The document summarizes a presentation on landslides given by Azmeraw W. It discusses: 1) Definitions of landslides and classifications based on material, movement, rate, water/ice content, and other factors. Common types include falls, topples, slides, spreads, and flows. 2) Factors that influence landslides like slope geometry, material, groundwater, and external triggers such as rainfall, earthquakes, and human activities. 3) Effects of landslides including damage to infrastructure and losses of life, property, and economic activity. 4) Methods for creating landslide inventories, susceptibility maps, hazard maps, and risk maps to assess landslide dangers and

1. ADDIS ABABA SCIENCE AND TECHNOLOGY UNIVERSITY
COLLEGE OF APPLIED SCIENCE
DEPARTMENT OF GEOLOGY
ADVANCED GEOHAZARD (GEOL 6088)
SEMINAR ON : GEOHAZARD (LANDSLIDES)
PRESENTER : AZMERAW W.
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2. Presentation on Landslides
Compiled by Azmeraw W.
M.Sc. Engineering geology
Department of Geology
4/25/2018 2

3. Presentation outline
1. Introduction
• Definition of landslides
• Classification of landslides
• Types of landslides
• Mechanism of slope failures
• Factors influencing landslides
• Effects and losses due to
Landslides
2. Description of landslide
inventory, susceptibility, hazard
and risk
3. Data management/database
preparation
4. Landslide hazard assessment
methods
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4. Introduction
What is geohazard ?
• is a geologic event that has the potential to
both destroy property and cause a loss of life
• Different types of Natural hazard
• Volcanism,
• Earthquakes,
• Landslide
• Tsunami
• Cyclone or Hurricane
• Tornado,
• Flooding,
• Drought
• Forest fire or Bushfire
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What is natural hazard?
Natural events causing great loss of life
or property damage

5. Definition of Landslides
• Landslide is defined as the movement of a mass of rock, debris or earth
down the slope, when the shear stress exceeds the shear strength of the
material.
• They result from the failure of the materials which make up the hill slope
and are driven by the force of gravity.
• The materials may move by falling, toppling, sliding, spreading, or
flowing.
U.S. Geological Survey 2004
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6. classification of landslides
• According to vernes, cruden and other researchers, landslides can be classified
based on :
• Types of material
• mode of movement.
• Rate of movements
• Contents of water, air and ice
• Landslide activity
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• Age
• Magnitude
• Depth

7. Cont.…..
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Varnes, 1978

8. • Classification based on speed
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• The speed of the movement may range from very slow to rapid.
• The speed of the landslide will make an even more or less avoidable and therefore, more or less risky.
• It is important to distinguish the different types of landslides to be able to understand how to deal with
each of them.

9. 4/25/2018 9
Classification based on landslide activity
Varnes (1978)
abandoned

10. Classification of Landslides on the basis of its
magnitude (afterUSSR State Committee on
Construction, 1981)
Classification of Landslides on the basis of its depth
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Features indicating Active and Inactive Landslides

11. types of landslides
• Rotational slide
• Translational slide
• Falls
• Topples
• Lateral Spreads
• Flows
• Combination/complex4/25/2018 11
• Debris flow
• Earth flow/Mudflow
• Debris/rock avalanches
• Creep
• slides
Varnes,1978

12. Mechanism of slope failures
• There are main types of slope failure mechanism which are:
• Rotational failure
• Wedge failure
• Toppling failure
• Plane failure
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13. Factors influencing landslides
• Factors of landslides are classified in to two major
classes such as
1. Intrinsic/inherent/static /conditioning factor
2. External /dynamic/temporal/triggering factor
1. Intrinsic parameters :
• slope geometry- slope morphometry and relief,
• slope material,
• Structural discontinuities,
• land use and land cover and
• groundwater into causative parameters
Anbalagan, 1992; Raghuvanshi et al., 20144/25/2018 13
2. External Factors :
According to Varnes (1984), Dai
and Lee (2001) and Raghuvanshi
et al. (2014) thy are relatively
variable or dynamic, /temporary ,
which are :
• rainfall ,
• seismicity,
• volcanic activity and
• manmade activities are
some of dynamic factors .

