The document discusses cyclones and provides details about their structure, formation, classification and impact in India. It notes that cyclones are rapid inward air circulation around a low-pressure area and are usually accompanied by violent storms. They are classified into tropical and extra-tropical cyclones. The document also examines cyclones that have impacted India in recent years, such as Amphan in 2020 and Fani in 2019, and discusses measures taken to manage cyclones.

1. NATURAL DISASTER
Dr. Neeraj Yadav
Assistant Professor
School of Basic and Applied Science
K. R. Mangalam University
Gurugram

2. CYCLONES:
 Cyclones are rapid inward air circulation around a low-pressure area. The air circulates in an anticlockwise direction
in the Northern hemisphere and clockwise in the Southern hemisphere.
 Cyclones are usually accompanied by violent storms and bad weather.
 The word Cyclone is derived from the Greek word Cyclos meaning the coils of a snake.
 It was coined by Henry Peddington because the tropical storms in the Bay of Bengal and the Arabian Sea appear like
coiled serpents of the sea.
CLASSIFICATION:
There are two types of cyclones:
1. Tropical cyclones; and
2. Extra Tropical cyclones (also called Temperate cyclones or middle latitude
cyclones or Frontal cyclones or Wave Cyclones).

3. NOMENCLATURE:
 Henry Piddington discussed about tropical storms from Calcutta between 1836 and 1855 in
The Journal of the Asiatic Society.
 He also coined the term cyclone, meaning the coil of a snake.
STRUCTURE: There are a number of structural characteristics common to all cyclones.
 A cyclone is a low-pressure area.
 A cyclone's center is the area of lowest atmospheric pressure in the region.
 Near the center, the pressure gradient force (from the pressure in the center of the cyclone compared to the pressure
outside the cyclone) and the force from the Coriolis effect must be in an approximate balance, or the cyclone would
collapse on itself as a result of the difference in pressure.
 Because of the Coriolis effect, the wind flow around a large cyclone is counterclockwise in the Northern Hemisphere and
clockwise in the Southern Hemisphere.
 In contrast to low pressure systems, the wind flow around high pressure systems are clockwise (anticyclonic) in the
northern hemisphere, and counterclockwise in the southern hemisphere.

4. FORMATION OF CYCLONE:
Tropical cyclones form only over warm ocean waters near the equator.
• To form a cyclone, warm, moist air over the ocean rises upward from near the surface. As this air moves up and away
from the ocean surface, it leaves less air near the surface. So basically as the warm air rises, it causes an area of lower
air pressure below.
• Air from surrounding areas with higher air pressure pushes in to the low pressure area. Then this new “cool” air
becomes warm and moist and rises, too. And the cycle continues…
• As the warmed, moist air rises and cools the water in the air forms clouds. The whole system of clouds and wind spins
and grows, fed by the ocean’s heat and water evaporating from the ocean surface.
• As the storm system rotates faster and faster, an eye forms in the centre. It is very calm and clear in the eye, with very
low air pressure. Higher pressure air from above flows down into the eye.
(But why does an eye form? The cause of eye formation is still not fully understood. It probably has to do with the
combination of "the conservation of angular momentum" and centrifugal force. The conservation of angular momentum
means is objects will spin faster as they move toward the center of circulation. So, air increases it speed as it heads
toward the center of the tropical cyclone.)

5. NOTE:
 When the winds in the rotating storm reach 39 mph (63 kmph), the storm is called a “tropical storm”.
 And when the wind speeds reach 74 mph (119 kmph), the storm is officially a “tropical cyclone” or hurricane.
 Tropical cyclones usually weaken when they hit land, because they are no longer being “fed” by the energy from the
warm ocean waters.
 However, they often move far inland, dumping many centimeters of rain and causing lots of wind damage before they
die out completely.

6. CYCLONE CATEGORIES:
 Cyclones are divided into categories depending on the strength of the winds produced.
 There are many different classification scales but one you may be familiar with is the Saffir-Simpson Hurricane Scale.
 This scale is used to describe storms in Hollywood movies, e.g. “Twister” and “The Day After Tomorrow”.

