A landslide is the movement of rock, earth, or debris down a slope, caused by factors such as rain, earthquakes, or human activity, posing significant hazards to populated areas. In India, landslides are exacerbated by climate change and human-induced factors like construction and deforestation, leading to numerous fatalities and large economic damages. Prevention measures include improving drainage, modifying slopes, and employing retaining walls, with ongoing research needed to understand and mitigate landslide risks.

1. Landslide

2. LANDSLIDE
A landslide is the movement of rock, earth, or debris
down a sloped section of land. Landslides are caused
by rain, earthquakes, volcanoes, or other factors that
make the slope unstable

3. LANDSLIDE
Geologists, scientists who study the physical formations of the
Earth, sometimes describe landslides as one type of mass
wasting. A mass wasting is any downward movement inwhich
the Earth's surface is worn away. Other types of mass wasting
include rockfalls and the flow of shore
deposits called alluvium. Near populated areas, landslides
present major hazards to people and property. Landslides cause
an estimated 25 to 50 deaths and $3.5 billion in damage each
year in the United States.

4. What Causes
Landslides?
Landslides have three major causes: geology, morphology, and human activity.

5. What Causes
Landslides?
Geology refers to characteristics of the material itself.The
earth or rock might be weak or fractured, or different
layers may have different strengths and stiffness.
Morphology refers to the structure of the land. For
example, slopes that lose their vegetation to fire or
drought are more vulnerable to landslides. Vegetation
holds soil in place, and without the root systems of trees,
bushes, and other plants, the land is more likely to slide
away.A classic morphological cause of landslides is
erosion, or weakening of earth due to water.

6. What Causes Landslides?
Human activity, such as agriculture and construction, can increase the risk of a
landslide. Irrigation, deforestation, excavation, and water leakage are some of
the common activities that can help destabilize, or weaken, a slope.

7. What Causes
Landslides in
India?
Over 2020, landslides severely harmed
lives and livelihoods in West Bengal,
Meghalaya, Assam, Arunachal Pradesh,
and Kerala. Landslides, caused by heavy
rainfall, flooding, erosion, and earthquakes
moving rocks, earth, and debris down a
slope, are becoming more of a threat in
India as climate change is making monsoon
seasons erratic and extreme.

8. What Causes
Landslides in
India?
But activities like construction, mining, quarrying, and
hydro-power projects loosen and remove soil, gravel, and
vegetation, leading to lower groundwater retention
capabilities, which increases the risk of flooding. Thus,
when heavy rain or earthquakes occur, the excess water or
the loosened debris create landslides. A recent example of
human-induced damage creating a higher risk of landslides
is the Char Dam Road construction process, which
activated new potential landslide zones in Uttarakhand due
to the damage the construction caused to the fragile
Himalayan ecosystem. According to the National Crime
Records Bureau data, 65% of 2019’s landslide fatalities
happened in either the Himalayas or the Western Ghats.

9. What Causes Landslides
in India?
More than 400,000 sq. km., or around 13%, of India’s land, is
prone to landslides (excluding snow-covered areas). According
to the 2018 report, which examined the years 2004-2016 and
more than 5,000 landslides, India registered the most deaths in
the world caused by human-triggered landslides (10,900 deaths
across 829 landslides). This made up 18% of the world’s
landslide casualties over those 12 years. Within this range, India
also accounted for maximum mining-triggered landslides
worldwide (12% of the total).

10. Importance
of land
slide...
Landslides are a serious geologic hazard common to almost every State in
the India. As people move into new areas of hilly or mountainous terrain, it
is important to understand the nature of their potential exposure to
landslide hazards, and how cities, towns, and counties can plan for land-use,
engineering of new construction and infrastructure which will reduce the
costs of living with landslides.
Although the physical causes of many landslides cannot be removed,
geologic investigations, good engineering practices, and effective
enforcement of land-use management regulations can reduce landslide
hazards. It is also important to understand the science of landslides – their
causes, movement characteristics, soil properties, the geology associated
with them, and where they are likely to occur.
The Landslide Hazards Program helps address these needs for improved
understanding by conducting research on several fundamental aspects of
landslides. Thus, landslide research seeks answers to such questions as
these:
● Where and when will landslides occur?
● How big will they be?
● How fast and how far will landslides move?

