5 Pollution and its Factors part 4
Disaster Management
Loss of life and property due to natural disasters like tropical cyclones, floods, droughts,
tornadoes, earthquakes, volcanic eruptions etc, is very large. Fortunately warning facilities
are available today and by mitigation measures, loss of lives and properties can be minimized.
National Meteorological Services of the world to provide warnings to the public for some of
the weather related natural disasters. It is not possible to forecast a long period ahead
precisely when and where a dangerous natural phenomenon will take place. While natural
disasters cannot be prevented, taking proper long-term and short-term disaster mitigation
measures can minimize the loss of life and property.
Some common disasters known to occur in our country are as under:
Floods
Floods are defined as a relatively high flow of water discharged from river and stream
network, which sets the riverbank margins to overflow and lead to the inundation of low
land areas surrounding the riverbed. It is essentially a physical phenomenon. Floods arise
from abnormally heavy rains, dam failures, snow melts, river blockages. Flood disasters
rank second only to droughts in the total number of people affected worldwide.
Types of Floods
Floods can be classified into three categories as under:
(i) River floods
Rivers get charged due to heavy rains over large catchments areas or by melting of
snow or sometimes both especially in the mountainous tracts. The floods take place in river
systems with tributaries that may drain into large geographic areas and encompass many
independent river basins. Amount of flooding depends on moisture in the soil, vegetation
cover, and depth of snow and size of catchments basin.
(ii) Coastal floods
Coastal flooding is associated with tropical cyclones/ harsh winds arising at the ocean
surface. Coastal floods are often aggravated by wind induced storm surges along the coastline.
Sea and ocean ‘water floods the inland coasts affecting kilometers of tracts. Ocean tides,
storm surges or tsunamis play a definite role. Prolonged and indefinite rains in the rainy
season marked from June-September results in extreme flood in coastal river basins.
(iii) Flash floods
These floods occur within six’ hours of the beginning of rainfall and; are characterized
with rising clouds, thunderstorms and tropical cyclones. These result from runoff from a
torrential downpour, particularly if the catchments slope is unable to absorb and hold a
significant part of water. Other causes of flash floods include dam failure, sudden break up
of glaciers etc. These offer potential threats in the areas where the terrain is steep, surface
runoff is high, water flows through canyons and where severe rainstorms are likely.
General Characteristics of Floods
1. Man made structures and forest vegetation exhibits different levels of tolerance
towards effects of floods.
2. Intensity of damage is governed by the time interval of standing floodwaters.
3. High velocity of running water may uproot or weaken foundations of buildings.
4. Rate of rise and discharge of a river is important as a basis for flood control.
5. Frequency of occurrence estimated over a length of period would determine the
kind of activities the flood plain should be put to.
6. Generally the rainy season is characterized by the floods during which agricultural
economy suffers a huge loss.
Effects of Floods
1. Rising water, erosion and the force damages the residential and commercial building.
They are dangerous for villages lying in the coastal areas as it sweeps away
everything, which comes into its path. In mountainous areas it is the chief cause
of landslides.
2. Fisherman, local people, cattle, animals and vegetation suffer a great loss of life
and property. Most of the deaths are reported to be from drowning.
3. Fresh water supplies by all sources are nearly destroyed and contaminated hence
the areas falling under its impact bear a great risk of suffering from water borne
diseases.
4. The destruction of food and fodder crops result in acute food shortage.
5. Floods also make soil infertile, as the topsoil is lost due to erosional activity.
6. Floods are also known to preserve, wetlands and recharge ground water.
Flood Control
1. Depth and width of the riverbed could be increased as its capacity to carry larger
loads increases manifold and thus reduce the area of the flood plain.
2. A network of canals can be established from the river systems, which generally
leads to floods. This would also benefit the agricultural economy/ section. Care
must be taken in the design and construction because of the possible environmental
impact and necessary safety features.
3. Reservoirs should be made for storing floodwater and releasing them at manageable
rates. This would require careful engineering. Dams, and reservoirs would further
lead to generation of resources.
4. Newly constructed residential as well commercial buildings should have foundations,
which are strong enough to respond to flood conditions.
