Experts have designed these Class 9 SST Notes and NCERT Class 9 SST Chapter 2 Shaping of the Earth’s Surface Notes for effective learning.
Class 9 Shaping of the Earth’s Surface Notes
Class 9 SST Chapter 2 Shaping of the Earth’s Surface Notes
Class 9 SST Chapter 2 Notes – Shaping of the Earth’s Surface Notes Class 9
- The Earth is continuously transforming due to movement of tectonic plates.
- The theory of plate tectonics explain how large pieces of the outer crust (layer) move slowly over the mantle layer.
- The continuous movement of these plates creates several different landforms like valleys, mountains, volcanoes and plains.
- Understanding plate tectonics helps scientists explain natural events such as earthquakes, volcanic eruptions, folding, and faulting, and the creation of ocean and continents.
Plate Tectonics
- W. J. Morgan gave the theory of plate tectonics to explain how the outer crust of the Earth moves.
- As per this theory, the outermost layer of the Earth is broken into tectonic plates.
- They move over the semi-molten layer below them.
- The Earth has three main layers called the crust, mantle, and core.
- Crust and the upper part of the mantle is called the lithosphere.
- Below the lithosphere lies asthenosphere.
- The asthenosphere is semi-molten that allows the tectonic plates to move.
- Tectonic plates are massive rock structures that move very slowly, covering a distance of only a few centimetres every year.
- There are three main types of tectonic plates called the continental plates, oceanic plates and mixed plates.
- Continental plates carry continents. Oceanic plates carry oceans. Mixed plates carry both continents and oceans.
- Some major tectonic plates on the earth are Eurasian Plate, North American Plate, South American Plate, Pacific Plate, Antarctic Plate and Indo-Australian Plate.
- The movement of tectonic plates is driven by convection currents that form in the mantle due to heat rising from the core.
Plate boundaries are the edges where tectonic plates meet.
There are three types of plate boundaries:
- Convergent boundaries: Plates move toward each other, creating fold mountains like the Himalayas or causing volcanic activity when one plate sinks.
- Divergent boundaries: Plates move apart, allowing magma to rise and form new crust like the Mid-Atlantic Ridge.
- Transform boundaries: Plates slide past one another and often cause earthquakes like the San Jacinto Fault.
- Most earthquakes and volcanic activities occur along plate boundaries, especially around the Pacific Ring of Fire.
The theory of plate tectonics is highly useful for identifying regions that are at risk of natural disasters and planning safety measures for them.
In ancient times, earthquakes were called bhukampa’, a term that signifies the shaking of the Earth.
The scholar Varahamihira dedicated a specific section to earthquakes in his text, the Brihatsamhita.
He noted that natural changes in wind, rain, clouds, planetary positions, and animal behaviour could act as warning signs for earthquakes.
He believed earthquakes were caused by four natural forces, namely Vayu, Agni, Indra, and Varuna, with each force connected to specific regions and constellations.
- The mud volcano located on Baratang Island is an unusual natural feature and a major attraction in the Andaman and Nicobar Islands.
- Instead of hot lava, this volcano releases bubbling mud which is pushed to the surface by underground gases and pressure.
Process Of Weathering And Erosion
- Weathering and erosion are necessary for creation of landforms.
- Over long periods, these two processes work together to wear away mountains and cut out valleys to form plains.
- They create distinct geographical features like cliffs, caves and river deltas, shaping natural landscape.
Weathering
- Weathering is the breaking down of rocks on the surface without moving them.
- There are three types of weathering called physical weathering, chemical weathering, and biological weathering.
- In physical weathering, rocks break into smaller pieces due to change in temperature, wind and frost.
- In chemical weathering, minerals in rocks change due to reaction with air, water, or acids that creates new substances.
- In biological weathering, plants, animals or micro-organisms create crack in rocks and split them.
- Weathering is essential for changing the appearance of the Earth’s surface and is also responsible for the formation of soil.
Erosion
- Erosion wears away soil, rocks, and other surface materials and transports to different locations by natural forces like water, wind, ice or waves.
- There are many types of erosion such as water erosion, wind erosion, glacial erosion and coastal erosion.
- Water erosion is caused by the action of rivers, rainfall, or ocean waves, while wind erosion occurs mostly in dry, sandy desert areas.
- Glacial erosion happens when moving ice sheets scrape and carry rocks away.
