WBBSE Class 9 Geography Solutions Chapter 6 Hazards and Disasters

Detailed explanations in West Bengal Board Class 9 Geography Book Solutions Chapter 6 Hazards and Disasters offer valuable context and analysis.

WBBSE Class 9 Geography Chapter 6 Question Answer – Hazards and Disasters

Very Short Questions and Answers : (1 mark for each question)

Question 1.
Which type of hazard is easiest to manage?
Answer:
Man-made hazards.

Question 2.
Which force is one of the factors behind the occurrence of avalanches?
Answer:
Gravitational force.

Question 3.
Which type of hazard is a tornado?
Answer:
Natural hazard.

Question 4.
Name a man-made cause for landslides in the mountains.
Answer:
Reckless deforestation.

Question 5.
What type of disaster may occur if absolutely no rain falls for a long stretch of time?
Answer:
Drought.

Question 6.
In which type of climate is snowfall a common affair?
Answer:
Extremely cold climate.

Question 7.
Which instrument is used to measure the intensity of earthquakes?
Answer:
Seismograph.

Question 8.
Which type of hazard is a volcano?
Answer:
Natural hazard.

Question 9.
Name a semi-natural hazard.
Answer:
Landslide.

Question 10.
Name a man-made disaster.
Answer:
War.

Question 11.
Name a flood-prone district in West Bengal.
Answer:
Cooch Behar.

Question 12.
Give a non-tectonic cause of earthquakes.
Answer:
Meteor impact.

Question 13.
Cite a recent example of a very severe cyclonic storm that occurred in India.
Answer:
Hudhud.

Question 14.
Which areas do tsunamis affect most severely?
Answer:
Coastal regions.

Question 15.
Name the wind that influences the occurrence of both droughts and floods in India.
Answer:
Monsoon wind.

Question 16.
Into how many divisions can hazards be classified?
Answer:
Three.

Question 17.
In which year was Uttarakhand affected severely due to a flash flood?
Answer:
2013.

Question 18.
What destroyed the city of St. Pierre in 1902?
Answer:
Volcanic eruption.

Question 19.
Which type of natural hazard occurs when trees rub against each other?
Answer:
Forest fire.

Question 20.
What percentage of the total land area in India is prone to flood?
Answer:
12.

Question 21.
Name a disaster that may result in landslides.
Answer:
Earthquake.

Question 22.
Which kind of disaster can be prevented by adopting proper patterns and methods of land-use on the hill-slopes?
Answer:
Landslides.

Question 23.
Which area of India is mostly affected by tsunamis?
Answer:
Coastal regions.

Question 24.
Which mountain range in India is most prone to earthquakes?
Answer:
The Himalayas.

Question 25.
What are the adverse effects resulting from natural processes of the earth called?
Answer:
Natural hazards.

Question 26.
Which type of disaster may result due to faulty and unscientific methods of farming in the hills?
Answer:
Landslides.

Question 27.
Cite an example of a geological disaster.
Answer:
Earthquake.

Question 28.
Cite an example of a hazard associated with landscape change.
Answer:
River bank erosion.

Question 29.
Which type of disaster are whirlwinds and snowstorms?
Answer:
Atmospheric disaster.

Question 30.
What type of disaster may result due to human intent, negligence or a failure of a man-made system?
Answer:
Man-made disaster.

Question 31.
What are the floods created suddenly in the hills due to heavy rainfall known as?
Answer:
Flash floods.

Question 32.
Name a natural cause of earthquakes.
Answer:
Movement of the earth’s plate.

Question 33.
Name a man-made cause of earthquakes.
Answer:
Nuclear tests.

Question 34.
What is the rapid flow of snow down a sloping surface known as?
Answer:
Avalanche.

Question 35.
Which region in West Bengal is most prone to landslides?
Answer:
The hilly regions in Darjeeling.

Question 36.
What is planning to cope with disasters known as?
Answer:
Disaster management.

Question 37.
Which type of rain causes damage to the aquatic ecosystem?
Answer:
Acid rain.

Question 38.
Which type of hazard may lead to a disaster in the forest regions?
Answer:
Forest fires.

Question 39.
What kind of disaster results from excessive rainfall?
Answer:
Flood.

Question 40.
Into how many divisions can seismic waves be classified?
Answer:
Three.

Question 41.
What type of disaster devastated the city of Bhuj in Gujarat in 2001?
Answer:
Earthquake.

Question 42.
What is the strong wind carrying ice flakes with it known as?
Answer:
Blizzards.

Question 43.
Into how many sub-types can disaster management be mainly classified?
Answer:
Two.

Question 44.
To control which type of disaster does the Ministry of Water Resources play a significant role?
Answer:
Flood.

Question 45.
Which ministry is responsible for dealing with the Integrated Drought Management Programme in India?
Answer:
Ministry of Agriculture.

Question 46.
Name one of the most prominent causes of tsunamis.
Answer:
Earthquake.

Question 47.
What type of disaster is the Phailin?
Answer:
Very severe tropical cyclone.

Question 48.
In which type of drainage basin is the probability of flash floods highest?
Answer:
Circular drainage basin.

Question 49.
Which type of disaster is most prominent in the coastal regions of South Bengal?
Answer:
Cyclone.

Question 50.
On which slopes are avalanches more likely to occur?
Answer:
Convex slopes.

Question 51.
Which type of disaster is most prominent in the Darjeeling district of West Bengal?
Answer:
Landslide.

Question 52.
Which type of disaster is most prominent in the Purulia district of West Bengal?
Answer:
Drought.

Question 53.
Cite an example of a type of severe cyclone.
Answer:
Tornado.

Question 54.
What are deep focus earthquakes known as?
Answer:
Plutonic earthquakes.

Question 55.
Name two important volcanoes in India.
Answer:
Narcondam and Barren.

Question 56.
What is the helpless condition caused due to the occurrence of hazards and disasters known as?
Answer:
Vulnerability.

Question 57.
What is the centre of a whirlwind known as?
Answer:
Eye.

Question 58.
According to the Indian Meteorological Department (IMD) if an area receives less than 75% rainfall then the area is affected by?
Answer:
Drought.

Short Questions and Answers : (2 marks for each question)

Question 1.
What is meant by a hazard?
Answer:
A dangerous condition or event that threatens or has the potential to cause injury to life or damage to property or the environment is known as a hazard. The word ‘hazard’ originates from the word ‘hasard’ in old French and ‘az-zahr’ in Arabic meaning ‘death’. Hazards can be classified into three broad categories- natural, seminatural and man-made.

Question 2.
What is meant by a disaster?
Answer:
According to the Oxford dictionary, a disaster is “a sudden accident or a natural catastrophe that causes great damage or loss of life”. A disaster is an event or series of events that results in casualties and damage or loss of property, infrastructure, environment, essential services or means of livelihood on such a scale that is beyond the normal capacity of the affected community to sustain. A disaster is a combination of hazard, vulnerability and insufficient capacity or measures to reduce the potential chances of risk.

Question 3.
What is meant by natural hazard?
Answer:
A natural event causing a great damage to human life, property and environment is known as natural disaster. Events such as flood, earthquake or hurricane is known as natural hazard.

Question 4.
What is meant by a semi-natural hazard?
Answer:
The hazards that are caused by any combination of natural and man-induced processes are known as semi-natural hazards. For instance, landslide is a seminatural hazard as it can be caused by natural processes (such as heavy or prolonged rainfall, earthquakes, volcanic eruptions, etc.) and can also be caused by man-made activities (such as slope excavation and loading, land use changes, irrigation, and such others).

Question 5.
What is meant by a flood?
Answer:
Flood may be defined as a situation caused due to the overflow of rivers and other water bodies due to excessive rainfall. Floods result in massive water-logging and thus is a threat to human life and property.

Question 6.
What is meant by a flash flood?
Answer:
A flash flood can develop within a few hours of heavy rainfall. Flash floods can be highly dangerous and have the potential to instantly turn a gasping rivulet into a thundering channel of water that sweeps away everything in its path. Most of the casualties from flooding occur as a result of flash floods. The intensity of flash flood cannot be classified. Desert regions are vulinerable to flash floods.

Question 7.
How can dam failure cause floods?
Answer:
Dams are water storage or diversion barriers that seize water upstream in reservoirs. Dam failure involves the overtopping, breach or collapse of a dam. It is an extremely destructive occurrence and in such an event, the energy of the water stored behind even a small dam is capable of causing loss and damage to life and property. For example, in 1977, Tamil Nadu experienced a dam failure from the Kodaganar Dam that led to over-topping by flood waters.

Question 8.
What is meant by a drought?
Answer:
Drought may be defined as a situation caused due to lack of rainfall or scarcity of rainfall for a long period. According to the Indian Meteorological Department (IMD) an area is considered to be affected by drought, if it receives less than 75% rainfall than its normal value.

