The document discusses geology-based natural disasters that occur in Sri Lanka. It describes the major disasters as landslides, subsidence, and tsunamis. Landslides frequently happen in Sri Lanka, affecting 30% of the country's land area, mostly in hilly regions. They are caused by factors like steep slopes, erosion, earthquakes, and deforestation. Subsidence occurs when underground spaces collapse, forming depressions at the surface. Sri Lanka suffered greatly from the 2004 Indian Ocean tsunami caused by an earthquake, which killed over 30,000 people and destroyed 100,000 homes. The earthquake lifted the seabed and generated huge waves that devastated coastal areas.

1. GEOLOGY BASED NATURAL
DISASTERS IN SRI LANKA
K.K.A.D. KUMAR
UWU/MRT/13/0018
UWU/EX/13/0426

2. What is a Disaster?
A disaster is a sudden, calamitous event that seriously disrupts
the functioning of a community or society and causes human,
material, and economic or environmental losses that exceed the
community’s or society’s ability to cope using its own resources.
Though often caused by nature, disasters can have human
origins.
Figures 1: Disasters7/17/2017 2

3. Types of Disasters
Disasters Natural Geological
Biological
Climatological
Hydrological
Man-made or
Technological
Chemical threat and
biological weapons
Nuclear power plant and
nuclear blast
Radiological emergencies
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4. Natural Disasters
The definition of natural disaster is any catastrophic
event that is caused by nature or the natural
processes of the earth.
Examples:
Floods
Tornadoes
Extreme Temperatures
Avalanches
Droughts
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5. Natural Disasters
Figures 2: Natural Disasters7/17/2017 5

6. Figures 3: Natural Disasters
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7. Man-Made Disasters
Figures 4: Man-made Disasters
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8. Figures 5: Man-made Disasters
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9. Geology Based Natural Disasters
Geology based disasters are defined as events
originating from solid earth.
They are classified as:
Earthquakes (ground shaking and tsunamis),
Volcanic Eruptions
Dry Mass Movements (rock fall, avalanche, landslide,
subsidence)
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10. Geology Based Natural Disasters in Sri
Lanka.
The most frequent natural hazards that affect Sri Lanka are
droughts, floods, landslides, cyclones, vector-borne
epidemics (malaria and dengue), and coastal erosion
 Tsunamis are infrequent but have caused severe damage
Recent understanding of the tectonics of the Indian Ocean
region points to an increasing risk of earthquakes
 The risk of volcanoes is small
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11. Cont.
The major geology based natural disasters in Sri Lanka are:
Landslides
Subsidence
Tsunami
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12. Landslides
A landslide is defined as the movement of a mass of rock,
debris, or earth down a slope due to gravity
Landslides affect to the life and property as well as it
affects to the economic situation
Figures 6: Landslide
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13. Cont.
Of the 65,610 sq km of land extent of Sri Lanka, an area of
nearly 20,000 sq km encompassing 10 districts is prone to
landslides
It is about 30% of Sri Lanka's land area
It spreads into several districts:
Badulla Nuwara Eliya Kandy
Kegalle Ratnapura Matale
Kaluthara Mathara Galle
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14. What causes a landslide?
The materials may move by falling, toppling, sliding,
spreading, or flowing.
Natural causes are;
• Steepness of hill slope
• Type of rock material
• Earthquake as a triggering factor
• Flood and reservoirs in hilly areas
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15. Cont:
• Deep weathering of rock material and the depth of the
weathered rock
• Density of the joint pattern and the structure of the rock
• Poor drainage conditions leading to excessive water
seepage in sub strata
• High intensity of precipitation
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16. Cont:
In addition to these reasons, human activities causes for
landslides
• Excavation of slope or its toe
• Loading of slope or its crest
• Deforestation
• Irrigation
• Mining
• Artificial vibration
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17. Types of Landslides
Figure 7: Types of Landslides
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18. Landslides Mitigation
•Covering the land with impermeable membranes
•Directing surface water sources away from the landslides
•Draining ground water streams away from the landslides
•Minimizing irrigation on the surface of the soil
•Removing soil mass from the top of the slope
•Apply engineering activities like nailing and shotcrete
•Forestation
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19. Subsidence
Subsidence is the downward shift in the ground surface that can be
caused by a variety of processes, both natural and human-related
Human processes that can cause subsidence include mining, natural
gas removal, and over use of groundwater
Natural processes that sometimes result in subsidence include the
erosion of bedrock, earthquakes, the faulting (breaking) of bedrock, and
the shifting of groundwater reservoirs
There are two types of subsidence:
1.Sag Subsidence
2.Pit Subsidence
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20. Cont:
Pit subsidence forms a bell-shaped hole, usually 6-8 feet deep and
from 2-40 feet across
Sag subsidence, the most common type of mine subsidence,
appears as a gentle depression in the ground and can spread over an
area as large as several acres
Figures 8: Types of Subsidence7/17/2017 20

21. Figures 9: Subsidence in Sri Lanka
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22. Tsunami
Tsunamis are giant waves caused by earthquakes, volcanic eruptions
or landslide under the sea
The impact of a large meteorite could also cause a tsunami
The speed of tsunami waves depends on ocean depth rather than
the distance from the source of the wave
Figures 10: Tsunami wave7/17/2017 22

23. Cont:
Sri Lanka was one of the countries struck by the tsunami
resulting from the Indian Ocean earthquake on December 26,
2004
It was a 9.0 magnitude earthquake off the coast of Sumatra
Death( confirmed) - 30,196
Destroyed houses (nearly) – 100,000
Refugees – 1,500,000
Loss of assets – US $ 1000 million
Missing - 5637
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24. Causes
•The earthquake was caused by the subduction of the Indo-
Australian plate (oceanic) under the Eurasian plate
(continental)
•This mega-thrust earthquake involved a 20 metre uplift of
the sea floor all the way along a fault line which was over
1000km in length
• It caused a displacement of billions of tonnes of water
setting in motion a tsunami wave
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25. Prevention from Tsunami
When in coastal areas, stay alert for tsunami warnings
Figures 11: Early Warning Tsunami System7/17/2017 25

26. Cont.
Learn details of the local warning systems
Plan an evacuation route that leads to higher ground
Know the warning signs of a tsunami: rapidly rising or
falling coastal waters and rumblings of an offshore
earthquake
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27. References
•McDonald,R.(2003). Introduction to Natural and Man-made Disasters and their
Effects on Buildings. Architectural Press, India
•Sri Lanka National Report on Disaster Risk, Poverty and Human Development
Relationship.pdf
•Zubair, Ralapanawe & Tennakoon, (2002). Natural Disaster Risks in Sri Lanka:
Mapping Hazards and Risk Hotspots
•http://www.eartheclipse.com/natural-disaster/causes-effects-and-types-of-
landslides.html [Accessed date: 11.06.2017]
•http://www.ifrc.org/en/what-we-do/disaster-management/about-
disasters/definition-of-hazard/ [Accessed date: 10.06.2017]
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28. Thank You
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