this is a report about geology based natural disasters in Sri Lanka

1. SEMINAR SERIES REPORT
GEOLOGY BASED NATURAL DISASTERS
IN SRI LANKA
Name : K.K.A.D. Kumar
Index Num : UWU/EX/13/0426
Reg Num : UWU/MRT/13/0018
Degree : Mineral Resources & Technology
Year : 4th
Year
SEMINAR SERIES IN MINERAL SCIENCE (MRT 493-1)

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Table of Contents
1. Introduction........................................................................................................................ 1
1.1 Disasters........................................................................................................................... 1
1.2 Types of Disasters............................................................................................................ 1
2. Geology Based Natural Disasters .......................................................................................... 2
3. Geology Based Natural Disasters in Sri Lanka...................................................................... 3
3.1 Landslides .................................................................................................................. 4
3.1.1 Landslide Types............................................................................................................ 5
3.1.2 Causes for Landslides ................................................................................................... 7
3.1.3 Landslide Mitigation..................................................................................................... 8
3.2 Subsidence ................................................................................................................. 9
3.2.1 Types of Subsidence ................................................................................................... 10
3.3 Tsunami ................................................................................................................... 10
3.3.1 Causes of Tsunami...................................................................................................... 11
3.3.2 Preventing from Tsunami ........................................................................................... 12
4. References........................................................................................................................ 13

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1. Introduction
1.1 Disasters
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.
1.2 Types of Disasters
Disasters can take many different forms, and the duration can range from an hourly disruption
to days or weeks of ongoing destruction. Below are the examples of the various types of
disasters – both natural and man-made or technological in nature – that can impact a community.
1. Natural Disasters
Natural hazards are naturally occurring physical phenomena caused either by rapid or slow
onset events which can be geological (earthquakes, landslides, tsunamis and volcanic activity),
hydrological (avalanches and floods), climatological (extreme temperatures, drought and
wildfires), meteorological (cyclones and storms/wave surges) or biological (disease epidemics
and insect/animal plagues).
Figure 1: Natural Disasters

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2. Man-made or Technological Disasters
Technological or man-made hazards (complex emergencies/conflicts, famine, displaced
populations, industrial accidents and transport accidents) are events that are caused by humans
and occur in or close to human settlements. This can include environmental degradation,
pollution and accidents. Technological or man-made hazards (complex emergencies/conflicts,
famine, displaced populations, industrial accidents and transport accidents)
2. Geology Based Natural Disasters
Geophysical disasters are defined as events originating from solid earth and are
classified as: Earthquakes (ground shaking and tsunamis), Volcanic Eruptions, and Dry
Mass Movements (rock fall, avalanche, landslide, and subsidence).
1. Earthquakes
Earthquakes are the result of forces deep within the earth's interior. Sudden break within
the upper layers of the earth, sometimes breaking the surface, resulting in the vibration
of the ground, which were strong enough will cause the collapse of buildings and
destruction of life and property. They strike with no early warning and can be
devastating, but after a major one, aftershocks may be as strong as a new earthquake.
Earthquakes usually happens along a fault plate, the border between plates. Earthquakes
often trigger landslides, tidal waves and tsunamis. Powerful aftershocks frequently
occur, causing further damage and increasing psychological stress.
Figure 2: Man Made Natural Disasters

