Ch 12Landforms and their Evolution — Class 11 Geography, concept-first.

The chapter opens by recalling that weathering acts on earth materials, and then the geomorphic agents — running water, groundwater, wind, glaciers, and waves — perform erosion.

In humid regions that receive heavy rainfall, running water is the most important geomorphic agent degrading the land surface.

Valleys begin as tiny, narrow rills — the smallest channels cut by running water. A rill is barely a trickle-line on a slope, but it does not stay that way.

Potholes and plunge pools are both products of river erosion, but they form in different parts of a stream course and under different conditions.

The key to understanding incised meanders lies in the contrast between where meanders usually form and where these particular ones are found.

A river terrace is, at its simplest, an old valley floor or an old floodplain that has been left standing above the present-day river.

Alluvial fans are landforms built where a stream suddenly loses its carrying power. The key to understanding them is the change in slope: a stream that has been rushing down a steep mountain slope, ca…

A delta forms when a river dumps its load at the point where it enters the sea. Think of it as an alluvial fan that has simply changed its address — the fan builds on land where a river leaves a mount…

A river doesn’t only carve — it also builds. Just as erosion carves out a valley, deposition builds up a floodplain, and this floodplain is one of the major landforms created by river deposition.

Rivers flowing across large flood plains and delta plains rarely follow a straight course. Instead, they develop a series of smooth, looping bends called meanders.

Groundwater is usually thought of as a resource, but here the interest is different. The focus is on what groundwater does to the land — how it erodes landmasses and shapes landforms over long periods…

Small to medium-sized, round or slightly oval shallow depressions called swallow holes are the first things to appear on a limestone surface.

Cave formation is a striking example of how groundwater, not just surface rivers, reshapes the land. In limestone country, the slow chemical work of water over long periods carves out underground open…

Caves are not empty chambers. Water that seeps through limestone carries dissolved calcium carbonate, and as that water drips from the cave ceiling, it slowly deposits the mineral back.

A glacier is a mass of ice that moves over land. The movement can take two broad forms. A vast sheet of ice spreading over the land is called a continental glacier; if such a sheet spreads over the pl…

Cirques are the most common landforms found in glaciated mountains, and they mark the very beginning of glacial erosion.

Horns are the sharp, pyramid-like peaks that form when glaciers attack a mountain from several sides at once.

A glacier moving through a river valley reshapes it completely. Where a river cuts a narrow, V-shaped notch, a glacier carves out a wide, deep trough.

Moraines are long ridges built up from deposits of glacial till — the unsorted rock debris a glacier carries and drops.

An esker is a landform that records the final act of a glacier's life — the meltwater. When a glacier melts, the water does not simply vanish; it organises itself into streams that flow beneath the ic…

The story of a glacier does not end where the ice stops. Beyond the snout of a mountain glacier, or past the outer edge of a vast continental ice sheet, the meltwater carries on the work.

Drumlins are depositional landforms made of glacial till, and they are among the most telling features a glacier leaves behind.

Coastal processes are among the most dynamic and destructive on Earth. Along a single stretch of coast, one season may bring erosion and the next, deposition. Most of this change is driven by waves.

High rocky coasts begin with a striking visual: rivers appear drowned, and the coastline is highly irregular and deeply indented.

Low sedimentary coasts are built, not destroyed. Where the land meets the sea along a gentle, low-lying margin, the dominant story is one of deposition — rivers dump their load, waves pile up sand, an…

Cliffs, terraces, caves and stacks are all products of wave erosion — the grinding, hammering and undercutting action of the sea against the land.

Beaches are the classic depositional landform of a coastline, but they are far less permanent than they look.

A coastline is not a fixed line. It is constantly being reshaped by waves, currents and the material they carry.

Wind is one of the two dominant agents shaping the hot deserts, the other being water in the form of sheet floods.

Desert landscapes are not just about sand dunes and wind. A large part of desert geomorphology is actually shaped by water — rare, violent, and short-lived.

Playas are the most prominent landforms in deserts. The word itself names a shallow lake, but what you see on the ground is usually a flat, salty plain.

The wind does more than just carry dust. When it blows steadily in one direction for a long time, it acts like a giant broom, sweeping away the loose weathered material lying on top of rocks or on bar…

Wind is a relentless sculptor in deserts, but it does not work alone. The same gusts that carry sand and dust also carve the rock they strike, and the same abrasive action that wears down surfaces can…

Sand dunes are mounds or ridges of sand built by wind, and they form only where three things come together: a dry, hot desert climate, a supply of loose sand, and an obstacle that interrupts the wind…