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natural disasters

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Title: natural disasters


1
NATURAL DISASTERS
  • PREPARED BY-
  • CLASS-

2
What is a natural hazard ?
  • Any natural occurrence that is infrequent and
    dangerous, posing a threat to life and property
    of humans.
  • What is natural disaster then?
  • Natural hazards that are very furious and cause
    extensive devastation

3
Differentiate between natural hazards and natural
disasters
Natural disasters Natural hazards
Extensive devastation Less devastation
In large areas In small area
4
Categories of natural hazards
  • Geological hazards natural hazards that are
    caused due to geological disturbances .they do
    not occur frequently but are very disastrous in
    nature .e.g. volcanic eruption , landslides and
    avalanches .
  • weather_-associated hazards natural hazards
    caused due to dramatic changes in weather
    conditions are called weather associated hazards
    . They occur frequently but are less devastating
    .e.g. cyclone, flood and droughts.

5
Natural hazards
  • Earthquakes
  • Volcanic eruptions
  • Landslides and avalanches
  • Cyclone
  • Floods
  • Droughts

6
earthquake
7
causes
  • Earthquakes are usually caused when rock
    underground suddenly breaks along a fault
  • . This sudden release of energy causes the
    seismic waves that make the ground shake.
  • When two blocks of rock or two plates are
    rubbing against each other, they stick a little
  • . They don't just slide smoothly the rocks catch
    on each other.
  • The rocks are still pushing against each other,
    but not moving.
  • After a while, the rocks break because of all
    the pressure that's built up.
  • When the rocks break, the earthquake occurs.

8
Precautions against Earthquake
  • Safer places indoors as well as outdoors must be
    clearly identified.
  • An Emergency communication plan should be made
    available.
  • Stay away from tall and heavy objects that may
    fall on you.
  • Take shelter under a table and stay there till
    the shaking stops.

9
CONSEQUENCES OF EARTHQUAKE
  • It shows that Earthquake is very dangerous to
    humans life.

10
VOLCANOEs
  • REASONS AND PRECAUTIONS

11
REASONS OF VOLCNAOES
  • A volcano erupts when magma escapes from inside
    the earth. As the magma is escaping from a
    confined space, a lot of energy is released with
    it, as happens with any other explosion.
  • The earths crust is its thinnest layer. It is
    broken up into large pieces, called tectonic
    plates. These plates lie above the hot, liquid
    mantle.

12
PRECAUTIONS AGAINST VOLCANOES
  • Have sufficient water, food and medical equipment
    supplies, when travelling and at base location
    (minimum 72hours)
  • have plans in place to return to a safe location
    and at a suitable distance
  • Monitor weather conditions particularly wind
    direction (wind changes direction with attitude)

13
Landslides
14
Landslides and avalanches
  • Landslides occur when the stability of the slope
    changes from a stable to an unstable condition. A
    change in the stability of a slope can be caused
    by a number of factors, acting together or alone.
    Natural causes of landslides include
  • Loss or absence of vertical vegetative structure,
  • weakening of a slope through saturation by snow
    melt, glaciers melting, or heavy rain
  • deforestation, cultivation and construction,
    which destabilize the already fragile slopes.
  • vibrations from machinery or traffic
  • earthwork which alters the shape of a slope, or
    which imposes new loads on an existing slope
  • Construction, agricultural or forestry activities
    (logging) which change the amount of water which
    infiltrates the soil

15
Protective measures
  • The use of slopes prone to landslides must be
    avoided, or uses suitably modified

16
Cyclones
17
Causes
  • This heat from the ocean combines with the
    Earth's rotation to create the cyclone's spin and
    propulsion. As the cyclone moves across cooler
    waters, land or into unfavourable wind systems,
    it gradually begins to dissipate as it loses
    energy.
  • There are a number of additional
    atmospheric conditions that must be present in
    order for a cyclone to form, including moisture
    layers in the mid-troposphere, approximately 3
    miles above the Earth's surface, and low vertical
    wind shear between the Earth's surface and the
    upper troposphere. Cyclones also need to be at
    least 310 miles from the equator, where the
    deflective Creoles force of the planet's rotation
    begins to take effect.

18
Protective measures
  • Before the cyclone season, check with your local
    council if your home has been built to cyclone
    standards.
  • Check that the walls, roof and eaves of your home
    are secure
  • Listen continuously to your local radio/TV for
    further warnings.
  • .in cyclone prone areas , settlements should not
    be built close to the coastline .

19
A FLOOD
  • REASONS AND PRECAUTIONS

20
REASONS OF FLOOD
  • Flooding occurs most commonly from heavy rainfall
    when natural watercourses do not have the
    capacity to convey excess water.
  • Floods can also occur in rivers when the flow
    rate exceeds the capacity of the river channel,
    particularly at bends or meanders in the
    waterway.
  • Dam failure, triggered for example by an
    earthquake, will result in flooding of the
    downstream area,

21
PRECAUTIONS AGAINST FLOOD
  • Do not eat fresh food that has come in contact
    with flood waters.
  • Do not attempt to cross a stream where water is
    above your knees.
  • Do not handle electrical equipment in wet areas.
  • Do not try to drive over a flooded road. The
    water can be much deeper than it appears and you
    could be stranded or trapped.

22
A VILLAGE SUFFERING FROM FLOOD
  • A FLOOD DOING DESTRUCTION

23
Droughts
24
Causes of drought
  • Drought is defined as a period in which a region
    has a deficit in its water supply. 
  • Less amount of rainfall
  • Excessive use of groundwater
  • Global warming
  • Defforestation

25
Protective measures
  • In drought prone areas water harvesting should be
    practiced .
  • Construction of small dams on rivers will be
    useful
  • Drought resistant crops should be grown
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