11. Landslide classification

12. Landslide
classification
Mass-wasting events are classified by type of movement
and type of material, and there are several ways to classify
these events. The figure and table show the terms used. In
addition, mass-wasting types often share common
morphological features observed on the surface, such as
the head scarp—commonly seen as crescent shapes on a
cliff face; hummocky or uneven surfaces; accumulations of
talus—loose rocky material falling from above; and toe of
the slope, which covers existing surface material.

13. Landslide
classification
Landslides are very diverse phenomena in shape and size,
movement speed and other characteristics. According to
geological structure in which landslides occur, we can
distinguish instability in soil and rock mass
In soil we distinguish the following types of instability:
Rotational landslide
Translational landslide
Debris flow
Debris avalanche
Earthflow
Creep
Lateral spread

14. Landslide
classification
In rock mass we distinguish the following
rock slope failure triggering mechanisms:
Block slide
Rockfall
Topple

15. Landslide parts
We can distinguish following parts of
rotational landslide : crown, toe, flanks,
slip surface, body, tension cracks.

16. Rotational Landslide
This is a slide in which the surface of rupture is curved concave upward and
the slide movement is roughly rotational about an axis that is parallel to the
ground surface and transverse across the slide

17. Translational slide:
● In this type of slide, the landslide mass moves
along a roughly planar surface with little rotation
or backward tilting,
● Translational landslide is a mass that slides
downward and outward on top of an inclined
planar surface
● Notice the flatter surface that the moving material
slides on. Material will accumulate at the toe of
the landslide. And probably slide intohomes.

18. Blockslide
A block slide is a translational slide in
which the moving mass consists of a
single unit or a few closely related units
that move downslope as a relatively
coherent mass

20. FALLS:
Falls are abrupt movements of masses of geologic
materials, such as rocks and boulders, that
become detached from steep slopes or cliffs.
Separation occurs along discontinuities such as
fractures, joints,
movement occurs
and bedding
by free-fall,
planes, and
bouncing, and
rolling. Falls are strongly influenced by gravity,
mechanical weathering, and the presence of
interstitial water.

21. Rock falls
Single and small rock falls from cliffs build
up to form aprons of scree or talus,
sometimes developing over long time
periods. Some scree slopes are relict,
where the scree apron almost buries the
crags that once released rock falls that
formed them.
A trait of actively forming rock fall screes is
the sorting of rock debris, with the largest
stones at the base of the scree and the
smallest at the top. Reworking of the scree
slopes by other processes – e.g. snow
avalanching, debris flows and gully erosion
by water – disrupts this sorting.

22. TOPPLES
Toppling failures are distinguished by the forward rotation of a unit or units
about some pivotal point, below or low in the unit, under the actions of gravity
and forces exerted by adjacent units or by fluids in cracks

23. Debris flow
●
● A debris flow is a moving mass of loose mud,
sand, soil, rock, water and air that travels
down a slope under the influence of gravity.
To be considered a debris flow, the moving
material must be loose and capable of "flow,"
and at least 50% of the material must be
sand-size particles or larger.
Debris-flow source areas are often
associated with steep gullies, and debris-flow
deposits are usually indicated by the
presence of debris fans at the mouths of
gullies.

24. Debris flow
● generally occur during periods of
intense rainfall or rapid snowmelt and
usually start on hillsides or mountains.
● A sudden flow of water from heavy rain, or
rapid snowmelt, can be channeled over a
steep valley filled with debris that is loose
enough to be mobilized. The water soaks
down into the debris, lubricates the material,
adds weight, and triggers a flow.

25. DEBRIS
AVALANCHE
● a mass of rock fragments and soil that has moved rapidly down a steep
mountain slope or hillside and because of its high water content has behaved
like an avalanche of snow
● A debris avalanche is the sudden catastrophic collapse (landslide) from an
unstable side of a volcano.
● Many volcanic cones are steep sided and unstable due to rapid growth of the
cone. Rising magma, earthquakes, weakening due to hydrothermal alteration
and heavy rain can trigger a debris avalanche of this unstable material.
Avalanched material follows valleys as it moves down the side of the volcano
under the force of gravity. Debris avalanches can be wet, dry or both.