- Coastal erosion occurs when sea waves wear down the land along the shoreline.
- Erosion directly impacts human occupations, such as farming, by washing away the fertile topsoil required to grow crops and reducing food production.
- For people living near rivers and coasts, erosion can destroy land, homes, and roads, leading to property damage and financial loss.
- In the construction and mining sectors, erosion makes the ground unstable, which creates serious safety hazards for workers.
- Industries like tourism and fishing are also negatively affected when scenic beaches, rivers, and fertile areas are damaged by erosion.
The ancient Sindhu-Sarasvati civilisation used advanced methods like contouring, building bunds^ terracing, dams, and canals to manage water resources effectively.
Traditional water and soil management practices are well-documented in old Sanskrit texts, including the Vedas, Krishi-Parashara, Kautilya’s Arthashastra, and Vrikshayurveda.
Kautilya’s Arthashastra provides specific guidelines on how to evaluate and classify land based on its natural fertility and agricultural productivity.
The Zebu System
- The Zabo system used in Nagaland is an organised farming method that uses mud walls on hill slopes to conserve soil and store water.
- Small check dams were built across streams to slow down water, stop soil erosion, collect mud deposits, and help refill underground water levels.
Agents of Gradation
- Agents of gradation are the natural forces that continuously reshape the Earth’s surface.
- Glaciers, running water, wind, waves, and groundwater are the main agents of gradation.
- Glaciers scrape the land to create U-shaped Valleys, while running water cuts through rock and soil to form valleys and plains.
- Wind alters desert landscapes by moving sand, sea waves wear down coasts to form cliffs and beaches, and groundwater dissolves limestones to create sinkholes and caves.
- Different landforms have played a critical role in shaping the growth and history of human civilisations.
- Highly fertile river plains like those of the Nile, Brahmaputra, Ganga, and Indus allowed early agricultural societies and cities to develop.
Mountains served as natural barriers and protectors, such as the Himalayas shielding India from invaders while allowing cultural exchange through mountain passes like the Khyber Pass.
Large deserts like the Thar limited regular human settlements but encouraged the setup of important trade networks like the Silk Route.
Coastal regions and natural harbours supported maritime trade, travel, and interaction with distant lands, helping kingdoms in southern India to grow.
Running Water
- Rivers shape the surface of the land through three main processes, which are erosion, transportation, and deposition.
- In their upper course, rivers have steep slopes and strong erosive power, leading to the formation of V-shaped valleys, waterfalls, and rapids.
- In the middle course, rivers lose speed and begin to bend, forming meanders, floodplains, and oxbow lakes as they deposit sediments.
- In the lower course, the river slows down significantly and drops large amounts of mud and sand, creating deltas, levees, and alluvial fans.
Waterfall
- Waterfall is created when river flows over a steep cliff.
- Waterfalls are formed where hard rocks resist erosion while softer rocks wear away. They are important for
tourism and hydroelectric power generation. - Waterfall also offers spaces for outdoor recreation like trekking and photography, and they often hold cultural or religious value in local regions.
Meander
- • Meanders are bends in rivers formed by erosion and deposition. They create fertile land suitable for agriculture.
- • Meanders influence where people choose to live, as towns and villages are frequently built on the safe, gentle slopes near these river banks.
- • These curving river paths are used for crop irrigation, tourism and navigation, as seen in the historic Kallanai dam (Grand Anicut) built for irrigation in Tamil Nadu.
Deltas
- Deltas are formed at the mouths of rivers by the deposition of sediments.
- They have fertile alluvial soil and support farming, fishing, and dense human settlements.
- Deltas are highly vulnerable to seasonal flooding which can disrupt human life and prosperity.
Waves and Currents
Sea waves and currents shape coastlines by erosion and deposition, forming beaches, cliffs, caves, arches, stacks, and wave-cut platforms.
A beach is a coastal landform composed of sand, pebbles or small stones deposited along the shoreline by wave action
Beaches protect coastlines from wave action and are important for tourism, fishing, and recreation.
Coastal erosion happens when waves and tides wear away the shoreline, creating steep rock faces called cliffs and flat areas known as wave-cut platforms.
Continued wave erosion hollows out weak rocks to make sea caves, which can break through to form sea arches, and eventually collapse to leave behind isolated pillars called stacks.
These erosional landforms attract tourists but also require active coastal protection strategies to keep nearby human settlements safe.
