Shaping of the Earth Surface Class 9 PPT & Notes PDF | USP

The Earth’s surface is always changing, shaped by forces from inside and outside the planet. This chapter answers five questions:

1. What shapes the Earth’s surface?
2. What is plate tectonics, and what are the effects of plate movement?
3. How are landforms formed and classified?
4. How are humans and living beings connected to landforms?
5. How do disasters linked to landforms affect human life?

• A landform is a natural feature on the Earth’s surface formed by weathering, erosion, deposition and crustal movement, for example mountains, valleys, plateaus, plains, deserts and coasts
• Plate tectonics is a theory (given by W. J. Morgan) that explains how the Earth’s crust moves. The outer layer of the Earth is not one piece: it is broken into large and small pieces called tectonic plates, which move slowly over the semi-molten layer below and cause mountains, earthquakes and volcanoes

• The lithosphere is the rigid outer layer: the crust plus the upper mantle. It is broken into tectonic plates, which float and drift
• The asthenosphere is the hot, semi-molten layer just below the lithosphere, which lets the plates move slowly

Tectonic plates are massive slabs of solid rock that move a few centimetres per year. Continental plates carry continents, oceanic plates carry ocean floors, and mixed plates carry both. The major plates include the Pacific, North American, South American, Eurasian, African, Indo-Australian and Antarctic plates.

Heat from the core makes hot, molten material in the mantle rise, while cooler material sinks. These looping convection currents push and pull the plates in different directions, like boiling water in a pot.

Plate movement forms mountains, valleys, ocean basins, volcanoes and earthquakes, and explains where the continents and oceans lie. Most earthquakes and volcanoes occur along plate boundaries, especially around the Pacific Ocean, the famous Ring of Fire.

Yes. India has faced major earthquakes, and in a densely populated country a big quake causes severe loss of life and damage to the environment. The Himalayan belt, Kachchh (Gujarat) and North-East India are highly vulnerable (for example, Gujarat 2001).

Long ago, earthquakes were called bhūkampa, “the shaking of the Earth”. The scholar Varāhamihira, in his text Brihatsamhita, wrote a whole section on earthquakes. He noticed warning signs in wind, rain, clouds, animal behaviour and planetary positions, and linked earthquakes to four forces: Vāyu, Agni, Indra and Varuṇa. It was an early blend of observation and cosmology in India.

At Baratang Island in the Andaman and Nicobar Islands lies India’s only mud volcano. Unlike fiery lava volcanoes, here cool mud bubbles out of the ground, pushed up by natural underground gases and pressure.

Weathering is the breaking down of rocks into smaller pieces without moving them. It helps form soil.

Erosion is the wearing away and moving of soil and rock by natural agents. The difference is that weathering only breaks the rock, whereas erosion breaks it and moves it.

• Water erosion: rivers, rain and waves
• Wind erosion: in dry, sandy areas
• Glacial erosion: moving ice scrapes the rock
• Coastal erosion: sea waves wear away the shore

• Contouring: trenches dug along the slope’s contour lines slow the run-off, hold and soak in rainwater and recharge groundwater
• Bunding: earthen embankments built along contour lines slow run-off, reduce erosion and keep the soil moist
• Terracing: level step-fields cut into a hillside to prevent soil erosion
• The Sindhu-Sarasvati civilisation used contouring, bunding, terracing, dams and canals, which are also described in the Vedas, the Krishiparashara, Kautilya’s Arthashastra and the Vrikshayurveda
• The Zabo system of Nagaland uses earthen bunds and check dams to conserve soil and water

Agents of gradation are natural forces that wear down, transport and deposit material to level the Earth’s surface: running water, waves and currents, glaciers, wind and underground water.

A waterfall is where a river drops over a steep cliff. It forms in the upper course: hard rock resists erosion while the softer rock below wears away, creating a sudden drop with a plunge pool at the bottom. Uses: tourism, hydroelectric power, recreation, and cultural or religious value.

A meander is a winding bend in a river’s middle or lower course, formed by erosion on the outer bank (the steep bank) and deposition on the inner bank (the bar), making large loops. An oxbow lake forms when a meander is cut off. The fertile soil supports farming, influences settlements, and is used for irrigation and navigation. Example: the Grand Anicut (Kallanai), Tamil Nadu.

A delta is a fan-shaped or triangular landform at a river’s mouth, where it meets a sea, ocean or lake and deposits sediment. The river splits into distributaries with islands or bars between them. Its alluvial soil is very fertile (rice and jute), and it is great for fishing and trade, but flood-prone. Example: the Sundarbans Delta.