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2. Volcanic Eruptions
Volcanic eruptions happen when lava and gas are discharged from a volcanic vent. The
most common consequences of this are population movements as large numbers of
people are often forced to flee the moving lava flow. Volcanic eruptions often cause
temporary food shortages and volcanic ash landslides called Lahar.
The most dangerous type of volcanic eruption is referred to as a 'glowing avalanche'.
This is when freshly erupted magma forms hot pyroclastic flow which have
temperatures of up to 1,200 degrees. The pyroclastic flow is formed from rock
fragments following a volcanic explosion, the flow surges down the flanks of the
volcano at speeds of up to several hundred kilometers per hour, to distances often up to
10km and occasionally as far as 40 km from the original disaster site.
3. Dry Mass Movements
Mass movement describes a quantity of debris/land/snow or ice that slides down a
mountainside under the force of gravity. It often gathers material that is underneath the
snowpack like soil, rock (debris avalanche) etc.
3. Geology Based Natural Disasters in Sri Lanka
Sri Lanka being a small island in the Indian Ocean in the path of two monsoons is mostly
affected by weather related hazards. Floods mostly due to monsoonal rain or effects of
low pressure systems and droughts due to failure of monsoonal rain are the most
common hazards experienced in Sri Lanka. Sri Lanka is also prone to hazards such as
landslides, lightning strikes, coastal erosion, epidemics and effects of environmental
pollution.
In 2004, almost two-thirds of the Sri Lankan coast were affected by the Indian Ocean
tsunami highlighting the country’s vulnerability to low-frequency but high impact
events.

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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.
Among those natural disasters geology based natural disasters are:
 Landslides
 Subsidence
 Tsunami
3.1 Landslides
A landslide is the movement of soil or rock controlled by gravity and the speed of the
movement usually ranges between slow and rapid, but not very slow. It can be
superficial or deep, but the materials have to make up a mass that is a portion of the
slope or the slope itself. The movement has to be downward and outward with a free
face.
Figure 3: People Affected By Different Disasters in Sri Lanka (1974-2004)

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Of the 65,610 km2
of land extent of Sri Lanka, an area of nearly 20,000 km2
encompassing 10 districts is prone to landslides. It is about 30% of Sri Lanka's land
area and spread into several districts, namely; Badulla, Nuwara Eliya, Kegalle,
Ratnapura, Kandy, Matale, Kaluthara, Mathara, Galle and Hambantota.
Investigations carried out by the National Building Research Organization indicate that
a haphazard and unplanned land use, inappropriate construction methods and wanton
human intervention have led to an increase in landslide susceptibility.
Apart from the damage to life and property, several infrastructural as well as
economically important facilities have also been affected, especially water distributary
pipes, hydro electricity generating centers, and communication systems. At times, social
interests such as education and health services are also severely disrupted. Moreover,
frequent landsliding has threatened the destruction to the environment, including the
flora and fauna of the area concerned. Such damage caused to the environment, at times,
is irreversible and therefore cannot be estimated and perhaps will never be known.
3.1.1 Landslide Types
Landslides or slope movements can be classified in many ways. There are many
attributes used as criteria for identification and classification including:
 Rate of movement: This ranges from very slow creep (millimetres/year) to
extremely rapid (metres/second).
 Type of material: Landslides are composed of bedrock, unconsolidated
sediment and/or organic debris.
 Nature of movement: The moving debris can slide, slump, flow or fall.

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Figure 4: Types of Landslides. Abbreviated Version of Verne’s' Classification of Slope Movements
 Falls
Falls are sudden movements of loads of soil, debris, and rock that break away from
slopes and cliffs. Falls landslides occur as a result of mechanical weathering,
earthquakes, and force of gravity.
 Slides
This is a kind of mass movement whereby the sliding material breakaways from
underlying stable material. The kinds of slides experienced during this type of landslide
include rotational and transitional. Rotational slides are sometimes known as slumps
since they move with rotation.
Transitional slides consist of a planer or 2 dimensional surface of rupture. They involve
landslide mass movement following a roughly planar surface with reduced rotation or
backward slanting. Slides occur when the toe of the slope is undercut. They move
moderately, and the consistency of material is maintained.
 Topples
Topple landslides occur when the topple fails. Topple failure encompasses the forward
spinning and movement of huge masses of rock, debris, and earth from a slope. This
type of slope failure takes place around an axis near or at the bottom of the block of
rock. A topple landslide mostly lead to formation of a debris cone below the slope. This
pile of debris is known as a Talus cone.

