Q 1 – What is Pangaea?
Ans. All landmasses of the world have been formed from one super continent called Pangaea.
Q 2 – Who first propounded the theory of continental drift?
Ans. Alfred Wegner propounded the theory of continental drift in 1912.
Q 3 – Which plate is composed of mainly oceanic crust?
Ans. The Pacific plate is composed of mainly oceanic crust.
Q 4 – How did the Himalayas rise?
Ans. The collision between the Indian Plate and the Eurasian plate took place north of the Indian plate giving rise to the Himalayas.
Q 5 – What is the evidence in support of continental drift theory?
- Ans. Geological matching
- Palaeoclimatic unity, and
- Palaeornagnetism.
Q 6 – Name the continents into which the supercontinent, Pangaea, got split.
Ans. They are Laurasia and Gondwanaland.
Q 7 – How many years ago Pangaea, the supercontinent has evolved?
Ans. Pangaea, the supercontinent, had evolved some 280, million years ago.
Q 8 – What are hot spots?
Ans. The centers of volcanic activity are called hot spots.
Q 10 – Name the three kinds of boundaries based on their Relative motion.
Ans.
- Zones or margins of divergence or spreading,
- Margins of convergence, and Fracture zones or transform faults.
Q 11 – How many plates the lithosphere is divided into?
Ans. Seven plates.
Q 12 – The collision between which two plates gave rise to the Himalayas?
Ans. The collision between Indian and Eurasian plates gave rise to the Himalayas.
Q 13 – Name two fossils that tell us that continents were once united.
Ans. The fossils of the plant Glossopteris and animals Mesosaurus and Lystosaurus, suggests that these continents were once joined.
Q 14 – What is Palaeornagnetism?
Ans. It is the fossil magnetism evident today in igneous rocks such as magnetite, hematite, pyrrhotite, etc.
Q 15 – What is the Pacific plate?
Ans. The latest plate in terms of its formation or origin.
Q 16 – What do you understand by the spreading of crust from the ridge and the widening of the ocean basin?
Ans. It is the seafloor spreading.
Q 17 – Name the northern and southern parts of Pangaea.
Ans. Laurasia and Gondwanaland.
Q 18 – Name the sea separating Laurasia and Gondwanaland.
Ans. The Tethys sea.
Q 19 – In which parts Pangaea was split?
Ans. Pangaea was split into northern continent Laurasia and Southern continent, Gondwanaland.
Q 20 – Name the original supercontinent. When was it formed?
Ans. Pangaea. It was formed about 280 million years ago.
Q 21 – State three causes of plate movements.
- AnsThermal convection,
- Hot spots of volcanic activity,
- Movement of currents.
Q 22 – What is meant by sea-floor spreading?
Ans. The crust spreads away from the ridge and the ocean basin widens. This phenomenon is known as sea-floor spreading.
Q 23 – Name the process in which one plate overrides the other and the overriding plate slips down into the mantle and is submerged.
Ans. Subduction.
Q 24 – What is thermal convection?
Ans. It acts as a driving force for the movement of plates.
Q 25 – Name the four different types of plate interactions.
Ans. Spreading, collision, subduction, and transform.
Q 26 – How was drifting of continents caused?
Ans. It was caused by two forces :
- pole fleeing force, and
- tidal force.
Q 27 – How do lithosphere plates behave along the transform fault?
Ans. The lithospheric plates slide over each other, neither creating nor destructing any landmass. Instead, the. friction arising from the f* movement of the plates usually causes severe earthquakes and earth tremors.
Q 28 – Why do geographers focus their attention on plate boundaries?
Ans. Geographers focus their attention on plate boundaries because each plate is a tectonic plate. It is rigid and moves as a single unit. Nearly all major tectonic activity occurs along the plate boundaries.
Q 29 – What does the term ‘supercontinent’ refer to?
Ans. The term ’supercontinent’ refers to a single common geological landmass called Pangaea. It has been proposed that all landmasses of the world had formed from this ‘supercontinent’. Pangaea had evolved some 280 million years ago, at the end of the Carboniferous period and by mid-Jurassic age, 150 million years ago. Pangaea land split into Laurasia, the northern continent, and Gondwanaland, the southern continent. About 65 million years ago, i.e. at the end of the cretaceous, bound mainland were further broken up to give rise to several other continents such as South America, Africa, Australia, and Antarctica.
Q 30 – Discuss the causes of plate movement.