5. Rivers and streambeds should be stabilized with stone, masonry or vegetation at
the banks. This should strictly be followed where rivers pass through cities, specially
near bridges.
Post Disaster Requirements
The initial response to flooding authorities/community should include:
Search and Rescue operations, water provision,
Medical assistance, Disaster epidemiological surveillance assessment, food and
and temporary shelter.
The secondary response should include:
Reconstruction of houses, equipment and tools, supply
Creation of employment, of animals, and assist with
Assistance to farmers, recovery of small business
Distribution of farm and fisheries.
Flood Problem In India
The nature of flood problem varies from one river system to another. Two great river
systems are discussed below considering the flood problems in India:
Brahmputra River
The main problem of flooding in the northeastern region arises from the Brahmaputra
river and its tributaries. The river in monsoon season overflows its banks and causes a great
damage to life and property both. Several times it has affected Kaziranga wildlife sanctuary
where rhinoceros population died due to rising floods. In recent years, the erosion along the
banks of the Brahmputra has assumed serious proportions. The rivers also carry considerable
amount of silt and have a tendency to change its course.
Ganga River System
In this region the northern tributaries of the Ganga, namely the Rapti, the Sharada,
the Ghaghra and the Gandak cause extensive flooding along their banks. Drainage congestion
is confined to the northwestern parts of U.P., Meerut, Mathura and Agra suffers the most.
Bihar suffers a considerable amount of damage due to the flooding of the Burhi Gandak, the
Baghirati, the Kamla Balan, the Kosi and the Mahananda. In addition to the crop submergence
the area experiences traffic dislocation also. In the Bengal region Baghirati, the Ajoy and
the Damodar cause extensive flooding. Here the tidal effect of Bay of Bengal also plays a
role in flooding. In Delhi and Haryana it is the Yamuna, the biggest tributary of the Ganga,
which causes a marginal amount of flooding. Most of these flooding regions suffer from
inadequate channel capacity as well as regulation of river water flow in these channels.
Earthquakes and Seismology
An earthquake is a major demonstration of the power of the tectonic forces caused by
endogenetic thermal conditions of the interior of the earth. An earthquake is a motion of the
ground surface, ranging from a faint tremor to a wild motion capable of shaking buildings
apart and causing gaping fissures to open in the ground. The Richter scale devised by
Charles F. Richter in 1935 measures the magnitude or intensity of energy released by an
earthquake. Good Friday Earthquake of March 27, 1964 in Alaska (USA) measuring 8.4 to
8.6 on Richter scale is among the greatest earthquakes of the world ever recorded.
The science that studies the behaviour and patterns of seismic waves is called seismology.
The place of origin of an earthquake is called focus, which is always hidden inside the earth,
but its depth varies from place to place. The place of the origin of an earthquake is called
‘focus’ which is always hidden inside the earth. The deepest earthquake may have its focus
at a depth of even 700 km below the ground surface. Major Himalayan earthquakes, such
as the Bihar-Nepal earth quake of August 2, 1988, have their focus around 20-30 km deep.
The place on the ground surface, which is perpendicular to the buried ‘focus’ or ‘hypocenter’
recording the seismic waves for the first time is called ‘epicenter’. The waves generated by
an earthquake are called ‘seismic waves’ which are recorded by an instrument called
seismograph. The lines joining the places of equal intensity of seismic waves on the maps
are called is oseismallines.
Causes of Earthquakes
Earthquakes are caused mainly due to disequilibria in any part of the crust of the
earth. A number of causes have been assigned to cause disequilibria in the earth’s crust such
as volcanic eruptions, faulting and folding, gaseous expansion and contraction inside the
earth, hydrostatic pressure of man-made water bodies like reservoirs and lakes, and plate
movements.
(1) Vulcan City
Volcanic activity is considered to be one of the major causes of earthquakes. Vulcan city
and seismic events are so intimately related to each other that they become cause and effect
for each other. Earthquakes follow each volcanic eruption and many of the severe earthquakes
cause volcanic eruptions. The explosive violent gases during the process of Vulcan city try
to escape upward and hence they push the crystal surface from below with great force and
thus is’ caused severe earth tremors of high magnitude.
