Tsunami (Gnv64)

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Chapter- 1

nceofTs n

A

Tsunami

(pronounced

soo-nah-mee)

like the one that East Asia of 26

ravaged

the coastal

areas of South

December 2004 is made up of a special sort of sea waves. But. the tsun, crash on the coastlines of this region unleashing terror

never

experienced

before.

Recognizing a TsunamiTsunamis are often referred to as tidal All Nature's vagaries are pointers of the power the violence of Nature to the overwhelming For mankind, the is an unattainable is to understand of natural disasters.

waves

but this is influences

incorrect. as tides occur due to the gravitational superiority controlling scientific of Nature.

dream, but what is sure!>' possible basis of the occurrence turned the terror

'l)}:K1,ow what

benevolent

sea into a raging monster 2004? in the bed of to northern mammoth scale, tip of

that unleashed

in the coastal areas of South East

Massive undersea earthquake in the bed of Indian Ocean gave birth to mammoth tsunami waves of 26 December 2004.

of the Moon, Sun, and planets. Tsunamis are not generated by the tidess. However, a tsunami that strikes a coastal area is influenced Powerful

by

the tide tsunamis.

level

at the time of impact. most ocean the normal

undersea earthQuakes or seismic activiry Unlike

common!>' generate

waves,

the tsunami

(distance between the km. These plane.

waves wave

have a

very

long wavelength

crests) - often more than 100

Asia in the ear!>' hours of 26 December It was a massive Indian tsunami with region released its Ocean undersea that Measuring close Island, earthQuake birth to the

waves

travel a deep ocean with a speed of more tsunamis are not always 'seismic sea

than 800 km per hour Le., more than the speed of a jet However, eruptions, falling Ocean. gave

waves.

waves',volcanic

as they may also be generated due to landslides, and rare!>' However, Sea and

9.0 on the Richter's this earthQuake

by

the impact

of a large occur in have

epicentre Sumatra

meteorite the Pacific

in the ocean6.

Most tsunamis

Indonesia's

shook this

violent!>'.

Indeed

so violent

was it that it According our planet

evento was

destructive

tsunamis

also been generated in the Atlantic the Mediterranean

and the Indian Oceans, within smaller bodies of

made the Earth wobble on its aXis!1 The enormous energy soon circled around the globe. the scientists still initial "ringing from the Earth Sciences National Universiry, like a bell" well According Space and Research School

even

water, like the Sea of Marmara in Turkey.

at the Australian catastrophe.

Tectonic PlatesAccording to the Plate Tectonic Theory, the surface of the of massive rigid plates, on top of These plates change size - rough!>, the rate Earth is made up of a patchwork the Earth's hot, fleXible and position interior7.

over

two weeks after the to the US National (NASA). and

Aeronautics this rare seismic Pole, slightly spin

Administration

about 80 km thick, which float in slow motion

event evenaltered a little

shifted the Earth's mean North of the planet, of each day making horrifjing that it has been

the shape the length faster2 has

even

over

time, as they are constant!>' moving at a

slight!>, decreased of this

speed of about I cm to 10 cm at which fingernails ~ologic

every year

the Earth impact

Yet another

grow! As these plates

move,

intense

earthQuake

activiry occurs at the plate edges.

2

Tsunami

The surface of the farthis made up of a patchwork of massive rigid tectonic plates, about 80 km thick, which float in slowmotion on top of the farth's hot, flexible interior.These plates change size and position over time.

