Landslides

Dr. G.P. Ganapathy

Professor
Centre for Disaster Mitigation and Management,
Vellore Institute of Technology (VIT), Vellore 632014, INDIA
Email: seismogans@yahoo.com, gpganpathy@vit.ac.in
Mobile : +91 9841771939
 Darjeeling Landslide, West Bengal 1968

The landslide happened around October 4, 1968. The

landslide was triggered by floods and the 60 km long
highway was cut in 91 parts. As per reports,
thousands of people died in the landslide
Source : http://savethehills.blogspot.com/2008/06/lest-we-forget-oct-1968-in-pictures.html
 Malpa Landslide,
Uttarakhand
1998

Consecutive landslides occurred between August 11 and August 17 in 1998 in

the village of Malpa where over 380 people died as the entire village washed
away in the landslide. The landslide is one of the worst landslides in India
 Mumbai landslide, Maharashtra 2000

The landslide was caused in July 2000. The landslide took place in the
suburbs of Mumbai due heavy rains which was followed by land erosion. As
per reports around 67 people died and the local trains were also stricken
 Amboori landslide, Kerala 2001

The landslide was known as the worst landslide in Kerala's history. The landslide occurred on
November 9, 2001 due to heavy rains and around 40 people died in the incident
 Kedarnath landslide, Uttarakhand 2013

The landslide took place on June 16, 2013 and was the result of Uttarakhand
floods. Over 5700 were reported dead and over 4,200 villages had been affected
by the floods and post-floods landslide
 Malin landslide, Maharashtra 2014

The landslide occurred on July 30, 2014, in a village in Malin. The landslide
occurred due to heavy rainfall and around 151 people died and 100 people went
missing after the disaster.
 Landslide
Landslide refers to “the movement of a mass of rock, debris or earth down a slope” (Cruden,
1991).

Slope failure takes place

when the gravitational force
at any point exceeds the
resistance offered due to
strength and cohesion of the
material, friction between it
and adjacent materials and
external support.
Types of landslides
(Modified from Highland, 2004).
 Rockfall

Very rapid to extremely rapid, free-fall;

bouncing and rolling of detached soil,
rock, and boulders. The rolling velocity
depends on slope steepness. Falling material can be life-threatening. Falls can damage
property beneath the fall-line of large rocks. Boulders can
bounce or roll great distances and damage structures or kill
people. Damage to roads and railroads is particularly high:
rockfalls can cause deaths in vehicles hit by rocks and can block
highways and railroads.
 Rock Topple

Extremely slow to extremely rapid,

sometimes accelerating throughout the
movement depending on distance of
Can be extremely destructive, especially when failure is
travel.
sudden and (or) the velocity is rapid.
 Rotational Slide

Extremely slow (less than 0.3 meter or 1 foot

every 5 years) to moderately fast (1.5 meters or
5 feet per month) to rapid.
Can be extremely damaging to structures, roads, and lifelines but
are not usually life-threatening if movement is slow. Structures
situated on the moving mass also can be severely damaged as the
mass tilts and deforms. The large volume of material that is
displaced is difficult to permanently stabilize. Such failures can
dam rivers, causing flooding.
 Translational Slide

Movement may initially be slow (5 feet per month or 1.5

meters per month) but many are moderate in velocity (5
feet per day or 1.5 meters per day) to extremely rapid. Translational slides may initially be slow,
With increased velocity, the landslide mass of damaging property and (or) lifelines; in some cases
translational failures may disintegrate and develop into they can gain speed and become life-threatening.
a debris flow. They also can dam rivers, causing flooding.
 Lateral Spreads

May be slow to moderate and sometimes

rapid after certain triggering
mechanisms, such as an earthquake.
Ground may then slowly spread over time
from a few millimeters per day to tens of
square meters per day.

