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NCERT Class 11 Geography Chapter 23 Natural Hazards and Disasters
Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. CBSE Class 11 Geography Solutions are part of All Subject Solutions. Here we have given NCERT Class 11 Geography Part I: Fundamentals of Physical Geography, Part II: Indian: Physical Environment, Part III: Practical Work in Geography. NCERT Class 11 Geography Chapter 23 Natural Hazards and Disasters Notes, NCERT Class 11 Geography Textbook Solutions for All Chapters, You can practice these here.
Natural Hazards and Disasters
Chapter: 23
GEOGRAPY [ PART – II ]
SHORT ANSWER TYPE QUESTIONS
Q.1. What are natural hazards?
Ans. Changes that affect humans adversely are called natural hazards.
Q.2. Name some common natural hazards.
Ans. Some common natural hazards are: Volcanic eruptions, earthquakes, tsunamis, droughts, floods, cyclones, soil erosion, mudflows etc.
Q.3. What are disasters?
Ans. Sometimes natural hazards are called disasters. Disaster is a clamity or tragedy or a consequences of a hazard that causes great loss to the human life and property.
Q.4. What is the magnitude of an earthquake?
Ans. Magnitude measured on the Richter scale is a measure of the seismic by an earthquake. energy radiated
Q.5. What is the intensity of an earth-quake?
Ans. The intensity is the measure of damage caused by the earthquake.
Q.6. What is the average speed of a cyclone and its normal duration?
Ans. The average speed of a cyclone is 20 km/h, and the duration is about 5 to 7 days.
Q.7. Name two human causes that have increased the incidence of flood in India.
Ans. The human factors that have increased the incidents of floods are: Deforestation, drainage congestion (caused by badly planned construction of bridges, roads, railway tracks and other developmental activities).
Q.8. Name some of the problems caused by drought.
Ans. Drought leads to scarcity of food grains, water, fodder. Famine, the effect of drought, leads mass migration of human and livestock.
Q.9. What is landslide?
Ans. A landslide is the rapid sliding of large masses of bed rocks or regoliths.
Q.10. What is disaster management?
Ans. The term ‘disaster management’ includes all aspects of preventive and protective measures, preparedness and organisation of relief operation for mitigating the impact of disaster on human beings and socio-economic aspects of the disaster-prone areas.
Q.11. What is the cause of floods?
Ans. Heavy rainfall and cyclones.
Q.12. Why do major floods not occur in southern peninsula?
Ans. The rivers are seasonal.
Q.13. Name the different units of land-slides.
Ans. Slumps, rockslides, rockfall.
Q.14. Name three states which are affected by cyclones.
Ans. Orissa, Andhra Pradesh, Tamil Nadu.
Q.15. What is the main cause of droughts?
Ans. Uncertain, variable rainfall and high temperature.
Q.16. To which theory are the earthquakes related?
Ans. Plate tectonics.
Q.17. On which scale is the intensity of earthquake measured?
Ans. Mercalli Scale.
Q.18. Name high and very high risk seismic areas of India.
Ans. The high risk seismic areas are the Ganga plains and western Rajasthan. Very high risk seismic areas are Himalayan mountains, north eastern India, Katchchh, west coast around Ratnagiri and Andaman and Nicobar islands.
Q.19. What are the major natural hazards occurring in India?
Ans. Natural disasters or hazards are the results of sudden earth movements which change the face of earth in short period causing heavy loss of life and property. Droughts, floods, tsunamis, cyclones, landslides and earthquakes are some of the major natural hazards occuring in India.
Q.20. Mention flood-prone areas of India.
Ans. The most flood-prone basins in the country are those of the Ganga plain in Uttar Pradesh, Bihar and West Bengal, the Brahmaputra in Assam and the Baiterni, the Brahmani, and the Subarnarekha basins in Orissa. Sometimes floods occur also in Andhra Pradesh, Rajasthan, Haryana and Gujarat.
Q.21. How have embankments worsen the problem of floods?
Ans. Due to the construction of embankments, the river water spreads out of the river stream. The width of the river stream becomes narrow and floods occur.
Q.22. Mention some effects of landslides on humans.
