Tsunami Video Lecture | Geography for Class 7

this story begins long before people
walked the earth even before the
dinosaurs before the first sentence of
life appeared on this planet before
anything existed at all the Big Bang the
birth of our universe
from this new matter the first galaxies
took shape nebulae formed inside the
galaxies and inside the nebulae the
first stars were born the Sun was about
to make its appearance in the same way
surrounded by a rotating disk of dust
and gas gravity pulled the dust
particles together and they turned into
huge masses that grew and attracted
other masses future planets the gases
gathered in the Sun which finally lit up
the planets cool thanks to large and
small meteorites that rained down from
the sky the energy each new impact was
transformed into heat
that gradually warmed up the young
planets eventually these became the
worlds we know today Jupiter Saturn
Mars and of course Earth but what
happened to the heat that was
accumulated while our planet was being
formed it's still there hidden in the
innermost layers of the Earth's core and
it's constantly reinforced by natural
radioactivity the heat is continually
transmitted to other layers before being
freed into space during its journey
toward the surface
the heat moves semi fluid rocks it meets
along the way like water boiling in a
pot the rocks in each layer rise upward
and shed their heat then they fall and
get heated again like huge and very slow
cogs in a machine their movements shift
the plates or enormous sheets that make
up the thin outer layer of the Earth's
crust in this way they move whole
continents after 200 million years this
is the result
but the pleats are interlocked that's
why when they shift the jerky movement
along the edges that separate them
causes what we call earthquakes most of
the earthquakes recorded in the world
aren't very strong but sometimes a
particularly great one causes
destruction and death earthquakes also
occur at the sea bottom when that
happens they can sometimes displace the
water column and originate waves these
waves are best known by their Japanese
name tsunami which simply means harder
wave regular sea waves caused by the
wind a very different from tsunami waves
let's find out why wind blowing over the
sea can only move the upper layer of
water forming waves but not affecting
movements deeper down the water
particles near the surface move with a
circular motion which helps to propagate
the wave along deep down the water
particles don't move the strength with
which these waves reach the coastline
depends exclusively on the movement in
the first few meters of water a tsunami
on the other hand can be generated at
the bottom of the sea in case of a
strong earthquake the sea floor abruptly
deforms and vertically displaces the
overlying water the entire water column
is disturbed by the uplift or subsidence
of the sea floor this sudden movement
releases a great impulse of energy which
is transferred to the whole column of
water between the surface and the sea
floor in this case the water deep down
moves as well as deep as a thousand
2,000 3,000 meters apart from submarine
earthquakes tsunami waves can also be
generated by underwater landslides or
when rocks or sediments slide into the
sea by volcanic eruptions or more rarely
when a me
you're right falls into the sea alarm
systems currently in use in the Pacific
and Indian Oceans give advance warning
when a tsunami is generated these
systems rely on sensors placed at the
sea bottom which measure variations in
the water above and transmit an alarm
via floating buoys and satellite
link-ups with observation stations on
the coast once generated tsunami waves
in the open sea travel very very fast up
to 800 km/h they can cover thousands of
kilometres and approach coasts far from
their point of origin with great energy
in the open sea the waves are rarely
over a meter high and a very long so
they're imperceptible the ship in open
sea for instance wouldn't notice
anything out of the ordinary the speed
of a tsunami wave depends on the depth
of the water the wave is traveling
through approaching the shore that
tsunamis speed diminishes although it's
still much much faster than an ordinary
wave also wave amplitudes will increase
dramatically this is due to the fact
that the tsunamis energy flux which is
dependent on both its wave speed and
wave height remains nearly constant
consequently as the tsunamis speed
diminishes as it travels into shallower
water its height grows this huge and
fast-moving mass of water shifts an
entire column of water from the sea
floor to the surface approaching the
coast with a destructive force far
superior to any wind generated wave it
can advance hundreds of meters in land
that's why even if it isn't very high
tsunami wave can still cause serious
damage along the coastline
when the trough of the wave first
reaches the coast
the tsunami appears to make the sea
withdraw often quite consistently
leaving harbors and beaches dry this can
