Geography Quiz: Continents & Oceans and Ocean Currents | 22 June, 2021

Prograde rotation indicates that the motion is in the same direction as the Sun’s rotation. Retrograde rotation is in the opposite direction.

• Most planets in our solar system, including Earth, rotate counter-clockwise or prograde direction, but Venus and Uranus are said to have a retrograde or clockwise rotation around their axis.
• The tilt angle of a planet is measured relative to the orbital plane of the planet, and most planets’ axes form an almost perpendicular angle to the orbital plane.
• Venus, twice the distance away from the sun, is the next closest planet after Mercury. It is often considered as Earth’s twin because of their close proximity in size, mass and density.

Source: G C leong

A Great Circle is any circle that circumnavigates the Earth and passes through the center of the Earth.

• A great circle always divides the Earth in half; thus, the Equator is a great circle (but no other latitudes) and all lines of longitude are great circles.
• The shortest distance between any two points on the Earth lies along a great circle. Circles which do not pass through the Centre of the earth are the small circles.

Source: G C Leong

The lithosphere is the solid, outer part of the Earth. The lithosphere includes the brittle upper portion of the mantle and the crust, the outermost layers of Earth’s structure.  

• It is bounded by the atmosphere above and the Asthenosphere (another part of the upper mantle) below. 

• Although the rocks of the lithosphere are still considered elastic, they are not viscous.  
• The Asthenosphere is viscous, and the lithosphere-Asthenosphere boundary (LAB) is the point where geologists and rheologists—scientists who study the flow of matter—mark the difference in ductility between the two layers of the upper mantle.  
• Ductility measures a solid material’s ability to deform or stretch under stress. The lithosphere is far less ductile than the asthenosphere. 
• There are two types of lithospheres: oceanic lithosphere and continental lithosphere. Oceanic lithosphere is associated with oceanic crust, and is slightly denser than continental lithosphere. 

Source: https://www.nationalgeographic.org/encyclopedia/lithosphere/ 

Vertical movements are mainly associated with the formation of continents and plateaus. They are also called as Epeirogenic movements.

Horizontal forces act on the earth’s crust from side to side to cause these movements. They are also known as orogenic movements (mountain building).

Source: https://www.nationalgeographic.org/encyclopedia/lithosphere/

Surface currents in the ocean are driven by global wind systems that are fueled by energy from the sun.

• Patterns of surface currents are determined by wind direction, Coriolis forces from the Earth’s rotation, and the position of landforms that interact with the currents.
• Surface wind-driven currents generate upwelling currents in conjunction with landforms, creating deepwater currents.

• Currents may also be caused by density differences in water masses due to temperature (thermo) and salinity (haline) variations via a process known as thermohaline circulation.
• These currents move water masses through the deep ocean—taking nutrients, oxygen, and heat with them.
• Occasional events such as huge storms and underwater earthquakes can also trigger serious ocean currents, moving masses of water inland when they reach shallow water and coastlines.
• Earthquakes may also trigger rapid down slope movement of water-saturated sediments, creating strong turbidity currents.

Source: G C Leong

Cold currents flow toward the equator on the eastern side of ocean basins. Examples of cold ocean currents include the Canary Current in the North Atlantic, the California Current in the North Pacific, and the Benguela Current in the South Atlantic.

• Cold currents can also flow out of far northern regions. The Labrador Current flows out of Baffin Bay and past Labrador, the coastal part of the Canadian province of Newfoundland.
• The current carries icebergs from Baffin Bay, creating a hazard for ships in the North Atlantic. The Labrador Current meets the Gulf Stream off the coast of Newfoundland.
• When warm, moist air from the Gulf Stream blows over the cold Labrador Current, water vapor condenses. This results in some of the thickest fogs in the world.

• Two other important cold currents originate in northern regions. The East Greenland Current flows into the North Atlantic through the Strait of Denmark.
• The Oyashio Current flows through the Bering Strait between Siberia and Alaska and into the North Pacific.

Source: G C Leong 

All waters in nature, whether rain water or ocean water, contain dissolved mineral salts. Salinity is the term used to define the total content of dissolved salts in sea water. Factors affecting ocean salinity are mentioned below:

• The salinity of water in the surface layer of oceans depends mainly on evaporation and precipitation.
• Surface salinity is greatly influenced in coastal regions by the fresh water flow from rivers, and in Polar Regions by the processes of freezing and thawing of ice.
• Wind, also influences salinity of an area by transferring water to other areas.
• The ocean currents contribute to the salinity variations. Salinity, temperature and density of water are interrelated. Hence, any change in the temperature or density influences the salinity of water in an area.

Source: NCERT – Fundamental of Physical Geography

Mountains that have been eroded by the agents of degradation such as winds, rain, frost and running water leaving behind only the hard rocks are known as residual mountains.

• These hard rocks that are left behind are known as the residual mountains.
• Examples of Residual Mountains in India are the Nallamala hills, Mahendragiri hills, the Aravali hills, the Javadi hills, the Veliconda hills, and the Palkonda range.

Source: ICSE – Total Geography Class – IX

Sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary rocks.

• Clastic sedimentary rocks such as breccia, conglomerate, sandstone, siltstone, and shale are formed from mechanical weathering debris.
• Chemical sedimentary rocks, such as rock salt, iron ore, chert, flint, some dolomites, and some limestone, form when dissolved materials precipitate from solution.

• Organic sedimentary rocks such as coal, some dolomites, and some limestone, form from the accumulation of plant or animal debris.

Source: G C Leong

Fold Mountains are created through a process called orogeny. An orogenic event takes millions of years to create a fold mountain.  

• When a tectonic plate gets pressure from two sides, it gets folded. Some of its portion becomes elevated and forms the mountains. 
• The depressions form the valleys. The Himalayas, the Rockies, the Andes and the Alps are examples of Fold Mountain.  
• They are the young mountains of the world and hence they have some of the highest peaks of the world. 

Source: ICSE – Total Geography Class – IX