Endogenetic Movements Class 9 Geography Notes Maharashtra State Board
Various natural events occur on the earth from time to time e.g. floods, storms, snowfall extreme rainfall, etc. Similarly, because of the movements below the earth’s surface, natural events like earthquakes and volcanic eruptions occur. For the organisms living on Earth, these events are disastrous. There is loss of life and property because of natural calamities. In this lesson, we will be introduced to these endogenetic (internal) movements.
As shown in figure, arrange your notebooks on each other. Place 3-4 objects like chalk, duster, sharpener, eraser, etc. on them.
Now, quickly take out a notebook without affecting the others according to figure. Observe what happens.
Arrange the notebooks and keep chalk, duster, sharpener, rubber, etc. on them as in previous step.
Now, give a slight push to this structure and observe what happens. Then again give a hard push. Observe what happens. Carry out a discussion on all these activities.
Earthquakes and volcanoes occur because of the instability in the interior of the earth. This instability is created due to the movements occurring in the earth’s interior. Generally, the movements in the earth’s interior occur in the upper layer of the mantle. Tremendous energy is released by radioactive materials in the mantle. These energy waves travel from one place to another. Due to such a flow of energy, instability is caused in the mantle. The movements are classified based on their velocity, direction, and the landforms they produce.
Classification of Internal Movements:
|Basis of Classification||Movements|
|1. Velocity||(a) Slow movements (occurring continuously) like formation of mountains and continents|
|(b) Sudden Movements ( in the form of events) like earthquakes, volcanoes|
|2. Direction||(a) Horizontal Movements|
|(b) Upward, Downward Movements|
|3. Landforms||(a) Continent-building (creating continents, plateaus, and highlands)|
|(b) Mountain-building (folding, faulting)|
The effect of slow movements can be seen in the form of the formation of mountains and continents on the earth’s crust. This can be explained as follows:
(a) Mountain-Building Movements (Orogenic):
Take a 30cm long paper strip. Place your hands on both ends of the strip. Move both hands towards each other giving pressure on the strip. Observe what happens to the strip.
The strip was moved by placing hands on both ends. The work performed on the strip at that time is called compression. The pressure was given on the center of the strip from both ends. As a result, the strip moves, and folds are formed. Similarly, due to pressure on the earth’s crust, movements are generated and folds are formed.
Energy is transferred from the interior of the earth. Because of these energy waves and pressure working towards each other and in the horizontal direction, the layers of the soft rocks form folds. If the pressure is very high, large folds are formed, and their complexity increases. As a result, the surface of the earth gets uplifted and fold mountains are formed. The Himalayas, the Aravalis, the Rockies, the Andes, and the Alps are the major fold mountains of the world.
Take a long strip of thin paper. Hold one end of the paper in your right hand. Hold the other in your left hand. Pull both the ends away from each other. Observe what happens to the paper strip.
‘Tension’ is created when you pull both ends away from each other. Similarly, when movements occur in opposite directions to each other, tension is generated, and ‘faults’ are formed in the earth’s crust.
Because of internal movements, horizontal waves moving away from each other are formed. This causes tension in the layers of rocks. This leads to the formation of fractures in the rocks. These are known as faults. Similarly, waves coming towards each other in hard rocks also form faults due to compression. When a part of the earth’s crust in between two parallel faults is lifted, it looks like a block.
See figure. Such a landform is known valley be steep. For example, the Rift Valley is a block mountain. The hilltops of block mountains are flat. In the early stages, they do not have any peaks. Their slopes are steep. For example, the Black Forest mountains in Europe. The Meghalaya Plateau of India has also been formed similarly.
Take 3 notebooks of the same size. Hold them on tightly on a table keeping a distance of 2-3 cm. Remove the two notebooks on each end away from the central one. Observe what happens. Draw the diagram emerging because of the notebooks in your notebook.
When horizontal movements on the earth’s surface act in opposite directions, it causes tension on the rocks in the earth’s crust. When tension increases, fractures develop in the rocks. This leads to the formation of faults. Consequently, rocks on both ends slide and the continuity in the layers of rocks is not found.
