Class – 6
Subject – Geography
Chapter – 6 (Study of Continents – North America )
Formation of continents :-
Continents and Oceans :- The large landmasses forming part of the earth’s surface are called continents. The major landforms of the Earth’s surface were formed over 3500 millions years ago and have been undergoing constant change.
However, Alfred Wegener, a Germen meteorologist and geophysicist, presented his theory of continent drift in 1915 in his book The Origin of Continents and Oceans. Wegener, who is today regarded as the father of the concept, based his theory not only on the shape of the continents, but also on geological and biological evidences, such as similarities in fossils found in Brazil and Africa. He drew a series of maps showing three stage in the drifting process, beginning with an original large landmass , which he called ‘Pangaea’ ( meaning ‘all lands’) surrounded on all sides by an extensive water mass called the Pantha Lassa .
North America – Introduction
North America is the third largest continent in the world. It is believed that it was first discovered by the Vikings in 10th century
Later the Italian navigator Christopher Columbus reached West Indies in 1492, believing he had reached India. However, another Italian navigator, Amerigo Vespucci, actually touched the mainland in 1497 and the continent was named America after his name.
Location and Extent
North America is located in the Western and Northern Hemisphere. Latitudially it extents between 7 degree N an 83 degree N. longitudinally North America extents between 53 degree W and 180 degree W longitudes.
Boundaries :-
• North America is surrounded by oceans except in south where it is joined with South America by the Isthmus of Panama.
• North America is bounded by Pacific Ocean in the west, the Atlantic Ocean in the east, Arctic Ocean in the north and Caribbean Sea in the south.
Coastline :- North America has a smooth coastline with many wide openings along its coast. It has many gulfs and bays, e.g., Gulf of Mexico, the Hudson Bay, the Gulf of St. Lawrence and the Gulf of California.
Political Divisions of North America North America’s main countries are Canada, United State of America and Mexico. Together these three countries make up about 95 per cent of the area of North America.
Island – There are many island in the Arctic Ocean lying to the north of the continent. Of these Greenland is the largest island. It is also the biggest island of the world. Some other island are Baffin Island, Victoria Island and Ellesmere Island which belong to Canada. The island of Newfoundland lies off the east coast of Canada. The islands of West Indies form a chain of small islands in the Caribbean. They include Cuba, Jamaica, Haiti, Dominican Republic and Puerto Rico. All these islands belong to North America.
Drainage :- the most important drainage systems of North America are the following:
• Mississippi River
• River Colorado
• St. Lawrence River
• Mackenzie River
Major Physical Features
North America covers a vast area. As such, it is characterized by a wide variety of landforms. It can be divided onto the following four relief regions-
The Canadian Shield :- It is also called Laurentian Shield after the Laurentian Plateau. It covers the eastern and northeastern parts of North America, occupying about half the area of Canada.
Lake Erie, Lake Ontario, Lake Winnipeg and the Great Bear are some of the important lakes. The St. Lawrence River in this region is the busiest inland waterway in North America. This region is made up of hard rocks. The general slope of Canadian Shield is towards the Hudson Bay. The glaciation of these rocks resulted in the formation of a number of basins which are now lakes and swamps. The Great Lakes – Superior, Michigan, Huron, Erie and Ontario form the southern boundary of Canadian Shield.
The Eastern Highlands or Appalachian Highlands :- The Appalachian Highlands, situated along the eastern side of the continent are the old fold mountains, also known as the Eastern Highlands. The two main mountain ranges are Blue Ridge and Allegheny. Once they were very high but have been reduced in height due to erosion over millions of years.
Many short rivers originate from the Appalachian mountains and flow into the Atlantic Ocean. Some of them flow swiftly and hence provide suitable sites for the hydroelectric power. Hudson river is linked to the Great Lakes through the Erie canal.
The Central Lowlands :- The central lowlands lie between the western cordilleras and the eastern highlands covering a distance of 2000 km from east to west and 6000 km from Arctic Ocean in the north to the Gulf of Mexico in the south. These plains are situated at the elevation of about 500 metres in the west and slope towards the Arctic Ocean. This slope is marked by Mackenzie river which began at Great Slave Lake in the north-west territories and flows north into the Arctic Ocean. The Western Cordilleras :- The Western Cordilleras are a number of mountain range parallel to each other. These ranges are about 6500 km long. They extend from Alaska in the north to Panama in the south along the western coast. The Rockies are the easternmost chain of mountains and have important ranges of the coastal range, Sierra Nevada and Sierra Madre. The formation of these fold mountains was accompanied by great volcanic activity. At present it has one volcano, Mt. McKinley in Alaska. Some of the chief plateaus from north to south are the Alaska plateau, the British Columbia plateau, the Great Basin, the Colorado plateau and the Mexican plateau. These plateaus are separated by depressions and fertile valleys of rivers.
The largest amongst the plateaus is the Great Basin. It is the largest basin if inland drainage in North America. The rivers from this area do not reach to the ocean. The Great Salt Lake is an example of such a lake.
The Great Canyon of Colorado is world famous. It is the largest canyon. Cordilleras have a number of active volcanoes and hot springs in the north, especially in Alaska. These volcanoes are the part of Pacific Ring of fire which surrounds the Pacific Ocean, e.g., Mt. Kanaga in Alaska.
Activity :-
On an outline map of North America, mark and name the following:-
• Mt. McKinley, (b) The Great Lakes, (c) Mississippi River, (d) Alaska, (e) Prairies, (f) Isthmus of Panama, (g) St. Lawrence River, (h) Hudson Bay, (i) Tropic of Cancer, (j) Gulf of Mexico,(k) Water bodies surrounding North America.
Question & Answers :-
Ques-1) State the North South and East West extent of North America.
Ans- North America extents between 7 degree N and 83 degree N latitudes. longitudinally North America extents between 53 degree W and 180 degree W longitudes.
Ques-2) How is North America linked to South America?
Ans- North America is linked to South America by the Isthmus of Panama.
Ques-3) Name three gulfs along the coastline of North America.
Ans- The three gulfs along the coastline of North America are – Gulf of Mexico, Gulf of California, Gulf of Alaska.
Ques-4) Why are Prairies known as the ‘Granaries’ of the world?
Ans- The Prairies are known as the ‘Granaries of the World’ , due to hug surplus of wheat production.
Ques-5) Sate the location of Western Cordilleras. Ans- The Western Cordilleras are a number of mountain range parallel to each other. These ranges are about 6500 km long. They extend from Alaska in the north to Panama in the south along the western coast.
Ques-6) Which is the most popular tourist attraction in Western Cordilleras?
Ans - The Old Faithfull geyser (a fountain of hot water) in Yellowstone Park in Western Cordilleras is the most popular tourist attraction point.
Ques -7) What is meant by Pangaea?
Ans- The original large landmass in the beginning is called Pangaea by Alfred Wegener.
Ques-8) Explain the following terms :- (a) Canyon, (b) Intermontane Plateau, (c) Isthmus.
Ans- (a) Canyon – Long and deep gorge are called canyons.
(b)Intermontane Plateau – A plateau enclosed by mountains on all sides is called Intermontane plateau.
(c)Isthmus – A narrow strip of land joining two large areas or separating two oceans is called an isthmus.