angle, its shearstrength perfectly counterbalances the force of gravity acting uponit.



Mass Wasting



Types of mass movement are distinguished based on howthe soil, regolith or rock moves down slope as a whole. It isbasically categorized into 5 basic types:

▪ Creeps▪ Landslides

▪ Flows

▪ Topples▪ Slump

Home > Types of Mass Movement





▪ Flows


Home > Types of Mass Movement >Creeps

+ It is the combination of small movements of soil or rock in

different directions over time are directed by gravity graduallydownslope.

+ The steeper the slope, the faster the creep. The creep makes treesand shrubs curve to maintain their perpendicularity, and they cantrigger landslides if they lose their root footing.

+ The surface soil can migrate under the influence of cycles of freezing and thawing, or hot and cold temperatures, inching itsway towards the bottom of the slope forming terracettes. Thishappens at a rate that is not noticeable to the naked eye.





▪ Flows


Home > Types of Mass Movement > Landslides

+ Where the mass movement has a well-defined

zone or plane of sliding, it is called a landslide. Thisincludes rock slides, slumps and sturzstroms.

+ It is also one of the common classification of mass

wasting





▪ Flows


Home > Types of Mass Movement > Flows

+ Movement of soil and regolith that more

resembles fluid behavior is called a flow.

+ These include avalanches, mudflows, debrisflows, earth flow, lahars and sturzstroms.

+ Water, air and ice are often involved in enablingfluidlike motion of the material.





▪ Flows


Home > Types of Mass Movement > Topples

Topples are instances when blocks of rockpivot and fall away from a slope.





▪ Flows


Home > Types of Mass Movement > Slump

A slipping of coherent rock material along the curvedsurface of a decline. Slumps involve a mass of soil orother material sliding along a curved surface (shapedlike a spoon). It forms a small, crescent-shaped cliff, orabrupt scarp at the top end of the slope. There can bemore than one scarp down the slope.





Gravitational pull of the earth seismic shaking increased overburden from structures increased soil moisture

reduction of roots holding the soil to bedrock undercutting of the slope by excavation or erosion weathering by frost heave Bioturbation Earthquake - Violent shaking due to an earthquake can cause unstable

slopes to collapse Quick Clay- Soil liquefaction causes land to collapse

… > Factors triggering mass wasting



Mass movements affects the following elements:

The topography of the earth's surface, particularly

the morphologies of mountain and valley systems

The quality of rivers and streams and groundwater flow

The forests that cover much of the earth's sub aerialsurface

… > Effects of mass wasting

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Cause floods by damming up bodies of water andresult to huge loss of lives and property.

Affect the agricultural lands

Loss of industrial productivity because of

interruption of transportation system by landslides.

Increase the number of environmental refugees.



Mass wasting causingroad damage

Avalanche as anexample of masswasting



In a flow the material moved is not coherent but moves in amore chaotic, disorganized fashion.

It flows with mixing with particles within the flowing mass asa fluid flows. Snow avalanches are one kind of flows.

Where soil Is the flowing material these flos are described asmudflows. When a flow involves a wide variety of material isknown as a debris avalanche.



Avalanche



+ Mass movement can occur on a variety of scales and at a variety of rates. They mayinvolve a few cubic meters of material or more than a million cubic material.

+ In the most rapid mass movements which include most rock falls and avalanchesand mudflow s, materials can travel at speeds of hundreds of kilometers per hour.

+ There is little time for people to react once these events start and such events arethe cause of the greatest proportion of mass movement casualties. They also causeextensive damage to buildings.



Landslides : can also be the cause of floods. A

stream in the process of cutting a valley may cause

unstable slopes. Landslides into the valley can damup the stream flowing through it, creating a naturalreservoir. The filling of the reservoir makes the are

behind the dam uninhabitable





Many types of construction lead to over steeping of slopes. Removal of material at the bottom of a hill may leave large rock

masses unsupported. Building of houses on an unstable slope can lead to excess

pressure being put on the slope. Planting of vegetation like trees can reduce the risk of unstable

slopes and slides. Irrigation and use of septic tanks increase the flushing of water

through soils and sediments. Artificial reservoirs can cause earthquakes as well as landslides. As the volume of the reservoir increases in volume, pressure

exerted on the rocks along the reservoirs increases and thestrength of the rocks also decreases.

This may cause the dam to collapse.





Slope reduction Retention Structures

Fluid removal Other slope stabilizing method Recognizing the hazard Landslide Warnings



Reducing the steepness of the slope Strengthening the slope by providing supporting materials at the base of

the slope Reducing the load on the slope by removing all the large rocks or soil at

the higher parts of the slope

The measures that should be takendepend upon the stability of the slope.A highly unstable slope might require

all these preventive measures to betaken at once. These steps should becarried out cautiously. For example, if earthmoving equipment is used theload of the equipment or the vibrationcaused by it might trigger the

landslide



The groundcover should be increased by the means of plantation. A plantthat grows quick and that has a strong root system is preferred.

Strong walls can be constructed on the basis of the magnitude of forcethat could act on the wall.

The success rate of these kinds

of structures has generally beenlow. Generally, high and thinwalls have not been successful.



Water is the most significant cause of mass movement.

One of the basic ways of preventing landslide is to reduce the waterpressure in the slope. Subsurface drainage can also be a method.

Any kind of moistureremoval system is highlyencouraged due to

which it become difficultfor the rocks and soil toslide off as the frictionalresistance to slidingincreases.



Vertical piles are placed on the base of the slope where the particles inthe slope are solid.

This is not to be used anywhere. If the soil

contains more fluid, the soil will just come

out or flow within the vertical piles. It is alsonot applicable in highly steep slope.

Generally, this technique is not very

successful.

The use of rock bolts to stabilize rocky

slopes and rock slides has had a greatersuccess. Rock bolts have been used in

tunneling and mining. Sometimes the

process of driving giant steel bolts in to

the stable rocks below the slip planes is

also used. This works best in low angle

slopes.



Basic climatic feature, topography and geology cause mass movement in aplace; they are independent of any human activities.

Mass movements tend to recur in the same place where they commonlyoccur.

It is very easy to recognize past rock falls in a vegetated area. Large rocks arenot suitable in a vegetated area and remain barren. Lack of vegetation mightalso lead to past debris avalanche and slides. These kinds of factors lead thelandscape to slope instability. .

When there are small slips in the soil. The trunk of the tress grows a bitslanted but later vertical growth continues. If the gradual movement of soil isprolonged then the tree trunks maybe curved.

Slanted utility poles and fences, tilting over of object can also act as anindicator of soil movement



Landslide warning system was developed by U.S. geological survey afterthe rain triggered landslide in San Francisco Bay in 1982. The basis of thewarning system was to establish a quantitative relationship amongrainfall intensity, storm duration, and a variety of slope and soil

characteristics relating to slope instability like slope angle, fluid pressureand so on.

These relationships are established using factual data of past landslides.It became possible to estimate the limits of storm intensity and duration

which when crossed might result in landslide, given it was known howsaturated the ground was due to the recent precipitation.

The system though incomplete

was tested in February 1986. Of

the ten landslides predicted, eight

took place when forecasted.



Landslide warning





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Available Topics..•

Mass Wasting•Factors causing it•Preventive Measures

Bibliography:

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