Interior of the Earth Notes in English Class 11 Geography Chapter-3 Book-Fundamental of Physical Geography

 

Introduction

• The configuration of the Earth's surface is mainly the result of processes occurring underground. 

• Exogenous and endogenous processes continually shape the landscape.

• To understand the physiography of any region, it is necessary to know the impact of geological activities.

• Human life is mainly influenced by its regional topography.

sources of geological information 

• The radius of the Earth is approximately 6,370 km. 

• Due to the internal conditions of the Earth, it is not possible for anyone to reach the centre of the Earth and observe it or obtain some sample of the matter there. 

• Even in such circumstances, scientists are able to tell us what the structure of the Earth is like and what types of materials are found at such depths.

sources of geological information 

1. Direct source

• The most easily available solid materials from the earth are surface rocks, which we obtain from mining areas. 

• The gold mines of South Africa are 3 to 4 km deep. 

• It is impossible to go deeper than this because the temperature at that depth is very high

• Scientists are working on two main projects.

• These are Deep ocean drilling project and Integrated ocean drilling project. 

• Till date, the deepest drilling has been done in the Kola region of the Arctic Ocean, to a depth of 12 km.

• Volcanic eruptions are another source of direct information. 

• Whenever a volcanic eruption releases lava to the Earth's surface, it is available for laboratory exploration.

2. Indirect sources

• Analysis of the properties of matter provides indirect information about the interior of the Earth. 

• As the depth increases, the density of the substance also increases.

• The rate of this change can be measured in temperature, pressure and density.

• Sometimes meteors reach the earth. 

• The materials obtained from meteorites and their composition are similar to that of the Earth.

Earthquake

• Vibrations of the earth. 

• This is a natural phenomenon. 

• Due to the release of energy, waves are generated, which spread in all directions and cause earthquakes.

1. Point of Origin

• The place from where the energy is released is called the focus of the earthquake. 

• It is also called hypocentre.

2. Epicenter

• The point on the surface of the earth that is nearest to the focus of origin is called the epicentre.

• The epicenter is directly above (at right angles to) the focus.

Seismic Waves

• All natural earthquakes occur in the lithosphere

• The part of the earth up to a depth of 200 km from the surface is called the lithosphere

I. Seismic waves

• Seismic waves are generated by the release of energy from an earthquake and travel in all directions through the Earth's interior. 

• These are called geologic waves.

1. Primary waves

• These are the fastest moving waves and are the first to reach the surface.

• These are also called P waves. 

• These gases can pass through liquids and solids.

2. Secondary waves

• The secondary waves reach the surface after some time interval. 

• These are called S waves. 

• These move only through solid substances.'

II. Surface waves

• Due to the interaction between seismic waves and surface rocks, new waves are generated which are called surface waves.

Types of earthquakes

1. Tectonic earthquakes

2. Volcanic earthquakes

3. Niyat earthquake

4. Explosion earthquake

5. Dam induced earthquakes

Measuring earthquakes

• Seismic events are measured on the basis of seismic intensity. 

• The scale of seismic intensity is known as 'Richter Scale'. 

• Seismic intensity is related to the energy release during an earthquake.

• The intensity of an earthquake ranges from 0 to 10. 

• The intensity scale is named after the Italian seismologist Mercalli. 

Effects of earthquakes

• Surface anomaly

• Ground shaking

• Landslide

• Soil liquefaction

• tilt of the ground to one side

• Avalanche

• Surface displacement

• flood due to breach of dam and embankment

• starting a fire

• Destruction of buildings and collapse of structures

• Falling of objects

• Tsunami.

Frequency of earthquakes

• Earthquake is a natural disaster. 

• Severe earthquake tremors cause great loss of life and property.

• Earthquakes with a magnitude greater than 8 on the Richter scale are very rare and occur only once in 1-2 years. 

• While mild earthquakes are felt almost every minute in some part of the Earth

internal structure of the earth 

1. Earth's crust 

2. Mental 

3. Core 

1. Earth's crust 

• It is the outermost part of the Earth. 

• This is a very brittle part and has the tendency to break easily. 

• The thickness varies beneath the continents and oceans. 

• The thickness in the oceans is less than that of the continents. 

• Its thickness in the oceans is 5 km

• It is up to 30 km beneath the continents. 

• This thickness is even greater in the area of ​​the main mountain ranges. 

• The thickness of the earth's crust beneath the Himalayas is approximately 70 km.

2. Mental 

• The part below the crust is called the mantle. 

