This GSEB Class 8 Social Science Notes Chapter 5 Natural Disasters covers all the important topics and concepts as mentioned in the chapter.
Natural Disasters Class 8 GSEB Notes
→ Natural disasters are of two types:
- those which occur due to changes In the interior of the Earth. E.g. earthquakes, tsunamis, etc. and
- those which occur due to changes on the surface of the Earth. E.g. floods, cyclones, forest fires, etc.
→ Due to catastrophic (sudden) movements like collision of plates in the interior of the earth or heavy pressure, the weak upper crust of Earth experiences sudden tremors. This is called ‘earthquake’.
→ The place from where the earthquake originates is called its Focus or Hypocentre, and it is located in the interior of the Earth. The place exactly above the focus on the surface of the earth is called Epicentre.
→ A Seismograph is used to find the Epicentre and measure the intensity of an earthquake.
→ There are three main reasons for occurrence of ‘ earthquakes. These are:
- Volcanic eruptions
- Strike-slip faults and
- Subduction in an active subduction zone.
→ Volcano is a fissure or a vent in the weaker rock strata of the crust of the Earth. During the volcanic eruption, rock material, ash, water vapour, gases and hot magma, etc. are thrown upwards towards the surface through this vent.
→ Volcanoes are caused due to
- High temperature in the interior of the Earth,
- Creation of magma
- Creation of gases and vapour and
- Rising of magma towards the Earth’s surface.
→ Magma is pushed upwards by the gases underlying it. Water trapped under the surface turns into vapour which in turn pushes the magma upwards.
→ Finally the gases, vapour and magma erupt through the vent with great force in the form of lava, ash, gases, rock pieces, etc. This is known as ‘Volcano’.
→ After the eruption, volcanic residuals like rock material, ash, magma, etc. are deposited around the vent and they form a conical hill like formation. Frequent eruptions create a tall and larger hill. This is called a volcanic mountain / hill.
→ There are three types of volcano:
- Active volcano
- Dormant (latent) volcano and
- Extinct (dead) volcano.
→ Volcanic eruptions cause massive destruction in local areas.
→ Volcanoes have certain benefits. Fertility of soil increases due to lava. So agriculture benefits.
→ Due to a volcanic eruption or an earthquake below I the surface of the oceans, very large, powerful and extremely high waves are created. They are known as ‘Tsunami’ waves. When these large waves strike the coast with great speed and force, they cause very heavy devastation.
→ Oceanic storms, the breaking of a large rock mass or a glacier or a meteoritic fall may create devastating waves. When the storm is over, these waves gain great height and can travel great lengths to reach the coastal region where they cause very heavy damage. This is also a ‘tsunami’.
→ Excess flow of water in a river is known as ‘flood’.
→ Scanty or almost no rainfall for 2-3 years continuously is known as ‘famine’.
→ Cyclone: Air that blows at very high speed. It is also known as storm or whirlwind. The coastal areas especially the Eastern Coast of India experiences cyclones every year.
→ ‘Forest fires’ which cause great damage to forest resources are caused due to friction between dry branches of trees in dense forests and other reasons.
→ Landslides : Sudden sliding of large masses of rocks, soil, etc. down the side of a mountain is known as a landslide.