Question 9.
What is meant by meteorological drought?
Answer:
A drought is categorised as a meteorological drought, when actual rainfall over an area is significantly less than the climatological mean. Definitions of meteorological droughts must be region-specific as the atmospheric conditions that result in deficiencies of precipitation are highly variable from region to region.

Question 10.
What is meant by hydrological drought?
Answer:
A drought is categorised as a hydrological drought, when there is a marked depletion of surface water causing very low stream flow and drying of lakes, reservoirs and rivers. Therefore, hydrological drought is related to the effects of periods of precipitation deficits on surface or subsurface water supply.

Question 11.
What is meant by agricultural drought?
Answer:
The situation when soil moisture is insufficient and results in the lack of crop growth and production, is known as agricultural drought. Agricultural drought has huge impact on the economy of the country.

Question 12.
What is a cyclone?
Answer:
A cyclone is a giant whirlwind or a very strong wind system moving rapidly in a cylindrical or funnel shape about a centre of low atmospheric pressure over tropical or subtropical waters. It advances at a speed of about 30 to 50 kilometre per hour and often brings heavy rain.

Question 13.
What is meant by the eye of a cyclone?
Answer:
The centre of the cyclone is known as its eye. The eye of the cyclone generally remains calm and cloudless.

Question 14.
What is vulnerability?
Answer:
Vulnerability can be defined as the impaired capability of any individual or group to conceive of, cope with, resist and recover from the impact of a natural, semi-natural or man-induced hazard. Vulnerability develops when an individual or a small group is isolated, insecure and defenceless as, before or after they face any hazard, shock or stress.

Question 15.
Name the districts of West Bengal that are prone to drought.
Answer:
The western uplands of West Bengal consisting of the districts of Bankura, Birbhum, Midnapore and Purulia are the most drought-prone districts of the state.

Question 16.
Name the districts of West Bengal that are prone to flood.
Answer:
The flood-prone districts of West Bengal can be classified into two groups-
1. Districts of North Bengal: Cooch Behar, Jalpaiguri, Malda, Uttar and Dakshin Dinajpur.
2. Districts of South Bengal: Nadia, Howrah, Murshidabad, North and South 24 Parganas, Hooghly, Burdwan, Birbhum, West Midnapore and East Midnapore.

Question 17.
What is meant by a landslide?
Answer:
A landslide is the movement of rocks or debris down a slope. Landslides occur when gravitational and other types of shear stress within a slope exceeds the shear strength of the materials that form the slope. Landslides are also known as landslips, slumps or slope failure.

Question 18.
What is meant by a snowstorm?
Answer:
Snowstorm is a severe weather condition where frozen precipitation falls in the form of snow and creates a hazardous condition. It is characterised by low temperature, strong winds and enormous quantities of either falling or blowing snow.

Question 19.
Where do snowstorms mostly occur?
Answer:
People experience snowstorms in middlelatitude to high-latitude areas during winters. The occurrence of snowstorms is most prominent in Antarctica, northern parts of North America, Canada, north of Europe and Asia as well as in the New South Wales in Australia. Also, the snowcapped high mountainous regions also experience snowstorms.

Question 20.
What is meant by a volcano?
Answer:
Volcanoes develop when magma reaches the earth’s surface through an opening in the earth’s crust, causing eruptions of lava and ash. They generally occur at destructive and constructive plate boundaries.

Question 21.
Name the most commonly faced hazards and disasters in West Bengal.
Answer:
The most commonly faced hazards and disasters in West Bengal are drought, flood, landslides and tropical cyclones.

Question 22.
What is meant by a forest fire?
Answer:
A forest fire, also known as a wild land fire or wildfire, is an uncontrolled fire often occurring in forest areas. The blazes are fueled by lightning, volcanic eruptions, pyroclastic flow from active volcanoes, heat waves, droughts, cyclical climate changes such as EI Nino as well as human carelessness. It is observed that more than four out of every five forest fires are humaninduced. Forest fires often begin unnoticed, but they spread quickly at a speed that extends up to 23 kilometre an hour igniting bushes, trees, homes and agricultural resources.

Question 23.
Name the districts of West Bengal that are prone to cyclones.
Answer:
The coastal area in West Bengal mostly faces the wrath of the tropical cyclones. The districts of East Midnapore, North and South 24 Parganas, Howrah, Hooghly and Kolkata are more susceptible to the hazard caused due to tropical cyclone.

Question 24.
What are the three phases in a disaster management cycle?
Answer:
The three phases in a disaster management cycle are-

• Pre-Disaster Phase
• During Disaster Phase
• Post-Disaster Phase

Short Questions and Answers : (3 marks for each question)

Question 1.
What is meant by hazard and disaster?
Answer:
1. A dangerous condition or event that threatens or has the potential to cause injury to life or damage to property or the environment is known as a hazard. Hazards can be classified into two broad categories-natural and man-made.
2. A disaster is an event or series of events that results in casualties and damage or loss of property, environment or means of livelihood on such a scale that is beyond the normal capacity of the affected community to sustain.
3. A landslide that occurs on a hill-slope can be termed as a hazard. But when this same landslide causes casualties and damage to life and property on the slope, it becomes a disaster.

Question 2.
What are the characteristics of a hazard?
Answer:
The characteristics of hazards are as follows –

1. Generally speaking, most hazards are difficult to predict and occur all of a sudden.
2. Hazards may be nature-induced, humaninduced or even a combination of both.
3. The expansion of hazards is generally over smaller areas, and its magnitude is comparatively low.
4. Hazards have the potential for causing injury to life or damage to property or the environment.
5. Hazards with higher potential leads to disasters.

Question 3.
Discuss the causes of man-induced hazards.
Answer:
The hazards that are caused by an element of human intent, negligence or error, or involves a failure of a man-made system are known as man-induced hazards. The notable causes of man-induced hazards are as follows-
1. Unscientific activities: Faulty and unscientific activities of man often lead to man-induced hazards. For instance, unplanned construction of houses on the hill-slopes, faulty farming in the hill-slopes or even carving roads across the slopes of hills intensifies the probabilities of landslides.
2. Illiteracy: Illiteracy leads to lack of knowledge, intolerance and even negligence. All these leads to common man-induced hazards like arson, civil disorder and even terrorist activities.
3. Ungoverned population growth: Ungoverned population growth can lead to competition for scarce resources and susceptibility to diseases, that in turn, may cause civil strife and even loss of human life.

Question 4.
What is meant by flash flood? What are the main causes for the occurrence of flash floods?
Answer:
A flash flood can develop within a few hours of heavy rainfall. Flash floods can be highly dangerous and have the potential to instantly turn a gasping rivulet into a thundering channel of water that sweeps away everything in its path. Most of the casualties from flooding occur as a result of flash floods. The intensity of flash floods cannot be classified.

The most common causes of flash floods are occurrence of heavy rains, dam failure, rapid snow melt and ice jams. The causes of flash floods can be classified into two categories. They are –
Natural causes of flash floods: The natural causes of flash floods are as follows-
1. A flash flood may occur when it precipitates rapidly on saturated soil or dry soil with poor absorption ability. The run-off collects in gullies and streams and as they join to form larger volumes, it often exceeds the carrying capacity of the streams. This may lead to occurrence of flash floods.
2. A flash flood may also occur in areas on or near volcanoes, when glaciers may have been melted by the intense heat after eruptions.
3. Multiple or slow moving thunderstorms occurring over the same area can also produce a flash flood.

Man-induced causes of flash floods: Dam failure is extremely destructive and can create a flash flood. In such an event, the energy of the water stored behind even a smail dam is capable of causing loss and damage to life and property in the downstream areas of the dam.

Question 5.
What are the effects of forest fires?
Answer:
The effects of forest fires can be categorised into two sub-types. They are as follows-
Primary effects of forest fires:

1. Casualties and injury to people and animals who are caught in the flames.
2. Damages to property and possessions.
3. Burning of vegetation and crops.
4. Release of large amounts of smoke.

Secondary effects of forest fires:

1. Health troubles for people as a result of the smoke and ash.
2. Loss of jobs for agricultural workers whose animals and crops get destroyed.
3. Diminution in the tourist industry, leading to loss of jobs and restriction to recreational areas.
4. Soil erosion and landslides because there is less vegetation to bind the soil together.
5. Loss of habitats for animals may lead to extinction of some species.

Question 6.
Discuss the causes of droughts.
Answer:
The causes of droughts can be classified into two categories. They are as follows-
The main natural factors that cause drought:
1. Rise in land and sea surface temperature increases water evaporation leading to droughts.
2. Atmospheric circulation patterns that influence the moisture content of the atmosphere. Reduction in atmospheric moisture in turn will reduce the average precipitation.
3. Soil moisture content can also influence the occurrence of drought. If the soil is dry, then there is little or no water available to evaporate. Consequently, the incoming sunlight can only continue to warm the surface, thereby making conditions hotter and drier, thus beginning the chain of events leading toward drought.

