UNIT 6: Concept of Disaster

Concept of Disaster

Q: Give a definition of disaster.

Ans : "Disaster" is sudden, unexpected and adverse natural or manmade event causing significant physical damage, loss of life or property, including permanent changes of the natural environment.

Q: True of false.

(a)     Disasters are the responsible to the hazards.                                    Ans : True.

(b)     Vulnerability is the probability of occurrence of a hazard.                    Ans : False.

Q: Fill in the blanks -

According to Peter Timmerman, "Vulnerability is the degree to which system may react, adversely to
the occurrence of a   .................. ".

Ans : Hazardous event.

Q: What are the main causes of flood?

Ans  :     (a) Natural causes (b) Manmade causes

Q: Write about the steps involved in the process of structural flood mitigation.

Ans : (a) Storage reservoirs  b)  Cutting of sinuses   c) Diversion of flood   d) Embankments

Q: Discuss the anthropogenic causes of flood.

Ans : (a) Deforestation  b) Urbanization  c) Breach of Dams/Embankments  d) Reservoirs  e) Agricultural practices       

Q: Write the definition of earthquake.

Ans : The earthquake is a vibration of the surface of j the earth with rocking energy of wave motion which is capable of shaking the buildings apart and causing gaping fissures to open up in the ground.

Q: Discuss the secondary effects of earthquake.

Ans : (a) Perceptible snaking, Seiche in rivers and ponds, Tsunami, Swaying of bridges, Shaking of buildings. Disaster

Q: Fill in the blanks :

(a)  Prolonged   drought   like   condition   leads   to   unemployment of farmers.

(b)  Tsunami is a Japanese word of which 'tsu' means  harbor and 'namee' means wave.  

(c)  The release of liquid petroleum hydrocarbons causes oil spill problem in water bodies.

(d)  In oil spills plumage penetrates through the feathers of a bird and affects its activities.

(e)  Oil   can   directly affect the invertebrates   by altering its   metabolic activities.

Q : Write in brief the natural causes of drought occurrence.

Ans : (a) Less amount of water vapour in the air due to the occurrence of heavy rainfall and hail storms results in dryness of the air. This sometimes causes drought.

(b) Wind is another natural factor which helps in the shifting of air masses.

Q: Write the definition of volcano.

Ans : Volcano is essentially a fissure of vent, communicating with the interior, from which erupt the flows
of lava, fountains of incandescent spray or explosive bursts of gases and volcanic ashes.      

Q: Write true or false.

a.     Volcanoes are always associated with the weaker zones of the earth's crust.             Ans : True.

b.     Volcanic eruptions and fallout of dusts and ash cause mass extinction of a few species.         Ans : True.

c.      Chernobyl disaster was a nuclear power plant accident.                                                      Ans : True.

d.      Oil spills cannot affect plants.                                                                                         Ans : False.

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Q. Bring out the differences between hazard and disaster.      

Ans : (i) Hazard: Environmental Hazard can be defined as those extreme events (anthropogenic/natural) which may cause catastrophic damage to property and loss of lives and degradation of environment. Hazards are considered the processes orthe causal factors resulting from most extreme events.

(ii) Disasters: Disasters are the results of-these extreme events, The intensity of the environmental disastter is always measured in terms of the total damage done to human lives, property and the environment. Disasters are the results of hazards and are very rapid and instantaneous. Such events cause great damage to human society.

