LESSON 9
Endogenic Process
Content Standard
The
learners demonstrate an understanding of the geologic processes that occur
within the Earth. The learners shall be able to make a simple map showing
places where erosion and landslides may pose risks in the community.
Learning Competencies
The
learners describe the different endogenic forces (S11/12ES-Ic-14 to 24)
Endogenic Forces – Internal forces in detail
Endogenic forces a can be classified as slow movements (diastrophic)
and sudden
movements. Slow movements cause changes very gradually
which might not be visible during a human lifetime.
Slow Movements (Diastrophic forces)
Diastrophic forces refer to forces generated by the movement of
the solid material of the earth’s crust. All the processes that move, elevate
or build portions of the earth’s crust come under diastrophism. Diastrophism
includes:
1. orogenic
processes involving mountain building through severe folding and affecting long
and narrow belts of the earth’s crust.
2. epeirogenic
processes involving uplift or warping of large parts of the earth’s crust.
3. earthquakes
involving local relatively minor movements.
4. plate tectonics
involving horizontal movements of crustal plates.
Slow movements can again be classified as vertical movements and
horizontal movements.
Vertical Movements (Epeirogenic movements):
·
Vertical movements are mainly
associated with the formation of continents and plateaus. They are also called
as Epeirogenic movements
·
The broad central parts of continents
are called cratons and are subject to epeirogeny.
·
They do not bring any changes in the
horizontal rock strata.
·
While they cause upliftment of
continent, they can also cause subsidence of continent.
·
These movements are originated from
the centre of the earth.
Horizontal Movements (Orogenic Movements):
·
Horizontal forces acts on the
earth’s crust from side to side to cause these movements.
·
They are also known as orogenic
movements (mountain building).
·
They bring a lot of disruptions to the
horizontal layer of strata leading to a large structural deformation of earth’s
crust.
·
They can be classified as forces of
compression and forces of tension.
Forces of Compression:
·
Forces of compression are the forces
which push rock strata against a hard plane from one side or from both
sides.
·
The compressional forces lead to the
bending of rock layers and thus lead to the formation of Fold Mountains.
·
Most of the great mountain chains of
the world like the Himalayas, the Rockies (N. America), the Andes (S. America),
the Alps (Europe) etc are formed in this manner.
Forces of Tension:
·
Forces of tension work
horizontally, but in opposite directions.
·
Under the operation of intense
tensional forces, the rock stratum gets broken or fractured which results
in the formation of cracks and fractures in the crust.
·
The displacement of rock upward or
downward from their original position along such a fracture is termed as faulting.
·
The line along which displacement of
the fractured rock strata take place is called as the fault line.
·
Faulting results in the formation of
well-known relief features such as Rift Valleys and Block Mountains. (E.g. Vindhya
and Satpura Mountains)
·
A rift valley is formed by sinking of
rock strata lying between two almost parallel faults. (E.g. Valley of Nile,
Rift valley of Narmada and Tapti )
·
Rift valleys with steep parallel walls
along the fault are called as Graben and the uplifted landmass with steep
slopes on both sides are called as Horst.
·
The very steep
slope in a continuous line along a fault is termed as Escarpment.
Sudden Movements
Examples: Volcanoes and earth quakes.
SUMMARY
Earthquakes: Points you should not miss!
·
The network of seismographic
(seismograph is the instrument used to measure earthquakes) stations all over
the world record dozens of earthquakes every day. Most of them are not felt by
human beings as they are minor quakes only.
·
The occurrence of a severe earthquake
is limited to a few regions in the world.
·
The point within the earth’s crust
where an earthquake originates is called as the focus or
hypocenter or seismic focus.
·
It generally lies within a depth
of 6 kms in the earth crust.
·
The point vertically above the focus
on the earth’s surface is called as the epicenter.
·
The intensity of earthquake will be
highest in the epicenter and decreases as one moves away.
·
All natural earthquakes take place in
the lithosphere (i.e, the region which constitutes the earth’s crust and rigid
upper part of the mantle).
Earthquake waves or Seismic waves
·
The earthquake which originates in the
lithosphere propagates different seismic waves or earthquake waves.
·
Earthquake waves are basically of two
types – body waves and surface waves.