The main man-induced factors that cause drought:

1. Reckless deforestation that leads to decrease in atmospheric as well as soil moisture.
2. Unplanned urbanization that restricts the replenishment of groundwater level and subsequently puts pressure on water resources.

Question 7.
What are the impacts of earthquake?
Answer:
The impacts of earthquakes can be devastating. Some of the most commonly observed impacts of earthquakes are as follows-

1. People may be killed or injured.
2. Built landscape such as houses may be destroyed.
3. Transport and communication links may be interrupted and shops and business may be destroyed. This can subsequently lead to difficulty in trade.
4. Water pipes may burst and water supplies may be contaminated.
5. Fires can spread due to gas pipe explosions that can even lead to forest fires in certain areas.
6. Landslides may occur.
7. Tsunamis may cause flooding in coastal areas.
8. Can lead to social unrest and heedless looting may take place.

Question 8
Discuss about the disaster-prone regions in West Bengal in brief.
Answer:
The disaster-prone regions in West Bengal are as follows-
1. Darjeeling-Himalayan region: This region frequently experiences landslides and floods.
2. Sunderban region: This region frequently experiences tropical cyclones and floods.
3. Plateau region: The areas under Purulia, West Midnapore, Bankura, Bardhaman and western part of Birbhum fall under the plateau region. This region frequently experiences the wrath of droughts.
4. Plain region: The areas that are situated on or near the Ganga plain falls under the plain regions in West Bengal. This region experiences heavy monsoon and thus are prone to flooding.

White the differences between the following –

Question 1.
Natural hazard and Man-made hazard
Answer:
The differences between natural and man-made hazards are as follows-

Points of diference	Natural Hazard	Man-made Hazard
1. Concept	Natural hazards characterise those elements of the physical environment that are detrimental to human beings and are caused by forces extraneous to us.	Man-made hazards are caused by an element of human intent, negligence or error, or involving a failure of a manmade system.
2. Extent	It has a widespread impact.	The extent of impact is lesser, nuclear explosion being an exception.
3. Control	Natural hazards cannot be resisted or controlled but precautions can be taken.	Man-made hazards can be controlled by increasing awareness among communities.

Question 2
Meteorological drought and Agricultural drought
Answer:
The differences between meteorological and agricultural drought are as follows-

Points of difference	Meteorological Drought	Agricultural Drought
1. Concept	Meteorological drought occurs when actual rainfall over an area is significantly less than the climatological mean.	Agricultural drought occurs when inadequate soil moisture produces acute crop stress and affects productivity.
2. Dependency	It is not dependent on agricultural drought.	It is dependent on meteorological drought.
3. Impact	It has a widespread impact.	The extent of impact is lesser than meteorological drought.

Question 3.
Flood caused by Snow Melt and Flood caused by Rain
Answer:
The differences between flood caused by snow melt and flood caused by rain are as follows-

Points of difference	Flood caused by snow melt	Flood caused by rain
1. Extent	Flood caused by melting of snow extends over a larger area.	Flood caused by heavy rainfall extends over a lesser stretch of area.
2. Region	It occurs mostly in the downstream areas of the hill-slopes.	It occurs in the plains, mostly near the river banks.
3. Season	It mostly occurs in summer.	It mostly occurs during the monsoon season.

Question 4.
Hazard and Disaster
Answer:
The differences between hazards and disasters are as follows-

Points of difference	Hazard	Disaster
1. Concept	A dangerous condition or event that threatens or has the potential for causing injury to life or damage to property or the environment is known as a hazard.	A disaster is an event or series of events that results in casualties and damage or loss of property, infrastructure, environment, essential services or means of livelihood on such a scale that is beyond the normal capacity of the affected community to sustain.
2. Extent	The extent of impact is limited to a smaller region.	The extent of impact runs to a comparatively larger area.
3. Nature	Hazards lead to disaster.	Disasters are impacts of hazards.
4. Casualty	Hazards have the potential for causing injury to life, but may not always be fatal.	Disasters result in casualties.
5. Economic damages	Accounts for damage or loss of property that is lesser in comparison to disasters.	Accounts for damage or loss of property that is at a scale which is beyond the normal capacity of the area to sustain.
6. Sub-types	Hazards can be classified into three broad categories-natural, semi-natural and man-made.	Disasters can be classified into two broad categories – natural disaster and man-made disaster.
7. Control	Hazards are manageable and precautions can be taken to a certain level.	Disasters are unmanageable and precautions cannot be taken most of the times.

give reasons for the following –

Question 1.
Mountainous regions are prone to landslides.
Answer:
A landslide refers a sequence of processes that results in the downward and outward movement of slope-forming materials like rocks, soil, artificial fill or a combination of all these. Landslides are mainly associated with mountainous regions. This is because of the following reasons-
1. Geological causes: Weak or sensitive materials of the hill-slopes and the abundance of weathered materials make the mountainous regions prone to landslide.

2. Climatic causes: Mountainous regions are inclined to freeze-thaw cycles and wetter conditions promote organic activity and associated weathering. Soil slopes and rocks are weakened through saturation by heavy rains or snow melt. Moreover, winter snowstorms may produce avalanche-like conditions. All these together cause a landslide-prone condition.

3. Human causes: Landslides are frequently caused by the undercutting of slopes during road construction or when fill materials are dumped onto already less stable slopes. Defectively constructed mine tailing piles, dams and waste landfills may result in landslides. Construction of houses on hillslopes and reckless deforestation are the most commonly observed causes of landslides in the hills.

Question 2.
The Himalayan regions are prone to earthquakes.
Answer:
The Himalayan mountain range was formed due to the collision of Indian and Eurasian plates – a process that began at least 50 million years ago. Where the two plates converge, the Indian plate plunges below the Eurasian. The two plates continue to rub against each other due to the northward movement of the Indian plate-this continuously generates immense geological stress. This builds up pressure, leads to seismic vulnerability and is later released as earthquakes.

The east-west lying fault line that separates the two plates is known as the Main Himalayan Thrust (MHT). Since there is no historical evidence of earthquakes in several portions of the Himalayan arc, it is predicted that, there is potential energy available to generate large earthquakes.

Question 3.
Adoption of disaster management techniques can be used to reduce the after-effects of a disaster.
Answer:
Occurrence of most natural disasters cannot be stopped but measures can be taken to reduce the after-effects. The organization and management of resources and responsibilities for dealing with all humanitarian aspects of emergencies, in particular preparedness, response and recovery in order to lessen the impact of disasters is termed as disaster management. The procedures to be followed are as follows-
Preventive measures: Even before the actual disaster occurs there are some prior measures that can be taken to reduce the intensity of the disaster. Such as

• Conducting awareness programmes
• Compiling suitable laws
• Conducting proper regional surveys and preparing maps
• Forecast of the disaster can be transmitted through radio and television channels to the common people.

Remedial measures: These measures are taken once the disaster has hit a region. There are two stages of remedial measures-

1. The first stage involves rescue and recovery of the affected people and providing them with relief facilities like food, medicine, clothing, temporary houses and such others.
2. The second stage involves working towards recovery in order to lessen the impact of disasters and revert to normal conditions. The measures taken under this stage is re-establishing the communication systems, rebuilding the roads, houses, schools and working toward’s supply of electricity, safe drinking water.

Long Questions and Answers : (5 marks for each question)

Question 1.
Classify hazards.
Answer:
A dangerous condition or event that threatens or has the potential for causing injury to life or damage to property or the environment is known as a hazard. Hazards can be classified into the following types-

The following broad categories of disasters are discussed below-

1. Natural hazard: Natural hazards characterise those elements of the physical environment that are detrimental to human beings and are caused by forces extraneous to us. More precisely, the term ‘natural hazard’ refers to all atmospheric, hydrological and geological phenomena that, because of their location, intensity and frequency have the potential to affect adversely the human beings, their constructions or their activities.

2. Semi-natural hazard: The hazards that are caused by any combination of natural and man-induced processes are known as the semi-natural hazards. For instance, landslide is a semi-natural hazard as it can be caused by natural processes (such as heavy or prolonged rainfall, earthquakes, volcanic eruptions, slope undercutting by rivers) and can also be caused by man-made activities (such as slope excavation and loading, land use changes, irrigation, blasting vibrations, water leakage from utilities and such others).

3. Man-made hazard: Man-made hazards are caused by an element of unscientific human activity, negligence or error, or involving a failure of a man-made system. Man-made hazards can be controlled by increasing awareness among communities.