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 Spreads
They are commonly known as lateral spreads and takes place on gentle terrains via
lateral extension followed by tensile fractures.
 Flows
This type of landslide is categorized into five; earth flows, debris avalanche, debris flow,
mudflows, and creep, which include seasonal, continuous and progressive. Flows are
further subcategorized depending upon the geological material, for example, earth,
debris, and bedrock.
3.1.2 Causes for Landslides
While landslides are considered naturally occurring disasters, human-induced changes
in the environment have recently caused their upsurge. Although the causes of
landslides are wide ranging, they have 2 aspects in common; they are driven by forces
of gravity and result from failure of soil and rock materials that constitute the hill slope.
Natural causes are;
 Steepness of hill slope
 Type of rock material
 Deep weathering of rock material and the depth of the weathered rock
 Density of the joint pattern and the structure of the rock
Figure 5: Types of Landslides

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 Thickness of colluvium deposits collected down slope due to gravity
 Poor drainage conditions leading to excessive water seepage in sub strata
 High intensity of precipitation
 Earthquake as a triggering factor
 Flood and reservoirs in hilly areas
Human Causes are;
 Excavation of slope or its toe
 Loading of slope or its crest
 Deforestation
 Irrigation
 Mining
 Artificial vibration
3.1.3 Landslide Mitigation
Vulnerability to landslide hazards is a function of location, type of human activity, use,
and frequency of landslide events. The effects of landslides on people and structures
can be lessened by total avoidance of landslide hazard areas or by restricting,
prohibiting, or imposing conditions on hazard-zone activity. Local governments can
reduce landslide effects through land-use policies and regulations.
Individuals can reduce their exposure to hazards by educating themselves on the past
hazard history of a site and by making inquiries to planning and engineering
departments of local governments. They can also obtain the professional services of an
engineering geologist, a geotechnical engineer, or a civil engineer, who can properly
evaluate the hazard potential of a site, built or unbuilt.

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The hazard from landslides can be reduced by avoiding construction on steep slopes
and existing landslides, or by stabilizing the slopes. Stability increases when ground
water is prevented from rising in the landslide mass by;
(1) Covering the landslide with an impermeable membrane
(2) Directing surface water away from the landslide
(3) Draining ground water away from the landslide
(4) Minimizing surface irrigation
Slope stability is also increased when a retaining structure and/or the weight of a
soil/rock berm are placed at the toe of the landslide or when mass is removed from the
top of the slope.
3.2 Subsidence
Subsidence is sinking of the ground because of underground material movement, it is most often
caused by the removal of water, oil, natural gas, or mineral resources out of the ground by
pumping, fracking, or mining activities.
Subsidence can also be caused by natural events such as earthquakes, soil compaction, glacial
isostatic adjustment, erosion, sinkhole formation, and adding water to fine soils deposited by
wind (a natural process known as loess deposits). Subsidence can happen over very large areas
like whole states or provinces, or very small areas. Land subsidence may be caused by a
combination of sediment loading (when rivers deposit sediment in an area that then sinks under
the additional weight) and sediment compaction after groundwater is removed.
Subsidence rarely occur in Sri Lanka. Mathale area is very popular for subsidence in our
country. There were several types of subsidence occurred in Mathale area within the last few
years. Most of them were formed due to the heavy rainfall season in the country.

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3.2.1 Types of Subsidence
There are two types of subsidence:
 Sag Subsidence
 Pit Subsidence
Pit subsidence forms a bell-shaped hole, usually 6-8 feet deep and from 2-40 feet across. Ground
movement will be swift and sudden. 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. The first signs may appear suddenly within a few hours or days, with gradual movement
continuing anywhere from a couple of years to more than a decade. Frequently, damage is
subtle, and perhaps dismissed as normal wear and tear until multiple signs appear.
3.3Tsunami
A tsunami is a series of waves caused by a rapid displacement of a body of water (ocean, lake).
The waves are characterized by a very long wavelength and their amplitude is much smaller
offshore. The impact in coastal areas can be very destructive as the waves advance inland and
can extend over thousands of kilometers. Triggers of a tsunami can be: earthquakes, volcanic
eruptions, mass movements, meteorite impacts or underwater explosions. The Japanese term
for this phenomenon "tsunami" ("Wave in the port" in Japanese), which is observed mainly in
the Pacific, has been adopted for general usage.
Sri Lanka was hit by a tsunami triggered by a 9.0 magnitude earthquake off the coast of Sumatra
on December 26, 2004. The tsunami was one of the worst disasters ever recorded in Sri Lankan
history. The tsunami left tens of thousands dead, many more homeless, and caused widespread
chaos throughout the island.
Figure 6: Types of subsidence