7. CYCLONES OCCURRED IN INDIA:
1. CYCLONE AMPHAN (2020): Cyclone Amphan was a powerful tropical cyclone which led to the destruction of lives
and property in the states of Odisha and West Bengal. Cyclone Amphan was the first pre-monsoon super cyclone of this
century and emerged from the Bay of Bengal.
2. KYARR AND MAHA (VAYU AND HIKKA), 2019: Cyclone Kyarr was the second strongest tropical cyclone since
cyclone Gonu in 2007. Cyclone Kyarr developed in the Arabian Sea and moved towards the Gulf of Aden from the
Indian coast. It hit the Western India, Oman, UAE, Socotra and Somalia.
3. FANI, 2019: Cyclone Fani is extremely severe cyclone and storm in the shape of hood of a snake, threatening Indian
states of Odisha and Andhra Pradesh and the first severe cyclonic storm of the 2019 in India.
4. TITLI, 2018: Very severe cyclonic storm Titli was part of the 2018 North Indian Ocean cyclone season and makes
landfall in Odisha’s Gopalpur and Srikakulam of Andhra Pradesh.

8. TYPES OF CYCLONE:
1. Tropical Cyclone: It occurs over tropical ocean regions. it is two types- Hurricanes and typhoons. Hurricanes are
found in the Atlantic and Northeast Pacific, whereas typhoons are found in the Northwest Pacific. On the basis of
intensity and wind speed, this cyclone is classified into five categories- 1, 2, 3, 4 or 5. Category 5 has a wind speed of
155 mph or above.
2. Polar Cyclone: It occurs over Polar Regions of Greenland, Siberia and Antarctica. It is strong during the winter
season.
3. Mesocyclone: It is a vortex of air within a convective storm. It is the air that rises and rotates around a vertical axis,
usually in the same direction as low-pressure systems in a given hemisphere. These types of cyclones are
accompanied by the rotating air within the thunderstorm.

9. CYCLONE PRONE AREA IN INDIA:
 India is highly vulnerable to natural hazards like earthquakes, floods, drought, cyclones and landslides.
 According to the meteorological department, there are 13 coastal states and Union Territories in India are Cyclone
prone region.
 Four states like West Bengal, Andhra Pradesh, Odisha, Tamil Nadu-and one UT Puducherry on the east coast and
Gujarat on the west coast are more vulnerable.
MANAGEMENT OF CYCLONES:
There are many structural and non-structural measures for effective disaster management of cyclones.
1. The structural measures include construction of cyclone shelters, construction of cyclone resistant buildings, road
links, culverts, bridges, canals, drains, saline embankments, surface water tanks, communication and power
transmission networks etc.
2. Non-structural measures like early warning dissemination systems, management of coastal zones, awareness
generation and disaster risk management and capacity building of all the stakeholders involved.
These measures are being adopted and tackled on a State to State basis under the National Cyclone Risk Mitigation
Project (NCRMP) being implemented through World Bank Assistance.

10. EARTHQUAKE:
 The earthquake is one of the world natural hazard which often convert into disaster causing widespread destruction
and loss of human life.
 An earthquake is what happens when two blocks of the earth suddenly slip past one another.
 Earthquake, any sudden shaking of the ground caused by the passage
of seismic waves through Earth’s rocks.
 Seismic waves are produced when some form of energy stored in
Earth’s crust is suddenly released, usually when masses of rock straining
against one another suddenly fracture and “slip.”
 The surface where they slip is called the fault or fault plane.
 The location below the earth’s surface where the earthquake starts is called
the hypocenter, and
 The location directly above it on the surface of the earth is called the epicenter.

11. WHAT CAUSES EARTHQUAKES AND WHERE DO THEY HAPPEN?
 The earth has four major layers:
the inner core,
outer core,
mantle and
crust.
 The crust and the top of the mantle make up a thin skin on the surface of our planet.
 But this skin is not all in one piece – it is made up of many pieces like a puzzle covering the surface of the earth.
 These puzzle pieces, also called tectonic plates keep slowly moving around, sliding past one another and bumping into
each other.
 The edges of the plates are called the plate boundaries.
 The plate boundaries are made up of many faults, and most of the earthquakes around the world occur on these faults.
Since the edges of the plates are rough, they get stuck while the rest of the plate keeps moving.
 Finally, when the plate has moved far enough, the edges unstick on one of the faults and there is an earthquake.