Question 2.
Classify and explain the various types of disasters.
Answer:
A disaster is an event or series of events that results into casualties and damage or loss of property, infrastructure, environment, essential services or means of livelihood on such a scale which is beyond the normal capacity of the affected community to sustain. External aid is usually needed to combat disasters

Natural disaster: An event or series of events that results in casualties and damages by natural causes are known as natural disasters. They can be classified as follows –
1. Geophysical disaster: The disasters that are caused due to tectonic disturbances are called geophysical disasters. Earthquakes and volcanoes are examples of geophysical disasters.

2. Landform-process related disaster: Landform processes like riverbank erosion, landslides in mountainous areas, coastal erosion due to sea waves, etc., may give rise to disasters if they occur on a macro-scale.

3. Meteorological/Climatic disaster: The disasters originating from events caused by short or long lasting periods of climatic variability processes come under this category. They include both hydrological as well as meteorological events.

Storms, tropical cyclones, heat/cold waves, floods and droughts are examples of climatic disasters.

4. Extra-terrestrial disaster: Meteorite strikes are examples of extra-terrestrial disasters.

Man-made disaster: An event or series of events that results in casualties and damages by man-induced causes are known as man-made disasters. They can be classified as follows –

1. Technology-related disaster: A technology-related disaster is the failure of modern systems, viz., unchecked exhaust fumes from vehicles, untreated wastes from industries, leakage of radioactive minerals from nuclear power plants, etc., which harms people and also pollutes the environment.
2. Economic disaster: An economic disaster is the widespread disruption or collapse of a national or regional economy, possibly causing financial loss, hoarding, famine, inflation, etc.
3. Biological disaster: Disasters caused due to the exposure of human beings to toxins, viruses leading to epidemics, are known as biological disasters. Extinction of any species is also possible.
4. Disasters due to other complex emergencies: These involve a breakdown of administration, riot, religious conflicts, war. etc.

Question 3.
What is meant by flood? Briefly discuss the main causes of a flood. [1 + 4]
Answer:
A flood occurs when water overflows and inundates the land that is usually dry. There are various reasons for floods to occur. The most common is overflowing of the rivers and streams due to heavy rains, a broken dam or rapidly melting ice in the mountain regions. Floods are the second-most widespread natural disaster on earth, after wildfires. About 12 % of the total land mass in india is prone to floods. West Bengal is one the most flood-prone states of India. The flood-prone areas of West Bengai include low-lying areas, coastal regions and settlements along rivers downstream from dams. The flood-prone districts of West Bengal can be classified into two groups-
1. Districts of North Bengal: Cooch Behar, Jalpaiguri, Malda, Uttar and Dakshin Dinajpur.
2. Districts of South Bengal: Nadia, Howrah, Murshidabad, North and South 24 Parganas, Hooghly, Burdwan, Birbhum, West Midnapore and East Midnapore.

The main causes of a flood are as follows-
1. Natural causes:
1. Excessive precipitation: Excessive levels of precipitation occurring over a prolonged period of time causes floods. Due to this excessive rainfall, the river’s discharge exceeds the capacity of its channel to carry that discharge. Thus the river overflows its banks causing floods. Therefore, excessive precipitation is positively related to flood.

2. The shape of a river course: The probability of flooding increases if the course of a river is meandering rather than straight since the flow of the river is hindered by obstacles along its course and hence overflowing occurs.

3. Snow melt: During the warm summers, the glacial snow in the mountains melt down. This results in the flow of large amounts of water downslope within a short period of time. As the ground is almost frozen, water cannot penetrate and be absorbed. The water therefore, flows off the surface and runs into lakes, streams and rivers. This cause excess water to spill over the respective banks and cause snow-melt floods.

4. Shape of the drainage basin: The possibility of flash floods increases in a drainage basin that is circular in shape rather than in an elongated drainage basin. This is because, in the latter case, rivers have the capacity to carry water over longer distances.

5. The relief of the land: The areas with steep slopes are less susceptible to flood as the rain water flows down the slopes. But the plain lands where the rain water cannot flow down the slopes are more susceptible to flood and water logging.

Man-made causes:

1. Deforestation: Vegetation type and cover play major roles in causing flood, with forests intercepting more rainfall than grasses. This interception enhances

the lag time and reduces the risk of a flood. Deforestation can increase soil erosion, reduce interception and increase the impact of floods.

2. Modification of the catchment area: The land-use pattern of the catchment area changes with development of increasing number of settlements, urbanisation, industrialisation and also change in agricultural patterns. All these may subsequently lead to flooding.

3. Change in the course of the river: Artificial modification in the course of a river such as construction of dams, development of irrigation system and such others to satisfy human needs may also lead to flooding in the long run.

Question 4.
What is meant by vulnerability? Discuss the main characteristics of a disaster. [2 + 3]
Answer:
Vulnerability can be defined as the impaired capability of any individual or group to conceive of, cope with, resist and recover from the impact of a natural, semi-natural or maninduced hazard. Vulnerability is a relative and dynamic concept. Vulnerability develops when an individual or a small group is isolated, insecure and defenseless, before they face any hazard, shock or stress. In this context, more preparedness to face a disaster means lesser vulnerability.
The main characteristics of a disaster are as follows-
1. Distressed public life: The normal public life and activities are hampered and disrupted because of a disaster.
2. Casualties: A large number of human and animal life is devastated by a disaster. Damages and loss of property also take place.
3. Magnitude: The magnitude of a disaster is not always the same. They vary from intense to moderate.
4. Speed of occurrence: Disaster can be slow and predictable, or they may even be sudden and temporary.
5. Affects the environment: The negative environmental effects of the disasters are by and large severe and persist for long.
6. Disfunctioning of essential services: The functioning of essential services such as transport and communication gets disrupted.
7. Vulnerability: A disaster is a combination of hazard, vulnerability and insufficient capacity or measures to reduce the potential chances of risk.

Question 5.
What are the major impacts of a flood? Name the flood-prone districts of West Bengal. [4 + 1]
Answer:
The major impacts of a flood can be divided into two categories. They are as follows-
The negative impacts of a flood: The various negative impacts of a flood are as follows-
Impact on physical nature:

• Can cause water pollution,
• disrupts the environmental balance,
• can cause soil pollution.

Impact on the ecosystem:

• Destroys the standing crops and other small vegetation covers
• disrupts the food chain
• causes inadequacy of food for the herbivores
• loss of large number of animals and birds.

Impact on the human:

• Hampers the agricultural activities
• causes loss of life and damage to property
• results in water-borne diseases (such as cholera and typhoid)
• disrupts public life by destroying settlements, communication and transport systems.

The positive impacts of a flood: Along with many negative impacts, a flood does have some positive impacts too. They are as follows-
1. Deposition of silt from the flood water enhances the soil fertility.
2. People living on or near the lower floodplains rely upon flood water for irrigation and pisciculture.

The flood-prone districts of West Bengal:
The flood-prone areas of West Bengal include low-lying areas, coastal regions and settlements on rivers downstream from dams. The floodprone districts of West Bengal can be classified into two groups –
1. Districts of North Bengal: Cooch Behar, Jalpaiguri, Malda, Uttar and Dakshin Dinajpur.
2. Districts of South Bengal: Nadia, Howrah, Murshidabad, North and South 24 Parganas, Hooghly, Burdwan, Birbhum, West Midnapore and East Midnapore.

Question 6.
What is meant by drought? Classify and discuss the various types of drought. [1 + 4]
Answer:
As per the Indian Meteorological Department (IMD), a region is considered to be under the influence of drought if it receives an average annual rainfall that is less than 75 % of its normal value. However, there is no internationally accepted definition of drought.
Droughts can be classified into the following categories –
On the basis of water availability: Drought is classified into three types on the basis of water availability-
1. Meteorological drought: A drought is categorised as a meteorological drought, when actual rainfall over an area is significantly less than the normal amount of rainfall. Meteorological droughts need to be defined specific to particular regions as the atmospheric conditions that result in deficiencies of precipitation vary highly from region to region.

Meteorological drought can also be defined as the actual precipitation departures from average amounts on monthly, seasonal or annual time scales. According to the Interim Management Policy, drought can be classified into the following sub-types: (i) Mild drought: When rainfall is 11 % to 25 % less from the normal rainfall. (ii) Moderate drought: When rainfall is 26 % to 50 % less than the normal rainfall. (iii) Severe drought: When rainfall is less than 50 % of the normal rainfall.

2. Hydrological drought: A hydrological drought occurs when there is a marked depletion of surface water causing very low stream flow and drying of lakes, reservoirs and rivers. Therefore, hydrological drought is related to the effects of periods of precipitation deficits on surface or subsurface water supply. It can again be classified into two types – (i) Surface water drought: This is caused when ponds, lakes and rivers dry up due to inadequate rainfall. (ii) Groundwater drought: When the level of groundwater decreases due to deficit of rainfall, this type of drought occurs.