Sometimes, two fractures develop side-by-side in the earth’s crust. The land in between the two fractures subsides. This subsided deep part is called the Rift Valley. Both the slopes of a rift valley are steep. For example the rift valley of river Narmada in India, The Great Rift Valley of Africa, and The Rhine River rift valley of Europe.
(b) Continent-building (Epeirogenic) Movements:
Slow movements occur towards the center or from the earth’s center towards the earth’s crust. Because of these movements, a vast part of the earth’s crust is uplifted or gets subsided. When part of the earth’s crust is uplifted (above the mean sea level,) continents are formed. Therefore, these movements are called continent-building movements. Extensive plateaus can also be formed because of such movements. If the originally continental portion of the crust subsides below the sea level, it forms a part of the sea bed.
At the beginning of the chapter, we discussed and studied the news item on earthquakes. ‘Earth’ means the ground and ‘quake’ means trembling. Earthquake is the movement of the earth’s crust. You have been acquainted with the magnitude and effects of the earthquake through the activity at the beginning of the chapter itself. Now we will look at the sudden movements called earthquakes and volcanoes in the earth’s interior in detail.
When you stand on a railway platform near the railway track, you experience trembling if a train passes by speedily. Tremors are also felt when a heavy vehicle crosses a bridge at speed. Through these examples, one can estimate the tremors caused by earthquakes.
Because of the movements occurring in the interior of the earth, tremendous tension is created in the earth’s crust. When the tension goes beyond limits, the energy is released in the form of waves. This results in the trembling of the earth’s surface, i.e. earthquake occurs. The magnitude of the earthquake is measured by the Richter scale.
Causes of Earthquakes:
- Moving the plates
- Colliding of plates
- Plates sliding one below the other
- Forming of fractures in rock layers due to tension in the interior of the earth.
- Occurring volcanic eruptions
Indo-Australia, Africa, Eurasia, North America, South America, the Pacific, and Antarctica are seven major plates. The earth’s crust is made up of such plates. Oceans and continents are spread over these plates. Depending on the compression and tension formed in the interior of the earth, these plates move in various directions.
Focus and Epicenter:
Because of the movements occurring below the earth’s surface, tension is created and it keeps on accumulating. High energy is released at the place where this tension mounts up. This is the center of the earthquake. It is called the focus or hypocenter. Energy waves scatter in all directions from this center. The place on the earth’s surface where these energy waves reach first is called the epicenter of the earthquake. It is the nearest place on the earth’s surface from the focus and it experiences the first tremor. The epicenter is perpendicular to the focus.
When the tension is released at the focus, the released energy travels in all directions. This energy comes towards the earth’s surface in the form of waves. The seismic waves can be divided into primary, secondary, and surface waves.
1. Primary or ‘P’ Waves:
These are the first ones to reach the surface of the earth after the energy is emitted into the earth’s interior. They travel at a very fast speed from the focus of the earthquake in the radial direction. Subject to a P wave, particles in the rock move in the direction of waves to and fro. The wave moves to and fro, therefore these waves are also called forward-backward waves. These waves can travel through all three states – liquid, solid, and gaseous. But while traveling through a liquid medium, their direction gets changed. It is because of the primary waves that the buildings on the earth’s surface move back and forth.
2. Secondary or ‘S’ Waves:
The waves which reach the earth’s surface after the primary waves are called secondary waves. These waves also scatter in all directions from the focus of the earthquake. Their velocity is lesser than the P waves. The particles lying in the way of these waves move up and down in the direction of energy transfer. These waves can travel only through the solid medium. They get absorbed as they enter the liquid medium. The buildings on the earth’s surface move up and down because of these waves. These are more destructive than the P waves.
3. Surface or ‘L’ Waves:
These waves are generated after the main P and S waves reach the epicenter. They travel in the direction of the circumference of the earth along the crust. They are highly destructive.
Through this instrument, a graph showing the movement of seismic waves (Seismograph) can be generated. After studying this graph, the magnitude of the earthquake is known. Figure shows a simple seismogram and a seismograph prepared from it. Now with the help of modern technology, advanced seismograms have been designed. With their help, even micro-seismic waves can also be measured.