Ans. Sub-crustal convection currents invoke the mechanism of thermal convection that acts as a driving force for the movement of plates. Hot currents rise, then cool as they reach the surface. At the same time, cool currents sink down. This convectional movement moves the crustal plates. .. Owing to current movements, the rigid plates of the lithosphere, which ‘float’ on more mobile asthenosphere, are in constant motion.
Q 31 – What is a geological time-scale?
Ans. The chronology of the geological history’ of the earth is revealed by its rocks. Geological time scale indicates the hierarchy of time periods during which different rocks of the earth have formed
Q 32 – What is subduction?
Ans.The process in which the overridden plate slips down into the mantle and is submerged is known as subduction. Besides volcanism and shallow to deep-focus earthquakes, boundaries also formed deep trenches and folded mountains
Q 33 – What is polar wandering?
Ans. There has been a periodic change in the position of the magnetic pole. These changes are recorded in rocks by way of permanent magnetism. Unraveling of the signatures of such changes in the geologically old rocks by scientific methods provides the changing position of poles in geological time scale. It is known as ‘polar wandering’. It demonstrates that the continents have frequently moved and changed their direction of motion from time to time.
Q 34 – Account for the formation of the Himalayas according to the theory of plate tectonics in three points.
- Ans.South-east Indian ocean ridge collided between the Indian plate and European plate. The Indian plate gave rise to the Himalayas.
- The suture between the Indian and Eurasian plates in the Himalayan region has been along the Indus and Brahmaputra.
- The mid-Indian ocean ridge has been spreading faster
Q 35 – What is ‘Zolrt of Convergence’?
Ans. Zone of Convergence is the boundary along which the edge of ‘ one plate overrides the other. It produces deep trenches and folds mountains. Volcanoes and deep-focus earthquakes mark it.
Q 36 – Describe the driving force for the movement of plates.
Ans. The sub-crustal convection currents invoke the mechanism of thermal convection that acts as a driving force for the movement of plates. As these currents reach the surface, the hot current rises, then cools. Sometimes, cooler currents sink down. This type of convectional movement causes the movement of crustal plates.
Q 37 – Name the major plates of the earth. Which plate is composed of the oceanic plate?
Ans. Pacific plate, Eurasian plate, Indo-Australian plate, African plate, North American plate, South American plate, and Antarctica plate are the major plates of the earth.
The zone of divergence is the boundary along which the plate is composed of mainly oceanic crust. It is known as the Pacific plate.
Q 38 – What is palaeoclimatic unity?
Ans. The uniformity in the nature of the sediment in the biological past indicates that these continents were together in the geological past and experienced similar climatic conditions. It is the native of glacial deposits of the separated continents indicating that these continents were together in the geological past and experienced similar climatic conditions.
Q 39 – What do you mean by ‘jig-saw-fit’? Describe the similarities found on the east and west coasts of the Atlantic ocean. What do they suggest?
Ans. The ‘jig-saw-fit’ means the landmasses on the east and west coast of the Atlantic ocean can be fitted together. There are many similarities found on the two coasts :
- The Gulf of Guinea can be fitted into Cape San-Rogue of Brazil, the shoulder of Africa can be fitted into Gulf of Mexico, Western Europe and Eastern coast of North America along with Greenland can be fitted together.
- Gold deposits of Ghana lands are found on the east and in Brazil on the west.
- The glacial deposits are found in all landmasses of Gondwana land.
These similarities suggest that these continents were together in the geological past.
Q 40 – Discuss the Continental Drift Theory.
Ans. Continental Drift Theory was proposed by Alfred Wegner in 1912. He postulated that all landmasses of the world have been formed from one super-continent called Pangaea.
The supercontinent, Pangaea, had evolved some 280 million years ago, at the end of the Carboniferous period and by the mid-Jurrasic age, 150 million years ago. Pangaea had split into a northern continent, Laurasia, and a southern continent Gondwanaland. About 65 million years ago, i.e., at the end of the Cretaceous, Gondwanaland further broke up to give rise to several other continents, such as South America, Africa, Australia, and Antarctica. Thus, the present distribution of the continental masses and the oceans are the n .uit of fragmentation of one or more pre-existing masses. These landmasses have drifted apart the intervening hollows having been occupied by the oceans.
There are several pieces of evidence that suggest the existence of Pangaea. This evidence is available in the form of geological watching, palaeoclimatic units, and paleomagnetism.
Q 41 – Describe sea-floor spreading in brief.