3. Agricultural drought: An agricultural drought occurs when inadequate soil moisture produces acute crop stress and affects productivity in the long run. Inadequate topsoil moisture during the planting stage may obstruct germination, leading to low plant populations per hectare and a reduction of final yield. However, if topsoil moisture is sufficient for early growth requisites, insufficiencies in subsoil moisture at this early stage may not impact final yield if subsoil moisture is replenished as the growing season progresses or if precipitation meets plant water needs.

On the basis of time period: Droughts differ in time and period of their occurrence. Thornwaite delineated drought as follows-

1. Permanent drought area: This area consists mostly of permanently dry or arid desert regions. Crop production is not possible without irrigation, due to inadequate rainfall. In these areas, xerophyte type of vegetation is generally observed, for example, cactus, thorny shrubs.
2. Seasonal drought: It occurs in the areas with clearly defined wet and dry climates. Seasonal drought occurs due to large-scale seasonal circulation. This occurs in monsoon areas.
3. Contingent drought: This results due to irregular and variable rainfall, especially in humid and sub-humid regions. The occurrence of such droughts may coincide with growth periods of the crops when the water needs are critical and greatest, resulting in severity of the effects i, e, yield reduction.

On the basis of medium: This is also done on the basis of the medium in which drought occurs. It can be of two types-

1. Soil drought: It is the condition when soil moisture depletes and falls short of meeting the potential evapotranspiration of the crop.
2. Atmospheric drought: This occurs due to low humidity, dry and hot winds that causes desiccation of plants.

Question 7.
How are cyclones generated? Briefly discuss the impacts of a cyclone. [2 \(\frac{1}{2}\) + 2 \(\frac{1}{2}\)]
Answer:
A cyclone is generated as a giant whirlwind or a very strong wind system moving rapidly in a cylindrical or funnel shape around a centre of low atmospheric pressure in tropical or subtropical regions. It usually advances at a speed of about 30 to 50 kilometre per hour and often brings heavy rain. The air circulates inward in an anticlockwise direction in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Suitable conditions for development of a cyclone:

• The sea-surface temperature should be above 26° C,
• the warm temperature of the sea causes air to rise upwards
• a strong low pressure is formed at the centre.

Stages of a cyclone: There are four stages that form a cyclone-
1. Formative stage: In this stage the circulation centre is not well developed. So the intensity is less and it generally tends to move inland but does not cause much damage. The sky is overcast with clouds.

2. Immature cyclone: The minimum surface pressure drops and wind speed increases. Convection winds organize themselves into a wind structure that spiral inwards. Due to well developed circulation, the ‘eye’ begins to form. Damage caused by a cyclone in this stage of the life-cycle is severe but the area affected is small.

3. Mature cyclone: Cyclonic circulation and extent of the giant whirlwind increases. There are only random fluctuations in central pressure and maximum wind speed. In a mature cyclone, the eye is welldeveloped.

4. Waning stage: The warm core is destroyed during this stage, the central pressure rises, and the belt of maximum wind expands near the centre. Waning may occur very rapidly if the system moves into an unfavourable atmospheric or geographic environment like on land or on cooler water surface.

Impacts of a cyclone:

Impact on the physical environment:

1. Disturbs the balance in the ecosystem: Vast number of animals and birds die due to the occurrence of a cyclone that subsequently leads to the imbalance of the local ecosystem.
2. Flood: Heavy rainfall may accompany a cyclone – this may lead to a devastating flood.
3. Coastal erosion: The strong waves formed by a cyclone near the coast may result in coastal erosion.

Impact on human beings:

Loss of life: Huge loss of human and animal life occurs due to cyclones. Vast areas of vegetation cover are also destroyed due to cyclone.

Loss of property: Cyclones disrupt the communication and the transport systems. They ravage and inundate the agricultural fields and subsequently may cause food scarcity. They also hamper public life by destroying houses.

Spreading of epidemics: The water gets polluted as a result of cyclones, resulting in water-borne diseases. Epidemics like cholera may spread from this polluted water.

For example, tropical cyclones like Sidr and Aila originated from the Bay of Bengal and caused immense devastation in the coastal regions of India and Bangladesh.

Question 8.
Briefly discuss the impacts of a drought. Name the drought-prone regions of West Bengal. [4 + 1]
Answer:
Droughts create immense environmental and socio-economic impacts. The impacts are as follows-
Impact on the environment:

The ecological balance is disturbed due to enhanced soil erosion (due to loss of soil moisture) and soil fertility decreases.
Loss or destruction of vegetation cover may lead to desertification of the region.
Spread of diseases in wild animals and migration of wildlife may be observed because of reduced food and water supplies.

Impact on the ecosystem:

It causes damage to plants and animals.
The plants struggle to survive due to the hampering of the process of photosynthesis.
Food scarcity is noticed for the herbivorous animals that leads to death of vast number of animals from all trophic levels.
Drought conditions can also provide a substantial increase in risk of wildfires as plants and trees wither and die from lack of precipitation and become fuel for wildfires.

Impact on the economy:

1. Droughts may lead to reduced production of agricultural yields (such as food crops, vegetables and fruits) and livestock production (such as egg, milk, meat and such others).
2. Lack of water and agricultural raw materials hampers the production of various industries.

Impact on the population:

1. Lack of precipitation may subsequently lead to lesser replenishment of ground water and as a result the ground water level falls. This makes irrigation more difficult and many of the farmers become jobless.
2. Excessive drought condition may lead to famine and starvation becomes a common picture.
3. Many people die due to lack of nutrition and tremendous heat.
4. Droughts lead to international and intra-national migration.

The districts of West Bengal that are prone to drought are as follows-

The western uplands of West Bengal consisting of the districts of Bankura, Birbhum, Midnapore and Purulia are most the droughtprone districts of West Bengal.

Question 9.
What is meant by an earthquake? Briefly discuss the causes of an earthquake. [1+4]
Answer:
Seismic waves are produced when some form of energy stored in the earth’s crust is abruptly released. This happens usually when masses of rock layers pushing against one another abruptly fracture and slip. Therefore, earthquake is any sudden shaking of the ground caused by seismic waves originating within the earth’s crust.

Earthquakes occur mostly along the geologic faults. The major fault lines of the world are located at the edges of the huge tectonic plates that form the earth’s crust.
The causes of an earthquake:
Natural causes: The natural causes of the earthquake can be divided into tectonic and non-tectonic causes.
1. Tectonic causes: The earthquakes occur due to tectonic causes, when rocks in the earth’s crust break due to geological forces created by the movement of tectonic plates. The various tectonic causes are-
i. Plate tectonics: Due to prevailing high temperature and pressure convection currents evolve in the viscous mantle below the earth’s crust. These convection currents cause the plates (parts of the earth’s crust) to move in different directions and at different speeds from those of the adjacent ones which at times causes earthquakes.

For example-
(A) Divergent plate boundaries: The boundaries where the plates pull away from each other are known as the divergent plate boundary. This type of earthquake is quite popular near the mid-Atlantic ridges.

(B) Convergent plate boundaries: The boundaries where two plates move towards each other and subsequently one plate dives under another are known as the convergent plate boundaries. The largest occurrence of earthquakes is usually seen under convergent plate boundaries.

(C) Transformational plate boundaries: The boundaries where the plates slide horizontally past each other are known as the transformational plate boundaries.

ii. Contracting earth theory: As the earth cooled, heavier metals such as iron sank down to form the core, while lighter metals such as aluminium remained up in the crust. The crust cooled and hardened, while the core remained in a hot, molten state. The contraction and expansion of the earth’s surface that occurs due to this gives rise to earthquakes.

iii. Isostatic causes: Isostasy is the state of gravitational equilibrium between the earth’s lithosphere and asthenosphere and in this process of trying to attain a hydrodynamic equilibrium, earthquakes may take place.

iv. Formation of fold mountains: Formation of new fold mountains may also result in occurrence of earthquakes.

v. Volcanism: Volcanic activity may also cause earthquakes.

2. Non-tectonic causes: Earthquakes may also occur due to various non-tectonic causes. They are as follows-
i. Meteorite: Meteorite impacts could cause larger earthquakes than have ever been observed.
ii. Collapse of subterranean cavities: Sometimes, because of the removal of soil from below (viz., by the action of underground water mostly in the Karst areas) the ground surface collapses suddenly – thus producing local tremors.

Anthropogenic causes: Unplanned anthropogenic activities may lead to earthquakes. For example,

Faulty construction of dams: It is well accepted that large dams can cause earthquakes. Dams cause earthquakes due to the extra pressure of water created in the minor cracks and fissures in the ground under and near a reservoir.
Nuclear testing: Nuclear testing may also trigger earthquakes.
Dynamite blasting for road construction: Blasting of rocks by dynamite for construction of roads may trigger earthquakes.