14. Man-made factors
• Highland and Bobrowsky (2008), Bekele Abebe et al. (2010), Kifle Woldearegay
(2103) explained that the demand of new land for settlement, infrastructure and
agriculture are primary means in which humans can contribute to slope instability
condition through
• Excavation of slope or its toe
• Loading of slope or its crest
• Drawdown (of reservoirs)
• Deforestation
• Irrigation
• Mining
• Artificial vibration
• Water leakage from utilities
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15. Effects and losses due to Landslides
A) Direct Effect
• block roads, supply lines (telecommunication,
electricity, water, etc.) and waterways.
• deaths and injuries to people and animals.
B) Indirect Effects:
• Flooding caused by movements of large masses
of soil into the reservoir of dam
• Debris flow can cause flooding by blocking
valleys and stream channels, forcing large
amounts of water to backup causing backup/
flash flood
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

.
13
C) Direct losses:
• Loss of life, property, infrastructure and
lifeline facilities, Resources, farmland
and places of cultural importance.
D) Indirect losses:
• Loss in productivity of agricultural or
forest lands,
• Reduced property values, Loss of
revenue,
• Increased cost, Adverse effect on water
quality and Loss of human productivity
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16. Description of landslide inventory, susceptibility, hazard and risk
• Landslide inventories are an inventory of the location, classification,
volume, activity and date of occurrence of individual landslides in an area
Use of Landslide inventories
• Used as basis for assessing landslide susceptibility, hazard and risk (Soeters
and Van Westen, 1996; Aleotti and Chowdury, 1999; Ardizzone et al., 2002;
Dai and Lee, 2008; Van Westen et al., 2008).
• Used to susceptibility models that predict landslide on the basis of past
conditions.
• used to validate landslide susceptibility, hazard and risk maps.
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17. How to generate landslide inventory map
• The methods that are considered useful for the generation of landslide inventory
maps can be classified into the following main groups (Van Westen et al., 2008):
• Image interpretation
• (Semi) automatic classification of landslides from satellite images or
Digital Elevation Models.
• Field investigation,
• Community reporting
• Archive studies,
4/25/2018
17Caribbean handbook

18. • The flowchart showing generating of the landslide inventory map
4/25/2018 18
Caribbean handbook

19. landslide susceptibility and map Preparation
• Landslide susceptibility is relative spatial likelihood for the occurrence of
landslide particular type and volume.
• The methodology for the preparation of the maps comprises the following
operations :
1. Landslides inventory from aerial photography and field work.
2. Analysis of determinant factors, using cross-correlation between slope
movements and factors derived from DTM (altitude, slope, aspect, curvature, etc)
and other thematic layers (lithology, structure, soil units, hydrography, etc).
3. classifying and mapping the unit into very high, high ,moderate, low, very low
susceptibility.
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20. Cont..
• Preparation of a landslide susceptibility map is usually based on two
assumptions:
• The past is a guide to the future, so that areas which have experienced
land sliding in the past are likely to experience land sliding in the
future.
• Areas with similar topography, geology and geomorphology as the
areas which have experienced land sliding in the past are also likely to
experience land sliding in the future.
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Robin et al (2008)

21. • Landslide susceptibility zoning maps should include:
• The inventory of historic landslides, the location and area (or number of
slides, e.g. for rock falls) of the source landslides;
• Travel paths after failure;
• The instability conditioning terrain factors
• The superficial formations (colluvium, till, alluvium, residual soils, etc.)
because failures usually take place in these formations.
• The interpreted susceptibility zoning classification areas.
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Robin et al(2008)

22. Landslides Hazard and Mapping
• Landslide hazard is a condition with the potential for causing an undesirable
consequence or
• It is the combination of both the probability occurrence of an event and
intensity of an event
• Its description should be include the location, volume (or area), classification
and velocity and the probability of their occurrence within a given period of
time.
• It requires determination of the space–time probability, i.e., the probability that
a phenomenon occurs in an area at a given return period of time.
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Robin et al (2008)

23. Landslide hazard Mapping
1. Frequency assessment
• It required to assess the frequency of rock falls, slides from cuts, fills and retaining walls,
and small landslides; and large landslides respectively.
2. Intensity assessment
• Landslide intensity may be assessed either as the spatial distribution of:
• The velocity of sliding coupled with slide volume, or
• The kinetic energy of the landslide; e.g. rock falls, rock avalanches, or
• Total displacement, or
• Differential displacement, or
• Peak discharge per unit width (m3/m/second), e.g. for debris flows.4/25/2018 23
Robin et al(2008)