Ans. The formation of new slopes is usually the consequence of landslides and mass wasting. The rivers often get blocked by the debris brought by landslide. Birahital in Garhwal was formed in 1983. Landslides damage the property and disruption of communication.
Q.23. How can humans live with earth- quakes? Suggest some measures.
Ans. There is a need to develop special types of structures and buildings in high risk seismic zones. People should be advised to construct earthquake-resistant houses and buildings in such areas.
SHORT ANSWER TYPE QUESTIONS
Q.1. When can a hazard become a disaster?
Ans. Any hazard can become a disaster when the magnitude of destruction and damage caused by it is very high.
Q.2. Why are there more earthquakes in the Himalayas and in the north-eastern region of India?
Ans. The Indian plate is moving at a speed of one centimetre per year towards north and north eastern direction and it is obstructed by Eurasian Plate. The sudden release of energy causes earthquakes along the Himalayan arch. That is why there are more earthquake areas in the Himalayan and north-eastern region.
Q.3. How are the floods in eastern India different from the ones in western India?
Ans. The floods in eastern India are different from the ones in western India. The floods are frequent in eastern India because of its nature and regularity while the floods are not so frequent and regular in western India.
Q.4. Why are there more droughts in the central and western India?
Ans. In central and western India, the droughts are more frequent because:
1. The monsoons do not occur in these areas frequently.
2. The rainfall is about 75 cm per annum.
3. The intensity of monsoon winds becomes weak as they reach in these areas.
Q.5. What are the basic requirements for the formation of a cyclone?
Ans. The basic requirements for the formation of a cyclone are as under:
1. Large and continuous supply of warm and moist air.
2. Strong Coriolis force.
3. Unstable condition through the troposphere that creates local disturbances around which a cyclone develops.
4. Absence of strong vertical wind wedge.
Q.6. What are the basic requirements for the formation of a cyclone?
Ans. The following are the basic requirements for the formation of a cyclone:
(i) Temperature of the oceanic surface over 26°C.
(ii) Appearance of a closed isobar.
(iii) Low pressure dropping below 1000 mb.
(iv) Areas of circular movement first spreading to a radius of 30-50 km then increasing gradually to 100-200 km and even to 1000 km.
(v) Vertically the wind speed first rising to a height of 6 km then much higher.
Q.7. Suggest some measures which may reduce the incidence of landslides.
Ans. To minimise the incidents of landslides, the following steps should be taken:
1. Trees should be planted on the slopes of the mountains.
2. Road construction should not be done on the slopes of the mountains.
3. The slopes of the mountains should not be levelled.
Q.8. Describe the factors that affect the intensity of disasters in a country.
Ans. The intensity of disasters is governed by the following factors:
1. Historical and social conditions and the level of economic development of a country or a region affect their vulnerability.
2. The scope of damage that natural hazards may cause depends upon the type of land use.
3. The scope of disasters depends on the geographical position of a country or an area.
4. Natural hazards are often not so dangerous when taken separately.
Q.9. What is drought? During drought which human values help to cop-up with?
Ans. The term drought is applied to an extended period when there is a shortage of water availability due to inadequate precipitation excessive rate of evaporation and over utilisation of water from the reservoirs and other storages including ground water.
During drought the values which help to cop up with the drought are stocks of foodgrains and aid programmes of central and state governments as well as those voluntary organisation. Drought Research unit was also set up to understand the climatology of drought in 1967.
Q.10. Distinguish between:
(i) Hazards and Disasters.
Ans. Hazards and disasters are closely related and are sometimes synonymous to each other. A hazard is a threat while a disaster is an event. Natural hazards that cause great loss to human life and economy are called disasters. Changes that affect man adversely are called natural hazards.
(ii) Aridity and drought.
Ans. Drought can occur in any area regardless of the amount of rainfall the area may receive. It can occur in small pockets or over a large area. Aridity is a permanent condition whereas drought is a temporary situation.
(iii) River levee and embankments.
Ans. River levees are the natural embankments of the river, while the embankments are built by man.
(iv) Landslide and mass wasting.
Ans. Landslide: A landslide is the rapid sliding of bed rock or regoliths. These are caused by earthquake or sudden rock failures. Landslide is a hazard.
Mass wasting: Natural removal of soil and rock from slopes is known as mass wasting.
(v) Magnitude and intensity of earthquakes.