Question 10.
What is meant by a tsunami? Briefly discuss its origin and impacts.
Answer:
A catastrophic ocean wave, generally caused by an earthquake on the seabed or by an underwater or coastal landslide or by the eruption of a volcano is known as tsunami. It is derived from a Japanese word meaning harbour waves. It is also commonly referred to as seismic sea wave or tidal wave.

Causes of tsunami: The major causes of tsunami are discussed below-
Submarine earthquake: Most severe earthquakes occur in convergent boundaries where an ocean plate slides under a continental plate. All earthquakes do not generate tsunamis. To generate a tsunami, the fault where the earthquake occurs must be underneath or near the ocean. It must also cause vertical movement of the sea-floor over a large area. Earthquakes originating at shallow depths of the seabed (focus) responsible for the most destructive tsunamis.

Landslides: Landslides resulting in rockfalls, submarine landslides or slumps can generate tsunamis. For example, movement of a significant amount of earth for the construction of an airport triggered an underwater landslide in 1980 in southern France. This resulted in a devastating tsunami hitting the harbour of Thebes.

Eruption of volcano: Volcanic eruptions can generate waves as a result of sudden displacement of water giving rise to tsunami. For example, one of the most devastating tsunamis ever recorded occurred on August 26, 1883 after the explosion and collapse of the Krakatoa in Indonesia.

Extra-terrestrial collision: Although tsunamis caused by extra-terrestrial collisions such as meteors and asteroidsinduced tsunami have not been recorded in recent history and the possibilities are rare, but tsunamis may be generated by such extra-terrestrial collisions.

Effects of tsunami: The major effects of tsunami are discussed below-

Physical changes: Tsunami may result in various physical changes. For example, the islands of Andaman and Nicobar experienced widespread devastation because of a tsunami in 2004. Some smaller islands in the Nicobars have entirely vanished and some others have changed shape, such as Trinket which has been split into two parts after the tsunami.

Change in soil characteristics: Tsunami may result in a change in the characteristics of soil, especially soil salinity. The coastal regions are bounded by vast expanses of salty, marine waters and thus the salinity of the soil may increase at certain times. This may negatively affect soil fertility and productivity.

Damages the marine ecosystem: Tsunamis cause great damage and even devastation to marine ecosystem.

Shortening the length of the day: The massive earthquake that struck Sumatra in 2004 has shortened the length of earth’s day. The intense tremor of 9.1 magnitude has accelerated the spin of the earth, shortening the length of the 24 hours day by 6.8 microseconds.

Casualties: Tsunamis are generally very devastating and cause huge loss to life of human and animals. The tsunami waves in the morning hours of December 26, 2004 around Bay of Bengal caused an official death toll of 812 and unofficial death toll is estimated to be about 7,000.

Damage to property: Tsunamis generally cause great damage to property especially in the coastal regions. Huge loss of houses, roads, agricultural fields, factories are caused by tsunami.

Question 11.
What is meant by a landslide? Briefly discuss the causes of a landslide. [1 + 4]
Answer:
A landslide is the movement of rock, debris or earth down a slope. Landslide occurs when gravitational and other types of shear stress within a slope exceeds the shear strength of the materials that form the slope. Landslides are known also as landslips, slumps or slope failure.

Natural causes: The natural causes of landslides are as follows-
Intense/prolonged rainfall: Prolonged and intense rainfall is the immediate and direct cause of landslides where water acts as a lubricant. With prolonged and intense rainfall large amount of rainwa-
ter seeps into the soil that results in the increase in water pressure in the pores of the soil. The friction and internal cohesion of slope materials reduces which subsequently destabilises the slopes and causes landslides.

Earthquake: Earthquakes can trigger landslides in the critical reaches of hill slopes if the magnitude reaches 6 and above.
Slope gradient: Slopes with steeper gradients are more prone to landslides as gravity has more influence on these slopes, increasing its sliding force.
Loose materials: Unstable materials like large boulders increase the vulnerability of the slope to landslides.

Anthropogenic causes: The anthropogenic causes of landslides are as follows-
Deforestation: Large-scale deforestation can make a place vulnerable to landslide. As the trees are cut, the soils become loose as the roots do not bind them any more. This makes the region prone to landslides.

Urbanization: Unscientific construction of roads and houses on steep slopes disturbs soil stability which may lead to landslides.
Shifting cultivation: Shifting cultivation is an unsustainable practice that depletes the soil nutrients and reduces the forest cover, causing landslides.
Overgrazing: Overgrazing may result into land degradation that may subsequently lead to landslides.

For example: Darjeeling district is one of the most landslide-prone districts of West Bengal. Paglajhora region is highly prone to landslides due to both natural factors and increasing human activities for the last five decades.

Question 12.
What is meant by a blizzard? Discuss with examples how a blizzard can cause hazards and disasters. [2 + 3]
Answer:
A blizzard is a severe storm condition characterized by low temperatures, strong winds, and heavy snow. Blizzards can restrict visibility to near zero. Blizzards have a negative impact on local economies.
Characteristics: The main characteristics of a snowstorm are discussed below-
1. Strength of wind: Winds that are at least 56 kilometre per hour or greater than the normal snowstorm are identified as blizzards.
2. Visibility: The visibility is reduced to almost 400 metre or even to zero at times.
3. Duration: Most blizzards last for a duration of almost 3 hours.

Location: The occurrence of blizzards is most prominent in the countries of Antarctica, northern parts of North America, Canada, north of Europe and Asia as well as in New South Wales in Australia. Apart from these, the snowcapped high mountainous regions also experience blizzards.
Hazards caused by blizzards: During blizzards, winds combined with fleeting snow produce extreme conditions and disrupt normal living conditions. The hazards caused by blizzards are as follows-
1. Physical illness: The extreme cold winds during blizzards are a cause of great discomfort to the local people which may subsequently lead to physical illness and may even cause hypothermia.

2. Disrupts transport system: The thick layers of snow that accumulate during blizzards may disrupt the local transport system. Blizzards paralyse the transport system and leave the roads in an unsafe condition. For example, from March 11 to 14,1888 , a blizzard dumped an average of 1 metre of snow over southeast New York and south New England. It killed over 400 people, of which New York City alone recorded 200 deaths.

3. Flooding: The sudden warm-up that may follow a blizzard can prove to be damaging as the rapid snow-melt may trigger serious flooding and accidents.

4. Disrupts public life: Blizzards generally disrupt public life by interrupting transport, electricity and water supplies and also normal day-to-day life by interrupting health and educational facilities.

Question 13.
What is meant by volcanism? Discuss briefly the causes of volcanism.
Answer:
Volcanism is the process that refers to hot molten magma escaping from the earth’s core, cooling down and forming hard rocks. Volcanism can be of three types depending on the place where it occurs. They are as follows-
1. Extrusive volcanism: Molten lava that escapes the earth and reaches the surface is known as extrusive volcanism.
2. Intrusive volcanism: Molten magma that cools and hardens beneath the surface of the earth is known as intrusive volcanism.
3. Plutonic volcanism: Molten magma that cools and hardens deep beneath the surface of the earth, far below the crust is known as plutonic volcanism.

Causes of volcanism: The major causes of volcanism are as follows-
Plate tectonics: The earth’s crust is divided into a number of tectonic plates moving in different directions and at different speeds. This gives rise to occurrence of volcanoes.
At the divergent plate boundary: When two oceanic plates move away from each other, a gap is created in the seabed. Magma rises from great depths below to fill the space resulting in seafloor spreading which occurs at a rate of about 10 centimetres a year.

Convergent plate boundary: The volcanoes that occur at the boundaries where two plates move towards each other and subsequently one plate dives under another i.e., the convergent plate boundary, creating an deistic lava. These volcanoes undergo more violent eruptions containing ash.

Transformational plate boundary: The volcanoes that occur at the boundaries where the plates slide horizontally past each other i.e., the transformational plate boundary, are not very violent.

The buoyancy of the magma: As a rock inside the earth melts, its volume increases, producing magma that is less dense than the surrounding rock. This lighter magma rises up because of its buoyancy. Since the density of the magma between the zone of its generation and the surface is less than that of the surrounding and overlying rocks, the magma will reach the surface and erupt.

The pressure from the dissolved gases in the magma: Magma contains dissolved volatiles like water, sulphur dioxide and carbon dioxide. The amount of dissolved gases in magma at atmospheric pressure is zero, but rises with increasing pressure. When magma moves toward the surface, the solubility of the water in the magma decreases, and excess water separates from the magma as bubbles. The closer it gets to the surface, more water comes from the magma, increasing the gas and magma ratio in the magma tube. When the volume of bubbles reaches about 75 %, the magma turns into partially molten and solid fragments and it erupts explosively.

Injection of new magma into an already filled magma chamber: As an additional amount of magma enters a chamber that is already at its full capacity, the new magma causes some of the existing magma to move to the surface and erupt.

