natural disasters

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NATURAL DISASTERS

• PREPARED BY-
• CLASS-

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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

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Differentiate between natural hazards and natural
disasters
Natural disasters Natural hazards
Extensive devastation Less devastation
In large areas In small area
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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.

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Natural hazards

• Earthquakes
• Volcanic eruptions
• Landslides and avalanches
• Cyclone
• Floods
• Droughts

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earthquake
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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.

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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.

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CONSEQUENCES OF EARTHQUAKE

• It shows that Earthquake is very dangerous to
  humans life.

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VOLCANOEs

• REASONS AND PRECAUTIONS

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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.

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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)

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Landslides
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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

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Protective measures

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

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Cyclones
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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.

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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 .

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A FLOOD

• REASONS AND PRECAUTIONS

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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,

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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.

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A VILLAGE SUFFERING FROM FLOOD

• A FLOOD DOING DESTRUCTION

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Droughts
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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

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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