12. WHY DOES THE EARTH SHAKE WHEN THERE IS AN EARTHQUAKE?
 While the edges of faults are stuck together, and the rest of the block is moving, the energy that would normally cause
the blocks to slide past one another is being stored up.
 When the force of the moving blocks finally overcomes the friction of the jagged edges of the fault and it unsticks, all
that stored up energy is released.
 The energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond.
 The seismic waves shake the earth as they move through it, and
 when the waves reach the earth’s surface, they shake the ground and anything on it, like our houses and us!
HOW ARE EARTHQUAKES MEASURED?
 The vibrations caused by an earthquake are detected by a seismometer and on a seismograph, it plots these
vibrations. Richter scale also measured the strength or magnitude of an earthquake.
 When an earthquake measured around 7 or 8 on the Richter scale, it can be devastating.

13. TYPES OF EARTHQUAKES:
Mainly, there are four types of earthquakes namely tectonic, volcanic, collapse and explosion.
1. Tectonic earthquake: This occurs when due to geological forces on rocks and the adjoining plate’s cause’s physical
and chemical change and results in the breaking of the Earth's crust.
2. Volcanic earthquake: Results from tectonic forces and occurs in conjunction with volcanic activity.
3. Collapse earthquake: are generally small earthquakes that occur in underground caverns and mines caused by the
seismic waves which are produced from the explosion of rock on the surface.
4. Explosion earthquake: Occur due to the detonation of a nuclear or chemical device.

14. EFFECTS OF EARTHQUAKES:
1.Damage to buildings
 High magnitude earthquakes can lead to complete collapse of buildings.
 Debris from collapsing buildings is the main danger in the course of an earthquake because the falling effects of huge,
heavy objects can be deadly to humans.
 High magnitude earthquakes result in shattering of mirrors and windows, which also present danger to humans.
2.Damage to infrastructure
 Earthquakes can cause electricity lines to fall.
 This is dangerous because the exposed live wires can electrocute humans or start fires.
 Major earthquakes can cause rupturing of roads, gas lines, and water pipelines.
 Broken gas lines can cause gas to escape. Escaping gas can result in explosion and fires, which may be difficult to
contain.

15. EFFECTS OF EARTHQUAKES:
3. Landslides and rockslides
 When an earthquake occurs, large rocks and sections of earth located uphill can be dislodged, consequently, rolling
rapidly down into the valleys.
 Landslides and rockslides can cause destruction and death to the people living downstream.
4.Can result in floods
 High magnitude earthquakes can instigate cracking of dam walls, collapsing in the long run.
 This would send raging waters into nearby areas leading to massive flooding.
5.Earthquakes can trigger tsunamis
 A tsunami is a series of long high sea tremors sparked by an earthquake or volcanic eruptions under the sea.
 A tsunami can wipe out an entire surrounding coastal area population.
 A typical example is the March 11, 2011, earthquake and tsunami that struck the coast of Japan leaving more than
18, 000 people dead in its wake.

16. 6. Leads to liquefaction
 Liquefaction is a phenomenon where the soil becomes saturated and loses it strength.
 When sediments consisting of high water content are subjected to constant trembling, water pressure held in the
sediment pores slowly increase.
 Ultimately, the sediments lose almost all cohesive strength and start acting like liquids.
 Buildings and other structures built on top of this liquefied soil overturn or sink into the ground.
 Earthquakes are responsible for most of the liquefaction occurring across the world.
 A typical example of liquefaction phenomenon is the earthquake of 1692 in Jamaica that resulted in the devastation of
the town of Port Royal.

17. LANDSLIDE:
 The movement of a mass of rock, debris, or earth down a slope.
 Landslides are a type of "mass wasting," which denotes any down-slope movement of soil and rock under the direct
influence of gravity.
 The term "landslide" encompasses five modes of slope movement:
 falls,
 topples,
 slides,
 spreads, and
 flows.
 Landslides occur when gravitational and other types of shear stresses within a slope exceed the shear
strength (resistance to shearing) of the materials that form the slope.