(2) Faulting and Elastic Rebound Theory
The horizontal and vertical movements caused by end genetic forces result in the
formation of faults and folds which in turn cause isocratic disequilibria in the crystal rocks
which ultimately causes earthquakes of varying magnitudes depending on the nature and
magnitude of dislocation of rock blocks caused by faulting and folding. The 1950 earthquake
of Assam was believed to have been caused due to disequilibria in crystal rocks;
(3) Hydrostatic Pressure and Anthropogenic Causes
Certain human activities such as pumping of ground water and oil, deep underground
mining, blasting of rocks by dynamites for constructional purposes, nuclear explosion, storage
of huge volume of water in big reservoirs etc. also cause earth tremors of serious consequences.
The introduction of additional load through the construction of large dams and impounding
of enormous volume of water in big reservoirs behind the dams cause disequilibria of adjusted
rocks below the reservoirs.
(4) Plate Tectonic Theory
The earth is composed of solid and moving plates having either continental crust or
oceanic crust or even both continental oceanic crusts. The earth’s crust consists of 6 major
plates (Eurasian plate, American plate, African plate, Indian plate, Pacific plate and Antarctic
plate) and 20 minor plates. These plates are constantly moving in relation to each other due
to thermal convective currents originating deep within the earth. All sorts of disequilibria
are caused due to different types of plate motions and consequently earthquakes of varying
magnitudes are caused.
CLASSIFICATION OF EARTHQUAKES
Each earthquake differs from the other and thus it becomes difficult to classify all the
earthquakes into certain categories.
(1) Classification on the Basis of Causative Factors
(A) Natural Earthquakes are those, which are caused by natural processes i.e. due
to end genetic forces. These are further divided into four subcategories.
(i) Volcanic Earthquakes are caused due to volcanic eruptions of explosive
and fissure types and are confined to volcanic areas. Severe earthquake
caused by violent explosions of Etna volcano in 1968.
(ii) Tectonic Earthquakes are caused due to dislocation of rock blocks during
faulting activity. Such earthquake is very severe and disastrous i.e. 1906
earthquake of California (USA).
(iii) Isostatic Earthquakes are triggered due to sudden disturbance in the
Isostatic balance at regional scale due to imbalance in the geological processes.
(iv) Plutonic Earthquakes are in fact, deep focus earthquakes, which occur at
greater depths.
(B) Anthropogenic Earthquakes are caused by human activities such as pumping of
water and mineral oil from underground aquifers. and oil reserves respectively,
deep underground mining, blasting of rocks by dynamites for constructional purposes
e.g. Koyna earthquake of Maharashtra of 1967 due to Koyna reservoir etc.
(2) Classification on the basis of Focus
On the basis of the depths of their foci these have been divided into 3 types.
(i) Moderate Earthquake: Foci are located at the depths between 0-50 km.
(ii) Intermediate Earthquake: Foci at the depths between 50-250 km.
(iii) Deep Focus Earthquake: Foci at the depths between 250-700 km.
Classification on the basis of Human casualties
(i) Moderately Hazardous Earthquakes: If deaths of human range below 50,000
due to seismic tremors e.g. Tabas earthquake of Iran 1978 A.D. (death toll 25,000).
(ii) Highly Hazardous Earthquakes: If deaths of human range between 51,000-
1,00,000 due to seismic tremors e.g. in 1935, Quetta, Baluchistan, (death toll
60,000).
(iii) Most Hazardous Earthquakes: If deaths of human casualties are above 1,00,000
mark e.g., in 1976 Tang-Shan, China (death toll 7,50,000).
World Distribution of Earthquakes
Earthquakes are, in fact associated with the weaker and are statically distributed areas
of the world. Most of the world earthquakes occur in the zones of young folded mountains,
the zones of faulting and fracturing, the junction of continental and oceanic margins, the
zones of active volcanoes and along the different plate boundaries. The world map of the
distribution of earthquakes prepared by seismologists show the occurrence of earthquakes
along the following belts.
(i) Circum-Pacific Belt: surrounding the Pacific Ocean.