Q. Elaborate on the structural and non structural mitigation measures for flood disaster.

Ans : Structural measures :

a.     Storage reservoirs: The volume of water during the flood may be reduced through a series of engineering devices such as construction of storage reservoirs which help in irrigation as well as power generation.

b.     Straightening of bends: The existence of too many of bends in the highly sinuous and meandering rivers retard the quick disposal of water. So, it may be necessary to straighten the meandering courses of a river by performing artificial cutoff of individual bends so that flood discharge may move downstream without causing flood along its banks.

c.     Diversion of flood: Flood diversion system implies the diversion of flood water in low lying areas through artificially constructed channels bordered by artificial dykes so that the devastation of floods can be reduced.

d.     Embankments: Embankments, dikes and flood walls are used to confine the flood water with the valley or within a narrow channel. These engineering works include the building of artificial levees of earthen materials along the river banks. These are considered as short-term measures for flood management. If these structures are used for a longer time, their usefulness is greatly reduced in managing flood flows.
Stone spurs are also used to protect the towns; cities and other populated areas from severe erosion during flood. Semi permeable spurs, pile spurs are also constructed to protect against flood and erosion.          

Non structural measures:

a.     Afforestation: It is the first step for controlling floods. Forest prevents the rain water from directly coming into the land. Rain waterfalls through tree leaves on the ground and forests also help in more percolation of rain water and reduce the surface run off. It significantly reduces soil erosion and helps in reducing the frequency of floods.

b.     Flood forecasting and early warning system: Flood control organizations and forecasting centers set up in various parts of India help in the forecasting of floods in river basins like the Ganga, Brahmaputra and their tributaries. These flood forecasting centers collect the data regarding rainfall, and the level of flood water etc. and people living in the lower basins' against the possible threat of flood.

c.     Zoning of flood prone areas: The flood prone areas are classified into certain zones based on the levels of risk the different areas have and the probability of hazard they face. This type of classification or zonation is useful in the management of flood hazard in the flood prone areas.

Q: What are the primary, secondary and transient effects of earthquake?

Ans : Primary effects : (i) Regional geological changes, (ii) Displacement of arid cracks in any matter (iii) Fissures and cracks in buildings, roads etc. (iv) Elevation and depression of land, (v) Accumulation of water, (vi) Change in the direction of river current. (vii) Formation of stream tremors iii ponds and water bodies (viii) Displacement of well and spring.

Secondary effects: (i) Landslide (ii) minor slippage (iii) Uprooting of poles and posts (iv) Death of fishes (v) Common damage to buildings (vi) Effects on glaciers (vii) Stopping of pendulum clocks (viii) Snapping of cables.

Transient effects: (i) Perceptible tremors   (ii) Sliche in rivers and ponds (iii) Tsunami (iv) Swaying of bridges (v) Shaking of buildings and disturbance in Birds/animals (vi) Fright and panic among human beings (vii) Hearing of sounds. 

Q: Write briefly about the internal and external factors associated with landslide hazards.

Ans : A landslide is a slow or sudden downhill movement of soil, glacier and rock materials due to the force of gravity. Landslides as erosional processes not only modify the existing topography and landscape, but also cause immense damage to man made structures causing heavy loss of lives arid properties.

(i) Internal factors :

a.     Increase in pore Water pressure

b.     Presence of Kaolinite, anhydric or expansive clays like montmorillonite

c.     Weathering and physico-chemical reactions.

(ii) External factors :

a.     Gravitational force

b.     Prolonged and continuous rainfall

c.     Ground water flow through lapse soils

d.     Wedging action of plants and tree roots e. Tremors due to earthquake-

Q: What are the environmental impacts of drought?

Ans : The problems associated with drouqht can have economic, environmental, and social impacts. Because nature and human society depend on water. Lack of water results the migration of people. It is a very common occurence. The agricultural sector is particularly affected by drought. The lack of water can often cause a decline in crop yields, leading to the reduction in income for farmers and an increase in the market price of products. A prolonged drought, may cause unemployment of farmers and problems for the retailers of agricultural products, having a significant impact on the economy of the area. Health problems like malnutrition, dehydration and spread of various diseases become a common sight in a drought-hit area. Drought can also result in insect

infestations and plant diseases, increasing erosion, habitat and landscape degradation, forest fire, wild fire etc. Prolonged drought like condition leads to desertification.

Q: Describe the causes and effects of Tsunami.

Ans : Causes : The tsunami is caused by earthquakes, volcanic eruptions, explosions under the sea.