Ans.The present distribution of continents has taken place in the last 65 million years. The drift of continents still continues. The ridges down the middle of ocean floors have been emitting lava continuously. Those mid-oceanic ridges are cracks on the floor of the ocean where molten rocks push up to form a new crust. The crust spreads among the ridge and the ocean basin widens. This phenomenon is known as sea-floor spreading. The Atlantic ocean is getting smaller and the Red Sea is the part of a crack in the crust that will widen to produce new ocean millions of years ahead in the future. In the past, the widening of the South Atlantic ocean has separated Africa and South America.
Q 42 – Explain the plate tectonic theory and its mechanism.
Ans. Plate tectonic theory proves that the earth’s crust consists of several plates that carry continents and the ocean floors and float on the asthenosphere, moving very slowly, the movement probably resulting from currents in the asthenosphere. As shown in fig., the lithosphere is broken into seven major plates. They include :
- Pacific plate
- Eurasian plate
- Indo-Australian plate
- African plate
- North American plate
- South American plate
- Antarctic plate
The latest among these is the Pacific plate which is composed of oceanic crust almost entirely. The other plates have both continental and ocean crust. No plate consists of only continental crust. Plates range in thickness from about 70 km. beneath oceans to 150 km. under continents. Each tectonic plate is rigid and moves on a single unit. Nearly all major tectonic activities occur along the plate boundaries.
Based on the relative motion of plates, three kinds of plate boundaries have been recognized. They are :
1. Zones of divergence: These are boundaries along which plates separate and in the process of separation molten materials upwell. This is commonly observed along linear ocean edge where the new lithosphere is created in the form of new ocean floors. Active volcanism and shallow focus earthquakes make such boundaries,
2. Zones of convergence: There are the boundaries along which, the edge of one plate overrides the other. The overridden plate slips down into the mantle and is absorbed. This process is known as subduction.
3. Fracture zones or Transform faults: The plates slide past each other effect creating or destructing the boundaries. However, shallow focus earthquakes may result due to this friction.
Q 43 – Describe the main features of the Indian plate.
Ans. Indian ocean floor presents striking topography consisting of a number of elevated ridges and plateaus. Two of the ocean ridges, namely, the Mascarene Plateau, Chagos-Maldweep-Lakshadweep island ridge are said to be the volcanic tracts of two hot spots. The Northward extension of Ninety-east Ridge indeed in the trench which consumed the seafloor to the north of the Indian continental mass. The Chagos- Lakshadweep ridge linked the ancient Carlsberg ridge with the Southeast Indian ridge during the Eocene period (50 million years ago).
Consequent to the Carlsberg-Southeast Indian ocean ridge, the collision between the Indian plate and the Eurasian plate took place north of the Indian plate giving rise to the Himalayas. The suture between Indian and Eurasian plates in the Himalayan region has been along the Indus and Brahmputra rivers.
Q 44 – What was the theory’ profounded by Alfred Wegener, a German meteorologist? With what principle was it associated?
Ans. Alfred Wegener, a German meteorologist put forth a comprehensive argument in the form of “the continental drift theory” in 1912. This was regarding the distribution of the oceans and the continents.
Q 45 – Which methods that developed in the recent period have facilitated correlating the rock formation from
Ans. The radiometric dating methods developed in the recent period have facilitated correlating the rock formation from different continents across the vast ocean.
Q 46 – What are Abyssal Plains?
Ans.; These are extensive plains that lie between the continental margins and mid-oceanic ridges. The Abyssal plains are the areas where the continental sediments that move beyond the margins get deposited.
Q 47 – What are Continental Margins?
Ans. These form the transition between continental shores and deep-sea basins. They include continental shelf, continental slope, continental rise and deep-oceanic trenches.
Q 48 – What are convection currents?
Ans. Convection currents are generated due to radioactive elements causing thermal differences in the mantle portion.
Q 49 – What was the condition of India when Pangaea broke? Before that what was the status of India?
Ans. India was a large island situated off the Australian coast, in a vast ocean. The Tethys sea separated it from the Asian continent till about 225 million years ago. India is supposed to have started her northward journey about 200 million years ago at the time when Pangaea broke. India collided with Asia about 40¬50 million years ago causing rapid uplift of the.
Q 50 – How was Deccan Traps formed?
Ans. During the movement of the Indian plate towards the Asiatic plate, a major event that occurred was the outpouring of lava. It led to formation of the Deccan Traps. This started somewhere around 60 million years ago and continued for a long period of time.