·
Body waves
·
They are generated due to the release
of energy at the focus and moves in all directions traveling through the body
of the earth. Hence, the name – body waves.
·
They travel only through the interior
of the earth.
·
Body waves are faster than surface
waves and hence they are the first to be detected on a seismograph.
·
There are two types of body waves as
primary waves and secondary waves.
Primary waves (p-waves):
·
Primary waves are the fastest body
waves (twice the speed of s-waves) and are the first to reach during an
earthquake.
·
They are similar to sound waves, i.e,
they are longitudinal waves, in which particle movement is in the same
direction of wave propagation.
·
They travel through solid, liquid and
gaseous materials.
·
They create density differences in the
earth material leading to stretching and squeezing.
Secondary waves (s-waves):
·
They arrive at the surface with some
time-lag after primary waves.
·
They are slower than primary waves and
can pass only through solid materials.
·
This property of s-waves led
seismologists to conclude that the earth’s outer core is in a liquid state.
(the entire zone beyond 105o from
the epicenter does not receive S-waves)
·
They are transverse waves in which
directions of particle movement and wave propagation are perpendicular to each
other.
Surface Waves
·
When the body waves interact with
surface rocks, a new set of waves is generated called as surface waves.
·
These waves move along the earth
surface.
·
Surface waves are also transverse
waves in which particle movement is perpendicular to the wave propagation.
·
Hence, they create crests and troughs
in the material through which they pass.
·
Surface waves are considered to be
the most
damaging waves.
·
Two common surface waves are Love waves
and Rayleigh waves.
Love waves:
·
This kind of surface waves causes
horizontal shifting of the earth during an earthquake.
·
They have much slower than body waves
but are faster than Rayleigh.
·
They exist only in the presence of
semi-infinite medium overlain by an upper finite thickness.
·
Confined to the surface of the crust,
Love waves produce entirely horizontal motion.
Rayleigh waves:
·
These waves follow an elliptical
motion.
·
A Rayleigh wave rolls along the ground
just like a wave rolls across a lake or an ocean.
·
Because it rolls, it moves the ground
up and down and side-to-side in the same direction that the wave is moving.
·
Most of the shaking felt from an
earthquake is due to the Rayleigh wave, which can be much larger than the other
waves.
Shadow regions of waves
·
We already discussed that p-waves pass
through all medium while S-waves passes only through solid medium.
·
With the help of these properties of
primary waves, seismologists have a fair idea about the interior of the earth.
·
Even though p-waves pass through all
mediums, it causes reflection when it enters from one medium to another.
·
The variations in the direction of
waves are inferred with the help of their record on seismographs.
·
The area where the seismograph records
no waves is called as ‘shadow zone’ of that wave.
·
Accordingly, it is observed that the
area beyond 1050 does
not receive S-waves and the area in between 1050 to
1400 does
not receive P-waves.
Measuring earthquakes
·
Seismometers are
the instruments which are used to measure the motion of the ground, which
including those of seismic waves generated by earthquakes, volcanic eruptions,
and other seismic sources.
·
A Seismograph is
also another term used to mean seismometer though it is more applicable to the
older instruments.
·
The recorded graphical output from a
seismometer/seismograph is called as a seismogram.
(Note: Do not confuse seismograph with seismogram. Seismograph is an
instrument while seismogram is the recorded output)
·
There are two main scales used in the
seismometers: (1) Mercalli Scale and Richter Scale.
Mercalli Scale:
The scale represents the intensity of
earthquake by analyzing the after effects like how many people felt it, how
much destruction occurred etc. The range of intensity is from 1-12.
Richter Scale:
The scale represents the magnitude of
the earthquake. The magnitude is expressed in absolute numbers from 1-10. Each
whole number increase in Richter scale represents a ten times increase in power
of an earthquake.
Distribution of Earthquakes
·
There are two
well-defined belts where earthquakes frequently occur – The Circum-Pacific Belt
and The Mid-World Mountain Belt.
·
About 68% of earthquakes in the world
occur in the Circum-Pacific Belt.
·
Mid-World Mountain belt extends from
the Alps with their extension into Mediterranean, the Caucasus, and the
Himalayan region and continues to Indonesia.
·
21% of earthquakes are occurring in
this belt.
·
The remaining 11% occur in the other
parts of the world.
