Earth Movements and Major Landforms - Class 7 Video Lecture

earth movements and major landforms the
earth surface is highly onion and
irregular the surface of the earth is
being shaped and reshaped by external
agents like running water wind glaciers
etc this is the reason why our
present-day landforms are diverse and we
read what we see today on the surface of
earth is the product of millions of
years of geological change earlier all
the continents formed were single mass
however under the influence of forces
generated within the earth they moved
away in different directions such forces
lead to slow earth movements and sudden
earth movements which modify existing
landforms the forces which originate
inside the earth and bring changes on
the surface of the earth are known as
endogenous forces the forces which
operate on the surface of the earth and
bring changes on the surface are called
exogenic forces the intergenic forces
try to uplift the Earth's surface while
exogenic forces try to level down the
surface of the earth
earth movements the powerful endogenous
forces operating from within the crust
are also known as tectonic movements
tectonic movements can be divided into
two types sudden movements they bring
abrupt changes on the Earth's surface
earthquakes and volcanic eruptions are
the examples of these movements such
changes can cause a part of the land to
be fractured or the course of a river to
be changed slow movements some changes
in the Earth's crust are so slow that
they take about hundreds of years to
become noticeable they are called
slow changes the Mahabalipuram temple
which now stands in the sea is an
example of this movement slow movements
are further classified into vertical and
horizontal movements the vertical
movements cause uplift or subsidence of
the earth's crust when a part of the
Earth's crust is thrown up by an
internal force it results in an uplift
the uplifted portion may become a
plateau or a continent in case of
subsidence a part of the Earth's crust
may sink in comparison to the
surrounding region and might give birth
to a valley horizontal movements give
birth to two forces compression or
pushing and tension or stretching such
movements can cause folding and faulting
of the crystal layers thus creating
mountains and rift valleys forces of
compression these forces act on the rock
strata from opposite directions due to
which the rock layers are bent up or
folded into a series of anticlines
and sink lines these forces are
responsible for the formation of fold
mountains the Himalayas the Andes the
ABS and the Rockies have been formed due
to the forces of compression and are
examples of fold mountains forces of
tension
these forces operate in opposite
directions thus causing a fall
or fracture in the Earth's crust the
fractured rock strata either slides
upwards or downwards along the fault
line the faulting then gives birth to
new relief features like the Rift Valley
or a block mountain if a block of land
is uplifted between two parallel faults
then it looks like a huge mountain known
as block Mountain if a block of land
subsides between two parallel faults a
trench is thus created which is known as
Rift Valley major landforms the
landscape is being continuously worn
away by two processes weathering and
erosion weathering is the breaking up of
rocks on the Earth's surface erosion is
the weathering away of landscape by
different agents like water wind and ice
the eroded material is carried away and
eventually deposited the process of
erosion and deposition creates different
landforms on the surface of the earth
work of a river when the river tumbles
at steep angle over very hard rocks or
down a steep valley side it forms a
waterfall as the river enters a plane it
twists and turns forming large bends
known as meanders due to continuous
erosion and deposition of the sides of
meander the ends of the meander loop
come closer and closer
in due course of time the meander loop
cuts off from the river and also forms a
cut-off lake like an oxbow lake at times
the river overflows its banks this leads
to the flooding of the neighboring areas
as it floods it deposits layers of the
fine soil and other material called
sediments along its bank this leads to
the formation of a flat fertile
floodplain the raised banks are called
levees as the river approaches the sea
the speed of the flowing water decreases
and the river begins to break up into
a number of streams called
distributaries each distributary forms
its own mouth the collection of
sediments from all the mouths forms a
delta work of sea waves the erosion and
the deposition of sea waves gives rise
to the coastal landforms sea waves
continuously strike at the rocks as a
result crabs develop and become wider
thus hollow light caves are formed on
the rocks they are called sea waves as
these cavities become bigger and enlarge
only the roof of the caves remain thus
forming sea arches further erosion
breaks the roof and only walls are left
these warlike features are called stacks
the steep rocky coast rising almost
vertically above the seawater is called
sea cliff the sea waves deposit
sediments along the shores forming
beaches work of ice glaciers are rivers
of ice which to road the landscape by
bulldozing the soil and stones to expose
the solid rock below as the ice melts
the eroded surface gets filled up with
water and become beautiful lakes in the
mountains the material carried by the
glacier such as rocks sand and silt gets
deposited these deposits form the
glacial moraines work of Range an active
agent of erosion and deposition in the
deserts is wind winds erode the lower
section of the rock more than the upper
section therefore such rocks have narrow
base and wider top it lifts and
transport sand from one place to another
when it stops blowing the sand falls and
gets deposited in low hill like
structures these are called sand dunes
when the grains of sand are very fine
the wind can carry it over very large
distances when SATs and is deposited in
large areas it is called low
volcanoes people generally think of a
volcano as a mountain that ejects lava
and flames of fire very often however
while Cano's are openings in the Earth's
crust through which materials are thrown
out from the interior of the earth the
material thrown out include hot molten
rock or lava along with ash some solid
rock particles steam and gas the opening
is called a wint around which a conical
mountain may be formed the funnel shaped
Basin surrounding the wint is called as
crater a volcanic eruption along a
linear crack called as fissure is called
a fissure eruption the whole process of
ejection and solidification of lava is
called Vulcan a city so long as the hot
liquid material of the volcano remains
within the surface of the earth it is
called magma but when this magma rises
to the surface of the earth it is called
lava the lava flow depends on its
viscosity the amount of silica and water
in magma affects the viscosity of lava
high viscosity of lava is associated
with great amount of silica and less of
water and vice versa kinds of volcanoes
according to the nature and frequency of
eruptions volcanoes have been divided
into three categories
active volcanoes dormant volcanoes
extinct volcanoes active volcanoes these
volcanoes erupt frequently there are
more than 500 active volcanoes in the
world most of them are found in a
circular belt around the Pacific Ocean
called as the Ring of Fire example Mount
Etna in Italy dormant volcanoes these
volcanoes have not erupted since a long
time they are also called sleeping
volcanoes they may erupt later though
they have not erupted since a long time
when they erupt they can be very
destructive example Mount Vesuvius in
Italy extinct volcanoes these volcanoes
are dead and inactive there is virtually
no movement the peak of these mountains
is now covered with ice example Mount
Kilimanjaro in East Africa