Can cause extensive property damage to buildings, roads,

railroads, and lifelines. Can spread slowly or quickly,
depending on the extent of water saturation of the various soil
layers. Lateral spreads may be a precursor to earthflows.
 Debris Flow

Debris flows can be lethal because of their rapid

Can be rapid to extremely rapid (35 miles per onset, high speed of movement, and the fact that
hour or 56 km per hour) depending on they can incorporate large boulders and other pieces
consistency and slope angle. of debris. They can move objects as large as houses
in their downslope flow or can fill structures with a
rapid accumulation of sediment and organic matter.
They can affect the quality of water by depositing
large amounts of silt and debris.
 Debris Avalanche

Rapid to extremely rapid; such Debris avalanches may travel several kilometers before stopping, or they
debris avalanches can travel close to may transform into more water-rich lahars or debris flows that travel
100 meters/sec. many tens of kilometers farther downstream. Such failures may inundate
towns and villages and impair stream quality. They move very fast and
thus may prove deadly because there is little chance for warning and
response.
 Earth Flow

Flows can range from small events of

100 square meters in size to large
events encompassing several square
kilometers in area. Earthflows in
susceptible marine clays may runout Rapid, retrogressive earthflows in susceptible marine clay may devastate
for several kilometers. Depth of the large areas of flat land lying above the slope and also may runout for
considerable distances, potentially resulting in human fatalities, destruction
failure ranges from shallow to many
of buildings and linear infrastructure, and damming of rivers with resultant
tens of meters. flooding upstream and water siltation problems downstream. Slower
earthflows may damage properties and sever linear infrastructure
 Slow Earth Flow (Creep)

Creep can be very regional in nature (tens

of square kilometers) or simply confined to
small areas. It is difficult to discern the Because it is hard to detect in some places because of the
slowness of movement, creep is sometimes not recognized
boundaries of creep since the event itself is
when assessing the suitability of a building site. Creep can
so slow and surface features representing slowly pull apart pipelines, buildings, highways, fences, and
perceptible deformation may be lacking. so forth, and can lead to more drastic ground failures that
are more destructive and faster moving.
 General causes of Landslides
• Addition of Moisture (Extensive Rainfall)

• Removal of Vegetation (Timbering)

• Addition of Weight (Buildings in Top)

• Over steepening

• Vibrations

These factors will act either individually or in combination.

 Technological Tools for
Evaluation of Landslides

Mapping, Remote Sensing,

and Monitoring
 Map Analysis

Map analysis is usually one of the first steps in a landslide

investigation.

•bedrock and surficial geology

•topography
•Soils
•geomorphology

Using knowledge of geologic materials and processes, a trained

person can obtain a general idea of landslide susceptibility from
such maps.
Three Important Criteria for Landslide Maps
landslide inventory Map
Three Important Criteria for Landslide Maps
landslide Susceptibility Map
Three Important Criteria for Landslide Maps
landslide Hazard Map
 Aerial Reconnaissance
InSAR Imaging
InSAR is an acronym for
Interferometric Synthetic Aperture
Radar. Both InSAR and LIDAR
(description follows) use active
sensors emitting a pulse of energy
(from a satellite) and recording its
return, from the ground, at the
sensor.

Aerial Photos
Identification can be made of
vegetation cover, topography,
drainage pattern, soil drainage
character, bedrock geology, surficial
geology, landslide type, and
relationship to other factors.
LiDAR Imaging

LiDAR is an acronym for Light Detection and Ranging, also known as ALSM or
Airborne Laser Swath Mapping. Using a narrow laser beam to probe through
dense ground cover, such as trees, LiDAR can produce accurate terrain maps
even where forest cover gets in the way of traditional photography. The
technique produces a very accurate Digital Elevation Model map (DEM)
Instrumentation
 Instrumentation

-electronic distance measurement

(EDM)
Instrumentation
inclinometers
 Instrumentation
-extensometers
 Instrumentation
-strain meters
Instrumentation
piezometers
 Geophysical Studies

measurement of soil’s electrical conductivity/resistivity, or measurement

of induced seismic behavior

can be used to determine some subsurface characteristics such as the

depth to bedrock, stratigraphic layers, zones of saturation, and
sometimes the ground-water table.

It can also be used to determine texture, porosity, and degree of

consolidation of subsurface materials and the geometry of the units
involved.
 Acoustic Imagery and
Profiles

Profiles of lakebeds, river bottoms, and the sea floor

can be obtained using acoustic techniques such as
side-scan sonar and subbottom seismic profiling.