Q 51 – What was emphasised by the sea floor spreading and tectonic plates theory?
Ans. It emphasised that the earth is divided into plates and these plates have been constantly moving over the globe throughout the history of the earth. It is not the continent that moves as believed by Wegener. Continents are part of a plate and what moves is the plate. All the plates, without exception, have moved in the geological past, and shall continue to move in the future as well.
Q 52 – What are the different ways in which convergence can take place?
Ans. There are three ways in which convergence can occur.
These are:
- between an oceanic and continental plate;
- between two oceanic plates; and
- between two continental plates.
Q 53 – Who was the profounder of plate tectonic theory?;
Ans. McKenzie Parker and Morgan
Q 54 – Who was the profounder of convection currents theory?
Ans. Arthur Holmes
Q 55 – According to Wegener, what are the causes of drifting of continents?
Ans. Two causes were responsible for the drifting of the continents:
- Pole-fleeing force and
- Tidal force
Q 56 – In how many plates has earth been divided according to plate tectonic theory?
Ans. According to this theory, the earth has been divided into seven major and some minor plates.
Q 57 – Give examples of placer deposits.
Ans. The occurrence of rich placer deposits of gold in the Ghana coast and the gold bearing veins in Brazil are examples of placer deposits.
Q 58 – With what is fleeing force related?
Ans. The polar-fleeing force relates to the rotation of the earth. The earth is not a perfect sphere; it has a bulge at the equator. This bulge is due to the rotation of the earth.
Q 59 – With what is tidal force related?
Ans. It is related to the attraction of the moon and the sun that develops tides in oceanic waters. Wegener believed that these forces would become effective when applied over many million years.
Q 60 – On what basis has continent drifting theory been discarded?
Ans. Arthur Holmes in 1930s discussed the possibility of convection currents operating in the mantle portion. These currents are generated due to radioactive elements causing thermal differences in the mantle portion. Holmes argued that there exists a system of such currents in the entire mantle portion. This was an attempt to provide an explanation to the issue of force, on the basis of which contemporary scientists discarded the continental drift theory.
Q 61 – The ocean floor may be segmented into howr many di visions based on the depth as well as the forms of relief?
Ans. The ocean floor may be segmented into three major divisions based on the depth as well as the forms of relief. These divisions are:
- continental margins,
- deep-sea basins and
- mid-oceanic ridges.
Q 62 – What are mid-oceanic ridges?
Ans. This forms an interconnected chain of mountain system within the ocean. It is the longest mountain-chain on the surface of the earth though submerged under the oceanic water. It is characterised by a central rift system at the crest, a fractionated plateau and flank zone all along its length. The rift system at the crest is the zone of intense volcanic activity.
Q 63 – Which fact helped the scientists to understand plate movement?
Ans. The rocks equidistant on either sides of the crest of mid-oceanic ridges show remarkable similarities in terms of period of formation, chemical compositions and magnetic properties. Rocks closer to the mid-oceanic ridges have normal polarity and are the youngest. The age of the rocks increases as one moves away from the crest.
Q 64 – Explain the movement in Indian plate.
Ans. The Indian plate includes Peninsular India and the Australian continental portions. The Tethys Sea separated it from the Asian continent till about 225 million years ago. India is supposed to have started her northward journey about 200 million years ago at the time when Pangaea broke. India collided with Asia about 40-50 million years ago causing rapid uplift of the Himalayas. About 140 million years before the present, the subcontinent was located as south as 50°S. latitude.
The two major plates were separated by the Tethys Sea and the Tibetan block was closer to the Asiatic landmass. During the movement of the Indian plate towards the Asiatic plate, a major event that occurred was the outpouring of lava and formation of the Deccan Traps. This started somewhere around 60 million years ago and continued for a long period of time. The subcontinent was still close to the equator. From 40 million years ago and thereafter, the event of formation of the Himalayas took place. Scientists believe that the process is still continuing and the height of the Himalayas is rising even to this date.
Q 65 – Explain the hypothesis, known as the “sea floor spreading” given by Hess.
Ans. Hess argued that constant eruptions at the crest of oceanic ridges cause the rupture of the oceanic crust forces and the new lava wedges into it, pushing the oceanic crust on either side. The ocean floor, thus spreads. Two facts made Hess think about the consumption of the oceanic crust.
- The younger age of the oceanic crust
- The spreading of one ocean does not cause the shrinking of the other.
