Lithosphere – I Endogenetic Processes Online Test 9th Social Science Lesson 19 Questions in English

The Earth can physically be described as a ball of rock (the lithosphere), partly covered by water (the hydrosphere) and wrapped in an envelope of air (the atmosphere).To these three physical zones it is convenient to add a biological zone which includes all the living organisms (the biosphere).”

Earth’s surface is a vast area of 510 million sq.km, where four spheres of the Earth interact. The abiotic spheres are the lithosphere, atmosphere and hydrosphere. The biotic sphere is the biosphere. Together, these spheres constitute the planet, Earth.

Lithosphere has been bifurcated for the sake of convenience. It is divided into Endogenetic processes (Internal processes) and Exogenetic processes (External processes).

The ‘Pedosphere’ is a part of the lithosphere made up of soil and dirt. It exists at the interface of lithosphere, atmosphere, hydrosphere and biosphere.a) Hydrosphere

The lithosphere is the solid outer part of the Earth. The atmosphere is a thin layer of gases that surrounds the Earth. The hydrosphere is the watery part of the Earth’s surface including oceans, rivers, lakes and water vapor. The biosphere is the layer of Earth where life exists.

The outer surface and inner core of the Earth are totally different in their nature and structure. The structure of the Earth’s interior is divided into three layers namely the crust, the mantle and the core.

Crust is the outer layer of the Earth, where we live. It is the skin of our Earth,

Crust ranges between 5 to 30 km. It is the solid and rigid layer of the Earth. The thickness of the crust is greater below the continents than the ocean floor.

The crust is classified as continental crust and oceanic crust.

The major elements of crust are Silica (Si) and Aluminum (Al) and thus, it is termed as SIAL.

The terms ‘lithosphere’ and ‘crust’ are not the same. The lithosphere includes the crust and the uppermost part of the mantle.

All terrestrial planets have lithosphere. The lithospheres of Mercury, Venus, and Mars are much thicker and more rigid than that of the Earth.

Mantle: The interior part beneath the crust is called mantle, which is about 2,900 km thick. The major elements of the mantle are Silica (Si) and Magnesium (Mg) and hence it is also termed as SIMA.

In the upper part of the mantle, the rock remains solid, whereas in the lower part of the mantle, rocks are in molten form. This molten rock inside the Earth is called ‘magma’.

The core is the innermost and hottest layer of the Earth which lies below the mantle. It is composed mainly of Nickel (Ni) and Iron (Fe). Hence it is called NIFE.

The core is divided into Solid inner core and Liquid outer core. The presence of large quantities of iron in the core is responsible for the Earth’s gravitational force.

As the Earth rotates on its axis, the liquid outer core spins over the solid inner core and generates the Earth’s magnetic field. This is responsible for the functioning of the magnetic compass. Due to high pressure, the materials in the inner core are unable to move and hence remain solid.

The Deepest Place ever reached by human technology vary from time to time. Till 2011 Kola Super Hole (12,262m) in Murmansk, Russia was the deepest place.

In 2012, Z-44 Chavyo Well (12,376m) broke the record, and is supposed to be 15 times the height of Burj Khalifa in Dubai.

The crust is a storehouse of rocks. An aggregate of minerals on the Earth’s crust is called ‘rock’. It may be hard and compact like ‘granite’ or soft as ‘clay’ or loose as ‘sand’.

Types of Rock Based on formation, rocks are classified as Igneous, Sedimentary and Metamorphic.

The ancient city of Petra in Jordan is an example of an entire city carved out of rocks. There are many specimens of magnificent rock-cut architecture in India, like the Ajanta and Ellora caves in Maharashtra, the Aihole and Badami temples in Karnataka, the Konark temple in Odisha and Mamallapuram in Tamil Nadu.

Igneous Rocks: The word ‘igneous’ is derived from the Latin word Ignis meaning ‘Fire’. The interior of the Earth contains very hot molten material called ‘Magma.

The magma reaches the Earth’s surface, it is referred to as ‘Lava’. The lava on the surface cools down and gets solidified as rocks called igneous rocks.

Granite and basalt are examples of such rocks. Igneous rocks are also called Primary or Mother rocks because all other rocks are directly or indirectly formed from them.

These sedimentary rocks are named after the Latin word ‘sediment’ meaning ‘ settle. Rivers, glaciers and winds carry bits of rock and soil and deposit them in layers.

The bodies of plants and animals that fall on the deposits get embedded in the layers and form Fossils.

Sandstone, limestone, chalk, gypsum, coal and conglomerate are examples of sedimentary rocks.

The term ‘metamorphic’ is derived from the word ‘metamorphosis’, which means, ‘change of form’.

When igneous or sedimentary rocks are subjected to extreme heat and pressure, they undergo a complete change in their form and character in course of time, granite may get transformed to gneiss, basalt to schist, limestone to marble and sandstone to quartzite.