Surveying of controlled grids, with accurate

navigation, can yield three-dimensional
perspectives of subaqueous geologic phenomena.

Modern, high-resolution techniques are used

routinely in offshore shelf areas to map geologic
hazards for offshore engineering.
 Computerized Landslide Terrain Analysis

In recent years, computer modeling of landslides has

been used to determine the volume of landslide
masses and changes in surface expression and cross
section over time.

This information is useful in calculating the potential

for stream blockage, cost of landslide removal
(based on volume), and type and mechanism
of movement.

Very promising methods are being developed that use

digital elevation models (DEMs) to evaluate areas
quickly for their susceptibility to landslide/debris-
flow events.

Computers also are being used to perform complex

stability analyses.
Landslide Hazard Zonation Map of India
Landslide Hazard Zonation (LHZ) simply means the division
and preferably subdivision of a land surface into various
zones according to the degrees of actual/ potential hazard
caused by landslides and related phenomena

3%
7%
30%
60%
Landslide Inventory
Map of Tamil Nadu
and Kerala
Slope Stabilisation Techniques
Backfilling with lightweight material
Rock fill Buttressing
Crib Wall Check Dam
Drain Trench
Drain Pipes
Timber Cribs
Steel Bin Wall
Reinforced earth Wall
Gabion Wall
Concrete Filled Piled Wall
Rock Fall - Mass concrete retaining walls
Rock Fall – Wire Mesh
Barrier Fensing
Rock Sheds
 Slope Stabilization

Soil Bio Engineering

 Functions

Catch

Support Armour

Reinforce

Anchor
Treatability Status
Feb, 2003
After Slope Trimming – July 2003
Under construction of Gabion Bolsters – July 2003
After Plantation August, 2003
August, 2004 August, 2006
April 2007
“You pay and talk for the
mund”

Ootacamund
Landslide Occurrences Since 1865 in Nilgiris

300 LS
Landslide Occurrences Since 1865 in Nilgiris
 Population growth in Nilgiri District

Area : 2500Sq.km

1901 0.37 Lakhs 2011 7.77 Lakhs

Geological Map
Geomorphological Map
Topography - Coonoor to Ooty
Aerial view of Coonoor to Ooty
Monthly Normal Rainfall in Nilgiri District
 November 2009 Landslides

• Heavy rains triggered a series of

landslides in Ooty, Coonoor and
Kotagiri regions of the Nilgiris

• Killed 42 people within 48 hours. Total

Deaths 80.

• Estimated loss about 300 Crores

 Spatial Distribution - November 2009 Landslides

RF: 19cm

RF: 82cm RF: 31cm

Daily Rainfall from 01 – 15 November 2009

900

Avalanchi
800 Burliyar

Coonoor
700 Devala

Emerald
600 G.Bazaar

Geddai dam
500 Glenmorgan Point
Total Rainfal in mm
Kundha dam
400 Kalhatty

Kethi
300
Kinnakkorai

Kodanad
200 A v a la nc hi
B urliya r
C o o no o r Kotagiri
D e v a la
E m e ra ld
Naduvattam
100 G .B a za a r
G e dda i da m
G le nm o rga n P o int Upper Bhavani
Kundha da m
Ka lha t t y
0 Ke t hi Uthagamandalam
Kinna k k o ra i
Ko da na d
Ko t a giri
N a duv a t t a m
Uppe r B ha v a ni
Date Ut ha ga m a nda la m
November 2009 Landslides Lessons Learned

• Many slides have taken place in

areas of intense cultural activity.
• agricultural operations,
• construction of buildings and roads
• removal of earth and rock
• levelling of slopes
• deforestation and
• blocking of natural drainage.
November 2009 Landslides Lessons Learned

Considering all these evidences the following factors

appear to have been involved, singly or in
combination, in inducing the landslides.