Release of energy: A volcanic event occurs when there is a sudden or continued release of energy caused by magma movement near the surface. The energy can be in the form of earthquakes, gas emission at the surface, release of heat through geothermal activity, explosive release of gases and the non-explosive extrusion or intrusion of magma.

Question 14.
Briefly discuss the impact of vulcanicity.
Answer:
The impact of vulcanicity has been broadly shown as follows-

Impact on nature:

1. Deveiopment of landforms: Different types of landforms like caldera, cinder cones, lacolith, dykes, sills, etc., are formed due to vulcanicity.
2. Change in ecosystem: The ecological balance of the affected area is disturbed as many species of plants and animals become endangered.
3. Change of soil formation: Soil characteristics get changed as lava spreads across the land.
4. Change in local environment: Local environment is considerably changed. For example, there is a possibility of acid rain as a reaction of toxic gases released during vulcanicity.
5. Earthquakes: When explosions take place during volcanic eruptions on a massive scale, earthquakes may be felt in the adjoining areas.
6. Change in temperature: The temperature of the surrounding areas of a volcanic eruption increases.

Impact on human life:
Loss of life: A massive loss of life occurs as a result of vulcanicity. E.g., about 3600 people died in the coastal areas of Java when the Krakatoa volcano erupted in 1883.
Loss of property: Huge loss of property like buildings, transport network, industries occurs and the economic life of the whole region is affected.
(Loss of agricultural land: Large tracts of land are rendered infertile as a result of being covered by hot molten lava gushing out of the volcanoes. For example, the famous Barren Island of Andaman and Nicobar islands.

Volcanic activity occurs all of a sudden without any warning. However, an analysis of the movement of magma below the earth’s surface can provide some clue for future occurrences of volcanic activity and warnings can be issued accordingly.

Question 15.
What is a forest fire? Briefly discuss the causes of a forest fire. What remedial measures can be taken to prevent the occurrence of forest fires? [1+2+2]
Answer:
Forest fire: When a fire is ignited in a forest due to natural or man-made reasons, it is called a forest fire. There are various reasons for this, for example, lightning, vulcanicity, heat wave, casual or irresponsible activities of men.

Causes of forest fire:
Natural causes:

1. If a lightning strikes, dry leaves of trees or tree-trunks may get ignited.
2. in the dry season, a boulder coming down a mountain slope may give rise to a spark that leads to a fire.
3. A volcanic eruption may also cause a forest fire.

Man-made causes:

1. When a forest is burnt for clearing land for agricultural activities like in shifting cultivation, the fire may spread, causing a forest fire.
2. The fire used for cooking in tents by mountaineers may also cause forest fires.
3. If a lit cigarette is discarded by someone unmindfully on the forest floor, the dry leaves on the forest floor may cause a fire to break out.

Preventive measures against forest fires: The different measures that can be taken to prevent forest fire are-

1. not to throw any inflammable object or lighted object on the forest floor
2. to remove dry leaves and parts of plants and trees to safe corners as much as possible
3. to keep pets and other valuables at a safe distance
4. to dig a circular canal and make arrangements for adequate water around the zone of forest fire
5. act as per emergency instructions broadcast by radio or other devices during a forest fire
6. to arrange for awareness programmes for forest dwellers and people residing in forests regarding measures to save themselves.

Question 16.
Describe the main disasters of West Bengal.
Answer:
West Bengal is prone to various disasters such as droughts, floods, landslides, cyclonic storms, etc. The following table reveals the features of each of them-

Besides the above, certain phenomena like forest fires, river bank erosion, erosion of shorelines, pollution of underground water (arsenic pollution) etc., can take the shape of disasters.

Question 17.
What is an avalanche? What are the factors that cause avalanche? [2 + 3]
Answer:
Avalanche: When accumulated snow and ice slide down along the steep slopes (35°-45°) of mountains, encompassing a wide area, it is called an avalanche.

In the higher altitude of the mountain slopes, the upper part of the accumulated ice breaks apart from the underlying layer of ice. It hurls down along the steep slopes as a vast expanse of white sheet mainly due to the earth’s gravity. This phenomenon mostly occurs during the winter months.

Such occurrence of avalanches may be predicted by analysing the nature of the terrain on mountain peaks and slopes as well as meteorological or climatic data. Avalanches are a common feature in the mountainous areas of the Himalayas and the Alps.

Factors causing avalanches:
1. Slope of the land: It has been observed that avalanches are a common occurrence on slopes ranging from 35°-45° and concave slopes are more favourable than convex slopes of the mountain.
2. Accumulation of snow: Avalanches are influenced by the amount of snow or ice on the mountain tops, wind speed and direction, increase in temperature and melting of snow. Usually, the north and northeast facing slopes of mountains are more prone to avalanches.
3. Smoothness of slope: In comparison to forested or vegetated slopes, bare and smooth slopes act as a trigger for avalanches.
4. Size of ice crystals: Since bigger ice crystals are weak and break easily, they are more prone to initiate an avalanche compared to compacted or packed ice.
5. Sun rays: Since the sun’s rays warm up the ice, they lead to avalanches.
6. Wind flow: Winds blowing from varying directions loosen up the ice and initiate an avalanche.
7. Human interference: Human activities such as cutting down of trees, construction of roads, explosion by dynamite, ice-sports etc., increase the possibilities of avalanches.

Question 18.
What measures should be taken to control disasters like floods and droughts?
Answer :
To reduce occurrence of floods:
1. If climatic conditions change naturally, rainfall intensity is decreased and as a result, there would be lesser floods.
2. Watershed management and proper drainage system, afforestation, changing the slope by constructing terraces, control of overgrazing, contour-farming etc., can check the occurrence of floods.

Change of direction of floods:

1. Construct barrages and reservoirs to store excess water of rivers,
2. construct dykes or dams across rivers at specific locations in order to prevent flooding of low-lying areas,
3. regular dredging of the river bed is needed to lower the level of silt for smooth flow of river water so that the banks do not overflow and cause floods.

Planning to prevent occurrence of floods:

1. Implementation of strict laws to bar construction of houses etc., in floodprone areas along rivers
2. dredging and reclaiming dead and decaying rivers
3. increasing public awareness through propaganda and advertisements – by these methods, losses incurred due to floods can be reduced.

Measures to be taken during floods:

• Stay back at home, or at a higher ground when the level of floodwater rises.
• Keep the following items handy-polythene packets, cord, torch, matchbox, candles, important documents, dry clothes, dry food, radio, mosquito net, pure drinking water etc.
• Switch off electrical switches and appliances, close taps and lock gas cylinders.
• Wait for relief to arrive from government agencies, NGOs etc., and abide by the advice given by them instead of panicking.

Measures to be taken to control droughts:

• Construction of reservoirs, implementation of water conservation projects, increasing the efficiency of irrigation etc.
• encourage and practice dry farming and use drought-resistant seeds of crops
• have food security and reduce wastage of water
• drill deep tubewells by adopting modern techniques
• arrange for proper distribution of relief to droughthit victims.

Question 19.
Discuss the importance of disaster management.
Answer:
Importance of disaster management: The main purpose of disaster management is to reduce losses in all spheres such as, social, economic, environmental etc.

Prevention of environmental damage:

1. Pollution control: Pollution can be controlled to a great extent if certain measures are taken. For example, air pollution can be controlled if the dust particles produced during landslides are reduced by attempting to check the occurrence of landslides (by adopting various measures).
2. To maintain ecological balance: By adopting appropriate measures of disaster management, the damage incurred to the environment can be reversed.
3. Prevention of loss due to natural disasters: Disasters can be reduced or even prevented by adopting disaster management measures like forecasting disasters, carrying on research, conducting mock drills and spreading awareness, warnings, etc.

Prevention of social damage:

1. Rehabilitation of affected people: A damaged area can be restored to its original normal state by acting on an emergency basis and on a war-footing. For example, rapid action taken for rescuing people and rehabilitating them would be of immense help.
2. Aids and supplies: Supply of necessary items like food, water, shelter, etc., is possible through the aids by state and central governments.
3. Prevention of loss of property: If a warning is issued prior to the disaster, much of the damage caused to life and property can be minimised.

Prevention of economic loss:

1. Prevention of agricultural loss: The fertility of the land diminishes and salinity of soil may also increase as a result of floods, droughts, earthquakes etc. Proper infrastructure can be developed for cultivation of crops if forecast of any disaster is made.
2. Prevention of disruption of transport system: When the transport system is disrupted due to calamities like, landslides, earthquakes etc., alternative modes of transport can be arranged to alleviate the problem.
3. Reducing economic loss: The economy of any region is hampered as a result of loss in the agricultural and industrial sector due to natural calamities. Appropriate measures can be taken for proper disaster management, thereby reducing such economic losses.
4. Prevention of industrial loss: Various industrial products and infrastructure are damaged which can be restored by undertaking proper disaster management programmes.