He further maintained that the ocean floor that gets pushed due to volcanic eruptions at the crest, sinks down at the oceanic trenches and gets consumed. The basic concept of sea floor spreading has been depicted in the given figure:
Q 66 – Explain the distribution of earthquake and volcanic plate on the earth,
Ans. Earthquake and Volcanic plate:
1. It goes from Atlantic Ocean almost parallel to the coastlines. It further extends into the Indian Ocean. It bifurcates a little south of the Indian subcontinent with one branch moving into East Africa and the other meeting a similar line from Myanmar to New Guiana.
2. Another area of concentration coincides with the Alpine-Himalayan system and the rim of the Pacific Ocean. In general, the foci of the earthquake in the areas of mid-oceanic ridges are at shallow depths whereas along the Alpine-Himalayan belt as well as the rim of the Pacific, the earthquakes are deep-seated ones. The map of volcanoes also shows a similar pattern. The rim of the Pacific is also called rim of fire due to the existence of active volcanoes in this area.
Q 67 – What information do we get from the mapping of the ocean floor and palaeomagnetic studies of rocks from oceanic regions?
Ans. The mapping of the ocean floor and palaeomagnetic studies of rocks from oceanic regions gave following information:
- Along the mid-oceanic ridges, volcanic eruptions are common and they bring huge amounts of lava to the surface in this area.
- The rocks equidistant on either sides of the crest of mid-oceanic ridges show remarkable similarities in terms of period of formation, chemical compositions and magnetic properties.
- The ocean crust rocks are much younger than the continental rocks. The age of rocks in the oceanic crust is nowhere more than 200 million years old. Some of the continental rock formations are as old as 3,200 million years.
- The sediments on the ocean floor are unexpectedly very thin. Scientists expected that if the ocean floors were as old as the continent, to have a complete sequence of sediments for a period of much longer duration. However, nowhere was the sediment column found to be older than 200 million years.
- The deep trenches have deep-seated earthquake occurrences while in the mid-oceanic ridge areas, the quake foci have shallow’ depths.
Q 68 – Explain the basic concept of continental drift theory.
Ans. Alfred Wegener, a German meteorologist, put forth a comprehensive argument in the form of “the continental drift theory” in 1912. This was regarding the distribution of the oceans and the continents. According to Wegener, all the continents formed a single continental mass and mega ocean surrounded the same. He called the super continent as PANGAEA, meaning all earth. He named mega ocean as PANTHALASSA, meaning all water. According to him. around 200 million years ago, the super continent, Pangaea, began to split. Pangaea first broke into two large continental masses as Laurasia and Gondwanaland forming the northern and southern components respectively. Subsequently, Laurasia and Gondwanalan d continued to break into various smaller continents that exist today. A variety of evidence was offered in support of the continental drift.
Q 69 – Explain different types of boundaries that form as a result of tectonic plates.
- Ans. Convergent Boundaries: Where the crust is destroyed as one plate dived under another, it is called convergent boundaries.
- Divergent Boundaries: Where new crust is generated as the plates pull away from each other, these are called divergent boundaries.
- Transform Boundaries: Where the
crust is neither produced nor destroyed as the plates slide horizontally past each other. ,
Q 70 – According to tectonic plates theory in how many plates has the earth been divided? Explain.
Ans. The theory of plate tectonics proposes that the earth’s lithosphere is divided into seven major and some minor plates. The major plates are as follows:
- Antarctica and the surrounding oceanic plate
- North American plate
- South American plate
- Pacific plate
- India-Australia-New Zealand plate
- Africa with the eastern Atlantic floor plate
- Eurasia and the adjacent oceanic plate. Some important minor plates are:
- Cocos plate: It is between Central America and Pacific plate
- Nazca plate: It is between South America and Pacific plate
- Arabian plate: It includes mostly the Saudi Arabian landmass
- Philippine plate: It is between the Asiatic and Pacific plate
- Caroline plate: It is between the Philippine and Indian plate (North of New Guinea)
- Fuji plate: It includes North-east of Australia.
- Pacific plate is largely an oceanic plate whereas the Eurasian plate may be called a continental plate. Plates are not static. Plates may converge or diverge. Plates may break as well.
Q 71 – Explain tectonic plate theory and its j working.
Ans. These plates have been constantly moving over the globe throughout the history of the earth.
- The theory of plate tectonics was introduced by Mckenzie, Parker and , Morgan in 1967.
- A tectonic plate is also called as lithosphere plate.
- It is a massive irregularly shaped slab of solid rock.
- Consists of oceanic and continental sphere.
