Good evening
and in the morning we
were looking at
some of the aspects of
what causes the landslide
so we were trying
to look at some
physical connection like
 the sliding board
and then we are
trying to see
how we can probably
 relate all of this
now
moving on, I have a few
things which I
thought I just
share with you
point number 1
today we'll see
some of the other
other natural calamities
which are associated with
with this geology
the geological aspect
or because of the
surface of the earth
now
Tsunami is not something
[Topic:**Tsunami]
very new because
India suffered a major Tsunami
and till then
the awareness that
there was something
called Tsunami was not at all there
so and so when
earthquakes truck India
the booch area
then only people started
to get aware that
 there something
called earthquake
which can also affect people
so when we started this
2000, we started
to colors very very big
on what do you
called as a
very big scale of disasters
which kind of shape the
public policy greatly
so
whenever there is a disaster
the government
will try to patch up the
what we call as the
things where we lacking
so that we can
respond better when
a disaster strikes again
so next time,
probably when a
pandemic comes
we are going to be
more prepared
okay but now let's restrict
out discussion to Tsunami
let's
have a small question
what is a wave
what is a wave
Aayushi, you have
joined, okay
Aayushi, what's the wave
Aayushi
okay, Ishaan
Are you around, yes sir
yes, Ishaan
what is a wave
[student's answer]
okay
[student's answer]
okay
so
basically
you are seeing
we are seeing that
it is a transfer of energy
so
now
whenever you are
what you call as
you know facing a
whenever there is a
movement of energy
it is usually in the
form of waves
so when you go
 through the
rest of the videos
you will be having
things like you know
what's a standing wave
and so on and so forth
and it is essentially
this waves
which get what you
 call as the
reflected, refracted,
so on and so forth
okay now one of the
very important things that
you will probably
remember is
when the
surface of the water is
disturbed by a stone
you will usually see some
ripples
the ripples move from
 the center
and move on to the end
and as it comes to the edge
typically you will find that
the
ring size is bigger
but the amplitude
of displacement is reduced
now
when you look at
the sea
you see waves
if you
if you remember
your geography
these waves are caused
because of the passage
of wind over the ocean
so it kind of you know
this is a surface
 of the water
the wind kind of pushes the
water slightly inside
and it starts
to generate some energy
it impart some
energy to the water body
now this water body
has this wave energy
move from the
 periphery to the center
now let us say that
the wave
the water was displaced by 1cm
so here what happens is
many thousand liters of water
has been moved by 1cm
the problem is
that there is no
problem at the
center, in the
middle of the ocean
because there is lot of space
for the water to
kind of
move up and down
but when it comes to a shore
the quantum of water says that
it has to go upward
it has to break the surface
now this is what causes
waves typically
in a sea
so when there is a
cyclone or the pressure
low pressure and other things
you will find that the
water body is getting pushed
sufficiently to cause
rough waves in the shore
so when it comes to a shore
the wave height
keeps increasing
because there is not much
space for the water
for the
wave to move or
displaced and lose its energy
now when we look at a Tsunami
what happens is
when its caused
due to an earthquake
the underground
plates could rupture
and it cause a motion
again this motion could
be very very small
it could be very very small
but as the wave travels
as the wave travels
the
wave keeps increasing in height
so
you can have very
small Tsunamis
which would be a few meters or
high say 2 meters
 or 3 meters
or you will find that
they can be
far far greater
now
what are the
science of a
Tsunami
what are the
 indications of Tsunami
what are the indication of Tsunami
any idea
so the first time
when I heard
about the Tsunami was
in my English book
English book are full of stories
so there was the story of
this japanese village
which was a very
prosperous village
the village was on
a mountain
so
one day
all of a sudden,
they saw a wonder
the sea was going backward
this was not something
anybody had seen
so they all rushed to see
what had happened
now what was
actually happening
the water was receeding because
one of the waves
have lifted up sufficiently
making all the
water go towards the ocean
but what happens
once the wave goes up,
it is again going to come down
so when the
when a old man heard it,
 he realized
the significance of
what had happened
and he went and sit
fair to all this bailes
of you know rice
which they had harvested
seeing this, seeing that their
rice was getting affected
all the villagers came running up
they were coming to
may be beat up the
old man not gone mad
but when they came
they saw that the sea
which had gone back had returned
and had they been in
 the low grounds
the entire village would
have lost the people
I mean the lives or lot
 of people has lost their lives
now this is what happened
when the Tsunami happened
in India also
some of the people
whom we know knew
their family had gone to beach
and they were trying
to return back
but unfortunately they were
 caught in the Tsunami
so when the person
was recounting
what happened
that's heart breaking
but the good part was
 after the Tsunami
he took so many children
who were
many times offend or lost
 were just looking lost
and he took care of them
irrespective of the fact
 that he had
lost his own children
so this was one story
that really challenge for me also
but the point
 I wish to make is
if you see the sea
receding
remember that it is the
indication of a Tsunami
the person who manage to save himself
he hung on to a coconut tree
he hung on to a coconut tree
and
yeah, so that was
 how he saved himself
now there is another
thing which
protected us
so whenever protected
what you call as the
damage due to the Tsunami
whenever you are
having some vegetation
there was a, there is a
resort in
what you call as
'Mahabalipuram'
and
it was the sunday
when this Tsunami came
so in that
camp site
they
had a you know, like
the breakfast around 8 o'clock
so they have called
everybody back
and when the Tsunami came,
 it came with a lot of fiery
and this particular area had
this bamboo brush
a small
I don't know they call
 it moongil
it's not
it's not exactly bamboo
but it is a one of
it's a tree which is,
which looks like bamboo
I am forgetting the
 name of the brush
so
so the trees blocked the
force of the wave
they bore the brunt of the wave
so when the sea water came
it lost all its energy
okay now the important word
 I want to speak to you is
