Rivers and coasts

Landforms have shaped history too. The book gives examples:

• Rivers and fertile plains of the Ganga, Brahmaputra, Indus and Nile gave rise to farming and early cities.
• Mountains were both barriers and protectors: the Himalaya shielded India, but passes like the Khyber Pass let people and ideas through.
• Deserts like the Thar limited large settlements but encouraged trade routes, such as the Silk Route.
• Coasts and harbours helped trade and travel, and helped kingdoms in south India flourish.

Now follow a river from the hills to the sea. A river does three jobs: it erodes (cuts), transports (carries) and deposits (drops). Which job it does most depends on how fast it flows.

Upper course (in the hills): the river cuts. The slope is steep and the water is fast and strong. It cuts down and makes V-shaped valleys, rapids and waterfalls (jalprapat).

"How does a waterfall form?" Where hard rock lies on top of softer rock, the river wears the soft rock away faster. A sudden drop forms, with a deep plunge pool at the bottom (Fig. 2.10). Waterfalls bring tourists, can make hydroelectric power from the force of falling water, are good for trekking and photography, and some are sacred.

Middle course: the river bends. The land is flatter and the river has less energy. It swings from side to side in big loops called meanders (Fig. 2.11). On each bend it cuts the outer bank (fast water) and drops mud on the inner bank (slow water). Over time a loop can be cut off, leaving a curved lake: an oxbow lake. Beside the river, floodplains of fertile soil form.

Meanders matter to people: the fertile soil is good for farming, villages and towns grow on the gentle slopes nearby, and the river can be used for boats, irrigation and even tourism. The Grand Anicut (Kallanai) in Tamil Nadu is an example of using a river for irrigation.

Lower course (near the sea): the river drops its load. It is slow now and cannot carry all its sediment, so it builds levees, alluvial fans and deltas.

A delta forms at the mouth of a river, where it meets a sea, ocean or lake. The sediment piles up into a fan-shaped or triangular piece of new land, cut through by smaller channels called distributaries (Fig. 2.12). Deltas are:

• very fertile, good for rice and jute;
• good for fishing, because fresh and salt water mix;
• crowded with people, and centres of trade and river transport;
• but prone to flooding.

The Sundarbans is a famous delta: find out why tourists love it.

Coasts. Waves and currents shape the shore. A beach is sand, pebbles or rocks laid down by waves. Beaches bring tourism, give fishing areas, sand and shells, and act as a natural wall against strong waves.

Waves also erode the coast (Figs 2.15, 2.16):

• sea cliffs: steep rock faces, made when waves undercut the bottom of the coast;
• wave-cut (shore) platforms: flat rock left behind as the cliff moves back;
• sea caves: waves hollow out weak parts of the rock;
• arches: caves on opposite sides of a headland (land sticking out into the sea) meet in the middle;
• stacks: when the arch's roof falls, a lonely pillar of rock is left standing.