Fundamentals of Physical Geography
Chapter 3: Interior of the Earth
Q1. What are the direct and indirect sources of information to know about the interior of the earth?
Q2. What is gravity anomaly?
Q3. What is hypocentre/focus and epicentre? explain with diagram.
Q4. Differentiate body wave and surface wave.
Q5. How the study of earthquake waves help us to know about information about interior of the earth?
Q6. Explain the formation of 'P - wave shadow zone' and 'S - wave shadow zone' with diagram.
Q7. Explain different types of earthquake.
Q8. Discuss about the structure of the interior of the earth with diagram.
Q9. Write a short note on asthenesphere.
Q10. Explain different types of volcanoes with example.
Q11. Differentiate between intrusive and extrusive igneous landforms with example.
Q. 1 What are the sources of information about the interior of the Earth? Differentiate them.
Ans:
Most of our knowledge about the interior of the Earth is largely based on estimates and conclusions. Yet, a part of the information is obtained through direct observations and indirect sources (analysis of materials). Analysis of properties of matter indirectly provides information about the interior.
Direct Sources: -
1) Mining: - Through mining activities, it has been observed that temperature and pressure increase towards the interior of the Earth surface.
2) Drilling: - Scientists have estimated the values of temperature, pressure and the density of materials at different depths. Scientists world over are working on two major projects such as “Deep Ocean Drilling projects” and “integrated ocean drilling project”. The deepest drill at kola, in Arctic Ocean, has so far reached a depth of 12 km.
3) Volcanic Eruptions: - When molten material is thrown onto the surface of the Earth during volcanic eruption it becomes available for analysis.
Indirect Sources: -
1) Laboratory Experiments: - When minerals and rocks processed at high pressure and temperature provides many insights of Earth's interior. Data on Earth's interior also comes from geological observation of surface rocks and studies of Earth motion in the solar system.
2) Gravitational Force: - It noticed that gravitational force is not the same at different latitudes on the surface. It is greater near poles and lesser at the equator. This type of Gravity anomalies gives information about the distribution of mass of the material inside the Earth.
3) Meteors: - It has been studied that material & structure found in meteors is similar to that of Earth, when some of the meteors fall on the Earth they became another source of information about the interior of the Earth.
4) Seismic Activity: - It is one of the most important sources of information about the interior of the Earth. For it, paths and characteristics of Earthquake waves traveling through the Earth are studied.
5) Magnetic Surveys: - They provide information about the distribution of magnetic materials in the crustal portion, and thus, provide information about the distribution of materials in this part.
Q. 2 Give the difference between Body waves and Surface waves?
Ans:
Body waves
Surface waves
1.
These are generated due to the release of energy at the focus.
The body waves interact with the surface rocks and generate new set of waves called surface waves.
2.
They move in all directions travelling through the body of the Earth.
These waves move along the surface.
3.
These are less destructive than the surface waves.
These waves are more destruction.
Q. 3 Differentiate between ‘Primary Waves’ and ‘Secondary Waves’.
Ans:
Primary Waves
Secondary Waves
1.
Other Name
These are called ‘P- Waves’.
These are called ‘S- Waves’
2.
Speed
These move faster and are the first to arrive at the surface.
These arrive at surface with sometime later.
3.
Shadow Zone
The shadow zone of P-wave is much smaller than that of the S-waves.
The shadow zone of S-wave is much larger than that of the P-waves.
4.
Source of Travelling
They travel through gaseous, liquid and solid materials.
S-waves can travel only through solid materials.
Q. 4 Why do Earthquake waves develop a ‘Shadow Zone’? Explain with a diagram.
Ans:
1) When Earthquakes occur, they produce primary and secondary waves (called compression and shear waves sometimes). P-waves can travel through liquid and solid while S-waves can only travel through solid.
2) While P-waves can travel through liquid, but with reduced speed as liquids having a lower density than solids. On the other hand, S-waves will completely stop and disappear once they hit liquids. This means that once these waves hit the liquid outer core at depth of 2900 km of Earth, P-waves are refracted and S-waves are stopped.