26. 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. It is an intermediate type of
mass wasting that is between downhill
creep and mudflow

27. EARTHFLOW
Earthflows are made up of disintegrating soil
and weathered rock, which moves by
inter-particle or inter-layer shear above a
failure plane in underlying rock. The failure
plane may be either planar or curved. The
ground surface breaks into hundreds of
hummocks, roughly aligned as curving ridges
at right angles to the direction of flow, and
separated by tension cracks which form low
scarps

28. EARTHFLOW Earthflows can occur beneath forest, but become
particularly severe after tree cover is removed from
susceptible terrain. Forest clearance not only
removes root reinforcement from the soil; it also
alters the soil’s water balance. Beneath grass cover,
ground dries out earlier in summer, but becomes
wetter in winter. Successive wetting and drying
cycles weaken fine-grained rocks. Mechanical
strength and chemical bonds are gradually lost, until
the subsurface layer of disintegrating rock and clay
starts to move whenever it becomes saturated with
water. Movement is typically slow and protracted,
amounting to no more than a few metres each winter

29. Creep in geology, slow downslope movement of particles that occurs
on every slope covered with loose, weathered material. Even
soil covered with close-knit sod creeps downslope, as
indicated by slow but persistent tilting of trees, poles,
gravestones, and other objects set into the ground on
hillsides.
The most important process producing creep, aside from
direct gravitational influences, is frost heaving: as interstitial
water freezes, surface particles are forced up and out
perpendicular to the slope; when let down by melting, these
particles are drawn directly downward by gravity and are
thereby gradually moved downslope. Other processes
involved are the wedging action of root growth and the wetting
and drying of soil layers.

30. 1Soil Creep is a very slow movement and it is
so hard to notice and hardly any damage is
done to the area.
2Slumping is a faster movement than Soil
Creep and the land will slip down the slope this
time.
3Debris Flow happens when the slope
becomes saturated with water, this then
triggers a landslide of water soaked mass of
rock and soil that slides down the slope.
4RockFall landslides are sudden slides
caused by heavy rain the rock on the slope
loosens and then slides down the slope.

31. Lateral spread

32. Lateral spread
● Lateral movement occurs when earthquake
shaking causes a mass of soil to lose cohesion
and move relative to the surrounding soil. Lateral
movement can be entirely horizontal and occur
on flat ground, but it is more likely to occur on or
around sloping ground, such as adjacent to
hillsides and waterways.
● In most cases, lateral movement involves an
intact block of land sliding downhill – a
phenomenon called a block slide or bulk lateral
movement. However, a lateral movement can also
stretch the ground as it moves – this is known as
lateral spread.

33. Lateral spread
When lateral spreading occurs, the ground tears,
opening surface cracks and fissures across the slope.
This type of stretching of the ground can introduce
significant lateral forces into foundation elements
and built structures. If the foundation is not strong
enough to resist the movement, the lateral spread
causes it to extend
In the case of an unreinforced concrete floor slab, it
is likely to crack in several places perpendicular to
the direction of spread. In its technical guidance
Repairing and rebuilding houses affected by the
Canterbury earthquakes, MBIE states that, if the
floor plate of the dwelling is not strong enough,
lateral spreading may cause an extension of the floor
plate (that is, the concrete floor slab may crack or
the timber floor may fracture generally at joints
between framing members).

34. Prevention measures of landslides
Landslides pose a recurrent hazard to human life and
livelihood in most parts of the world, especially in some
regions that have experienced rapid population and
economic growth. Hazards are mitigated mainly through
precautionary means—for instance, by restricting or even
removing populations from areas with a history of
landslides, by restricting certain types of land use where
slope stability is in question, and by installing early
warning systems based on the monitoring of ground
conditions such as strain in rocks and soils, slope
displacement, and groundwater levels.
There are also various direct methods of preventing
landslides; these include modifying slope geometry,
using chemical agents to reinforce slope material,
installing structures such as piles and retaining walls,
grouting rock joints and fissures, diverting debris
pathways, and rerouting surface and underwater
drainage. Such direct methods are constrained by
cost, landslide magnitude and frequency, and the size
of human settlements at risk.