Ans. Magnitude: The magnitude, measured on the Richter scale is a measure of the seismic energy radiated by earthquake.
Intensity: The intensity is the measure of the damage caused by the earthquake and is measured on Mercalli Scale.
LONG ANSWER TYPE QUESTIONS
Q.1. When can developmental activities become the cause of disasters?
Ans. Disasters are caused also by some human activities. Some activities carried out by human beings are directly responsible for man-made disasters. These are development activities which become the causes of disasters, sometimes. Example:
1. Bhopal gas tragedy.
2. Chernobyl nuclear disaster and wars.
3. Release of CFCs and increase of green-house gases.
There are some other activities of human beings that accelerate or intensify disasters indirectly. Landslides and floods are due to deforestation, unscientific land use and construction activities in fragile areas.
Q.2. Identify the landslide-prone regions of India and suggest some measures to mitigate the disasters caused by them.
Ans. The landslide-prone regions are:
1. Areas of Himalayas and Andaman and Nicobar islands.
2. High rainfall regions with steep slopes in Western Ghats and Nilgiri hills.
3. North eastern region.
4. Landslides due to the mining and subsidence are most common in the states like Jharkhand, Orissa, Chhattisgarh, Madhya Pradesh, Maharashtra, Andhra Pradesh, Karnataka etc. Landslides are determined by highly localised factors.
It is advisable to adopt area specific measures to deal with them. Some measures are as follow:
1. Restriction on construction of roads and dams.
2. Limiting agriculture to valleys and areas of moderate slopes.
3. Terrace farming should be encouraged.
Q.3. What should people do and not do in areas that have been affected by flood?
Ans. The people should do the following in an area that has been affected by flood:
1. Listen to the radio for advance information and advice.
2. Disconnect all electrical appliances and move all valuable personal and house-hold goods and clothing out of reach of flood water if you suspect that flood water may reach the house.
3. Move vehicles, farm animals and movable goods to the highest ground nearby.
4. Prevent dangerous mixing move all insecticides out of reach of the water.
5. Turn off the electric switches and gas if you leave the house.
6. Lock outside doors and windows if you have to leave the house.
Do not’s:
1. Do not enter flood water on foot or in a car if you can avoid it.
2. Never wander around a flood area on your own.
Q.4. What is vulnerability? Divide India into natural disaster vulnerability zones based on droughts and suggest some mitigation measures.
Ans. Vulnerability is the potential for loss or the extent to which an individual, community or place can be affected because of a disaster.
India can be divided into natural disaster vulnerability zones based on droughts as under.
1. Extreme drought-affected areas: These are the parts of Rajasthan, Aravalli hills and Kutchch region in Gujarat.
2. Severe drought-prone areas: These are parts of Eastern Rajasthan, most parts of Madhya Pradesh, eastern parts of Maharashtra, Andhra Pradesh, Karnataka and northern Tamil Nadu.
3. Moderate drought-affected areas: These are northern Rajasthan, Haryana, Southern Uttar Pradesh, remaining parts of Gujarat, Maharashtra, Jharkhand and part of Tamil Nadu.
Measures to mitigate:
1. Identification of ground water potential in the form of aquifers.
2. Transfer of river water from the surplus to the deficit areas and particularly planning for interlinking of rivers.
3. Construction of reservoirs and dams etc.
4. Remote sensing and satellite imageries can be useful in identifying the possible river basins that can be interlinked.
Q.5. What is a landslide? Explain their effects.
Ans. Groundwater increases the weight of the rock or the soil which contains it. Sometimes a mass of earth saturated with water slides down a hill slope causing landslides. There are many varieties of landslides depending on the mass, sliding and the distance traversed by it. Those which move only through short distances are called slumps. When millions of cubic of material moves through thousands of feet distance, they are known as rock slides. When under gravity rock material falls down a high cliff, debris fall or rockfall occurs.
Effects of landslides: Landslides produce great scars on the sides of mountains, and sometimes give a rippled shape to the hillside on account of mixed rock slumps on the back slope. Landslides and rockslides are of frequent occurrence in many mountains. In 1957, such a huge landslide came down in Kashmir. The traffic was suspended for many days. Recently a landslide in Tehri-Garhwal region occurred due to cloud burst.
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