Hang a heavy bag or pouch on the hook of a spring balance as shown in the figure. Pull the bag down and release it. Observe the spring and note the movement of spring.
As shown in the figure, make the students stand holding the ends of a rope. Ask one student to give a jerk to the rope by pulling it up and down with hand. Observe what happens and note the movement of the rope.
Spread ‘rangoli’ on a large plate. Flick on the lower side of the plate slightly with your fingers. Observe what happens.
Effects of Earthquake:
- Cracks /fractures develop on the ground.
- Causes landslides which leads to the sliding of rocks.
- Sometimes the groundwater changes its course. For example, wells may get water or may dry up.
- Some areas get uplifted while some may subside.
- Tsunamis are generated in oceans. These waves can cause great loss of life and property in the coastal areas.
- In snow-covered areas, avalanches may occur.
- Buildings collapse and loss of life and property occurs.
- Transportation routes get disrupted.
- The communication system collapses.
Hot solid, liquid, and gaseous materials are thrown out from the mantle of the earth onto the surface of the earth. This process is called volcanic eruption. During this process, ash, water vapour, various types of poisonous and inflammable gases, hot molten magma, etc. are thrown out. When the molten magma comes out on the surface, it is called lava.
Based on the type of eruption, volcanoes can be divided into the following types:
1. Central-type or Conical Volcano:
During eruption, the molten magma comes out through a pipe-like vent inside the earth’s surface. The lava spreads around the mouth of this vent when it comes out. As a result, cone-shaped mountains start forming and conical volcanic mountains are formed. Mt. Fujiyama in Japan and Mt. Kilimanjaro in Tanzania are examples of central-type volcanoes and conical mountains.
2. Fissure-type Volcanoes:
During eruption, when the magma comes out not from a single vent but from many cracks (fissures), it is called fissure-type volcanic eruption. The molten material coming out with the eruption spreads on both sides of the fissure. As a result, volcanic plateaus are formed. The Deccan Plateau of India has also been formed due to such a type of volcanic eruption.
According to the periodicity of the volcanic eruptions, three types of volcanoes can be identified:
- If the volcanic eruptions are regular even in the present times, then such volcanoes are called active volcanoes. For example, Mt Fujiyama in Japan, and Mt. Stromboli in the Mediterranean Sea.
- When a volcano has not erupted for long, but may become active suddenly it is called a dormant volcano. For example, Mt. Vesuvius in Italy, Mt. Katmai in Alaska, and Barren Island, in India.
- Those volcanoes which have not erupted in the past for long and are not likely to erupt in the future are called extinct volcanoes. For example Mt. Kilimanjaro in Tanzania.
By looking at the figure you will understand that plate boundaries are directly related to areas of earthquakes and volcanoes. Most of the volcanoes are located on the plate boundaries. Similarly, the earthquake zones are also seen in the border areas.
The part of the plate boundary that slides under the crust subdues. There is a loss of material. Such boundaries are called plate-consuming (subduction) boundaries. In areas, where new material is coming up onto the earth’s crust, are called plate-creating (constructive) boundaries. Both processes happen continuously. They are shown in the map in the figure.
Effects of Volcanoes:
- Loss of life and property
- Sometimes tsunamis get generated due to volcanic eruptions occurring below ocean floors.
- Dust, smoke, ash, gases, water vapour, etc. remain in the atmosphere for a long time. This may create an imbalance in the environment.
- Land may become fertile due to volcanic ash.
- Many minerals are found near the earth’s surface because of lava.
- New land is formed due to volcanic eruption or at times, an island may even disappear.
- Lakes are formed at the mouth of the craters of dead volcanoes when rainwater accumulates in them.
Barren Island (Andamans):
Andaman and Nicobar Islands are located to the south-east of the mainland of India. On this archipelago lies the Barren Island, India’s only active volcano. This volcano was dormant for a long time. But, in February 2017, it started erupting. Dust, smoke, and mud are coming out of this eruption along with some lava.
Good Maharashtra State Board Class 9 Geography Notes Endogenetic Movements can simplify complex concepts and make studying more efficient.