• Water (Heavy rainfall)

• Toe Removal

• Increase of Head Load

 Lovedale Road view from Coonoor Road 10.11.2009

Increase of Head
Load

Toe Removal

Water
Closer View
Closer View
Closer View
Lovedale Road View from Coonoor Road Landslide Scenario

10.11.2009 28.11.2009
 Zone of Crack

Lovedale Road at Thalayattu

Mandu on 10.11.09 top and
bottom side showing the Zone Zone of Failure
of Crack and Zone of Failure
Houses built in the Stream Channel –
Severe Damage at Naduhatti
Debris covered at Naduhatti
Severely Damaged Road - Ooty Coonoor Road near
Thalayattu Mund Junction.
Ooty Coonoor NH. 2 kms from Valley View point.
No way beyond this point.
Near Sagar Holiday Resorts, Valley View.
Unplanned colonization
Lessons for the Planners and public

2009
landslides

Severe to High
Landslide Areas
identified by GSI
in 1982
Landslide hazard zonal significance
(BMTPC, Landslide Hazard Zonation Atlas of India 2003)
Vulnerability
 Critical Facilities
1. Essential facilities
hospitals, medical clinics,
schools/educational institutions, fire
stations, police stations and emergency
operations facilities
2. High potential loss facilities
dams, levees, military installations, nuclear
power plants and hazardous material sites
 Lifeline Inventory

1. Transportation
highways, railways, bus, ports, ferry and airports

2. Lifeline Utility
potable water, wastewater, natural gas, crude &
refined oil, electric power and communications.
 Vulnerability

Sl.No Facilities Total Falls Under Percentage

High to
Moderate
Hazard
Areas
1 Essential 114 24 21%
2 Lifeline 96 7 7.3%
3 Transportation 20 6 30%
4 Village/Towns 42 7 16.7%
Dangerous Slopes
Blocking the Natural Draines
We Don’t Bother
 Malin landslide, Maharashtra 2014

The landslide occurred on July 30, 2014, in a village in Malin. The landslide
occurred due to heavy rainfall and around 151 people died and 100 people went
missing after the disaster.
 Crown

School Building Burried Houses

Unaffected

Continuation in Next Slide

 Continuation ….

2
3
1
 Crown

Survived
Buildings

School
Building

Debris Flow
Direction
 1

Back Side of School Building (Photo from Media)

Water Tank
1.5m
Cut
 Weathered Rock

Joints
Joints
Dipping SE
Nalla
Origin
Rock Out crop
Right Side
of the Scar

Right
Left Side
of the
Scar

Left
 Disturbed
soil
Sample
location

Undisturbe
d soil
Sample
location
Debris
Sample at
Crown
Tree fallen along the
flow Direction

Weathered Rock
Exposure along the Slope
Rock exposure Clearly seen
on the Eroded Nalla
Falling of Tree
along the Flow
of slide
 School
Building
Back Side
Road View
1

Crown Side
Closer View During
rain

School Building
Back Side View
School
Building

Fresh Cutting of
Slope
 Crown

Road

Nalla
 Road
River
Debris fall in
the River Bank
 1m height River
Bank

Silty Debris
20cm foot went
inside
Building Partly
Damaged
School Building
Survived (RCC)

Damaged
Houses (Mud)
 Water Tank

School Building 2
 School Building 1
School Building 2
Cracks found in
School Building 2

This may be after

Landslide???
Tilting of Trees
Outside of Slide
Boundary
Photo from Media during
Rescue Operation Photo by me

5 m Debris Removed
Photo from Media
during Rescue Photo by me
Operation

5 m Debris Removed
Photo from Media Photo by me

Water Tank
 Schoo
l

Temple During
Construction (Photo
from Media)
Paddy field filled
with Mud flow
 Draining Water from Paddy field

Diverting water from main

Channel
Landslide Velocity Scale and Probable Destructive
Significance (Cruden and Varnes 1996)
Landslide
Warning
Signs
Landslide Warning Signs
• Rapid increase in creek water levels, possibly accompanied by increased
turbidity (soil content).
• Sudden decrease in creek water levels though rain is still falling or just
recently stopped.
• A faint rumbling sound that increases in volume is noticeable as the
landslide nears.
• Unusual sounds, such as trees cracking or boulders knocking together,
might indicate moving debris.
• Soil moving away from foundations.
• Ancillary structures such as decks and patios tilting and/or moving
relative to the main house.
• Leaning telephone poles, trees, retaining walls or fences.
 Areas that are generally prone to
landslide hazards
• On existing old landslides.
• On or at the base of slopes.
• In or at the base of minor drainage hollows.
• At the base or top of an old fill slope.
• At the base or top of a steep cut slope.
• Developed hillsides where leach field septic
systems are used.
 Areas that are typically considered safe
from landslides

