Static Quiz 20 May 2022 (Geography)

Ans;- a) Only 1,2 and 3

Explanation;
• An alluvial fan is a cone-shaped depositional landform built up by streams, heavy with sediment load.
• Alluvial fans are formed when streams flowing from mountains break into foot slope plains of low gradient.
• Normally very coarse load is carried by streams flowing over mountain slopes. This load gets dumped as it becomes too heavy to be carried over gentler gradients by the streams
• Furthermore, this load spreads as a broad low to a high cone-shaped deposit called an alluvial fan that appears as a series of continuous fans.
• Alluvial fans in humid areas show normally low cones with a gentle slope from head to toe and they appear as high cones with a steep slope in arid and semi-arid climates.

Ans;- d) None of the above

Explanation;-

• All are incorrectly matched.

• River erosion takes place in three ways:-

1. Headwards erosion it is a process by which a river increases its upstream length. This is achieved by a river cutting back at its source
2. Lateral erosion it is a process through which river channel is extended in its width due to sideways erosion at the outside banks of the rivers
3. Vertical erosion Vertical erosion takes place at the base of the river. The channel of the river gets deepened through vertical erosion

Ans;- a) Only 1

Explanation;-

• Except V shaped valley, remaining 2 forms in Mature and Old age of rivers.

Youth
• Streams are few during this stage with poor integration and flow over original slopes
• The valley developed is thus deep, narrow and distinctly V-shaped with no floodplains or with very narrow floodplains.
• Downcutting predominates over lateral corrasion
• Streams divides are broad and flat with marshes, swamp and lakes.
• Some of the outstanding features which are developed in this stage are gorges, canyons waterfalls, rapids and river capture etc.

Mature
• During this stage, streams are plenty with good integration.
• Lateral corrasion tends to replace vertical corrasion
• The valleys are still V-shaped but wide and deep due to an active erosion of the banks;
• Trunk streams are broad enough to have wider floodplains within which streams may flow in meanders confined within the valley.
• Swamps and marshes of youth stage, as well as flat and broad inter-stream areas, disappear. The stream divides turn sharp.
• Waterfalls and rapids disappear.
• Meander and slip off slopes are the characteristic features of this stage

Old
• The river moving downstream across a broad level plain is heavy with sediments.
• Vertical corrasion almost ceases in this stage though lateral corrasion still goes on to erode its banks further
• Smaller tributaries during old age are few with gentle gradients.
• Streams meander freely over vast floodplains. Divides are broad and flat with lakes, swamps and marshes.
• Depositional features predominate in this stage
• Most of the landscape is at or slightly above sea level
• Characteristic features of this stage are floodplains, oxbow lakes, natural levees and Delta etc.

Ans;- d) None of the above

Explanation;-

• Both the statements are reversed.

• Rapids are stream sections with extremely strong currents, numerous obstacles, and steps in their streambeds. A waterfall is a vertical drop in a streambed. Both are sites of vigorous erosion . Rapids often form where resistant bedrock confines a stream to a narrow channel, and forces an increase in water velocity.

Ans;- c) Both 1 and 2

Explanation;-

• Both the statements are correctly matched.

• Potholes are more or less circular depressions over the rocky beds of hills streams. Once a small and shallow depression forms, pebbles and boulders get collected in those depressions and get rotated by flowing water.

• Plunge pools are nothing but large, deep potholes commonly found at the foot of a waterfall.