CBSE Class 9, Disaster Management
Chapter 4, Specific Hazards and Mitigation
NCERT (CBSE) answers of Class IX Disaster Management Textbook Exercise Questions
Question.1: How do soils affect vulnerability to an earthquake?
Answer: Soils affect vulnerability to an earthquake to a great extent. If the settlements are made on alluvial or wind blown soil deposits there is ever likelihood of their destruction by landslides or earthquakes. Building should always be made on solid soils.
Question.2: describe the beneficial effects of flooding.
Answer: Except for a few instances, floods have mostly harmful. The few beneficial effects of flooding are the following:
(i) Sometimes the rivers spread a layer of fertile soil in the surrounding areas.
(ii) The ponds and pits filled by river water help pisciculture and promote the fish-culture.
Question.3: How sand bag stacking are built and what makes them more effective?
Answer: In order to control floods sand bag stacking prove very useful. They keep the flood water away. When sand bags are stacked one above the others, they act as a wall to keep the flood water away.
Question.5: What are ‘Cyclones’?
Answer: Cyclones are violent storms of vast extent characterized by high winds rotating about a calm center low atmospheric pressure.
Question.6: Which are the areas generally prone to landslides?
Answer: Landslides are common in mountainous regions especially those which are situated along the river banks or near the coastline. The flow of water continuously goes on doing the eroding work which results in landslides sooner or later. Especially when the rivers are in flood they greatly add to landslides.
In India, landslides are common in the mountainous regions of the north and north-eastern parts.
Question.7: What are the causes (common factors) of landslides?
Answer: Causes of landslides
(1) When some mountain ranges, like those of Shivalik hills in the Himalayas, are made up of loose or not-so-compact sediments then there exists a possibility of sliding down part of such hills during heavy rains or due to gravitational pull of the earth.
(2) The rivers flowing through these ranges (hills) go on weakening the foundation of the hills sometimes resulting into a collapse or landslide at any time.
(3) Sometimes human activities also contribute to the landslides especially when they build heavy structures on these unconsolidated hilly lands. Under the weight of these structures sometimes, these hills give way to landslides.
(4) Rapid deforestation is also responsible for causing landslides.
Question.8: What steps can be taken to control floods? Or,
Describe the different types of flood control measures.
Answer: Floods are natural hazards but if we are prepared to deal with them in time we can check them from becoming a disaster. The various steps of flood control are given below -
(1) Proper arrangements should be made in advance for evacuating people to safer places.
(2) If proper warning is given to the people in time, many lives and properties can be saved. In this connection TV and Radio can be of immense help.
(3) For those people who were still caught in floods, food, drinking water, medicine etc. should be air-dropped to them.
(4) Proper embankments should be made to check advancing water.
In this way by following different flood control measures, we can reduce the risks and damages of floods.
Question.9: What are Tropical Cyclones? Describe their general characteristics.
Answer: Intense storm which develop over warm tropical oceans between 5O and 20O north latitudes and between 5O and 20O south latitudes are called tropical cyclones.
General characteristics of the Tropical Cyclones
(1) These tropical cyclones are violent storms.
(2) They are often of vast extent and are characterized by high winds.
(3) The center of these winds is a low pressure area, so wind with higher pressure all around rushes towards the center. But due to the rotation of the earth these winds assume a circular form. In the northern hemisphere, these cyclones blow in anti-clockwise direction and in the southern hemisphere, they blow in clockwise direction.
(4) These winds blow with a great velocity which often exceeds 100 km per hour. Since these winds blow with a great force towards the center, so this center goes on continuous shifting from one place to another.
(5) These winds are known with different names in different parts of the world e.g. ‘hurricanes’ in North America, ‘typhoons’ in Asia etc.
(6) According an estimate about 100-120 tropical cyclones develop throughout the world every year.
(7) In India these cyclones originate between 10ON and 15ON latitudes both in the Bay of Bengal and the Arabian Sea. It has been observed that the frequency of the cyclones in this region is the most as compared to other parts of the world.