TN 8th Social Science All Unit Question & Answers Tamil medium & English Medium Samacheer Kalvi Guide

8th Social Science Guide Geography Unit 5 Hazards

8th Social Science Guide Geography Unit 5 Hazards

8th Standard Social Science Guide Lesson. Hazards | English Medium

8th Standard Social Science Guide Geography Unit 5 Hazards English Medium Guide Book Back Question and answers download pdf. 8th STD All Subject Guide. Tamil Nadu Start Board Syllabus Samacheer kalvi 8th std all Lesson / Units question and answers. 8th Social Science TEXT Books download pdf. Tamil and English Text books. 8th Standard Tamil Guide.

TN 8th Social Science All Unit Question & Answers Tamil medium & English Medium Samacheer Kalvi Guide


8th Social Science Guide Geography Unit 5 Hazards

I. Choose the correct answer

1. _________ percentage of nitrogen is present in the air.

  1. 09 %
  2. 08 %
  3. 07 %
  4. 63 %

Ans : 78.09 %

2. Tsunami in Indian Ocean took place in the year _________.

  1. 1990
  2. 2004
  3. 2005
  4. 2008

Ans : 2004

3. The word tsunami is derived from _________ language.

  1. Hindi
  2. French
  3. Japanese
  4. German

Ans : Japanese

4. The example of surface water is

  1. Artesian well
  2. Groundwater
  3. Subsurface water
  4. Lake

Ans : Lake

5. Event that occurs due to the failure of monsoons.

  1. Condensation
  2. Drought
  3. Evaporation
  4. Precipitation

Ans : Drought

II. Fill in the Blanks.

  1. Hazards may lead to _________.Ans : Disaster
  2. Landslide is an example of _________ hazard.Ans : Natural
  3. On the basis of origin, hazard can be grouped into _________ categories.Ans : 8
  4. Terrorism is an example of _________ hazard.Ans : Human – made
  5. Oxides of Nitrogen are _________ pollutants which affects the human beings.Ans.: Primary
  6. Chernobyl nuclear accident took place in _________.Ans : 1986

III Match the following.

  1. Primary pollutant – Terrorism
  2. Hazardous waste – Tsunami
  3. Earthquake – Outdated drugs
  4. Meteorological drought – Oxides of Sulphur
  5. Human induced hazard – Reduction in rainfall

Ans : 1 – D, 2 – C, 3 – B, 4 – E, 5 – A

IV. Answer in brief

1. Defne ‘hazard’.

  • Hazards are defined as a thing, person, event or factor that poses a threat to people, structures or economic assets and which maycause a disaster. They could be either human-made or naturally occurring in the environment.

2. What are the major types of hazards?

Hazards are classified as follows.

1. Based on their causes of occurrence.

  • Natural hazards
  • Human-made hazards
  • Socio-natural hazards (Quasi-natural hazards)

2. Based on their origin.

  • Atmospheric hazard
  • Geologic/Seismic hazard
  • Hydrologic hazard
  • Volcanic hazard
  • Environmental hazard
  • Biological hazard
  • Technological hazard
  • Human-induced hazard

3. Write a brief note on hazardous wastes.

  1. The wastes that may or tend to cause adverse health effects on the ecosystem and human beings are called hazardous wastes.
  2. The following are the major hazardous wastes.

Radioactive substance:

  • tools and unused fuel rods of nuclear power plants.


  • synthetic organics, inorganic metals, salts, acids and bases, and flammables and explosives.

Biomedical wastes:

  • hypodermic needles, bandages and outdated drugs.

Flammable wastes:

  • organic solvents, oils, plasticisers and organic sludges.


  • the wastes resulting from ordnance manufacturing and some industrial gases.

Household hazardous wastes:

  • pesticides, waste oil, automobile battery and household battery.

4. List out the major food prone areas of our country.

The following are the major flood prone areas in India.

The major flood prone areas in north and northeast India.

  1. Gangetic plains covering the states of Punjab, Haryana, Uttar Pradesh, North Bihar and West Bengal.
  2. Brahmaputra valley.

Other regions are:

  1. Coastal Andhra Pradesh
  2. Odisha and
  3. Southern Gujarat
  4. Mention the types of drought.

5. Mention the types of drought.

The drought can be classified into three major types as,

  1. Meteorological drought
  2. Hydrological drought
  3. Agricultural drought

6. Why should not we construct houses at foothill areas?

  • As the foothills areas are highly prone to landslide, we should not construct houses at foothill areas.

V. Distinguish the following

1. Hazards and disasters



Hazards are defined as a thing, person, event or factor that poses a threat to people, structures or economic assets and which may cause a disaster.

A disaster is a hazardous event that occurs over a limited time span in a defined area and causes great damage to property/ loss of life, also needs assistance from others.

2. Natural hazard and human-made hazard.

Natural hazard

Human-made hazard

1. A natural hazard is a natural process and event that is a potential threat to human life and property

These are the results of natural processes and man has no role to play in such hazards.

2. The examples of natural hazards are earthquakes, floods, cyclonic storms, droughts, landslides, tsunamis and volcanic eruptions.

The examples of human-made hazards are explosions, hazardous wastes, pollution of air, water and land, dam failures, wars or civil conflicts and terrorism.