Volcanoes: Everything You
Need To Know
A volcano is an opening in the earth’s crust through which gases,
molten rocks materials (lava), ash, steam etc. are emitted outward in the
course of an eruption. Such vents or openings occur in those parts of the
earth’s crust where the rock strata are relatively weak. Volcanic activity is
an example of endogenic process. Depending upon the
explosive nature of the volcano, different land forms can be formed such as a
plateau (if the volcano is not explosive) or a mountain (if the volcano is
explosive in nature).
Review: Magma vs Lava
·
Magma is
the term used to denote the molten rocks and related materials seen inside
earth. A weaker zone of the mantle called asthenosphere, usually is the source
of magma.
·
Once this magma came out to the earth
surface through the vent of a volcano, it is called as the Lava.
Therefore, Lava is nothing but the magma on earth surface.
·
The process by which solid, liquid and
gaseous material escape from the earth’s interior to the surface of the earth
is called as Volcanism.
Types of Volcanoes
Volcanoes are classified on the basis of nature of eruption and
the form developed at the surface.
Shield Volcanoes
·
How to identify: They are not very
steep but are far and wider. They extend to great height as well as distance.
·
They are the largest of all volcanoes
in the world as the lava flows to a far distance. The Hawaiian volcanoes are
the most famous examples.
·
Shield volcanoes have low slopes and
consist almost entirely of frozen lavas.
·
If you were to fly over top of a
shield volcano, it would resemble a warrior’s shield, hence the name.
·
These volcanoes are mostly made up of
basalt (less viscous), a type of lava that is very fluid when erupted. For
this reason, these volcanoes are not steep.
·
They are of low explosive in
general, but if somehow water gets into the vent they
may turn explosive.
·
The upcoming lava moves in the form of
a fountain and throws out the cone at the top of the vent and develops into
cinder cone
Cinder Cone Volcanoes:
·
Cinders are
extrusive igneous rocks. A more modern name for cinder is
Scoria.
·
Small volcanoes.
·
These volcanoes consist almost
entirely of loose, grainy cinders and almost no lava.
·
They have very steep sides and usually
have a small crater on top.
Composite
Volcanoes:
·
Shape: Cone shaped
with moderately steep sides and sometimes have small craters in their
summits.
·
Volcanologists call these “strato-” or
composite volcanoes because they consist of layers of solid lava flows mixed
with layers of sand- or gravel-like volcanic rock called cinders or volcanic
ash.
·
They are characterized by the eruption
of a cooler and more viscous lavas than basalt.
·
These volcanoes often result in
explosive eruptions.
·
Along with lava, large quantities of
pyroclastic materials and ashes find their way to the ground.
·
This material accumulates in the
vicinity of the vent openings and leading to the formation of layers, and this
makes the mount appears as composite volcanoes.
Caldera:
·
These are the most explosive of the earth’s
volcanoes.
·
They are usually so explosive that
when they erupt they tend to collapse on themselves rather than building any
tall structure. The collapsed depressions are called calderas.
·
Their explosiveness indicates that its
magma chamber is large and in close vicinity.
·
A caldera differs from a crater in
such a way that a caldera is a huge depression caused by a collapse after a
large-scale eruption, whereas a crater is a small, steep side, volcanic
depression bored out by an eruptive plume.
Flood Basalt Provinces
·
These volcanoes outpour highly fluid
lava that flows for long distances.
·
The Deccan Traps from India, presently
covering most of the Maharashtra plateau, are a much larger flood basalt
province.
Mid-Ocean Ridge Volcanoes
·
These volcanoes occur in the oceanic
areas.
·
There is a system of mid-ocean ridges
more than 70,000 km long that stretches through all the ocean basins.
·
The central portion of this ridge
experiences frequent eruptions.
Volcanoes can also be classified based on the frequency of eruption,
mode of eruption and characteristic of lava.
Volcanic Landforms:
·
The lava that is released during
volcanic eruptions on cooling develops into igneous rocks.
·
The cooling may take place either on
reaching the surface or from the inside itself.
·
Depending on the location of the
cooling of lava, igneous rocks are classified as:
Volcanic Igneous rocks (Extrusive igneous rocks):
Cooling of the rock occurs at the surface of the earth. E.g.
Basalt, Andesite etc.
