Hazard (Source of risk) are defined as phenomenon that pose a
threat to people, structure, environmental resources and economy assets and
which may cause a disaster.
Also
hazard is a source of risk that may cause damage to or loss of life and
property.
Classification of Hazard
1 Relative Hazard is assessed by
assigning rating to different factors contributing to Hazard.
2 Absolute Hazard is expressed
deterministically. (e.g. Factor of safety).
3 Monitored Hazard is assessed by
actual measurement of the effects.
(Eg deformations).
Types of Hazard
1. Natural Hazard
1)
Water and Climatic re-laid:- flood, cyclones,
tornadoes, huricans, hailstone, drough.
2)
Geologically: - earthquake, tsunami, landslide.
3)
Biologically: - epidemics, pest attack.
4)
Chemically: - industries and nuclear.
5)
Accidentally related: - Forest Fire, serial bomb blast,
air, rail, road accidents.
2. Man made Hazard
1)
War
2)
Armed Conflict
3)
Technological failure
4)
Oil spillage
5)
Factory
expansion
6)
Fire
7)
Gas leakage
8)
Transport collisions ,etc
Disaster: it is a serious disruption of the functioning of society
causing human material and environmental losses which exceeds the ability of
society to cope using its own resources.
* The impacts of disaster are
multidimensional, social, economic and environmental
* A Disaster is a product of
Hazards and vulnerability.
Vulnerability [V] as the extreme
to which a community,structure,service or geographic area is likely to be
damaged or disrupted by the impact of particular hazard, on occrent of their
nature, construction and proximity to hazardneous terrain.
Vulnerability means the degree of
loss to a given elements or set of elements at risk, resulting from the
occurrence of a natural phenomenon of a given magnitude. It is expressed on a
scale from 0(no damage) to 1 (total loss).
Risk= Hazard X Potential worth of loss
Is
a potential loss of life and property and may be defined as “the combined
effect of the probability of occurrence of an undesirable events and the
magnitude of the event”.
Specific Risk [Rs] means the expected degree of loss due
to a particular natural phenomenon. It may be expressed by the product of H
times V.
Rs
= H x V
Element at Risk [E] means the population, properties, economic
activities, encluding public services etc at risk in a given area.
Total Risk [Rt] means the expected number of lives lost,
person enjured, damage to property or disruption of economic activity due to a
particular natural phenomenon and is therefore the product of specific risk [Rs]
and elements at risk [E].
Rt
= E x Rs = E x (V x H)
Stages of Risk Assessments
i)
Identification
- possible risk
ii)
Estimation
- possible damage
iii)
Evaluation
- mitigation effect should be
undertaken
Risk Elements in Different Disaster
Hazard Risk
Flood Every thing located in the
flood plain.
Earthquake Every thing
located in earthquake prone zone.
Tsunami/cyclone Anything close to costal
area.
Landslide Anything
located on or at base of steep slopes or cliff tops.
Drought Live
and health of those involved in drought prone area.
Assessment of Hazard and Risk
i)
State of nature
mapping
ii)
Danger mapping
iii)
Hazard
mapping
iv)
Risk Determination
v)
Action
Geological Sub-division of the Himalaya of Nepal
The
process of collision of the Indian subcontinent with the Tibetan plate and the
subsequent folding ,faulting and upheavals of rock masses led to the formation of the world’s highest
and one of its most active mountain ranges the Himalaya. The Himalaya
range can be subdivided into the following zones for South to North.
1)
The Gangetic plain formed on the Indian shield as a
result of the accumulation of sediments transported by rivers and streams from
the Himalayas .
2)
Sub-Himalaya (Siwalik)-MFT delineated the Gangetic
plain and Siwalik.
