A landslide is the movement of rock, debris, or earth down a slope, which can be caused by geological, morphological, physical, or anthropogenic factors. Major types of landslides include debris flows, earth flows, debris avalanches, rock falls, and topples. Landslides frequently occur in Chittagong, Chittagong Hill Tracts, and northeastern Sylhet in Bangladesh due to the unstable soil structure. Mitigation approaches include restricting development in prone areas, monitoring systems, and engineering investigations to define hazard levels.
2. 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.
3. 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
5. 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.
6. 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.
7. 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.
8. 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
10. 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.
13. 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
14. 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
15. 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.
16. 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.
17. 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
18. 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
19. 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.
20. 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
21. 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
22. 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