Question 20.
What is meant by disaster management? What are the various measures adopted for it? [1 + 4]
Answer:
Disaster management: Disaster is any kind of temporary or permanent damage entailing a loss of human life and disruption of normal activities (due to natural or man-made causes) and cannot be dealt without external aid. Disaster management is the means to control and restore such a disruptive situation (through various measures).
Measures taken for disaster management: They are as follows-

Pre-disaster measures:
1. Data collection: Data related to causative factors of disasters should be collected. For example, in the case of floods and droughts, rainfall data for the past years should be taken.
2. Data analysis and mapping: The collected data is then analysed to determine the intensity and extent of the disaster and mapping is done on that basis. For example, 375 mmannual rainfall for drought, 375-750 mm annual rainfall for semi-arid conditions are the usual determinants.
3. Research: After mapping, a thorough research is undertaken in order to assess the past as well as future predicaments.
4. Forecast: If proper forecast is done through data analysis using modern technology, the amount of loss or damage caused by any disaster can be minimised.
5.Training: Training can be imparted to all including common people, army personnel etc., by the authorities at the centre, state and district levels so that the loss and damage incurred in a disaster is minimal.
6. Warning: Steps should be taken for increasing public awareness and precautionary measures should be taken.

Measures taken during disasters:

1. Rescue operations: These should be done on an emergency basis by both the general public and army personnel in order to save maximum number of people and animals.

2. Relief operations: Relief materials can be made available to the people of the affected area by central and state government agencies and the extent of loss and damage can be estimated. Preventive measures can also be taken to control further deterioration of the situation. For example, necessary medicines, food and safe drinking water can be provided to them to prevent the spread of an epidemic in the near future.

Post-disaster measures :

1. Rehabilitation: Normal life can be restored by providing aid and making arrangements for reconstruction of damaged houses, roads, transport and other civic amenities and services including agricultural and industrial establishments. Temporary shelters must also be made on an urgent basis.

2. Reconstruction: A host of measures can be taken, like planning different projects and creating jobs in different sectors, to normalise the economic condition of the affected people. For example, in the case of drought-prone areas, watershed projects, irrigation projects etc., can aid in reducing the chances as well as the impact (where a disaster has already taken place) of such disasters.

Although natural calamities like earthquakes, vulcanicity, etc., cannot be prevented and are beyond human control, proper pre-disaster planning by conducting surveys and analysing previously recorded data can reduce the impact of such a calamity. By providing precautionary measures and spreading general awareness in the concerned areas, the disastrous effects can be minimised.

Question 21.
What are the measures taken for managing disasters like earthquakes and landslides? [3 + 2]
Answer:
The measures taken to control and manage such disasters are as follows-
Measures taken before an earthquake:

1. Earthquake-resistant houses should be constructed for people living in earthquake prone areas.
2. Electricity, gas and water connections should be promptly disconnected when an earthquake strikes.
3. The basic amenities needed for survival, like drinking water, food, torch, candles, etc., should be stored in adequate amounts.
4. People should also know how to contact the nearest fire station, health-centre etc., in case of exigencies.

Measures to be taken during an earthquake:

1. One should leave the house and move to any vacant, open place.
2. One can take shelter beneath any sturdy furniture, like a table, bed, etc.
3. Any kind of inflammable objects like matchboxes, candles, gas ovens should not be used.
4. One should not try to jump from windows or doors from great heights.

Measures to be taken after an earthquake:

1. If the house is damaged, one must take shelter in any relief camp, but necessary medicines, water and dry food should be taken along.
2. One should be calm and listen carefully to the advice given on radio or any other public announcements made outside the house.
3. One should not go to the seashore or to a lowlying river bank as there are chances of rising of water level.
4. First-aid should be given to the injured people.
5. One should not touch any electrical wire or metal object as he may get electrocuted due to short circuit.
6. Lighting of matches, lighters and cigarette smoking should be avoided. In case of any emergency, for example, a leak property) can be reduced to a great extent.

The students have a major role to play here. Usually, there are 3 steps of disaster management –

1. pre-disaster stage,
2. during disaster stage,
3. post-disaster stage.

Pre-disaster stage:
Evaluation of risk: The students must have an idea of the area in which they reside and how prone it is to a disaster. E.g., Nadia is a highly flood prone area while East Midnapore is prone to thunderstorms.

Preparedness: Any place or area can experience a disaster, hence mock-drills must be done to make people aware about what measures can be taken to combat it. For example, if any area is prone to floods, how should people reach higher grounds to save themselves, what types of food and medicines they should carry with them, etc., must be rehearsed.

Warning measures: If the students get the warning beforehand, they can not only prepare themselves, but can also warn their neighbours at the same time.

Development of infrastructure: The students can learn from their teachers the names and addresses of those government and non-governmental organisations and agencies, which usually provide with relief, evacuation, rehabilitation measures, etc. Examples of such organisations are the Meteorological Office, police administrations, hospitals, NGOs, etc.

Spreading awareness among general public: The students’ volunteers should impart lessons on measures to be taken for disaster management. The local people can thus be educated and made aware of tackling such situations.

Enlisting property: The students must make a list of certain properties that may be used as safety props during a disaster. For examples, suitable buildings and schools-for converting them into relief camps, dry food, torch and other emergency articles like medicines etc.

During disaster stage: Every student must undertake the responsibility of protecting and rescuing himself or herself and their family members. Their neighbours must also receive the same helping hand.

Post-disaster stage:
1. During the urgent need for providing relief (in the form of food, water, medicines, clothes, temporary shelters, etc.), the students must properly contact the relevant organisations which provide these in order to accelerate the relief process.
2. The students should work hand in hand with the professional rescue operators.

From the above discussion, it is clear that if the students are imparted relevant lessons and given proper training, a substantial amount of life and property can be saved. The teachers have an important role in this regard as well.

Question 24.
Discuss the measures taken to tackle disasters in West Bengal.
Answer:
In West Bengal, different types of measures are taken to tackle various disasters. The following are some of the measures taken-
Tangible measures: They are as follows-
In case of droughts:
1. Reclamation of dying and decaying rivers, ponds, lakes and wetlands are to be done for storing water for times of crises.
2. Sources of water are to be conserved carefully and rainwater harvesting measures are to be taken.

In case of floods:

1. Level of the rivers are lowered by dredging of silt accumulated in them, so that the water-bearing capacity is increased to allow smooth flow of the river.
2. Reservoirs are constructed adjacent to rivers in order to store excess water.
3. Embankments are constructed along the river banks to prevent water from overflowing and inundating the floodplains.

In case of landslides:

1. Soil erosion can be prevented on mountain slopes by planting trees.
2. Landslides can also be prevented by putting boulders, building concrete walls, etc., at the base of the mountain slopes.

In case of cyclonic storms:

1. Construct stable shelters so that people can save their lives during storms.
2. Plant big stormresistant trees along the shoreline to obstruct gusty winds.
3. Make announcements to warn the fishermen against going for fishing in the open sea.

In case of tsunamis: Tall embankments are being constructed and sturdy trees are being planted along the coastline of West Bengal.
In case of earthquakes: A geological study of specific areas is conducted prior to building houses. For constructing multistoreyed buildings, earthquake-resistant structures are recommended.

Intangible measures: The measures taken are as follows –

In case of droughts:

1. Maps of drought prone areas of West Bengal are being prepared.
2. Land conservation measures are being taken.

In case of floods:

1. Maps of flood-prone areas of West Bengal are being prepared by surveying flood-affected and flood-prone areas.
2. People are warned before water is discharged from any dam to release excess flood water.
3. Various projects are under way in different parts of West Bengal, where several two-storeyed houses are constructed for villagers to take shelter during floods.

In case of landslide:

1. Maps are being prepared for landslide prone areas of West Bengal.
2. Proper land-use practices in mountainous areas and scientific farming methods (like terrace-farming, contourfarming, etc.) are being adopted here.
3. Laws are being made and implemented to prevent overgrazing of animals in areas where landslides are rampant.
4. Planned urbanisation, including building of houses and construction of roads, etc., should be done.

In case of cyclonic storms:

1. Minimum settlement areas have to be developed in coastal areas where prevalence and impact of cyclonic storms are the greatest.
2. Arrangements are made so that announcements of forecasts of such storms can reach the people of the area well in advance and should therefore be made on an emergency basis.

In case of tsunamis: Various projects are being planned to construct shelters on higher grounds so that people can be shifted there during a tsunami.

In case of earthquakes:

1. Various kinds of training are being imparted to the people by the Government as to how to tackle such occurrences.
2. Preventive measures have been taken for after-effects of earthquakes like landslides, forest fires, houses catching fire, etc.

A ‘Disaster Management Team’ has been formed by the government of West Bengal. Moreover, propaganda through seminars, posters, documentary films, slideshows, etc., are being made so that people can save themselves when faced with a natural disaster.