Effects: Tsunami has a devastating and catastrophic effect when it becomes a hazard. Tsunami affects the coastal  areas very harshly. The records of the tsunamis that have already taken place point to the destruction of huge number of coconut trees in the coastal areas besides causing a devastating impact on human lives and properties. The hazards of tsunami have taken a heavy toll of human lives. Many people had left their.home and hearth in the tsunami affected areas and being homeless came to live in refugee camps.

Q: Briefly describe the effects of volcanic hazard on the environment.

Ans : Volcanic eruption causes heavy damage to human lives, property and all ecosystems through emitting hot lavas and volcanic materials. Huge volumes of hot and liquid lavas moving at considerably fast speed burry structures, kill people and animals, destroy agricultural farms, forests. These volcanic substances including dusts and ashes, smokes etc, cover the large ground surface and farm lands, forests, men and animals and create acid rains. Volcanic eruption also changes the radiation balance ofthe earth the and atmosphere and thus helps in causing climatic changes. According to some scientists volcanic eruptions cause mass extinction of a few species. Volcanos occuring before and after an earthquake generate destructive tsunamis seismic waves.

Q: How does oil spill affect the wild life?

Ans: The release of liquid petroleum hydrocarbon into the water bodies due to anthropogenic activities is referred to as oil spills which cause severe pollution of the water body and the whole environment as well. These types of incidents are very common in the marine environment.

         Oil spill is mostly caused by sudden accidents or leakage of oil tankers, cleaning of the tankers in shore areas, leakage of oil from the refinery and other fuel industries.

Effects:

a.     Effects on birds: This oil penetrates through the feathers to the body of a bird and impairs the bird's flight abilities, making it difficult or impossible for it to defend itself against predators. This oil also damages, kidneys and the liver function, poisoning the digestive tract. Seals and Dolphins are also affected while feeding on the contaminated species. The reproductive function of the animals is also affected by the oil spill.

b.     Effects on fishes: Fish species are badly affected by this kind of pollution. Oil enters into their bodies through gills, affects the eggs and the larval survival. Reduced growth, enlarged livers, changes in heart and respiration rates, fin erosion, and reproductive impairment are the other adverse effects of oil spills on fishes noticed. Oil has the potential to impact the spawning success, as eggs and larvae of many fish species, including Salmon, are highly sensitive to this toxic substance.

c.     Effects on invertebrates   : Oil can directly affect the invertebrates by altering their metabolic activities.

d.     Effects on plants: Some small, plants, algae, and other aquatic plants are also affected badly. The pollution caused by oil spills can be reduced by some bioremediation and phyto remediation techniques using some bacteria to remove the oils from the water body. Some chemical methods are also used to reduce this pollution.

Q. Write about some events which are called disasters, Why are they called disasters?

Ans: Geological processes, like earthquakes, volcanoes, floods and landladies are normal natural events which have resulted in the formation of the earth that we have today. They are, however, disastrous in their impacts when they affect human settlements. Human societies have withnessed a large number of such natural hazards in different parts of the world and have tried to learn to control these processes, to some extent.

Q. How do earthquakes occur?

Ans : Earthquakes occur due to sudden movements of earth's crust. The earth's crust has several tectonic plates of solid rock which slowly move along their boundaries, ^(hen friction prevents these plates from slipping, stress builds up and results in sudden fractures which can occur along the ' boundaries of the plates in sudden fractures which can occur alongthe boundaries-of the plates or fault lines within the plates. Thiseauses earthquakes, the violent, short-term vibrations in the earth.. The point on a fault at which the first movement occurs during an earthquake is called the epicentre.

Q. How can damages by earthquake be prevented?

Ans : (i) Construction of earthquake-resistant buildings in the earthquake prone zones.

(ii) Weak spots are strategically placed in the buildings that can absorb vibration form the rest of the building, pade or floats are placed beneath the building on which it can shift harmlessly during ground motion.

(iii) Wooden houses are preferred in earthquake prone areas.

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