NCERT Class 11 - Fundamentals of Physical Geography, Chapter 7

Landforms of Rivers, Ice, Wind and Sea

Each agent of erosion leaves a characteristic set of landforms - erosional forms where it removes material and depositional forms where it drops the load. Recognising the agent from the landform is the commonest question pattern in this chapter.

Running water

• A meander forms because water erodes the outer bank and deposits on the inner bank; when the loop is cut off it becomes an ox-bow lake.
• An alluvial fan forms where a stream leaves the hills and its load spreads out; a delta forms where it enters the sea and drops the load as the current dies.
• Himalayan rivers are in the youthful stage and are still cutting down, while peninsular rivers are in the mature or old stage and have broad shallow valleys.

Glaciers

• Cirque - an armchair shaped hollow at the head of a glacial valley, often holding a small lake called a tarn.
• Arete - a knife-edged ridge between two cirques; a horn is a sharp peak where three or more cirques meet, as with the Matterhorn.
• U-shaped valley - a glacier widens and deepens a river valley into a broad U; a smaller side valley left high above it is a hanging valley, often ending in a waterfall.
• Fjord - a drowned glacial valley along a coast, with very deep water and steep sides.
• Depositional forms - moraines of unsorted debris, oval hills called drumlins, winding ridges called eskers, and the flat outwash plain beyond the ice.

Wind in deserts

• Deflation is the lifting and removal of loose sand by wind, which creates shallow deflation hollows.
• Yardangs are ridges carved parallel to the wind direction; inselbergs are isolated residual hills rising from a plain.
• Depositional forms are sand dunes - the crescent shaped barchan with horns pointing downwind, the long seif or longitudinal dune parallel to the wind, and transverse dunes at right angles to it.
• Loess is a thick deposit of very fine wind-blown silt, extremely fertile where it occurs.

Waves and underground water

• Coastal erosional forms - sea cliff, wave-cut platform at its base, sea cave, sea arch where a cave is cut through a headland, and a stack when the arch roof collapses.
• Coastal depositional forms - beach, spit growing out from the shore, bar across a bay, lagoon enclosed behind a bar, and tombolo joining an island to the mainland.
• Where the rock is limestone, water dissolves it and produces karst topography.

How a karst landscape develops

Imagine a plateau of limestone. Rainwater, made slightly acid by carbon dioxide, seeps into the joints and slowly dissolves the rock. On the surface the joints widen into grooves, leaving a bare ridged surface called a limestone pavement, and funnel shaped sinkholes appear. Underground, the water hollows out caves and passages, so that surface streams disappear into the rock and reappear far away. In the caves, water dripping from the roof leaves lime behind and builds stalactites hanging down; the drops that fall build stalagmites rising from the floor, and where the two meet they form a pillar.