As some tectonic plates for new ocean noor each other without potentiallY beneath collide collision Ocean. under of

move

away from each other, space Some plates slide past However. in a towards each other.

is created.

causing much disturbance.

there are some plates moving dangerous

way

as one plate

may submerge plates

the other. As the sides of two tectonic violentlY, enormous that triggers the generation where denser oceanic continental plates.

energy is released. It is this of tsunamis. This is the margins of the Pacific plates are known to slip process is known as This

exactlY what happens around

The devastation caused on the Jndian shores by the tsunamis that hit the South East Asian coastlines recently has proved that India is too on the vulnerability chart, though chances of such an onslaught are rare.It is a horrifying tsunamis occur fact that an average of two destructive per year in the Pacific basin. although in all the oceans and inland

subduction

and the area where the chances of occurrence and earthQ!.lakes are zone8. effective

tsunamis can be generated seas of the world. About Fire extends northward the Philippines, Russia. It also

volcanoes

very

high is called the earthQuakes are

80% of all recorded earthQuakes through Fiji. Papua New Guinea, the eastern coast of

subduction particularlY

The subduction in generating

occur around the edge of the Pacific Plate. The Ring of and lapan along

tsunamis.

Ring of FireCircling there has a the Pacific Basin, on the bottom lies a series Called of volcanic of region. the 'Ring This of the seabed. and deep and the this region called arcs of Fire', also ocean trenches. high

covers

the region east to the southern edge Since India does not fall in of our country to the to be low. However. shores

of Alaska as well as the western coast of Canada. North

occurrence

earthQuakes

volcanicworld's

eruptions9.

circum-Pacific

seismic belt. is home to

over

75% of the

It is a horrifying fad that an average of two destrudive tsunamis occur per year in the Pacific basin.

America and South America. the Ring of Fire. the devastation has proved

the vulnerability caused

experience tsunamis was considered

on the Indian

by

tsunamis that hit the South East Asian coastlines that India is too on the vulnerabiliry are rare. though chances of such an onslaught

recentlY chart,

As the tedonic plates collide, separate, or slide past one another, some plates gain while others lose material at their edges, which is why the plate boundaries change over geologic time.

active and dormant

volcanoes.

Birth of the Killer WavesTsunami waves may be generated because of certain phenomena that include the following:

t han 7 .5

Undersea EarthquakesEarthQuakesusually occur in regions of the Earth along tectonic plate boundaries called faults. where different tecton ic plates meet. The chances of occurrence of earthQuakes are very high in these regions due to the collision of tectonic plates as these plates are constantly moving past each other'o. UnderstandablY. when two tectonic plates collide. a large amount of the built-up stress is released. On the other hand. intraplate earthQuakes.which are less than 10% of all earthQuakes. occur within the tectonic plates in the more stable interiors of continents. far away from plate boundaries". Although the cause of occurrence of intraplate earthQuakes is not Quite clear. these are possiblY related to the driving forces of plate tectonics. As the tectonic plates collide, separate. or slide past one another. some plates gain while others lose material at their edges. which is why the plate boundaries change over geologic time. If weakened former plate boundaries become part of the interiors of plates. stresses originating at the edges of the plates or in the deeper crust may result in intraplate earthQuakes. The most destructive tsunamis are generated by massive undersea earthQuakes.occurring at a depth shallower than 50 km with an epicentre or fault line near or on the ocean floor. Such an undersea earthQuake.of magnitude greater

Volcanic~

on the Richter's scale. tilts and deforms large f the sea floor ranging from a few kilometers to areaS O even more than \.000 km. This sudden vertical diSplacement over large ~reas grossly di~places the seawater.which under the Influence of gravlry. tends to regain its eQ].Jilibrium.It is this vertical movement of the entire water column that generates destructive tsunami waves.As energy cannot be created or destroyed but can be only transferred from one form to another (Law of Conservation of Energy). the potential energy that results from pushing water above mean sea level is transferred to kinetic energy that initiates the horizontal propagation of the tsunami waves. If the sea floor movement is horizontal. a tsunami is usually not generated. Besides. not all undersea earthQ].Jakes create tsunamis. as it depends on the nature and degree of displacement of the seawater column. It is onlY the vertical displacement of seawater due to abrupt. jerky movement of fault blocks on the seabed that gives birth to powerful tsunamis. Once formed. the monstrous waves soon begin their journey towards the nearest coastlines. ringing the bells of doom.

Tsunamis arrive at a c