Hazards and Natural Disasters

source: https://www.tes.com/lessons/AtWMzefELBHSiQ/natural-disasters


  • The situation that brings a threat to life, health, property or environment
  • e.g of Natural Hazards: flood, volcanic eruption, earthquake, cyclone etc.

Natural disaster:

  • When natural hazards destroy people‚Äôs life & livelihood, they are called natural disasters.

Causes for natural disasters:

1.Geographical: are out of our control

e.g. Earthquake, Volcanic eruption

2.Meteorological: can be controlled to some extent by our efforts

e.g. flood & hurricanes

Types of Disasters:

1. Natural: caused by natural energies

a. Major Natural Disasters: e.g. flood, cyclone, drought, earthquake

b. Minor Natural Disasters: e.g. cold waves, heat waves, thunder storms

2. Anthropogenic (Manmade) : caused by human activities

a. Major Manmade Disasters: e.g. setting of fire, epidemics, deforestation, pollution etc.

b. Minor Manmade Disasters: e.g. accidents, riots, food poisoning etc.

Disaster Management Cycle:

The steps of disaster management cycle are:


  • Activities prior to a disaster come under preparedness.
  • Planning for facing the disaster, emergency exercises and trainings, management of warning systems, conduction of public awareness programs, storage of relief materials come under this step.


  • Activities done during a disaster come under response.
  • Conduction of public warning systems, emergency operations, search and rescue comes under this step.


  • Activities done following the disaster come under recovery step.
  • Disaster management, temporary housing, claim processing and grants, management of hygienic food, clean water, medicines, clothes for victims comes under recovery.


  • Activities that reduce the effects of disaster come under mitigation.
  • Process of building codes and zoning, vulnerability analysis, public education comes under mitigation.

Some Natural Disasters:

  1. Snow-slide:
  • Rapid flow of snow down a sloping surface is called snow-slide.
  • When the force of gravity exceeds on a mechanically weak snow pack, it accelerates downwards in the form of snow-slide.

Causes of snow-slide:

  • Climate change or global warming
  • Earthquake
  • Use of explosives
  • Volcanic eruption under snow.

Effects of snow-slide:

  • Causes deforestation, floods and loss of life and property.
  • Destroys human settlements and reduces wildlife.
  • Destructs road, hydro-electric projects and communication system.

Preventive measures of snow-slides:

  • Avalanche prone areas should be identified and afforestation should be done.
  • The residents should be guided about the emergency evacuation shelters and awareness programs should be conducted.
  • Relief materials should be pre-managed.
  • Explosive techniques should be used in controlled manner.

2.Glacial Lake Outburst Flood (GLOF):

  • Glacial lakes are found in the Himalayan regions. In winter, the water of the glacial lakes is changed into snow and it looks like a plain of snow. But in summer, the ice caps melt and due to visible water, it looks like a lake.
  • When a glacier erodes the land and melts filling the space, glacial lakes are formed. The water of glacial lakes comes out due to different reasons, it causes flood in the rivers and the area around them. This is called a glacial lake outburst flood or GLOF.
  • Potentially dangerous glacial lakes of Nepal are Tsho Rolpa, Dig Tsho, Lower Barun and Thulagi. According to recent study of ICIMOD, there are 20 potentially dangerous glacial lakes in Nepal.

Causes of GLOF:

  • Erosion of the rocks damming the glacial lakes.
  • Avalanche of rocks or heavy snow mass in a glacial lake.
  • Earthquake

Effects of GLOF:

  • Causes flood in the nearby rivers and landslides.
  • Destroys human settlements, cultivable land and wildlife.
  • Causes loss of life and property.

Preventive measures of GLOF:

  • A regular monitoring should be done to identify dangerous glacial lakes.
  • In case of critical condition of a glacial lake, gradual outlet of water of lake should be managed.
  • Warning system should be managed to make the people of the region, who can be affected by GLOF, alert. The region should be evacuated to protect its life and property.

Hurricane or Cyclone (Greek= Cyclos i.e. coils of snake)

  • A hurricane is a migratory tropical cyclone that originates over the ocean in certain regions near the equator.


Name Place of Origin
Hurricane Northern Atlantic and Eastern Pacific Ocean
Typhoon North- Western Pacific Ocean
Willy-willy Southern- Pacific Ocean


  • It forms in doldrums i.e. the region between 50 to 250 north and south latitude from the equator.
  • It has the highest pressure at its margins and the lowest pressure at its centre. The area of few kilometers around the central region of a hurricane is called the eye of the storm. It is oval in shape and has radius about 20-40km.
  • The decreasing size of the eye shows the increasing strength of the hurricane.
  • The size of hurricane is measured in terms of radius of the hurricane i.e. the distance between the eye and its marginal than 900km.
  • It is migratory and can come over land also. e.g. Gilbert, Hundhund, Haiyan, Pam etc.
  • The strength of a hurricane is measured in Sofir-Simpson scale which ranges from 1 to 5.
  • Mildest category 1= 120km/hr (wind velocity)
  • Strongest category 5= 250km/hr
  • Hurricane of magnitude 3 cause loss of lives and property in large scale.

Cause of Hurricane:

  • When ocean water at a region gain the temperature of 26.50C to the depth of about 50ms, it reduces the atmospheric pressure of that region. It is the beginning of the hurricane.
  • Due to the development of low pressure centre, the warm saturated air in the doldrums is forced upwards by denser cooler air.
  • The atmospheric pressure drops sharply from the edge of the storm towards its centre and the wind velocity rises.
  • The wind attains maximum force to the point of the lowest pressure. It is about 724mm Hg (or torr).
  • The wind becomes a hurricane only when it gains the speed of 120km/h.
  • The temperature of the central region of hurricane is found to be higher than in the marginal region. This forms a convectional current that helps to conduct the regular movement of air in the hurricane.

Effects of Hurricanes:

  • Storm-surge or sea-surge (increase of sea level due to hurricane upto 7m high) causes floods which sweep life and property.
  • All means of transportation in the ocean is not suitable during a hurricane. It may sink even a very strong ship.
  • It sometimes causes a heavy rainfall and landslides.
  • It deposits debris in fertile lands and turns them infertile.

Preventive measures against a hurricane:

  • The government should predict the time, direction and magnitude of hurricanes with the help of hurricane monitoring centres.
  • The structures made in coastal regions must be strong.
  • Emergency shelters should be constructed near oceans to save the lives of the people.
  • The people of the particular region must follow the instruction given through different media.

Author: Sulaksha Purna Shrestha

Hazards and Natural Disasters