35. Prevention measures
for Landslides
Improving surface and subsurface drainage: Because
water is a main factor in landslides, improving surface and
subsurface drainage at the site can increase the stability of
a landslide-prone slope. Surface water should be diverted
away from the landslide-prone region by channeling water
in a lined drainage ditch or sewer pipe to the base of the
slope. The water should be diverted in such a way as to
avoid triggering a landslide adjacent to the site. Surface
water should not be allowed to pond on the landslide-prone
slope.Groundwater can be drained from the soil using
trenches filled with gravel and perforated pipes or pumped
water wells. Swimming pools, water lines, and sewers
should be maintained to prevent leakage, and the watering
of lawns and vegetation should be kept to a minimum.
Clayey soils and shales have low hydraulic conductivity and
can be difficult to drain.

37. Excavating the
head
Removing the soil and rock at the head of the landslide decreases the driving
pressure and can slow or stop a landslide. Additional soil and rock above the
landslide will need to be removed to prevent a new landslide from forming
upslope. Flattening the slope angle at the top of the hill can help stabilize
landslide-prone slopes.

38. Buttressing the toe
If the toe of the landslide is at the base of the slope, fill can be placed over the toe
and along the base of the slope. The fill increases the resisting forces along the
failure surface in the toe area. This, in turn, blocks the material in the head from
moving toward the toe. However, if the toe is higher on the slope, adding fill would
overload the soil and rock below the toe, thus causing a landslide to form
downslope of the fill.

39. Constructing piles and retaining walls:
Piles are metal beams that are either driven into the soil or placed in drill holes. Properly placed piles should extend into a competent
rock layer below the landslide. Wooden beams and telephone poles are not recommended for use as piles because they lack strength
and can rot.Because landslides can ooze through the gaps between the piles, retaining walls are often constructed. Retaining walls can
be constructed by adding lagging (metal, concrete, or wooden beams) horizontally between the piles. Such walls can be further
strengthened by adding tiebacks and buttressing beams. Tiebacks are long rods that attach to the piles and to a competent rock layer
below the ground surface. Buttressing beams are placed at an angle downslope of the piles to prevent the piles from toppling or tilting.
Retaining walls also are constructed of concrete, cinder blocks, rock, railroad ties, or logs, but these may not be strong enough to resist
landslide movement and could topple.

40. Constructing piles and retaining walls:

41. -Diagram of a retaining wall with tiebacks and
buttress beams. Tiebacks are metal rods that
extend from the piles to a competent rock layer
below the ground surface. Buttress beams are
metal beams that are inclined downslope from the
piles that prevent the piles from toppling. Lagging
consists of wooden, metal, or concrete beams
placed upslope and between the piles to fill in the
gaps.

42. Removal and replacement:
Landslide-prone soil and rock can be removed and
replaced with stronger materials, such as silty or sandy
soils. Because weathering of shales can form
landslide-prone soils, the removal and replacement
procedure must include measures to prevent continued
weathering of the remaining rock. Landslide material
should never be pushed back up the slope. This will
simply lead to continued motion of the landslide.

43. Preserving vegetation: Trees, grasses, and vegetation can minimize the amount of water infiltrating into the soil, slow the
erosion caused by surface-water flow, and remove water from the soil. Although vegetation alone cannot prevent or stop a
landslide, removal of vegetation from a landslide-prone slope may initiate a landslide.
Rock fall protection: Rock falls are contained by (1) ditches at the base of the rock exposure, (2) heavy-duty fences, and (3)
concrete catch walls that slow errant boulders that have broken free from the rock outcrop. In some cases, loose blocks of rock
are attached to bedrock with rock bolts, long metal rods that are anchored in competent bedrock and are threaded on the outside
for large nuts. A metal plate with a center hole, like a very large washer, is placed over the end of the rod where it extends from
the loose block, and the nut is then added and tightened. Once constructed, remedial measures must be inspected and
maintained. Lack of maintenance can cause renewed landslide movement.

44. Preserving
vegetation:
Trees, grasses, and vegetation can
minimize the amount of water infiltrating
into the soil, slow the erosion caused by
surface-water flow, and remove water
from the soil. Although vegetation alone
cannot prevent or stop a landslide,
removal of vegetation from a
landslide-prone slope may initiate a
landslide.