last for several minutes and is a sign
to get as far away from the shore as
quickly as possible
the crest of the wave will arrive at any
minute it may look like a sudden high
tide that keeps getting higher or a wall
of water moving faster than any normal
wave it carries with it the energy of
the earthquake not that of the wind this
is exactly what happened along the coast
of Thailand a morning of December 26th
2004 that tsunami generated by the
strongest earthquake of the past 40
years of the island of Sumatra spread
death and destruction along the coasts
of the Indian Ocean images filmed by
people who were there helped us better
understand the devastating effects
produced by the huge amounts of energy
of the tsunami wave
catastrophic events of these proportions
are extremely rare in the past the most
destructive tsunamis hit the coasts of
the Pacific and Indian Oceans but even
the coast of the Atlantic Ocean and the
Mediterranean Sea to a lesser degree are
at risk and have experienced sometimes
destructive tsunamis during the course
of history studies developed by the
istituto national ad geophysical
volcanologist seventy more or less
destructive tsunamis along the coast of
Italy alone over the past 2,000 years
moreover destructive tsunamis in the
eastern Mediterranean have had a slight
impact on the southernmost coasts of the
Italian peninsula an analysis of the
catalogue of Italian tsunamis shows that
southern Calabria the Messina Strait and
eastern Sicily have been the areas of
Italy's coastline most affected by
tsunamis in the past some are the result
of strong earthquakes submarine or near
the coast others have been caused by
volcanic activity and submarine
landslides the most famous of them all
were the tsunamis that hit Calabria in
1783 and the Messina Strait in 1908
between 1783 and 1784 Calabria was
struck by one of the longest most
violent seismic crises of the past 2,000
years five very strong earthquakes took
place between February and March 1783
and some of them caused tsunamis recent
studies have shown that during this long
seismic crisis there were 10 tsunamis
seven of them were low intensity to
where fairly strong and one was
destructive the destructive tsunami
occurred on February 6th 1783 due to a
huge portion of Mount Kampala near
Sheila suddenly fallen into the sea
about an hour after the first shock many
people living in the town of Sheila were
frightened by the continuing earthquakes
and took refuge on the beach at
Gandhi it was there they were hit by the
tsunami generated by the massive
landslide three huge waves crashed onto
the beach of marina grande the water was
as high as the roofs of the houses as
high as nine meters and it spread inland
for over two hundred meters the waves
also struck the beaches of Galileo and
marina de lavit or passed the promontory
of Sheila
a thousand five hundred people died as a
result the tsunami was seen in other
places along the Calabrian coast from
Nicotra to reggio calabria
at Messina and toradol Faro on the coast
of Sicily the sea went inland for over
two hundred metres and reached a height
of over six meters
the earthquake that struck Messina on
December 28 1998 was one of the
strongest ever experienced in Italy the
cities of Messina and reggio calabria
along this many towns and villages were
completely destroyed and over 60,000
people died about 10 minutes after the
earthquake a particularly violent and
destructive tsunami struck the coasts of
Sicily and Calabria around the Messina
Street causing serious damage and
killing hundreds of people to a greater
or lesser degree that tsunami affected
the entire area of the eastern Sicilian
coastline part of the northern coastline
and most of Calabria Turanian coast it
started with the sea withdrawal as far
as 200 metres a few minutes later at
least three violent waves crashed into
the shore in some places the first wave
was the biggest in others it was the
second wave the sea swells lasted for
several hours and only gradually
diminished along the Calabrian coast the
tsunami reached heights of over 13
meters while along the Sicilian
coastline at Giardini Naxos and santol
seo over 12 metres of run-up was
measured a run-up is the height reached
by the water above sea level studies of
the catalogues of Italian tsunamis have
allowed to identify the coasts most
prone to this risk the instituto
nacional ad geophysical a Volcanology ax
together with the University of Bologna
is setting up a monitoring network to
recognize tsunamis in these areas at the
same time on an international level a
unesco initiative has created working
groups of researchers representing
different nationalities their task is to
plan and set up a tsunami warning system
for the whole of the Mediterranean
the project is another important
contribution towards research aimed at
studying and better understanding the
Earth the only planet that's home to
life we need to protect ourselves and to
protect the earth
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