Interior Of The Earth Class 11 Notes Geography Chapter 3 - CBSE
Chapter : 3
What Are Interior Of The Earth ?
- Ever since the evolution of earth happened, the surface of earth is constantly changing due to endogenic and exogenic processes.
- To demystify the interior of the earth, it is crucial to gather relevant evidences based on some realistic studies. So far, there are some direct and indirect sources of information about earth’s interior.
Direct Sources
Easier way to know about the structure and composition is to get real evidence through mining and drilling the oceanic crust, volcanic eruptions.
Indirect Sources
Like temperature and pressure, density also varies as the depth increases. Thus, the variation in density at different levels also gives us information, through meteors, gravity of earth at different location, and seismic wave.
Earthquake
An earthquake is an intense shaking or tremor of Earth’s surface which is caused by movements in Earth’s outermost layer by seismic waves.
- An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane.
- The location below the earth’s surface where the earthquake starts is called the hypocentre, and the location directly above it on the surface of the earth is called the epicentre.
- When an earthquake occurs, it releases tremendous energy in the form of waves known as seismic waves. The types of seismic waves are as follows:
Seismic Waves
Body Waves
- Body waves are generated at focus and travel in all directions at amazing speed through the body of the earth. When body waves hit the surface, they give birth to surface waves.
- P-waves
- P-waves or primary waves can travel through gaseous, solid, and liquid composition of interior in a linear direction.
- S-waves
- S-waves or secondary waves are slower than P-waves, pass only through the solids, and travel in a transversal direction.
- P-waves
Surface Waves
Surface waves are those waves that travel on the surface of the earth. The destruction caused by earthquakes is primarily done by these waves.
Propagation Of Seismic Waves
- Since P-waves move in a linear direction, they create density variation which further leads to expansion and contraction of interior.
- Whereas, the secondary waves travel in a transversal direction and generate vibrations in perpendicular in a vertical plane; thus creating a wave-like structure (trough and crest).
Emergence Of Shadow Zone
The areas from the epicenter where the earthquakes are not recorded are called as Seismic Shadow Zone. Moreover, the shadow zone also varies for different seismic waves.
Earthquakes
Types Of Earthquakes
Collapse
Due to intense mining activities, sometimes the roof of the mine fall and cause Collapse Earthquake.
Explosion
Due to nuclear testing or explosions, the ground tremors are realized which fall in the category of Explosion Earthquakes.
Tectonic
The natural movement of tectonic plates lead to earthquakes called as Tectonic Earthquakes.
Volcanic
The areas of active volcanoes feel tremors which fall in the category of Volcanic Earthquakes.
Reservoir-induced
The construction of large water reservoirs cause Reservoir-induced Earthquakes.
- Seismographs are instruments used to record the motion of the ground during an earthquake.
- Earthquakes are measure in two ways, i.e., on magnitude scale by Richter Scale and on intensity scale by Mercalli Scale.
| Richter Magnitude | Earthquake Effects |
| 0-2 | Not felt by people |
| 2-3 | Felt little by people |
| 3-4 | Ceiling lights swing |
| 4-5 | Walls crack |
| 5-6 | Furniture moves |
| 6-7 | Some builidings collapse |
| 7-8 | Many builidings destroyed |
| 8-Up | Total destruction of builidings, bridges, and roads |
After Effects of Earthquakes
Based on intensity, earthquakes have their after-effects. Usually it ranges from ground shaking (minimum) to Tsunami (higher level).
- Consequences of landforms could be Ground Shaking, Differential ground settlement, Land and mud slides,
Soil liquefaction, Ground lurching, or Avalanches. - The loss of life and property results from effects such as Floods from dam and levee failures, Fires, Structural collapse, falling objects, or Tsunami which are higher-degree magnitude earthquakes.
Major Sections of Structure of the Earth
Crust
- The Crust describes the outermost shell of a terrestrial planet. Earth’s thin, 40-kilometer (25-mile) deep crust is just 1% of Earth’s mass which contains all known life in the universe. The crust is made of solid rocks and minerals.
Mantle
- The mantle lies between Earth’s dense, super-heated core and its thin outer layer, the crust. The mantle is about 2,900 kilometers (1,802 miles) thick, and makes up an 84% of Earth’s total volume.
Core
- Earth’s core is the extremely hot, and quite dense centre of our planet. The ball-shaped core lies beneath the cool, brittle crust, and the mostly-solid mantle. The core is found about 2,900 kilometers (1,802 miles) below Earth’s surface and has a radius of about 3,485 kilometers (2,165 miles). Core constitutes mainly Iron and Nickel, thus also called as nife layer.
Volcanoes
Types of Volcanoes
Asthenosphere
- The source of eruption of a volcano lies in the zone of semi-liquid material (magma) under the crust called Asthenosphere.
Lava
- Magma constitutes lava flows, pyroclastic debris, volcanic bombs, ash and dust, and gases that come out of the surface as Lava.
On the basis of their nature of eruption and the form developed at the surface, volcanoes can be classified as:
- Shield Volcano: When the basaltic lava of a volcano is of low viscosity that can quickly flow and cover large areas, it forms Shield Volcano. For example, Mauna Loa in the Island of Hawaii, Wolf volcano in Galapagos Islands, and Nyamuragira in the Democratic Republic of Congo.
- Composite Volcano: It is a cone-shaped volcano built from several layers of viscous lava. Due to its viscous
lava, a composite volcano tends to form tall peaks rather than rounded cones. Mount Fuji in Japan and Mount Shasta in California are examples of composite volcanoes. - Caldera: Due to destructive eruption, the volcano collapses on eruption and forms a depression called as Caldera. A famous example is Crater Lake in Oregon.
- Flood Basalt Province: It is a result of series of highly fluid lava eruptions that cover humungous region or ocean floor. For example, the Deccan trap of India.
- Mid-oceanic Ridge Volcanoes: Mid-oceanic ridges are created by the upwelling of basaltic lava and lateral rifting of ocean crust that account for around 75% of total volcanic activity on Earth.
Volcanic Landforms
When the magma successfully comes out of the surface it, forms land features termed Extrusive landforms. On the other hand, when the magma cools down within the surface, it forms Intrusive landforms. Some of the key intrusive landforms are as follows:
- Batholiths are the large masses of intrusive igneous rocks formed beneath the Earth’s surface by solidification of magma or simply cooling down of dome-shaped magma chambers deep inside the earth.
- Latholiths are sheet-like intrusions that occur when the pressure of magma is high enough to move the strata of the sedimentary rock upward or to make them folded.
