Landslides

A landslide is the movement of a mass of rock, debris or earth
down a slope (Cruden, 1991). More specifically, it is a catastrophic
event where a block of earthen mass slides downhill which
includes a wide range of ground movement, such as rock falls,
deep failure of slopes and shallow debris flows, which can occur in
offshore, coastal and onshore environments.

Causes of Landslides
 Geological causes
 Weathered materials
 Jointed or fissured materials
 Discontinuities
 Material contrasts
 Rainfall and snow fall
 Earthquakes
 Working of machinery
 Morphological causes
 Slope angle
 Uplift
 Rebound
 Wave erosion
 Glacial erosion
 Erosion of lateral margins
 Slope loading
 Physical causes
 Intense rainfall
 Rapid snow melt
 Rapid drawdown
 Freeze-thaw
 Ground water changes
 Soil pore water pressure
 Surface runoff
 Anthropogenic causes
 Loading
 Drawdown
 Land use change
 Water management
 Mining
 Vibration
 Water leakage
 Deforestation

Classification:
Sharpe's classification (1938)
The Well known is Sharpe's classification (1938), made on type of
movement and type of material.

Major Types of Landslides
 Debris flow: Slope material that becomes saturated with water may
develop into a debris flow or mud flow. The resulting slurry
of rock and mud may pick up trees, houses and cars, thus blocking
bridges and tributaries causing flooding along its path.

Earth Flow: Earthflows
are downslope, viscous
flows of saturated, fine-
grained materials, which
move at any speed from
slow to fast. Typically, they
can move at speeds from
0.17 to 20 km/h.
Debris Avalanche: A debris
avalanche is a type of slide
characterized by the chaotic
movement of rocks soil and debris
mixed with water or ice (or both).
They are usually triggered by the
saturation of thickly vegetated
slopes.

Rock Falls: are movements in
which masses of rock or other
material fall freely from cliff or steep
slope through the air, and may
bounce and roll. Earthquakes
commonly trigger this final type of
movement.
Topple: Topple is the end-over-
end motion of rock down a slope.
In this, mass rotates forward about
some pivot point. If a toppling
mass pivots far enough, a fall may
result.

Creep: This is the gradual movement
of slope materials down the slope.
Block slides: most common on
steep slopes (roadcuts, valleys)
velocities of 100+ miles per hour

Historical Landslides in Bangladesh
Landslides in Bangladesh

Occurrence:
 Chittagong & Chittagong hill tracts
 Hill Ranges of Northeastern Sylhet
 Hill along the narrow northern strip
of Mymensingh.
***Chittagong hill tracks have most
frequent landslide
The bedrock and soil structure of these
hills are not stable, for which reason
these areas are highly prone to landslide.

Statistics of causalities in Chittagong, Cox’s Bazar, Bandarban
and Rangamati

Statistics of causalities in CTG over 18 years

 Since 1997, landslides have caused the death of nearly 235
people in various informal settlements within Chittagong city
and its adjacent small urban centers.
 Different studies show that approximately 500,000 impoverished
people are currently living in informal settlements on the risky
foothills of Chittagong city.
High Risk Areas
 Lebubagan Area
 Baizid Bostami Area
 Kushumbag Residential Area
 Batali Hill Area
 Motijharna Area
Landslide Vulnerability in Chittagong

Effect of Landslides:
 Short term effect:
 Property Damage
 Human loss
 Affects all resources, such as power supply, water supply,
hospital, school , and many other things
 Long term effect:
 Loss of property value
 disruption of transportation route
 Loss of forest
 Water availability, and quality also affected

Minimizing the effects of Landslides:
 By geological mapping, detecting slope hazards and determining
the likelihood of landslide occurrence, geoscientists can assist
engineers, developers, planners and building inspectors in
avoiding high-risk areas.
 Structures such as homes, schools, hospitals, power-lines, fire
stations and roads can be safely located away from potential
landslide risk areas.
 Mapping of landslide vulnerability that can help with the
development of emergency response scenarios.
 Engineering and geotechnical investigation that define the
landslide hazard and risk at site specific levels of investigation.

Stability of landslide:
 Covering the landslide with an impermeable membrane
 Directing surface water away from the landslide
 Draining ground water away from the landslide
 Minimizing surface irrigation.

Approaches for mitigation:
 Restricting development in Landslide prone area
 Codes for excavation, construction
 Protecting existing developments
 Monitoring and warning system
 Landslide insurance and compensation for losses

Mitigation measures-
 Prepare a landslide inventory map of the area which help to
develop emergency scenario
 Implementation of regional hazard and risk assessment into land
planning policies.
 Engineering and Geotechnical investigations that define the
landslide hazard and risk at sites specific levels.
 Proper Drainage

Our roles to prevent landslides
 Learn more about potential geologic hazards in your area.
 Consult an engineer or geoscientist for potentially hazardous
locations.
 Avoid activities that result in the undercutting of steep banks
 Avoid the construction of buildings near the top or base of steep
slopes.
 Do not place fill on steep slopes.
 Do not undercut steep banks, develop near the top or base of
steep slopes, or place fill on steep slope, without expert
geotechnical advice.
 Do not stand or seek cover below or near coastal cliffs or
overhangs and be aware of potential dangers they represent.
 Take notice of signs giving warning of loose rocks and debris.
 Do not dig into sand cliffs or dig deep hole in sand that may bury
you if a cave-in happens.

Things to do if a home is suspected as being at risk for
Landslide Danger:
 Get a ground assessment of your property.
 Minimize home hazards
 Plant ground cover on slope and build retaining walls.
 In mudflow areas, build channels or deflection walls to direct
the flow around buildings.
 Learn to recognize the landslide warning signs
 Make evacuation plans
 Develop an emergency communication plan in case family
member get separated

Action to be considered after a landslide:
 Avoid the landslide area as much as possible. There may be a
danger of additional slides
 Check for injured or trapped persons near the slide area.
 Survival is more likely to occur near the slide periphery.
 Provide first aid to injured persons and activate emergency
medical services if necessary.
 Report the event to your local fire, police, or public works
department.
 Inform and assist affected neighbors, especially those who may
require special assistance such as infants, the elderly, or person
with disabilities.
 Listen to a radio or television for the latest emergency information.
 Watch for flooding, which may occur after a landslide or debris
flow.
 Support the local government

Referrences:
• Landslide (Mudslide) Saftey. Washington D.C.: Centers for
Disease Control and Prevention, 2003.
• Matthews, William H. “Landslides.” Encyclopedia Americana.
Deluxe Library ed. 1990.
• Spilsbury, Louise & Richard. Landslides and Avalanches in
Action. New York, NY: Rosen Central, 2009.
• http://www.ussartf.org/landslides.htm
• http://landslides.usgs.gov/research/other/centralamerica.php

Landslides

More Related Content

Landslides