18. CAUSES OF LANDSLIDE:
 Landslides occur when the slope (or a portion of it) undergoes some processes that change its condition from stable
to unstable.
 This is essentially due to a decrease in the shear strength of the slope material, to an increase in the shear stress borne
by the material, or to a combination of the two.
 Natural causes of landslides include:
• saturation by rain water infiltration, snow melting, or glaciers melting;
• rising of groundwater or increase of pore water pressure
• increase of hydrostatic pressure in cracks and fractures,
• loss or absence of vertical vegetative structure, soil nutrients, and soil structure erosion of the toe of a slope by
rivers or ocean waves;
• physical and chemical weathering
• ground shaking caused by earthquakes, which can destabilize the slope directly or weaken the material and
• cause cracks that will eventually produce a landslide;
• volcanic eruptions;

19. CAUSES OF LANDSLIDE:
 Landslides are aggravated by human activities, such as:
• deforestation, cultivation and construction;
• vibrations from machinery or traffic;
• blasting and mining;
• earthwork (e.g. by altering the shape of a slope, or imposing new loads);
• in shallow soils, the removal of deep-rooted vegetation that binds colluvium to bedrock;
• agricultural or forestry activities (logging), and urbanization, which change the amount of water infiltrating the soil.

20. EFFECTS OF LANDSLIDES:
1.Lead to economic decline
 Landslides have been verified to result in destruction of property.
 If the landslide is significant, it could drain the economy of the region or country.
 After a landslide, the area affected normally undergoes rehabilitation involves massive capital outlay.
2.Decimation of infrastructure
 The force flow of mud, debris, and rocks as a result of a landslide can cause serious damage to property.
 Infrastructure such as roads, railways, leisure destinations, buildings and communication systems can be decimated
by a single landslide.
3.Loss of life
 Communities living at the foot of hills and mountains are at a greater risk of death by landslides.
 A substantial landslide carries along huge rocks, heavy debris and heavy soil with it.
 This kind of landslide has the capacity to kills lots of people on impact.

21. EFFECTS OF LANDSLIDES:
4.Affects beauty of landscapes
 The erosion left behind by landslides leaves behind rugged landscapes that are unsightly.
 The pile of soil, rock and debris downhill can cover land utilized by the community for agricultural or social
purposes.
5.Impacts river ecosystems
 The soil, debris, and rock sliding downhill can find way into rivers and block their natural flow.
 Many river habitats like fish can die due to interference of natural flow of water.
 Communities depending on the river water for household activities and irrigation will suffer if flow of water is
blocked.

22. TYPES OF LANDSLIDES:
1. Falls
 Falls are sudden movements of loads of soil, debris, and rock that break away from slopes and cliffs.
 Falls landslides occur as a result of mechanical weathering, earthquakes, and force of gravity.
2. Slides
 This is a kind of mass movement whereby the sliding material breakaways from underlying stable material.
 The kinds of slides experienced during this type of landslide include rotational and transitional.
 Rotational slides are sometimes known as slumps since they move with rotation.
 Transitional slides consist of a planer or 2 dimensional surface of rupture.
o They involve landslide mass movement following a roughly planar surface with reduced rotation or
backward slanting. Slides occur when the toe of the slope is undercut.
o They move moderately, and the consistency of material is maintained.

23. TYPES OF LANDSLIDES:
3. Topples
 Topple landslides occur when the topple fails.
 Topple failure encompasses the forward spinning and movement of huge masses of rock, debris, and earth from a
slope. This type of slope failure takes place around an axis near or at the bottom of the block of rock.
 A topple landslide mostly lead to formation of a debris cone below the slope.
 This pile of debris is known as a Talus cone.
4. Spreads
They are commonly known as lateral spreads and takes place on gentle terrains via lateral extension followed by
tensile fractures.

24. TYPES OF LANDSLIDES:
5. Flows
This type of landslide is categorized into five;
 earth flows,
 debris avalanche,
 debris flow,
 mudflows, and
 creep, which include seasonal, continuous and progressive.
 Flows are further subcategorized depending upon the geological material, for example, earth, debris, and bedrock.
 The most prevalent occurring landslides are rock falls and debris flow.