Glaciers, wind and underground water

A glacier (himnad) is a huge, slow river of ice. As it moves, it scrapes the land like a giant bulldozer and carries rocks along. The landforms of glacial erosion:

• U-shaped valleys: a river makes a V; a glacier widens and deepens it into a U;
• cirques: bowl-shaped hollows at the head (top) of a glacier;
• aretes: sharp, knife-edge ridges between two valleys;
• hanging valleys: where a small glacier joined a big one, its valley is left 'hanging' high above;
• fjords: deep, narrow inlets where the sea floods a glacial valley.

Why they matter: U-shaped valleys and cirques attract trekkers, skiers and mountaineers; fjords make harbours and fishing places; some glacial valleys have fertile soil for farming; and glaciers feed rivers that give fresh water to millions downstream.

When a glacier melts, it drops the rock, soil and debris it carried, called till. These piles are moraines (Fig. 2.19):

• lateral moraines: along the sides of a glacier;
• terminal moraines: at the end, marking the farthest the glacier reached;
• medial moraines: in the middle, where two glaciers meet and their side moraines join.

Moraines can give fertile soil, and can block valleys to form lakes used for water, irrigation and sometimes power.

Glacier valleys can be dangerous too. In February 2021, a sudden flood struck Chamoli district in Uttarakhand. People and animals died, and buildings, roads, bridges and power projects were damaged. The book asks you to find out what caused it.

Wind is the main shaper of deserts. Strong winds pick up loose sand and soil and throw them against rocks, like sandpaper. Landforms of wind erosion:

• yardangs: long, streamlined rock ridges carved by wind;
• ventifacts: rocks polished and shaped by sandblasting;
• deflation hollows (blowouts): shallow dips where wind has removed the loose material. If one goes down to the water table, water appears: an oasis (Fig. 2.22);
• desert pavements: flat, stony surfaces left after the fine grains blow away.

Wind also builds. Dunes (ret ke tile) are hills or ridges of sand:

• barchan dunes: crescent-shaped; little sand, and wind from one direction;
• longitudinal dunes: long ridges along the main wind direction;
• star dunes: many arms; wind from many directions;
• parabolic dunes: U-shaped, often held in place by plants.

Dunes slow the spread of deserts, protect coasts from sea winds and waves, attract tourists, and give sand for building.

Underground water works in rocks like limestone, which slowly dissolve in slightly acidic water. The landscape it makes is called karst. Its landforms:

• caves (gufa): hollows where water dissolved the rock;
• stalactites: icicle shapes hanging from the ceiling;
• stalagmites: shapes rising from the floor; when the two meet they make a pillar;
• sinkholes (dolines): dips where the ground collapses into a hollow below;
• underground rivers flowing through caves.

They give fresh water, attract tourists and scientists, and some caves are sacred.