• The upper part of the mantle is called the asthenosphere. 

• The word 'Astheno' means weakness. 

• Its extension has been estimated to be 400 km. 

• It is in solid state.

• This is the main source of lava that reaches the surface during volcanic eruptions. 

• The crust and the upper part of the mantle together are called the lithosphere. 

• Its thickness is found between 10 to 200 km. 

• The lower mantle extends beyond the end of the asthenosphere. 

3. Core

• The outer core is in liquid state while the inner core is in solid state. 

• The core is made of heavy materials, mainly nickel and iron. 

• It is also known as 'Nife' layer.

Volcano

• It is the place from where gases, ash and liquid rock material called lava escape and reach the Earth's surface.

•  Liquid rock material escapes from the asthenosphere and reaches the surface. 

• As long as this material is in the upper part of the mantle, it is called magma. 

• When it reaches above the earth's surface or on the surface of the earth, it is called lava. 

• The material that reaches the surface includes lava flows, debris from frozen pieces of lava, volcanic bombs, ash, dust particles, and gases such as nitrogen compounds, sulfur compounds, and small amounts of chlorine, hydrogen, and argon.

Types of volcanoes

1. Shield volcano 

2. Mixed volcano 

3. Volcanic crater 

4. Basalt flow field 

5. Mid-ocean ridge volcanoes 

1. Shield volcano

• Shield volcanoes are the largest of all volcanoes found on Earth. 

• These volcanoes are mainly composed of basalt, which is formed when liquid lava cools down.

• Their speciality is that they are less explosive. 

• Lava from these volcanoes comes out in the form of fountain and forms a cone at the exit which develops into a cinder cone.

2. Mixed volcano

• These volcanoes erupt lava that is colder and more viscous than basalt. 

• These volcanoes are often very explosive. 

• Due to this, along with the lava, huge amount of pyroclastic material and ash also reaches the surface. 

• This material accumulates in layers around the vent, resulting in a formation that resembles a composite volcano.

3. Volcanic crater 

•  These are the most explosive volcanoes found on Earth. 

• When they explode, they collapse into the ground rather than forming a tall structure. 

• The sunken craters of destruction are called calderas. 

• The hill formed by them appears like a composite volcano.

4. Basalt flow field 

• These volcanoes spew liquid lava which flows great distances. 

• Some parts of the world are covered with thousands of square kilometres of dense lava flows. 

• Some of these flows grow to be more than 50 m thick. 

• Sometimes a single flow extends over hundreds of kilometres. 

• The Deccan Traps of India, on which much of the present-day Maharashtra Plateau lies, is a massive basalt lava flow region.

5. Mid-ocean ridge volcanoes

•  These volcanoes erupt in the oceans. 

• The mid-ocean ridge is a chain of ridges that is more than 70,000 km long and extends across all ocean basins. 

• There is continuous eruption in the central part of this ridge.

Volcanic topographies

• Igneous rocks are classified based on the location of cooling of the lava:

• Volcanic rocks (when lava cools down after reaching the surface)  Plutonic rocks (when lava cools down and solidifies beneath the surface). 

• When lava cools within the Earth's crust, many shapes are formed. 

• These shapes are called intrusive forms.

Topographies

1. Batholith

2. Laccolith

3. Lapolith

4. Faecolith

5. Seal

6. Dyke 

1. Batholith

• When a large body of magma cools at greater depths in the Earth's crust, it develops into a dome shape.

•  These are spread over a vast area and sometimes their depth can be up to several kilometers.

2. Laccolith

• These are huge dome-shaped intrusive rocks whose surface is flat and connected to a pipe-like carrier tube from below.

3. Lapolith

• Some part of the rising lava moves into the weak surface found in the horizontal direction.

• If it solidifies in the shape of a saucer then it is called lapolith.

4. Faecolith

• Sometimes, deposits of lava are found at the top of the anticline and at the bottom of the syncline in the folded state of intrusive igneous rocks. 

• These sedimentary/wavy rocks are connected to the magma reservoirs by a certain convector tube. 

• This is called faecolith.

5. Seal

• The lava that cools in the form of a sheet in the horizontal plane is called a sill or sheet. 

• These are divided based on the thickness of the deposits-depositions with less thickness are called sheets and deposits with dense thickness are called sills. 

6. Dyke

• When the flow of lava in the cracks is almost at a right angle to the surface and if it cools down in this condition, it forms a structure like a wall. This structure is called a dyke.