The Rock cycle is a continuous process through which igneous, sedimentary and metamorphic rocks are transformed from one form to another.

The formation and deformation of landforms on the surface of the Earth is a continuous activity of two broad processes i.e. internal and external

These processes cause stress and deformation on Earth materials and finally bring changes on the surface of the Earth. These are referred as Geomorphic Processes.

The forces that act from the Earth’s interior towards the Earth’s surface are called internal processes or Endogenetic processes. These forces build the landscape and create topographic relief.

The forces that act on the surface of the Earth due to natural agents like running water, glacier, wind, waves etc. are called External processes or Exogenetic processes. These external processes tear the landscape down into relatively low elevated plains.

The internal processes generate heat and eject materials from deep below the Earth’s crust. Internal radioactivity is the principal source of power for this process.

The lithosphere is divided into a number of huge slabs of rocks called ‘Tectonic plates.’ These tectonic plates are divided into major and minor plates.

Plates float independently over the mantle. Collisions of these plates produce mountain ranges and other irregular surface features, both on land and the ocean floor. This phenomenon is called ‘plate tectonics.

The movement of tectonic plates is due to thermal energy from the mantle. we have a better understanding about the plate movements and its relation to Earthquake and volcanic activities.

Convergent Boundary – Here the plate moves toward each other and sometimes, a plate sinks under another. The location where the sinking of a plate occurs is called a subduction zone.

Divergent Boundary – Here the plates pull away from each other as magma pushes up from the mantle.

Transform Boundary – Here the plates slide horizontally past each other.

Due to lateral compressional forces, the plates are forced to move upwards and downwards. This is called ‘Folding’.

Mountains formed by folding are called Fold Mountains. The Process of folding creates lofty mountain ranges such as the Himalayas and the Alps.

The movement of plates creates stress and tension in the rocks, causing them to stretch and crack. This is called ‘Faulting’.

The great rift valley of East Africa is a notable example for the process of faulting. The process of folding and faulting together with volcanoes and Earthquakes continually reshape the continents and seafloor.

According to plate tectonics, the plates are in constant motion with an average rate of few centimeters per year. The movement might seem slow, but over millions of years, the plates and the continents riding on them move a long way.

About 250 million years ago, the Indian Plate was a part of the Gondwana land, which comprised of modern Africa, Australia, Antarctica, and South America.

Approximately 140 million years ago, the Indian plate broke away from the ancient super continent ‘Gondwana’ and began moving north and collided with Asia.
The collision with the Eurasian Plate along the boundary between India and Nepal formed the Orogenic belt that created the Tibetan Plateau and the mighty Himalayan Mountains.

Earthquakes are generally caused by the sudden vibrations in the Earth’s crust, which spreads outward in all directions as waves from the source of disturbance.

The point of origin of an Earthquake is called ‘Focus’ (Hypocenter) which generates a series of elastic waves. ‘Epicentre’ is a point on the Earth’s surface that lies directly above the focus. The impact of the Earthquake is felt the most at the epicentre.

Earthquakes generate seismic waves. The nature, force and speed of these seismic waves depend on the nature of the medium through which it passes.

There are three major types of seismic waves depend on the nature of the medium through which it passes.

The highest magnitude ever recorded is 9.5 on Richter scale (Bio-Bio, Chile in 1960).

C.F. Richter devised a scale to measure the magnitude of Earthquakes.

This Richter scale relates to the energy released at the epicentre and provides an estimation of the severity of an Earthquake. It is an open ended scale.

Primary or P-waves are the fastest of all the Earthquake waves and the first to reach the epicentre.

The P-waves waves pass through solids, liquids and gases, either through push or pull with an average velocity of 5.3km per second to 10.6 km per second.

Secondary or S-waves travels only through solids. These transverse waves shake the ground perpendicular to the direction in which they propagate. The average velocity of these waves is 1Km per second to 8 km per second.

Surface Waves (or) L-waves are similar to P-waves but they travel primarily along the ground surface. These waves travel comparatively slower and are the most destructive waves. The average velocity of these waves is 1 km per second to 5 km per second.

The instrument which records the Earthquake waves is called ‘seismograph’ or ‘seismometer’. The science that deals with Earthquakes is called ‘seismology.

The word ‘Tsunami’ is a Japanese term, meaning harbour waves. It is adopted to describe large seismically generated sea waves caused by Earthquakes, submarine explosions and landslides.

The Tsunami waves travel at a great speed (more than 500 km per hour) and the length of the waves exceeds 600 km. These waves reach to a height of more than 15 m near the sea shore and are capable of causing destruction along the coastal area.