Loss of life and property due to natural disasters like tropical cyclones, floods, droughts,
tornadoes, earthquakes, volcanic eruptions etc, is very large. Fortunately warning facilities
are available today and by mitigation measures, loss of lives and properties can be minimized.
National Meteorological Services of the world to provide warnings to the public for some of
the weather related natural disasters. It is not possible to forecast a long period ahead
precisely when and where a dangerous natural phenomenon will take place. While natural
disasters cannot be prevented, taking proper long-term and short-term disaster mitigation
measures can minimize the loss of life and property.
Some common disasters known to occur in our country are as under:
Floods
Floods are defined as a relatively high flow of water discharged from river and stream
network, which sets the riverbank margins to overflow and lead to the inundation of low
land areas surrounding the riverbed. It is essentially a physical phenomenon. Floods arise
from abnormally heavy rains, dam failures, snow melts, river blockages. Flood disasters
rank second only to droughts in the total number of people affected worldwide.
Types of Floods
Floods can be classified into three categories as under:
(i) River floods
Rivers get charged due to heavy rains over large catchments areas or by melting of
snow or sometimes both especially in the mountainous tracts. The floods take place in river
systems with tributaries that may drain into large geographic areas and encompass many
independent river basins. Amount of flooding depends on moisture in the soil, vegetation
cover, and depth of snow and size of catchments basin.
(ii) Coastal floods
Coastal flooding is associated with tropical cyclones/ harsh winds arising at the ocean
surface. Coastal floods are often aggravated by wind induced storm surges along the coastline.
Sea and ocean ‘water floods the inland coasts affecting kilometers of tracts. Ocean tides,
storm surges or tsunamis play a definite role. Prolonged and indefinite rains in the rainy
season marked from June-September results in extreme flood in coastal river basins.
(iii) Flash floods
These floods occur within six’ hours of the beginning of rainfall and; are characterized
with rising clouds, thunderstorms and tropical cyclones. These result from runoff from a
torrential downpour, particularly if the catchments slope is unable to absorb and hold a
significant part of water. Other causes of flash floods include dam failure, sudden break up
of glaciers etc. These offer potential threats in the areas where the terrain is steep, surface
runoff is high, water flows through canyons and where severe rainstorms are likely.
General Characteristics of Floods
1. Man made structures and forest vegetation exhibits different levels of tolerance
towards effects of floods.
2. Intensity of damage is governed by the time interval of standing floodwaters.
3. High velocity of running water may uproot or weaken foundations of buildings.
4. Rate of rise and discharge of a river is important as a basis for flood control.
5. Frequency of occurrence estimated over a length of period would determine the
kind of activities the flood plain should be put to.
6. Generally the rainy season is characterized by the floods during which agricultural
economy suffers a huge loss.
Effects of Floods
1. Rising water, erosion and the force damages the residential and commercial building.
They are dangerous for villages lying in the coastal areas as it sweeps away
everything, which comes into its path. In mountainous areas it is the chief cause
of landslides.
2. Fisherman, local people, cattle, animals and vegetation suffer a great loss of life
and property. Most of the deaths are reported to be from drowning.
3. Fresh water supplies by all sources are nearly destroyed and contaminated hence
the areas falling under its impact bear a great risk of suffering from water borne
diseases.
4. The destruction of food and fodder crops result in acute food shortage.
5. Floods also make soil infertile, as the topsoil is lost due to erosional activity.
6. Floods are also known to preserve, wetlands and recharge ground water.
Flood Control
1. Depth and width of the riverbed could be increased as its capacity to carry larger
loads increases manifold and thus reduce the area of the flood plain.
2. A network of canals can be established from the river systems, which generally
leads to floods. This would also benefit the agricultural economy/ section. Care
must be taken in the design and construction because of the possible environmental
impact and necessary safety features.
3. Reservoirs should be made for storing floodwater and releasing them at manageable
rates. This would require careful engineering. Dams, and reservoirs would further
lead to generation of resources.
4. Newly constructed residential as well commercial buildings should have foundations,
which are strong enough to respond to flood conditions.