3. Flood and drought.



1. Flood is an event in which a part of the earth’s surface gets inundated.

Any lack of water to satisfy the normal needs of agriculture, livestock, industry or human population may be termed as a drought

2.Heavy rainfall and large waves in seas are the common causes of flood.

Low to very low monsoon rainfall is the cause for drought.

4. Earthquake and tsunami.



1. Earthquake is a violent tremor in the earth’s crust, sending out a series of shock waves in all directions from its place of origin.

Tsunami refers to huge ocean waves caused by an earthquake, landslide or volcanic eruption.

2. The primary effects of earthquakes are ground shaking, ground rupture, landslides, tsunamis, and liquefaction.

Tsunamis pose serious danger to the inhabitants of the coastal areas.

VI. Answer in a paragraph

1. Write an essay on air pollution.

  • Air is a mixture of several gases.
  • The main gases are nitrogen (78.09%) for forming products such as, fertilisers for plants and for making the air inert, oxygen (20.95%) for breathing and carbon dioxide (0.03%) for photosynthesis.
  • Some other gases like argon, neon, helium, krypton, hydrogen, ozone, zenon and methane are also present. Besides, water vapour and dust particles make their presence felt in one way or the other.
  • Air pollution is the contamination of the indoor or outdoor air by a range of gases and solids that modify its natural characteristics and percentage.
  • Air pollutants can be categorised into primary and secondary pollutants.

Primary Pollutants :

A primary pollutant is an air pollutant emitted directly from a source.

  1. Oxides of Sulphur
  2. Oxides of Nitrogen
  3. Oxides of Carbon
  4. Particulate Matter
  5. Other Primary Pollutants

Secondary Pollutants :

A secondary pollutant is not directly emitted as such, but forms when other pollutants (primary pollutants) react in the atmosphere.

  1. Ground Level Ozone
  2. Smog

2. Defne earthquake and list out its efects.

Earthquake is a violent tremor in the earth’s crust, sending out a series of shock waves in all directions from its place of origin.

  • They cause loss of human life due to collapse of buildings.
  • Transport is affected due to disruption of railway and road systems.
  • Infrastructure like buildings, dams and bridges develop cracks due to earthquakes
  • Earthquakes have economic effects like setback in trade and agriculture. Assets like houses and other buildings are also destroyed.
  • Problems arise due to shortage of electricity. At the same time, underlying cables are disturbed leading to disruption of communication systems.
  • It becomes difficult to meet basic necessities of people like food and water.
  • Water shortage also leads to rise of epidemics due to lack of proper sanitation.
  • It causes Tsunami which can pose serious danger to the inhabitants of the coastal areas.

3. Give a detailed explanation on the causes of landslides.

Landslide is a rapid downward movement of rock, soil and vegetation down the slope under the influence of gravity. Landslides are generally sudden and infrequent.

1. Natural Causes of Landslides

Climate :

  • A significant upsurge in precipitation or ground saturation would dramatically increase the level of ground water. When sloped areas are completely saturated with water, landslides can occur.

Earthquakes :

  • When earthquakes strike areas with steep slopes, on numerous occasion, the soil slips leading to landslides.

Weathering :

  • Weathering is the natural procedure of rock deterioration that leads to weak, landslide-susceptive materials. When the rocks are weak enough, they slip away causing landslides.

Erosion :

  • Erosion caused by sporadic running water such as streams, rivers, wind, currents, ice and waves wipes out latent and lateral slope support enabling landslides to occur easily.

Volcanoes :

  • Volcanic eruptions can trigger landslides. If an eruption occurs in a wet condition, the soil will start to move downhill instigating a landslide.

2. Human causes of landslides

Mining :

  • Mining activities that utilize blasting techniques contribute mightily to landslides. Vibrations emanating from the blasts can weaken soils in other areas susceptible to landslides. The weakening of soil means a landslide can occur anytime.

Deforestation :

  • Deforestation can also cause natural disasters like landslides. This is due to the fact that there is no forest trees left to hold the soil after deforestation.

4. Elaborately discuss the effects water pollution.

Effects of Biological Oxygen Demand (BOD) :

  • Aerobic bacteria utilizes the dissolved oxygen to decompose the organic wastes thereby depleting the dissolved oxygen concentration. In polluted water, due to abundant growth of algae, the oxygen content becomes lesser, causing the death of fishes and other organisms.

Effects of Pesticides, Detergents and Synthetic Fertilizers:

  • Pesticides are synthetic chemicals used for pest control. A major source of pesticides in water bodies is the runoff from agricultural fields. Pesticides adversely affect a wide range of organisms including insects and fish.

Effects of Hazardous Pollutants (Toxic Metals and Other Chemicals):

  • Inorganic pollutants include arsenic and the metals cadmium, mercury, lead, nickel, zinc and copper. These can kill or sicken fish and other aquatic animals.

Effects of oil spills (Marine Pollution):

  • Oil and grease are also considered serious pollutants of water. Oil spills are a major problem in many coastal waters and can kill or adversely affect fish, phytoplankton and zoo plankton, and birds and mammals.

Effects of Thermal Pollution:

  • A large number of industrial plants use cold water from the rivers and discharge it hot. It may cause direct mortality of fish and other desirable organisms.

Effect of Eutrophication:

  • Eutrophication means the excessive growth of aquatic plants, both rooted and planktonic, to levels that are considered to be an interference with desirable water uses.

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