The 2004 Indian Ocean Earthquake that caused tsunami is the sixth-deadliest natural disaster which travelled at a speed of 600 km per hour with an estimated death toll of 2,80,000.The Earthquake which occurred near Indonesia at 00.58 hours took nearly 7 hours to reach Chennai.

On 26 December 2004 a tsunami occurred in the Indian Ocean. It was the result of the Indio-Australian Plate subduction below the Eurasian Plate. It was caused by an Earthquake measuring a magnitude of above 9 in the Richter scale. The Earthquake caused the seafloor to uplift, displacing the seawater above.

A volcano is a vent or an opening on the surface of the Earth crust, through which hot solid, liquid and gaseous materials (Magma) erupt out to the surface from the Earth’s interior. Magma rises up and ejects on the surface as Lava. Volcanoes are also formed when plates move apart.

Volcanoes generally have the following major components. They are Magma chamber, Vents, Volcanic cone and Crater.

Magma chamber – a large pool of liquid rock found beneath the surface of the Earth
Vents – an opening serving as an outlet for air, smoke, fumes, magma etc
Volcanic cone – a landform built by the magma ejected from the vent in the shape of a cone
Crater – a bowl shaped depression found at the top of the volcano through which the magma flows out.

The term ‘volcano’ is derived from the Latin term VULCAN, which is the name of Roman “God of Fire”.

Based on the periodicity of eruptions, volcanoes are classified into (i) Active volcano, (ii) Dormant volcano, (iii) Extinct volcano.

Active volcanoes are those which constantly eject volcanic lava, gases and fragmented materials. (eg.) Mount St. Helens in the United States.

Dormant Volcano: Volcanoes that do not show any sign of volcanic activity for a long period of time are known as dormant volcanoes. Sometimes there may be a sudden explosion which may cause unimaginable loss to life and property (e.g.) Mt. Fuji , Japan

Extinct or Dead Volcano: When a volcano permanently stops its volcanic activity, then it is called as extinct or dead volcano (e.g.) Mt. Kilimanjaro, Tanzania

Explanation
Active volcano: Mount St. Helens
Dormant Volcano: Mt. Fuji, Japan
Extinct or Dead Volcano: Mt. Kilimanjaro, Tanzania

Volcanoes can also be classified based on their structure and composition as composite volcano, shield volcano and dome volcano.

Composite volcano, also known as strata volcano, is a conical volcano built by many layers of hardened lava, pumice and volcanic ash. These are commonly found in the Pacific Ocean Eg. Mt. Fuji, Japan.

Volcanic Dome: A lava dome or volcanic dome is roughly a circular mound formed due to the slow ejection of viscous lava from a volcano. As the lava is rich in silica with intense viscosity, it is prevented from flowing far from its vent. e.g. Paricutin, Mexico

Shield Volcano: Shield volcanoes are formed by intense viscous lava. These are shallow depositions with gently sloping sides. Hence the lava flows out in all directions to create a shield. E.g., Mauna Loa, Hawaii

Composite volcano, also known as strata volcano, is a conical volcano built by many layers of hardened lava, pumice and volcanic ash. These are commonly found in the Pacific Ocean Eg. Mt. Fuji, Japan. Volcanic Dome: A lava dome or volcanic dome is roughly a circular mound formed due to the slow ejection of viscous lava from a volcano. As the lava is rich in silica with intense viscosity, it is prevented from flowing far from its vent. e.g. Parícutin, Mexico.
Shield Volcano: Shield volcanoes are formed by intense viscous lava. These are shallow depositions with gently sloping sides. Hence the lava flows out in all directions to create a shield. E.g., Mauna Loa, Hawaii.

Most Earthquakes and volcanic eruptions do not strike randomly, but occur along the plate boundaries. One such area of volcanic eruptions is the circum-Pacific Ring of Fire, where the Pacific Plate meets many surrounding plates.

The Ring of Fire is the most seismically and volcanically active zone in the world. The other distinctive major belts are Mid-Oceanic Ridges and Mid-Continental Belts.

Constructive Effects: Volcanic materials enrich the soil fertility that promotes agricultural activities. The hot volcanic region helps in generating geothermal energy. Many dormant and active volcanoes are the most attractive tourist spots of the world. Most of the volcanic materials are used as building materials.

Destructive Effects: Volcanic eruption causes Earthquakes, fast floods, mud slide and rock fall. Lava can travel very far and burn, bury, or damage anything in its path. The large amount of dust and ash makes breathing hard and irritable. Volcanic eruptions can alter the weather conditions and disrupt transport.

The 28 September 2018 magnitude 7.5 Palu, Indonesia earthquakes (0.178°S, 119.840°E, depth 13 km) occurred at 1002 UTC. The major earthquake triggered catastrophic liquefaction, landslides, and a near-field tsunami that resulted in direct damage, impact, economic loss, and loss of life.