3) On reaching the core ‘S’ waves disappear and P waves are refracted as a result there is no wave is found between 105° to 145°. This area is known as shadow zone.
4) Shadow zones are produced on the other sides of the planet due to waves being refracted or blocked by the liquid outer core of Earth.
5) There are 2 different types of shadow zones. The P-wave shadow zone is 105-140 degrees and the S-wave shadow zone is 105-105 degrees.
Q. 5 Explain different types of Earthquakes.
Ans:
The various types of Earthquakes are: -
1) Tectonic Earthquake: - The most common ones are the tectonic Earthquakes. These are generated due to sliding of rocks along a fault plane and the movement of tectonic plates.
2) Volcanic Earthquake: - A special class of tectonic Earthquake is sometimes recognised as volcanic Earthquake. These are found on the areas of active volcanoes.
3) Collapse Earthquake: - In the areas of intense mining activity sometimes the roofs of underground mines collapse due to seismic waves produced from the explosion of rock on the surface. These are called collapse Earthquakes.
4) Explosion Earthquake: - Ground shaking may also occur due to the explosion of chemical or nuclear devices. Such tremors are called explosion Earthquakes.
5) Reservoir Induced Earthquake: - The Earthquakes that occur in the areas of large reservoirs are referred to as reservoir induced Earthquakes. Sometimes Earthquakes also occur in mines due to mining processes. Sometimes Earthquakes also occur below the oceans on surface of the ocean causing tsunamis.
Q. 6 What are the effects of Earthquake?
Ans:
The immediate hazardous effects of Earthquake are: -
1) Loss of life and Property: - Ground shaking takes place in Earthquake. It leads to loss of life and property. Many buildings fall off and take life of people who were in and around the building.
2) Change in Land: - Due to Earthquake we can see many changes in the land. Many areas get converted into pits. There are cracks in mountains.
3) Causes Landslides and Tsunami: - It leads to landslides in mountainous regions and tsunami in oceans. It may further increase the calamity and loss of human and property.
4) Destruction of Means of Communication and Transportation: - It leads to destruction of means of communication and transportation. It creates problem in sending help and relief to victims.
5) Other Effects: - Earthquake may also lead to breaking or damage of dams which may lead to floods.
Q. 7 Give the structure/ layers of the Earth with suitable diagram.
Or
Explain the interior structure of the Earth.
Ans:
On the basis of composition structure of Earth is divided into three layers.
The Crust: - It is the outermost solid part of the Earth. It is brittle (hard but able to break) in nature.
1) Thickness: - The thickness of the crust varies under the oceanic and continental areas. Oceanic crust is thinner as compared to the continental crust. The mean thickness of oceanic crust is 5 km whereas that of the continental is around 30 km. The continental crust is thicker in the areas of major mountain systems. It is as much as 70 km thick in the Himalayan region.
2) Composition: - It is made up of heavier rocks.
3) Types: - The crust can be divided into two parts i.e. the upper crust or ‘Sial’ composed of the minerals like Silica and Aluminium and the lower crust or ‘Sima’ composed of the minerals Silica and Magnesium.
4) Density: - It is having density of 3 g/cm3. The basalt type of rock is found in the oceanic crust. The mean density of material in oceanic crust is 2.7 g/cm3.
The Mantle: - The portion of the interior beyond the crust is called the mantle also called ‘Mesosphere’.
1) Depth: - The mantle extends from Moho’s discontinuity to a depth of 2,900 km.
2) Asthenosphere: - The upper portion of the mantle is called asthenosphere. The word ‘Astheno’ means weak. It is considered to be extending up to 400 km. It is
the main source of magma that finds its way to the surface during volcanic eruptions.
3) Density: - It has a higher density of 3.4 g/cm3.
4) Composition: - The most common mineral found here is called Olivine (a magnesium iron silicate) because of its olive green-colour.
5) Division: - The crust and the uppermost part of the mantle are called lithosphere. Its thickness ranges from 10-200 km. The lower mantle extends beyond the asthenosphere. It is in solid state.