5. Rivers and streambeds should be stabilized with stone, masonry or vegetation at
the banks. This should strictly be followed where rivers pass through cities, specially
near bridges.
Post Disaster Requirements
The initial response to flooding authorities/community should include:
Search and Rescue operations, water provision,
Medical assistance, Disaster epidemiological surveillance assessment, food and
and temporary shelter.
The secondary response should include:
Reconstruction of houses, equipment and tools, supply
Creation of employment, of animals, and assist with
Assistance to farmers, recovery of small business
Distribution of farm and fisheries.
Flood Problem In India
The nature of flood problem varies from one river system to another. Two great river
systems are discussed below considering the flood problems in India:
Brahmputra River
The main problem of flooding in the northeastern region arises from the Brahmaputra
river and its tributaries. The river in monsoon season overflows its banks and causes a great
damage to life and property both. Several times it has affected Kaziranga wildlife sanctuary
where rhinoceros population died due to rising floods. In recent years, the erosion along the
banks of the Brahmputra has assumed serious proportions. The rivers also carry considerable
amount of silt and have a tendency to change its course.
Ganga River System
In this region the northern tributaries of the Ganga, namely the Rapti, the Sharada,
the Ghaghra and the Gandak cause extensive flooding along their banks. Drainage congestion
is confined to the northwestern parts of U.P., Meerut, Mathura and Agra suffers the most.
Bihar suffers a considerable amount of damage due to the flooding of the Burhi Gandak, the
Baghirati, the Kamla Balan, the Kosi and the Mahananda. In addition to the crop submergence
the area experiences traffic dislocation also. In the Bengal region Baghirati, the Ajoy and
the Damodar cause extensive flooding. Here the tidal effect of Bay of Bengal also plays a
role in flooding. In Delhi and Haryana it is the Yamuna, the biggest tributary of the Ganga,
which causes a marginal amount of flooding. Most of these flooding regions suffer from
inadequate channel capacity as well as regulation of river water flow in these channels.
Earthquakes and Seismology
An earthquake is a major demonstration of the power of the tectonic forces caused by
endogenetic thermal conditions of the interior of the earth. An earthquake is a motion of the
ground surface, ranging from a faint tremor to a wild motion capable of shaking buildings
apart and causing gaping fissures to open in the ground. The Richter scale devised by
Charles F. Richter in 1935 measures the magnitude or intensity of energy released by an
earthquake. Good Friday Earthquake of March 27, 1964 in Alaska (USA) measuring 8.4 to
8.6 on Richter scale is among the greatest earthquakes of the world ever recorded.
The science that studies the behaviour and patterns of seismic waves is called seismology.
The place of origin of an earthquake is called focus, which is always hidden inside the earth,
but its depth varies from place to place. The place of the origin of an earthquake is called
‘focus’ which is always hidden inside the earth. The deepest earthquake may have its focus
at a depth of even 700 km below the ground surface. Major Himalayan earthquakes, such
as the Bihar-Nepal earth quake of August 2, 1988, have their focus around 20-30 km deep.
The place on the ground surface, which is perpendicular to the buried ‘focus’ or ‘hypocenter’
recording the seismic waves for the first time is called ‘epicenter’. The waves generated by
an earthquake are called ‘seismic waves’ which are recorded by an instrument called
seismograph. The lines joining the places of equal intensity of seismic waves on the maps
are called is oseismallines.
Causes of Earthquakes
Earthquakes are caused mainly due to disequilibria in any part of the crust of the
earth. A number of causes have been assigned to cause disequilibria in the earth’s crust such
as volcanic eruptions, faulting and folding, gaseous expansion and contraction inside the
earth, hydrostatic pressure of man-made water bodies like reservoirs and lakes, and plate
movements.
(1) Vulcan City
Volcanic activity is considered to be one of the major causes of earthquakes. Vulcan city
and seismic events are so intimately related to each other that they become cause and effect
for each other. Earthquakes follow each volcanic eruption and many of the severe earthquakes
cause volcanic eruptions. The explosive violent gases during the process of Vulcan city try
to escape upward and hence they push the crystal surface from below with great force and
thus is’ caused severe earth tremors of high magnitude.