- Plates move horizontally over the asthenosphere.
- Average thickness is 100 km of oceanic part and 200 km of continental part.
- It may be oceanic or continental.
- Pacific plate is largest oceanic plate whereas Eurasian plate is the largest continental plate.
- These plates are moving constantly throughout geological time not the continent, believed by Wegener.
It creates three types of boundaries. - Divergent boundaries
- New crust is generated
- Plates move away from each other
- These are called spreading sites
- Ex. Mid atlantic ridge
- Convergent boundaries |
- Crust is destroyed
- Sinking of plate is called “subduction zone”. There are three ways in which subduction occurs (i) between an oceanic and continental plates; (ii) between two oceanic plates; and (iii) between two continental plates.
- Transform boundaries: Where the crust is neither produced nor destroyed as the plates slide horizontally past each other.
Q 72 – Explain important theories associated with the movement of continents.
Ans. Continental drift: Abraham Ortelius a Dutch map maker in 1596 first proposed the possibility of joining the continents such as America with Europe and Africa. Antonio Pellegrini drew a map showing the three continents together. Alfred Wegener, a German meteorologist put forth the continental drift theory. According to him, all continents formed a single continental mass called Pangaea.
All oceans formed a single universal ocean called Panthalassa around 200 million years ago. The Pangaea began to split into two large continental masses called Laurasia and Gondwanaland. By further splitting Laurasia formed northern continents and Gondwanaland formed southern continents.
Sea Floor Spreading: The deep trenches have deep-seated earthquake occurrences while in the mid- oceanic ridge areas, the quake foci have shallow depths. These facts and a detailed analysis of magnetic properties of the rocks on either sides of the mid-oceanic ridge led Hess in 1961 to propose his hypothesis. It was called the “sea floor spreading”. Hess argued that constant eruptions at the crest of oceanic ridges cause the rupture of the oceanic crust forces and the new lava wedges into it, pushing the oceanic crust on either side. The ocean floor, thus spreads. Two facts made Hess think about the consumption of the oceanic crust.
- The younger age of the oceanic crust.
- The spreading of one ocean does not cause the shrinking of the other.
He further maintained that the ocean floor that gets pushed due to volcanic eruptions at the crest, sinks down at the oceanic trenches and gets consumed. Plate Tectonics: It was in 1967, McKenzie and Parker and also Morgan, independently collected the available ideas and came out with another concept termed Plate Tectonics. The theory of plate tectonics proposes that the earth’s lithosphere is divided into seven major and some minor plates. These plates have been constantly moving over the globe throughout the history of the earth. It is not the continent that moves as believed by Wegener. Continents are part of a plate and what moves is the plate. All the plates, without exception, have moved in the geological past, and shall continue to move in the future as well.
Q 73 – The ocean floor may be segmented into how many divisions based on the depth as well as the forms of relief?
Ans. The ocean floor may be segmented into three major divisions based on the depth as well as the forms of relief. These divisions are:
(i) Continental margins,
(ii) Abyssal plains and
(iii) Mid-oceanic ridges.
- Continental margins
- Form transitional zone between continental shore and deep sea basins
- They include continental slope , shelf, continental rise and deep oceanic trenches
- Abyssal plains
- Extensive plains
- Found between continental margin and mid oceanic ridge
- Continental sediments get deposited
- Mid-oceanic ridges
- Distribution of volcanoes and earthquakes
- All volcanoes and earthquakes are parallel to the coast
- This line also co-incides with mid- Atlantic ridge and Alpine Himalayan system
- Around the Pacific Ocean it is called ring of fire mid oceanic ridges.
Q 74 – The rate of plate movement varies considerably. Justify.
Ans. It is very rightly said. The strips of normal and reverse magnetic field that parallel the mid-oceanic ridges help scientists determine the rates of plate movement. These rates vary considerably.
- Slowest Rate: The Arctic Ridge has the slowest rate. It is less than 2.5 cm/yr.
- Fastest Rate: The East Pacific rise near Easter Island, in the South Pacific about 3,400 km west of Chile, has the fastest rate. It is more than 15 cm/yr.
Q 75 – Show on the physical map of the world,
- The Tectonic Plates
- Volcanic Eruptions
- Ring of Fire
- Hot Spots.
Ans.
Q 76 –Himalayas. How was Himalaya formed?
Ans. India started her northward journey about 200 million years ago at the time when Pangaea broke. India collided with Asia about 40-50 million years ago causing rapid uplift of the Himalayas.