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 Death ( confirmed) - 30,196
 Destroyed houses (nearly) – 100,000
 Refugees – 1,500,000
 Loss of assets – US $ 1000 million
 Missing - 5637
In addition to the human impacts, the tsunami had widespread effects on Sri Lanka's
environment and ecosystems. It is still too early to express the long-term effects caused by the
tsunami, but short-term effects are clearly evident.
The tsunami first arrived on the eastern coast and subsequently refracted around the southern
point of Sri Lanka (Dondra Head). The refracted tsunami waves inundated the southwestern
part of Sri Lanka after some of its energy has been reflected from impact with the Maldives. Sri
Lanka is located 1,700 km (1056.33 miles) far from the epicenter and the tsunami source, so no
one felt the ground shake and the tsunami hit the entire coastline of Sri Lanka around 2 hours
after the earthquake. It seems that the tsunami flooding consisted of three main waves, with the
second being the largest and most destructive. The first tsunami waves had initially caused a
small flood (positive wave) as it struck the Sri Lankan coastline. Moments later, the ocean floor
was exposed to as much as 1 km (0.62 miles) in places due to drawback (negative wave), which
was followed by a massive second tsunami wave, which is in the form of a flood. Certain
locations managed to reduce the power of the waves through construction of seawalls and
breakwaters.
3.3.1 Causes of Tsunami
The earthquake that caused the tsunami struck at 7:58am on December 26th 2004. The focus,
which is where the earthquake originates, was 30 km underwater off the western coast of
Sumatra and was a result of the Sunda mega thrust, which means a long body of land along the
southwestern side of Sumatra, rupturing after scientists had claimed it was dormant. This
rupture was devastating because it is where the Eurasian and Australian plates are located. The
plate shifting between these two caused what became the third largest earthquake recorded in
history with a magnitude between 9.1 and 9.3 on a seismograph which is used to measure
motions in the ground. The earthquake was caused by the subduction of the Indo-Australian
plate (oceanic) under the Eurasian plate (continental) 240km off the coast of Indonesia. This
mega-thrust earthquake involved a 20 meter uplift of the sea floor all the way along a fault line
which was over 1000km in length. The uplift of the sea floor caused a displacement of billions
of tons of water setting in motion a tsunami wave which hit the coast of Indonesia within half
an hour of the earthquake.

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3.3.2 Preventing from Tsunami
 When in coastal areas, stay alert for tsunami warnings.
 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.
 Never stay near shore to watch a tsunami come in.
Figure 7: Tsunami early warning system

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4. References
 Sri Lanka National Report on Disaster Risk, Poverty and Human Development
Relationship.pdf
 McDonald,R.(2003). Introduction to Natural and Man-made Disasters and their Effects
on Buildings. Architectural Press, India
 Zubair, Ralapanawe & Tennakoon, (2002). Natural Disaster Risks in Sri Lanka: Mapping
Hazards and Risk Hotspots
 http://www.ifrc.org/en/what-we-do/disaster-management/about-disasters/definition-of-
hazard [Accessed Date: 10.06.2017]
 http://www.eartheclipse.com/natural-disaster/causes-effects-and-types-of-landslides.html
[Accessed Date: 11.06.2017]
 https://pubs.usgs.gov/fs/2004/3072/fs-2004-3072.html [Accessed Date: 15.07.2017]
 https://oceanservice.noaa.gov/facts/subsidence.html [Accessed Date: 14.07.2017]
 http://www.imsif.com/about-mine-subsidence/types-of-mine-subsidence [Accessed Date:
14.07.2017]