3)
Lesser Himalaya
a)
Mahabharata
Range
b)
Ludands
4)
Higher Himalaya the
boundary between LH and HH is the MCT
5)
The Higher Himalaya Which is gradually passed into the
sedimentary belt of the Tibetan –Tethys Zone.
a) Sub-Himalaya
or Siwalik (Unstable Zone)
i)
The
youngest rock in the Himalaya
ii)
The main rock types are mudstone, sandstone and
conglomerate.
iii)
It is further classified in to-
a.
Lower Siwalik
b.
Middle Siwalik
c.
Upper Siwalik
The lower
Siwalik are represented by interbreed soft mud rock and sst.
The Middle
Siwalik comprised of thick bedded sst and mudstone and Constituted steep river gorges’ Tinau Khola.
The upper
Siwalik comprised of conglomerate of gravel. It has also
Experienced tectonic movement and therefore the beds are tilted.
iv)
The Siwaliks Rocks are gently folded and often
dislocated by steep faults
Which become
gentler below the surface and join with each other. They are called Imbricate Faults
v)
It is seismically the most active region of the Himalaya .
vi)
The Siwaliks are delimited from the North by the MBT,
one of the active fault of the Himalaya Rocks are generally crushed near the
fault.
vii)
They are generally covered with thick forest,
b) The Lesser Himalaya (4000 m)
1)
Mahabharata
Range is an outer lesser Himalaya exhibits a young topography with active gullies
deep slope and many imbricate faults.
2)
The Mud lands is
an inner lesser Himalaya are characterized by
the mature topography and wide development of red soil in slate, Phyllite and
Schist.
3)
Consists of thick sequence of low grade metamorphic
rock in the bed while the upper beds are of high grade metamorphic rock lesser Himalaya crystal lines.
4)
It is also intricately folded and faulted.
5)
The lesser Himalaya is
divided in to Sedimentary belts and Metamorphic
Belt
Sedimentary Belts
i)
Covered North of MBT in central west Nepal
ii)
Imbricate fault, tight fold and various system of joint
are occasionally encountered.
iii)
Rock range from weak slate to massive and thick bedded
Dolomite.
iv)
Common type of mass movements, rock side, rock fall,
rock topple, avalanches debris , deep
gully erosion etc.
Rock type
1)
Very fracture and crumbly slate easily breakable land.
Immediately
north of the MBT
2)
Inter bedded high joint quartzite and shale near the
MBT and inner part of lesser Himalaya .
3)
Medium to thick bedded Dolomite with thin beds of clay
stone or slate.
4)
Massive and cliff fairly Dolomite and Quartzite- stable
and normal.
5)
Deeply weathered soil, colluvium and loose mass.
6)
Weatherly product, rotated slide as common ,slope less
than 250
Water may
crust, Hazard.
Metamorphic Belt
1)
Low graded metamorphic rocks with high grade
metamorphic rock such as gneiss.
2)
Phyllite, Marble, Quarzite, Schist, Gneissis.
A)
Phyllite and Quartzite alternate
1.
Thick succession
2.
No of small scale fold
3.
less rugged the Mahabharata range
4.
River flows from N to S, various river terraces level
are encountered.
5.
Major mass waste process is debris slides, debris flow
and slurry.
B)
Thick bedded Quartzite, marble or Limestone.
i.
Narrow band of about 500 m in thickness.
ii.
Formed steep slope.
iii.
Rock is quite stable, good site for bridge construction.
iv.
Rock fracturing – wedge failure.
c) Higher Himalaya
1. Rock type: - Gneiss,
Magnetite, Schist, Marble and Granite.
2. Competent and Massive.
3. Produced very rugged and high
mountain terrain (8000 m)
4. Rock are divided in to
-The
Tibetan Tethys Zone-fossils, ferrous, sedimentary rock
-
The Central Crystalline.
5. Debris falls, Gully
Avalanches.
6. Glacier lake- creates a high
hazard for the area below the region.
The Tibetan zone
Incompetent
rock such as Shale, Sandstone, Siltstome and Conglomerate.
-
Are many river terraces.
-
Rocks are folded and faulted
-
Rapid mass wasting
-
Rock and ice avalanches are common.