Plutonic Igneous rocks (Intrusive igneous rocks):
Cooling takes place in the crust and not over the surface. E.g.
Granite, Gabbro, Diorite etc. Intrusive igneous rocks are classed into the
following types according to their forms.
1. Batholiths: A
large body of magmatic material that cools in the deeper depth in the form of a
large dome. These are granitic bodies. They sometimes appear on the earth
surface when the denudation processes remove the overlying materials.
2. Laccoliths: Large
dome shaped intrusive bodies with a level base and pipe-like conduit from below.
Resembles a composite volcano structure, but beneath the earth. (Eg: Karnataka
Plateau)
3. Lapoliths: They
are saucer
shaped, concave to the sky.
4. Phacoliths: Wavy materials which
have a definite conduit to source beneath.
5. Sheets/
sills: They are the near horizontal bodies of
intrusive igneous rocks. Thinner ones are called as sheets and while thick
horizontal deposits are called sills.
6. Dykes: When
the lava comes out through cracks and fissures, they solidify almost perpendicular to the ground to
form wall like structures called dykes. (Eg: Deccan traps in
Maharastra region).
Distribution of Volcanoes:
Most of the volcanoes in the world are found in three well defined
belts:
1. The
Circum-Pacific Belt (The Pacific Ring of Fire).
2. The
Mid-World Mountain Belt.
3. The
African Rift Valley Belt.
Volcanic Activity – Points to note down:
·
Volcanoes are closely related to the
regions of intense folding and faulting.
·
They occur along coastal mountain
ranges, on islands and in the mid oceans.
·
Interior parts of the continent are
generally free from their activity.
·
Most of the active volcanoes are found
in the pacific region which is thus called as the Pacific Ring of Fire.
Plate Tectonics Theory
The
theory of plate tectonics is what brings together continental drift and
seafloor spreading. Plates are made of lithosphere topped with oceanic and/or
continental crust. The plates are moved around on Earth's surface by seafloor
spreading. Convection in the mantle drives seafloor spreading. Oceanic crust is
created at mid-ocean ridges. The crust moves outward from the ridge over time.
The crust may eventually sink into the mantle and be destroyed. If a continent
sits on a plate with a mid-ocean ridge, the continent will be pushed along.
Plate Boundaries
Two
plates meet at a plate boundary. There are three types of plate boundaries
since there are three ways that plates can meet. Plates can move away from each
other. They can move toward each other. Finally, they can slide past each
other. The three types of plate boundaries are divergent, convergent, and
transform. They are described in the following three concepts.
Most
geological activity takes place at plate boundaries. This activity includes volcanoes,
earthquakes, and mountain building. The activity occurs as plates interact.
Giant slabs of lithosphere moving around can create a lot of activity! The
features seen at a plate boundary are determined by the direction of plate
motion and by the type of crust found at the boundary.
·
Divergent
boundaries -- where new crust is generated as the plates pull away from each
other.
·
Convergent
boundaries -- where crust is destroyed as one plate dives under another.
·
Transform boundaries -- where crust is neither
produced nor destroyed as the plates slide horizontally past each other.
·
Plate
boundary zones -- broad belts in which boundaries are not well defined and the
effects of plate interaction are unclear.
What The Theory Explains
The
theory of plate tectonics explains most of the features of Earth’s surface. It
explains why earthquakes, volcanoes and mountain ranges are where they are. It
explains where to find some mineral resources. Plate tectonics is the key that
unlocks many of the mysteries of our amazing planet. Plate tectonics theory
explains why:
·
Earth's geography has changed over time and
continues to change today.
·
some places are prone to earthquakes while
others are not.
·
certain regions may have deadly, mild, or no
volcanic eruptions.
·
mountain ranges are located where they are.
·
many ore deposits are located where they are.
·
living and fossil species of plants and
animals are found where they are.
·
some continental margins have a lot of
geological activity, and some have none.
·
Plate tectonic motions affect Earth’s rock
cycle, climate, and the evolution of life.
Summary
The
theory of plate tectonics brings together continental drift and seafloor
spreading.
At
a plate boundary, two plates can be moving apart, together or past each other.
Plate
tectonics theory explains many things in geology, such as where volcanoes,
earthquakes, mountain ranges, ore deposits, and other features are located.
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