Geography Optional

Model Answer

Question #1. Discuss the Orogenesis of Himalayan Mountain ranges on the basis of plate tectonics. Elaborate with geographical evidence supporting collision of different types and nature of tectonic plates during process of orogeny.

Plate tectonics has emerged as the most acceptable theory in modern time regarding formation of continents and oceans, Orogenesis, epeirogenesis and different other landforms. Himalayan mountains are young fold mountains and said to be still in the process of formation has been well defined by the theory of plate tectonics.

Formation of Himalayas by the process of plate tectonics

•   100 million years ago, the Indian plate collided with the Eurasian plate. Before the collision there was a swampy sea between the two plates called the Tethys Sea.

First stage: Collision Oceanic-Oceanic crusts and formation of festoons or Island arcs

•   The oceanic crust of the Indian plate collided with the oceanic crust of the Eurassian plate and later being heavier subducted. This resulted in the formation of an island arc of explosive volcanic activity which developed in the Tethys Sea. Later they formed part of Ladakh and Tibet.

Second stage: Collision Oceanic-Continent crusts and formation of young fold mountains on margin of contienents

•   Indian plate continued its march towards Eurasian plate which led to subduction of its oceanic crust into the Eurasian continental crust. This led to formation of young fold mountain on the margin of the Eurasian land mass in the form of Karakoram Range.

Third Stage: Collision of continent-continent crusts and formation of Himalayas

•   Continent-Continent crusts of the Eurasians and Indian plate collided which resulted in folding of sediments of Tethy’s sea. Due to folding activity, young fold mountain, the Himalayas started to rise up. There are various evidences which support this theory.

Evidences that support the formation of Himalayas as explained by plate tectonics

•   Evidences of Island arcs in Drass sector of Himalayas.
•   Evidences support that Karakorum ranges are of volcanic origin.
•   Karewas in Kashmir valley prove that the valley was essentially a lake in the Pleistocene Epoch.
•   Discovery of a hippopotamus' skull at 14,000 ft at Ladakh indicating that till recently the Himalayan region was a warm, low-lying swampy region.
•   Evidence of stone-age man in the higher reaches, showing that the mountains' rapid rise was more recent than earlier believed and was even witnessed by primitive man.
•   Proof that swarms of earthquakes and periods of quietude occur just before a giant earthquake strikes the region making prediction fairly accurate that Himalayas is still rising.

Conclusion:

Various evidences which support the theory of Orogenesis of Himalayan mountain ranges are in line with the process which was illustrated by the theory of plate tectonics. Predictions by the geologists about the Great Himalayan Earthquake and unconsolidated materials which leads to landslides in the Shiwalik region of Himalayas prove that the region is still tectonically active due to movement of the Indian plate towards the Eurasians plates and authenticate the plate tectonics as the most suitable theory to explain it.

Question #2. Discuss the forces which influence the Ocean Currents. Also, explain with examples why oceanic circulation patterns roughly correspond to the earth's atmospheric circulation pattern.

Water is always on the move. Ocean currents are like giant conveyor belts flowing through the oceans moving huge amounts of water all the time. From cold to hot (and vice versa), oceans transport water. The major ocean currents roughly follow a common set of circular paths. Ocean currents are like river flow in oceans. They represent a regular volume of water in a definite path and direction. Ocean currents are influenced by two types of forces namely:

(i) Primary forces that initiate the movement of water;

(ii) Secondary forces that influence the currents to flow.

The primary forces that influence the currents are:

• Heating by solar energy: causes the water to expand. That is why, near the equator the ocean water is about 8 cm higher in level than in the middle latitudes. This causes a very slight gradient and water tends to flow down the slope.
• Wind: Wind blowing on the surface of the ocean pushes the water to move. Friction between the wind and the water surface affects the movement of the water body in its course.
• Gravity: Gravity tends to pull the water down the pile and create gradient variation.
• The Coriolis force: The Coriolis force intervenes and causes the water to move to the right in the northern hemisphere and to the left in the southern hemisphere. These large accumulations of water and the flow around them are called Gyres. These produce large circular currents in all the ocean basins.

Secondary Forces Responsible For Ocean Currents

• Differences in water density affect vertical mobility of ocean currents. Water with high salinity is denser than water with low salinity and in the same way cold water is denser than warm water.
• Denser water tends to sink, while relatively lighter water tends to rise. Cold-water ocean currents occur when the cold water at the poles sinks and slowly moves towards the equator.
• Warm-water currents travel out from the equator along the surface, flowing towards the poles to replace the sinking cold water

The reasons for circulation pattern which roughly corresponds to the earth’s atmospheric circulation pattern.

• Wind blowing on the surface of the ocean pushes the water to move. Friction between the wind and the water surface affects the movement of the water body in its course. Winds are responsible for both magnitude and direction [Coriolis force also affects direction] of the ocean currents. Example: Monsoon winds are responsible for the seasonal reversal of ocean currents in the Indian Ocean.
• The oceanic circulation pattern roughly corresponds to the earth’s atmospheric circulation pattern.

The sun heats water at the equator. The wind and sun make ocean currents move. At the equator, the sun is strongest heating water the most there.

When water heats, water molecules vibrate faster and eventually move farther apart. Hot water moves to the poles. From the equator, hot water pushes outward to North and South Pole.

• At the same time, cold water from the north and south poles collide with this warm water.

Water spins in a circle pattern because of Earth's rotation. Because Earth spins on its axis, water flows in a circular pattern.

• Oceans in the northern hemisphere move mostly clockwise. But in the southern hemisphere, ocean currents move mostly counter-clockwise.
• Landmass and shape of coastal regions also forces currents to follow the wind pattern. E.g. less land mass around the Southern Antarctica Ocean has direct bearing on ocean currents.
• Due to lack of obstruction by landmass, currents follow the straight path. Further these currents are made furious by high speed winds.