• On hard, non-jointed bedrock that has not

moved in the past.
• On relatively flat-lying areas away from
sudden changes in slope angle.
• At the top or along the nose of ridges, set
back from the tops of slopes.
 What To Do Before a Landslide

Do not build near steep slopes, close to mountain edges,

near drainage ways, or natural erosion valleys.

Learn about the emergency-response and evacuation

plans for your area
What To Do During a Landslide
Stay alert and awake. Many debris-flow fatalities occur
when people are sleeping.

Be aware that intense, short bursts of rain may be

particularly dangerous, especially after longer periods of
heavy rainfall and damp weather.

If you are in areas susceptible to landslides and debris

flows, consider leaving if it is safe to do so.

Remember that driving during an intense storm can be

hazardous. If you remain at home, move to a second
story if possible. Staying out of the path of a landslide or
debris flow saves lives.
 What To Do During a Landslide
Listen for any unusual sounds that might indicate moving debris, such as
trees cracking or boulders knocking together. A trickle of flowing or falling
mud or debris may precede larger landslides. Moving debris can flow quickly
and sometimes without warning.

If you are near a stream or channel, be alert for any sudden increase or
decrease in water flow and for a change from clear to muddy water. Such
changes may indicate landslide activity upstream, so be prepared to move
quickly. Don't delay! Save yourself, not your belongings.

Be especially alert when driving. Bridges may be washed out, and culverts
overtopped. Do not cross flooding streams!! Turn Around, Don't Drown.
Embankments along roadsides are particularly susceptible to landslides.
Watch the road for collapsed pavement, mud, fallen rocks, and other
indications of possible debris flows.

Be aware that strong shaking from earthquakes can induce or intensify the
effects of landslides.
What to Do if You Suspect Imminent Landslide Danger
• Contact your local fire, police, or public works department.
Local officials are the best persons able to assess potential
danger.

• Inform affected neighbors. Your neighbors may not be aware

of potential hazards. Advising them of a potential threat may
help save lives. Help neighbors who may need assistance to
evacuate.

• Evacuate. Getting out of the path of a landslide or debris flow

is your best protection.
 What To Do After a Landslide
• Stay away from the slide area. There may be danger of additional slides.
• Listen to local radio or television stations for the latest emergency
information.
• Watch for flooding, which may occur after a landslide or debris flow.
Floods sometimes follow landslides and debris flows because they may
both be started by the same event.
• Check for injured and trapped persons near the slide, without entering
the direct slide area. Direct rescuers to their locations.
• Help a neighbor who may require special assistance - infants, elderly
people, and people with disabilities. Elderly people and people with
disabilities may require additional assistance. People who care for them
or who have large families may need additional assistance in emergency
situations.
 What To Do After a Landslide
• Look for and report broken utility lines and damaged roadways and railways
to appropriate authorities. Reporting potential hazards will get the utilities
turned off as quickly as possible, preventing further hazard and injury.

• Check the building foundation, chimney, and surrounding land for damage.
Damage to foundations, chimneys, or surrounding land may help you assess
the safety of the area.

• Replant damaged ground as soon as possible since erosion caused by loss of

ground cover can lead to flash flooding and additional landslides in the near
future.

• Seek advice from a geotechnical expert for evaluating landslide hazards or

designing corrective techniques to reduce landslide risk. A professional will be
able to advise you of the best ways to prevent or reduce landslide risk,
without creating further hazard.
Traditional early warning System
for Landslides
 Monitoring
Additional rain gauge stations may be installed in close interval
and monitor the intense rainfall as well as the existing unstable
slopes.
IOT based Early warning using Rainfall
Thresholds
Traditional early warning System
for Landslides in Darjeeling
Destination - Disaster Risk Free
India

150