• Waves and currents constantly move over the ocean and reshape the coast. Coastal landforms include beaches, sand bars, sea cliffs, sea caves, arches and stacks
• A beach is a landform of sand, pebbles or rocks along a shore, made by wave deposition. Uses: tourism, fishing, sand and shells, and it acts as a natural barrier against waves and erosion
• Coastal erosion landforms: a cliff (a steep rock face undercut by waves), a wave-cut or shore platform, a sea cave, a sea arch and a sea stack

• Glaciers are slow-moving rivers of ice that carve and shape the land
• Erosion landforms: U-shaped valleys (wide, deep valleys carved by ice), cirques (bowl-shaped hollows at the glacier head), arêtes (sharp ridges between two valleys), hanging valleys (small valleys meeting a larger one, often with a waterfall) and fjords (deep, narrow sea inlets flooding a glacial valley)
• Deposition: moraines are rocks, soil and debris (called till) carried and dropped by a melting glacier. A lateral moraine lies along the sides, a medial moraine in the middle where two glaciers meet, and a terminal moraine at the end, marking the furthest advance
• Uses: tourism, trekking and skiing; fjords for harbours and fishing; fresh water; fertile soil for farming; moraines can form natural dams and lakes

• Wind erosion happens when strong winds pick up and carry loose sand and soil, shaping the land mainly in deserts
• Erosion landforms: a yardang is a streamlined rock ridge carved by wind, showing hard and soft rock layers; a ventifact is a rock polished and shaped by sandblasting, with smooth facets and sharp edges; a deflation hollow (blowout) is a shallow depression where loose material is blown away; a desert pavement is a pebbly surface of stones left after fine particles blow away
• Dunes are hills or ridges of sand built by wind: barchan (crescent-shaped, one wind direction), longitudinal (long ridges parallel to the wind), star (many arms, winds from all sides) and parabolic (U-shaped, held by plants)
• An oasis is a deflation hollow reaching the water table
• Dunes guard against desertification, and the sand is used for construction

• In limestone or other soluble-rock areas, underground water dissolves the rock through chemical weathering and erosion, creating a special landscape called karst topography
• Landforms: caves, stalactites (hanging from the roof), stalagmites (rising from the floor), pillars (where the two join), sinkholes (dolines) and underground rivers
• Uses: fresh water, tourism, and cultural or religious value

• A landslide is the sudden downhill movement of rock and soil when slopes become unstable
• Natural causes: heavy continuous rainfall, earthquakes, volcanic eruptions, steep slopes, and loose or weathered rock
• Human causes: deforestation, mining, road and hillside construction, and poor drainage
• Prone areas include the Himalayan states, the Western Ghats and the North-East hills. Mitigation: planting trees on slopes, retaining walls, proper drainage, no construction on steep slopes, and early warning. A recent example is the Wayanad landslides in Kerala (2024)

• An avalanche is the sudden sliding of large amounts of snow down steep mountain slopes
• Triggers: heavy snowfall adding weight, weak or loose snow layers, a sudden temperature rise (melting reduces friction), strong winds piling snow unevenly, earthquakes or vibrations, and human activity (skiing, trekking, construction)
• Prone areas: the high Himalayan regions of Jammu and Kashmir, Himachal Pradesh, Uttarakhand and Sikkim. Mitigation: avalanche barriers, early warning, and avoiding risky slopes

• A GLOF is the sudden release of a huge amount of water from a glacial lake when its natural ice or moraine dam breaks
• Causes: rapid glacier melting makes bigger lakes, heavy rain and snow add to the lake, and earthquakes, avalanches and landslides break the moraine dam. The result is a sudden, destructive flood downstream
• Prone areas: Himalayan glacial lakes. Mitigation: monitoring the lakes, early-warning systems, lowering the lake levels, and no building in the flood path. A recent example is the South Lhonak lake flood in Sikkim (2023)

In February 2021 a sudden, devastating flood struck the Chamoli district of Uttarakhand. Many people and livestock lost their lives, and buildings, roads, bridges and hydro-power projects were badly damaged. Villages were cut off. Studies of the event point to a huge rock and ice avalanche that triggered the flood, a good example of how landforms and disasters are linked.

• In a dust storm, strong winds lift large amounts of loose, dry soil and sand into the air
• Causes: prolonged drought and low rainfall (dry soil), sparse vegetation (deforestation, overgrazing, poor farming), and climate change with extreme weather. They are common in deserts and semi-arid regions
• Prone areas: Rajasthan, Gujarat, Haryana, Punjab and western Uttar Pradesh. Mitigation: planting shelterbelts and trees, protecting vegetation, and early warning

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