24. Preparation of landslide hazard zoning map
• It may be developed from inventory and susceptibility zoning map with the areas
classified according to the frequency(annual probability) of land sliding(very high,
high ,moderate, low, very low hazard).
Use of landslide hazard maps
• Development planning
• Planning and mitigation purpose
• Decision making like land use and engineering practice
• hazard monitoring
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25. Landslide risk
• It is the probability of harmful consequences or expected losses (deaths,
injuries, property, livelihoods, economic activity disrupted or environment
damaged) resulting from interactions between natural or human induced
hazards and vulnerable conditions” (UN/ISDR 2004).
• Risk = Hazards x Vulnerability x element at risk
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26. Landslide risk mapping
1. Elements at risk
• For risk to be determined and hence for landslide risk zoning to be implemented the elements at
risk have to be assessed.
• The elements at risk include the persons and property potentially affected by lands liding on,
below and up-slope of the potential landslides.
• They may include indirect impacts such as reduced economic activity resulting from the
landslide; e.g. due to loss of a road, and environmental impacts.
2. Temporal–spatial probability and vulnerability
• The activities required to assess the temporal–spatial probability of the elements at risk.
• Vulnerability is generally assessed empirically for persons and property using published
information.
• There are not as yet available more advanced methods.4/25/2018 26
Robin et al (2008)

27. Preparation of landslide risk zoning maps
• Landslide risk zoning maps are prepared using the inventory, susceptibility and hazard zoning
maps and allowing for the elements at risk, the spatial–temporal probability and vulnerability by
classifying the unit into very high, high ,moderate, low, very low risk.
• Separate zoning maps will be required for life loss risk and property loss risk.
• It should be at the same scale as the susceptibility and hazard zoning maps.
• For life loss, the risk should be expressed as individual risk (annual probability of the person
losing his/her life).
• For property loss, the map may show annualized loss ($/year) but the report should also list the
pairs of loss value and annual probability of the loss (e.g. 0.001 annual probability of $10
million loss).4/25/2018 27

28. Potential landslide risk indicators
• simple observations and inspection may assist in assessing potential landslide hazards.
• Soil moving away from foundations
• Tilting or cracking of concrete floors and foundations
• Broken water lines and other underground utilities
• Leaning telephone poles, trees, retaining walls or fences
• New cracks and scarps in the ground, roads or pavements
• Movements of floors and yards in relation to house
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29. Data management/ landslide database
• It constitute a detailed register of the distribution and characteristics of past landslides
(Hervás, in press).
• It is a key infrastructure for landslide susceptibility, hazard and risk assessment and
management, as well as for disaster emergency management ,but
• The production of landslide databases is a tedious procedure.
• In contrast to other natural hazards (e.g. floods, earthquakes) which affect large areas,
landslides are generally isolated, localized features which individually may not be very
large in size but which can occur with a high frequency in a region.
• They have to be mapped and described one by one, and each one may have different
characteristics.4/25/2018 29

30. Data management/ landslide database
• The first step is collecting all available information and data for the study
area,
• Most of data will found in paper format so it should convert into digital
format through scanning and georeferencing
• Then, data can register and store using Geographical Information Systems
(GIS).
• Two fundamental rules must be observed when creating a database (Leroi
1996):
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31. Cont..
a) the information must be homogeneous,
i.e. it must-have the same work-scale and
the same geographic projection system
b) the database must be organized into
basic monothematic layers, each of which
contains homogeneous data.
• In addition, a database should include at
least the following basic information
(Chowdhury and Flentje1998a):
a) a census of existing landslides including
their nature, size, location and history4/25/2018 31
b) a reliable site reference code
c) any available information from previous site
investigations (aerial photo interpretation,
laboratory testing, field analyses including back
analyses of failures)
d) any remedial or preventive measures
installed and their effectiveness
e) data from any installed instrumentation
(inclinometers, piezometers).
f. Any factor of landslide data

32. hazard assessment methods
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33. •This is all what I have to say.
•Thank you too much for your
eyeful attention!
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End of presentation.