The Core: - The Core is the innermost layer of the Earth also called ‘Barysphere’.
1) Information: - The Earthquake wave velocities helped in understanding the existence of the core of the Earth.
2) Depth: - The core- mantle boundary is located at the depth of 2,900 km.
3) Form: - The outer core is in liquid state while the inner core is in solid state. The pressure on the core is very high and the temperature is estimated to be 3000° (degree) C to 6000° C.
4) Density: - The density of material at the mantle core boundary is around 5 g/cm3 and at the center of the Earth at 6,300 km, the density value is around 13g/cm3.
5) Composition: - The core is made up of very heavy material mostly constituted by nickel and iron (ferrous) so it is sometimes referred to as the ‘NiFe’ layer.
Q. 8 In how many groups are volcanoes classified on the basis of nature of eruption and the form developed at the surface? Explain.
Or
Explain the different types of Volcanoes.
Ans:
On the basis of nature of eruption and the form developed at the surface Volcanoes are classified into: -
1) Shield Volcanoes: - A Shield volcano is a wide volcano with low sloping sides. It is named for its low profile, resembling a warrior's shield lying on the ground. They are formed by basaltic Lava flows of low viscosity (घाडापन- the state of being thickness of a substance) - (lava that flows easily for long distances). Except the basalt flows, the shield volcanoes are the largest of all the volcanoes on the Earth. For example The Hawaiian volcanoes.
2) Composite Volcanoes (Stratovolcanoes): - Composite volcanoes are also called strato volcanoes named for their composition as the word ‘Strato’ means ‘Layers’. These volcanoes are built from layers, or strata, of pyroclastic material (derived from the Greek (pyr), meaning "fire", and (klastos), meaning "broken in pieces"), including lava, pumice (Dust), volcanic ash, and tephra (a Greek word means "ash"). They are steep sided cones as the lava doesn't flow very far before it solidifies. Mount Fuji in Japan, Mount Cotopaxi in Ecuador and Mount. Shasta in California etc. are the examples.
3) Caldera: - The term caldera comes from Spanish caldera, and Latin caldaria, meaning "cooking pot". A caldera is a large, bowl-shaped volcanic depression forms when the top of a volcanic cone collapse inwards after magma is ejected during a violent volcanic eruption. These are the most explosive of the Earth’s volcanoes. For example ‘Laguna de Quiltoa’ in Ecuador and ‘Crater Lake’ in Oregon (the western United States).
4) Flood Basalt Provinces: - Flood basalt is the result of a large volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. These volcanoes outpour (discharge) highly fluid lava that flows for long distances. Some parts of the world are covered by thousands of sq. km of thick basalt lava flows. For example ‘The Deccan Traps’ from India, covering most of the Maharashtra plateau, are a much larger flood basalt province. {The Deccan Traps of India are often called traps, after the Swedish word trappa (meaning "stairs"), due to the characteristic stair step geomorphology of many landscapes.}
5) Mid-Ocean Ridge: - This is an underwater mountain system, consists of various mountain ranges that are made up of volcanic eruption on the ocean floor range, due to movement of plate tectonics. There is a system of mid-ocean ridges more than 70,000 km long that stretches through all the ocean basins. ‘The Mid-Atlantic Ridge’, which is spreading one to two inches a year, and ‘the East Pacific Rise’, which is spreading two to six inches per year, are two examples of very long mid-ocean ridges.
Q. 9 What are the difference stages of a volcano?
Ans:
1) Active Volcano: - An active volcano is a volcano that has had at least one eruption during the past 10,000 years. An active volcano might be erupting or dormant.
2) Erupting Volcano: - An erupting volcano is an active volcano that is having an eruption.
3) Dormant: - A dormant volcano is an active volcano that is not erupting, but supposed to erupt again.
4) Extinct Volcano: - An extinct volcano has not had an eruption for at least 10,000 years and is not expected to erupt again in a comparable time scale of the future.