(2) Faulting and Elastic Rebound Theory
The horizontal and vertical movements caused by end genetic forces result in the
formation of faults and folds which in turn cause isocratic disequilibria in the crystal rocks
which ultimately causes earthquakes of varying magnitudes depending on the nature and
magnitude of dislocation of rock blocks caused by faulting and folding. The 1950 earthquake
of Assam was believed to have been caused due to disequilibria in crystal rocks;
(3) Hydrostatic Pressure and Anthropogenic Causes
Certain human activities such as pumping of ground water and oil, deep underground
mining, blasting of rocks by dynamites for constructional purposes, nuclear explosion, storage
of huge volume of water in big reservoirs etc. also cause earth tremors of serious consequences.
The introduction of additional load through the construction of large dams and impounding
of enormous volume of water in big reservoirs behind the dams cause disequilibria of adjusted
rocks below the reservoirs.
(4) Plate Tectonic Theory
The earth is composed of solid and moving plates having either continental crust or
oceanic crust or even both continental oceanic crusts. The earth’s crust consists of 6 major
plates (Eurasian plate, American plate, African plate, Indian plate, Pacific plate and Antarctic
plate) and 20 minor plates. These plates are constantly moving in relation to each other due
to thermal convective currents originating deep within the earth. All sorts of disequilibria
are caused due to different types of plate motions and consequently earthquakes of varying
magnitudes are caused.
CLASSIFICATION OF EARTHQUAKES
Each earthquake differs from the other and thus it becomes difficult to classify all the
earthquakes into certain categories.
(1) Classification on the Basis of Causative Factors
(A) Natural Earthquakes are those, which are caused by natural processes i.e. due
to end genetic forces. These are further divided into four subcategories.
(i) Volcanic Earthquakes are caused due to volcanic eruptions of explosive
and fissure types and are confined to volcanic areas. Severe earthquake
caused by violent explosions of Etna volcano in 1968.
(ii) Tectonic Earthquakes are caused due to dislocation of rock blocks during
faulting activity. Such earthquake is very severe and disastrous i.e. 1906
earthquake of California (USA).
(iii) Isostatic Earthquakes are triggered due to sudden disturbance in the
Isostatic balance at regional scale due to imbalance in the geological processes.
(iv) Plutonic Earthquakes are in fact, deep focus earthquakes, which occur at
greater depths.
(B) Anthropogenic Earthquakes are caused by human activities such as pumping of
water and mineral oil from underground aquifers. and oil reserves respectively,
deep underground mining, blasting of rocks by dynamites for constructional purposes
e.g. Koyna earthquake of Maharashtra of 1967 due to Koyna reservoir etc.
(2) Classification on the basis of Focus
On the basis of the depths of their foci these have been divided into 3 types.
(i) Moderate Earthquake: Foci are located at the depths between 0-50 km.
(ii) Intermediate Earthquake: Foci at the depths between 50-250 km.
(iii) Deep Focus Earthquake: Foci at the depths between 250-700 km.
Classification on the basis of Human casualties
(i) Moderately Hazardous Earthquakes: If deaths of human range below 50,000
due to seismic tremors e.g. Tabas earthquake of Iran 1978 A.D. (death toll 25,000).
(ii) Highly Hazardous Earthquakes: If deaths of human range between 51,000-
1,00,000 due to seismic tremors e.g. in 1935, Quetta, Baluchistan, (death toll
60,000).
(iii) Most Hazardous Earthquakes: If deaths of human casualties are above 1,00,000
mark e.g., in 1976 Tang-Shan, China (death toll 7,50,000).
World Distribution of Earthquakes
Earthquakes are, in fact associated with the weaker and are statically distributed areas
of the world. Most of the world earthquakes occur in the zones of young folded mountains,
the zones of faulting and fracturing, the junction of continental and oceanic margins, the
zones of active volcanoes and along the different plate boundaries. The world map of the
distribution of earthquakes prepared by seismologists show the occurrence of earthquakes
along the following belts.
(i) Circum-Pacific Belt: surrounding the Pacific Ocean.