Test: Natural Hazards And Disasters

Disasters due to landslides, are in general, far less dramatic than due to earthquakes, volcanic eruptions, tsunamis and cyclones but their impact on the natural environment and national economy is in no way less severe.

Landslide is the mass movement of rock, debris or earth down a slope. It includes a broad range of motions whereby falling, sliding and flowing under the influence of gravity dislodges the earth material.

Lahar mudflow or debris flow originates on the slope of a volcano. It is usually triggered by heavy rainfall eroding volcanic deposits, sudden melting of snow and ice due to heat from volcanic vents, or the breakout of water from glaciers, crater lakes or lakes dammed by volcanic eruptions.

During winter, the North-east dry Monsoon winds blow over the Bay of Bengal. Tamil Nadu receives rainfall in the winter season due to northeast trade winds. which causes a flood.

The scheme was implemented in India to check the floods as Domadar river was considered as "River of Sorrow" due to frequent floods.

The cause for floods in India is due to deforestation,colonisation of flood plains and chocking of drainage channels.

Geographical statistics of India show that almost 54% of the land is vulnerable to earthquakes, in which ‘Zone V’ expects the highest level of seismicity whereas ‘Zone II’ is associated with the lowest level of seismicity.

The speed of wave in the ocean depends upon the depth of water. It is more in the shallow water than in the ocean deep. As a result of this, the impact of tsunami is less over the ocean and more near the coast where they cause large-scale devastations.

Earthquakes and volcanic eruptions that cause the sea-floor to move abruptly resulting in sudden displacement of ocean water in the form of high vertical waves are called tsunamis (harbour waves) or seismic sea waves. A tsunami is generated when an earthquake comes or a volcano erupts.