Page 127 - SST Class 07

Depending upon several factors, such as wind, floor. The ocean floor was displaced and tilted, so
underwater earthquakes, temperature etc., the a huge mass of ocean water flowed to fill in this
waves can be high or low. The waves approach gap at a tremendous speed. Due to this, the water
the coastal areas and crash there. Strong waves withdrew from the coastlines in south and south-
can cause damage. A tsunami is a high wave east Asia. After this displaced area was filled with
which causes widespread damage to the coastal water, the water mass rushed back towards the
areas. coastlines, travelling at a speed as high as 800 km
per hour.
Info Bits At this speed, the helicopter will find it difficult to
Info Bits
compete and the fastest trains will lag behind. At
Tsunami is a Japenese word that means harbour such a tremendous speed, the tsunami crashed on
waves as the harbours get destroyed whenever the seacoasts of countries in south and south-east
there is tsunami. Asia. It completely washed away some islands in
the Indian Ocean. The countries of Sri Lanka, India
A tsunami may be caused due to an underground
earthquake, the eruption of a volcano or and other south-east Asian countries were badly
underwater landslide, because a large mass of affected.
water is shifted which results in high waves. On an estimate, 3,50,000 people were killed in
Generally, the high waves do not exceed over 15 different countries. Large areas were inundated.
m in height and are very forceful, causing small Fields and buildings on the seacoasts were
ships and boats to overturn. The higher waves can destroyed.
prove very destructive. The highest wave which One of the primary causes of the high casualties
has ever been measured was 150 m high. You can was the curiosity. When the water withdrew from
just imagine what such a high wave can do to the the coastlines to fill the gap due to the earthquake,
ships and coastal areas. A tsunami can travel as the people gathered to see this amazing miracle,
fast as 500-800 km per instead of going to high ground. They never knew
hour. It can travel that a tsunami was approaching fast.
thousands of km without
losing its power. Its Since tsunamis are not common in the Indian
speed coupled with Ocean, there was no early warning system , it also
height results in a large contributed to the casualties.
destruction. A tsunami wall in Japan
Activity
The destruction from a tsunami can be prevented Find out the names of places that are frequently
or minimised by installing early warning systems. ravaged by tsunami. Also find out what
The planting of trees and construction of walls precautionary measures are taken there to minimise
around the coastal villages and towns too have the damages caused by tsunami.
proved effective.
Tides
Case Study : Tsunami Of 26th December, 2004
A tide is the rise and fall motion of the seawater. It
An earthquake struck the western boundary of occurs twice a day at almost regular intervals. This
Sumatra on 26 December, 2004; its magnitude was interval is generally 12 hours 25 minutes. This rise
9.0 on the Richter and fall of seawater is in
Scale. The earthquake response to the force of
was caused because the gravitation of the moon
Indian plate went under and the sun. High tide
the Burma plate, occurs when the water
starting a sudden level rises to its highest
movement of the sea Destruction caused by tsunami level and fills the shores.
High tide
The Hydrosphere
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