Geography Quiz: Landforms formed due to erosion and depositional agents | 25 June, 2021

There are two components of running water. One is overland flow on general land surface as a sheet. Another is linear flow as streams and rivers in valleys.

• Most of the erosional landforms made by running water are associated with vigorous and youthful rivers flowing over steep gradients.
• With time, stream channels over steep gradients turn gentler due to continued erosion, and as a consequence, lose their velocity, facilitating active deposition.
• There may be depositional forms associated with streams flowing over steep slopes. But these phenomena will be on a small scale compared to those associated with rivers flowing over medium to gentle slopes.
• The gentler the river channels in gradient or slope, the greater is the deposition.

Source: NCERT – XI Fundamentals of Physical Geography

Peneplain is a region that is almost a plain. It is formed due to erosion by rivers (stream erosion) and rain, that continues until almost all the elevated portions are worn down; the most resistant rocks generally stand above the general level of the land.

When a peneplain is raised, it becomes a Plateau, which is then dissected by the river as they pass through a fresh cycle from youth to old age.

Source: NCERT – XI Fundamentals of Physical Geography

Over the rocky beds of hill-streams more or less circular depressions called potholes form because of stream erosion aided by the abrasion of rock fragments.

• Once a small and shallow depression forms, pebbles and boulders get collected in those depressions and get rotated by flowing water and consequently the depressions grow in dimensions.
• A series of such depressions eventually join and the stream valley gets deepened.

• At the foot of waterfalls also, large potholes, quite deep and wide, form because of the sheer impact of water and rotation of boulders.
• Such large and deep holes at the base of waterfalls are called plunge pools.

Source: NCERT – XI Fundamentals of Physical Geography

Natural levees and point bars are some of the important landforms found associated with floodplains.

• Natural levees are found along the banks of large rivers. They are low, linear and parallel ridges of coarse deposits along the banks of rivers, quite often cut into individual mounds.
• Point bars are also known as meander bars. They are found on the concave side of meanders of large rivers and are sediments deposited in a linear fashion by flowing waters along the bank.

• They are almost uniform in profile and in width and contain mixed sizes of sediments.

Source: NCERT – XI Fundamentals of Physical Geography

Stalactites hang as icicles of different diameters. Normally they are broad at their bases and taper towards the free ends showing up in a variety of forms.

Source: NCERT – XI Fundamentals of Physical Geography

Cirques are the most common of landforms (erosional) in glaciated mountains. The cirques quite often are found at the heads of glacial valleys.

• The accumulated ice cuts these cirques while moving down the mountain tops.
• They are deep, long and wide troughs or basins with very steep concave to vertically dropping high walls at its head as well as sides.
• A lake of water can be seen quite often within the cirques after the glacier disappears. Such lakes are called cirque or tarn lakes.
• There can be two or more cirques one leading into another down below in a stepped sequence.

• When the glaciers retreated leaving behind their freight of crushed rock and sand (glacial drift), they created characteristic depositional landforms.
• Examples include glacial moraines, eskers, and kames. Drumlins and ribbed moraines are also landforms left behind by retreating glaciers.

Source: NCERT – XI Fundamentals of Physical Geography

Mass Movements transfer the mass of rock debris down the slopes under the direct influence of gravity. That means, air, water or ice does not carry debris with them from place to place but on the other hand the debris may carry with it air, water or ice.

• The movements of mass may range from slow to rapid, affecting shallow to deep columns of materials and include creep, flow, slide and fall.
• Creep can occur on moderately steep and soil covered slopes. Movement of materials is extremely slow and imperceptible except through extended observation. Material involved can be soil or rock debris.
• Landslides are relatively rapid and perceptible movements. The materials involved are relatively dry. The size and shape of the detached mass depends on the nature of discontinuities in the rock, the degree of weathering and the steepness of the slope.
• Movement of water saturated clayey or silty earth materials down low-angle terraces or hillsides is known as Earthflow.
• Avalanche is more characteristic of humid regions with or without vegetation cover and occurs in narrow tracks on steep slopes. Debris avalanche is similar to snow avalanche.

Source: NCERT – XI Fundamentals of Physical Geography

In the process of metamorphism in some rocks grains or minerals get arranged in layers or lines. Such an arrangement of minerals or grains in metamorphic rocks is called foliation or lineation.

• Sometimes minerals or materials of different groups are arranged into alternating thin to thick layers appearing in light and dark shades.
• Such a structure in metamorphic rocks is called banding and rocks displaying banding are called banded rocks.
• Types of metamorphic rocks depend upon original rocks that were subjected to metamorphism.

• Metamorphic rocks are classified into two major groups-foliated rocks and non-foliated rocks.
• Gneissoid, granite, syenite, slate, schist, marble, quartzite etc. are some examples of metamorphic rocks.

Source: NCERT – XI Fundamentals of Physical Geography

Carbonation is the reaction of carbonate and bicarbonate minerals and is a common process helping in breaking down of feldspars and carbonate minerals.

• Carbon dioxide from the atmosphere and soil air is absorbed by water, to form carbonic acid that acts as a weak acid.
• Calcium carbonates and magnesium carbonates are dissolved in carbonic acid and are removed in solution without leaving any residue resulting in cave formation.

Source: NCERT – XI Fundamentals of Physical Geography

Mass movements transfer the mass of rock debris down the slopes under the direct influence of gravity.  

• That means, air, water or ice doesn’t carry debris with them from place to place but on the other hand the debris may carry with it air, water or ice.  
• The movements of mass may range from slow to rapid, affecting shallow to deep columns of materials and include creep, flow, slide and fall. Gravity exerts its force on all matter, both bedrock and the products of weathering.  

• So, weathering is not a pre-requisite for mass movement though it aids mass movements. Mass movements are very active over weathered slopes rather than over un-weathered materials.  
• Mass movements are aided by gravity and no geomorphic agent like running water, glaciers, wind, waves and currents participate in the process of mass movements.  
• That means mass movements do not come under erosion though there is a shift (aided by gravity) of materials from one place to another.  
• Materials over the slopes have their own resistance to disturbing forces and will yield only when force is greater than the shearing resistance of the materials.  
• Weak unconsolidated materials, thinly bedded rocks, faults, steeply dipping beds, vertical cliffs or steep slopes, abundant precipitation and torrential rains and scarcity of vegetation etc., favor mass movements. 

Source: NCERT – XI Fundamentals of Physical Geography