energy, so the
energy was dissipated
the Tsunami did not do
 as much damage
as it could have,
otherwise done, okay
so
the two things which
come to Tsunami is
probably you know like
animals getting distract
and of course
the other thing is
the sea receding
these are indications which
you observe physically
now in Tsunami,
advance warning system
what happen, they
have hydrophones
in the sea and in
many other places
which can pick
 up disturbances
it might be a seismogram
or
anything else
I mean like you know
now we have so
many technologies
which are able to correlate
occurrence of a tsunami to
certain geological activities
so it can be a hydrophone,
 it can be a
because these are all
 strategically placed in boys
are in and around
Pacific Ocean, okay
because and also the
Indian ocean is there
and these are all one, what do
 you call as you know
part of a
Tsunami warning system
and
when, when these
systems pick up
something abnormal
they send signal to
the ground station
and they also communicated
to the people
and again, it may
give you around
three minutes to
five minutes warning
at the most
its three minute to
five minute warning at the most
now, in
as I told you earlier
very few people countries
 actually have the
emergency alerts
so, you see suppose
you see your phone
you'll have something
called "Emergency alerts"
but typically we don't get
any of these emergency alerts
so one, may be we don't
have many natural disasters
and two problem is we are
 not even aware such a system is
existing
however these are 
very widely used in
countries which are very prone for
prone to such
natural disasters
so
in as a summary
Tsunami is typically when are
caused when there is
disruption and then
energy wave is generated
and this can cause the
 sea water especially to recede
the sea water will go back and
then when it comes back into the land
it's going to come 
with a lot of force
but of course, the 
other way around also
it can happen where water 
just comes into the
comes into the land, okay
so typically
what we do is
we have a what you call 
as "Energy Dissipators"
we have Energy dissipators
so, strategically placed walls
are
will prevent the
wave
I mean like prove, will reduce the  
energy associated with that wave
again it's a mere reduction
so if suppose the energy content is
much more than what
 the energy dissipated
was designed for, you still 
will find that it's feeling
okay, so
moving on
one of the other things 
which cause Tsunami is
when landslides occur
 into water bodies
when landslides occur
 into water bodies
Tsunamis take place
so it's like you know
if you just take a small stone
put it some water splashes
when you take a larger 
of more water splashes
but just imagine like the 
landslide which we saw
in yesterday's videos
a huge mass of land
 suddenly spills into the reservoir
or for dam, or you know 
for lake or any water body
this pushes the water
 with a great force
all the energy which was
which was you know
 imposed on the water body
has to be dissipated
so this causes the waves
to take place, even in 
standing water body
so, they are now one
 of some of the things
which you would have observed is
where are the places
where Tsunamis are 
likely to take place
the second thing is
how we can prevent Tsunamis
from damaging
that is we are constructing
 energy dissipators
basically that is the
 only thing which
we can do, some of 
the other things
which typically try to do is like
you know ensure 
that the shelter
for people who
from so I mean like a
Tsunami occurs
there is at a much higher level
so you can see the
you tube videos which
 highlight all of these
systems which are present
so the other thing is
 where we can have some
emergency alerts
this emergency alerts 
will be based on
specifically place sensors in 
and around the globe
and again these sensors will
you know like they are
  self learning mechanisms
which understand when a Tsunami is
likely to happen and which
conditions, a Tsunami is
not likely to happen
so there is a lot of probability
also involved so much of which
I hope that you guys are
kind of you know the 
constitute of probability
and other things 
I hope you are familiar with
okay now apart from this
I don't really think 
there is much to
talk about Tsunamis
so in the past few
lectures we will seeing
what we call as the 
natural disasters
which are having
the cause as I mean 
which can be traced to geological aspects
geology is nothing but you know
what is due to the earth
so we saw that
everything is resting on soil
so, if you understand 
how this soil behaves
a lot of things can be predicted
so we saw some of 
the properties of soil
we saw that
like yesterday and day before,
 we have been seeing about the
angle of internal friction
today we saw that you know
amount water can change
and water is required
to some extent when 
water is added
it increases strength, but beyond it
it will make the system fail
so again there is the problem
of buoyancy which increase
which is induced in the soil mass
plus we also have
 the additional weight
which is given because there is
moisture in the soil
okay
and
when we have a landslide
when land slips
Tsunami could take place
when there is an earthquake
especially underwater
or Tsunami could
take place
sometimes volcanic reactions also
actions also are 
the cause of Tsunamis
okay
and if you look at landslides
when a volcano erupts
the lava is nothing but a
moving mass of
soils, okay its super 
heated liquid mountain
this one material 
which is coming out
and this mass is 
also like a landslide
just that here there is a slip
soil just goes
but here probably
the soil itself is
taking a liquid state
and you know, its not 
going to be very nice
need to think about
so if
do you have questions
 in what we have done till now
any questions from
 any of you, please
right
so we
I just hope that you know
try to keep it as
what you call as practical
 as possible
so
we have
almost covered two units
we have infact 
covered two units
and if suppose you are really
looking at you know one of the
things which would 
have wanted to speak
to you is the
what you call as the
way
this earthquake is measured
so we got quite 
a lot of scales
a modified mercalli 
scale, the richter scale
which we are very
commonly which we know
so each of these are
scales to evaluate
the force
of the earthquake, so it provides
a wave by which we can compare
one earthquakes effect with 
another, okay
so you can go through this
because one is a logarithmic scale
other is based on perception
of the people
so
this one I
I think you know you can just 
do a little bit of reading
and it is not really
what I call as
 very big
so I will probably 
leave this to you
as a exercise which 
you can undertake, right
so, any other
I think you told as no question
if you don't have 
any other questions
I think I will say bye for now
