The document discusses landslides as the movement of earth, rock, and debris down slopes, detailing their causes, types, effects, and mitigation strategies. It outlines various geological, morphological, physical, and anthropogenic causes and classifies landslides based on movement rate, materials involved, and nature of movement. The document also emphasizes the importance of preventive measures, community awareness, and emergency preparedness to minimize the impact of landslides.

1. Assignment on “Landslides”
Submitted by
Md. Asif Hasan
Roll: SH-037
Date: August 25, 2019

2. 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 rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore,
coastal and onshore environments.
Causes of landslide:
The causes of landslides are usually related to instabilities in slopes. It is usually possible to identify one or
more landslide causes and one landslide trigger. The difference between these two concepts is subtle but
important. The landslide causes are the reasons that a landslide occurred in that location and at that time.
• Geological causes
➢ Weathered materials
➢ Jointed or fissured materials
➢ Adversely orientated 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

3. Landslide Classification Criteria
The Well known is Sharpe's classification (1938), made on type of movement and transporting agent.
According to Hansen (1984):
➢ Rate of movement: This ranges from very slow creep (millimeters/year) to extremely rapid
(meters/second).
➢ Type of material: Landslides are composed of bedrock, unconsolidated sediment and/or organic debris.
It can be mudslides, debris flows, rock falls, debris avalanches, debris slides, and earth flows.
➢ Nature of movement: The moving debris can slide, slump, flow or fall.
Description of Different 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. Debris flow is often mistaken for flash flood, but they
are entirely different processes.
➢ 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. Though these
are a lot like mudflows, overall they are slower moving and are covered with solid material carried along
by flow from within. The velocity of the earthflow is all dependent on how much water content is in the
flow itself: if there is more water content in the flow, the higher the velocity will be.
➢ 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

4. thickly vegetated slopes which results in an incoherent mixture of broken timber, smaller vegetation and
other debris. Debris avalanches differ from debris slides because their movement is much more rapid.
This is usually a result of lower cohesion or higher water content and commonly steeper slopes.
➢ Falls: 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.
➢ Debris torrent: is a rapidly moving slurry of soil, alluvium and large organic debris that occur in
response to intense storms and are commonly triggered by debris avalanches entering a channel from
adjacent hill slopes. As the debris avalanche moves down the channel, it becomes a debris torrent as it
scours the stream bank and bed.
➢ Creep: This is the gradual movement of slope materials down the slope.
➢ Rockslides: most common on steep slopes (roadcuts, valleys) velocities of 100+ miles per hour

5. ➢ Slumps: sliding of material along curved surface common in unconsolidated sediments, weaker rock
units
➢ Deep-Seated Landslide: Landslides in which the sliding surface is mostly deeply located below the
maximum rooting depth of trees (typically to depths greater than ten meters). These typically move
slowly, only several meters per year, but occasionally move faster.
➢ Shallow Landslide: Landslide in which the sliding surface is located within the soil mantle
or weathered bedrock (typically to a depth from few decimetres to some metres). They usually include
debris slides, debris flow, and failures of road cut-slopes. Landslides occurring as single large blocks of
rock moving slowly down slope are sometimes called block glides.
State of activity in landslides:
Distribution of Mass in landslides:

6. Styles of Landslides:
Glossary of landslides:

7. 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. Slope stability is also increased when a retaining structure and/or the
weight of a soil/rock are placed at the toe of the landslide or when mass is removed from the top of the
slope.
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.

8. ➢ Proper Drainage & Drainage correction- The most important triggering mechanism for movement is
water infiltrating into overburden during heavy rains and consequent increase in pore pressure within the
overburden. When this happens in steep slopes the safety factor of the slope material gets considerably
reduced causing it to move down. Hence the natural way of preventing this situation is by reducing
infiltration and allowing excess water to move without hindrance. As such the first step in mitigation is
drainage correction. In rural and urban areas, responsibility should be borne by local self Government,
the community and the family.
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, and 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

9. 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