Glaciers
Glacial erosion reshapes landscapes as glaciers move slowly across the land, carving out distinctive features. The
main landforms include:
- U-shaped valleys — formed when glaciers widen and deepen river valleys.
- Cirques — bowl-shaped depressions at the head of a glacier.
- Aretes — sharp ridges between adjacent valleys.
- Hanging valleys — created where smaller glaciers join larger ones, often leading to waterfalls.
- Flords — deep, narrow inlets formed when the sea floods glacial valleys.
Glaciers are valuable sources of freshwater and support agriculture, tourism, and hydroelectric projects.
Moraines are landforms made up of soil, rocks, and debris (till) deposited by glaciers as they melt.
There are three main types of moraines:
- Lateral moraines: Ridges along glacier sides.
- Terminal moraines: Deposits at the glacier’s end, marking its furthest advance.
- Medial moraines: Debris lines formed when two glaciers merge.
- Moraines are useful because they develop into fertile agricultural soil and can form natural blockades that create lakes for water storage and electricity generation.
Wind
- Wind erosion happens when strong winds lift and carry away loose sand and soil particles, changing the appearance of the landscape.
- Wind erosion creates several landfonns which are called ventifacts, yardangs, deflation hollows or blowouts, and desert pavements. These landfonns are useful for settlement pattern, tourists and geologists.
- Dunes are hills of sand formed in desert areas. There are barchan dunes, longitudinal dunes, star dunes, and parabolic dunes.
- Dunes serve as natural barriers that stop deserts from expanding and protect coastal villages from strong sea winds and waves.
- They provide spaces for adventure sports and tourism, and their sand is sometimes collected for construction purposes.
Underground Water
- Underground water forms Karst topography by erosion and chemical weathering.
- Caves, stalactites, stalagmites, sinkholes or dolines and underground rivers are the landforms of underground
water.
Acidic water dissolves rock layers over time to form empty spaces called caves and underground river channels. Mineral deposits form icicle-shaped stalactites hanging from cave ceilings and stalagmites rising up from cave floors.
When the ground collapses into an underground cavity, it creates surface depressions called sinkholes or do lines.
These features are important because caves and underground rivers supply fresh water, offer places for tourism, and hold cultural or religious value.
Landforms And Disasters
Different landforms face different types of disasters.
Landslides
- Landslides happen when both natural forces and human actions make hill slopes unstable.
- Constant and heavy rainfall makes soil and rock layers heavy while reducing friction, which triggers sudden slope failure.
- Volcanic activity, steep slopes, earthquakes and the presence of loose rocks also weaken the ground and cause landslides.
- Human activities such as mining, cutting down trees to build infrastructure, and poor drainage systems further disturb the natural balance of slopes.
Avalanches
- Avalanches occur when snow suddenly becomes unstable and slides down steep mountain slopes.
- Heavy snowfall adds quick weight to the snowpack, especially when the fresh snow rests on top of weak or loose layers.
- A sudden rise in temperature melts the snow and reduces the friction holding the snowpack together.
- Strong winds pile snow unevenly, while skiing, trekking, earthquakes can trigger a sudden collapse.
GLOFs
- GLOFs (Glacial Lake Outburst Floods) happen when large volumes of water are suddenly released from lakes formed by melting glaciers.
- Rising temperatures cause glaciers to melt faster, which increases water levels and puts pressure on natural dams made of ice or loose rocks.
- Heavy rain or intense snow adds excess water to these lakes, increasing the risk of a sudden overflow.
- Avalanches, landslides or earthquakes can break or weaken these natural dams, causing severe and destructive floods in downstream areas.
Dust Storms
- Dust storms occurs when powerful winds lift massive amounts of loose, dry soil and sand high into the air.
- Long periods of drought and low rainfall dry out the soil completely, making it easier for the wind to carry away fine particles.
- These storms are very common in dry and semi-arid regions where the ground is loose and there is very little plant cover to hold it together.
- Climate change, deforestation, overgrazing by animals, poor farming methods etc. increase the frequency and strength of these storms.
Shaping of the Earth’s Surface Class 9 Short Notes
→ Alluvial Soil: Fertile soil deposited by rivers.
→ Arete: A sharp ridge formed between two glacial valleys.
→ Asthenosphere: A hot, semi-molten layer beneath the lithosphere that allows tectonic plates to move.
→ Avalanche: A sudden flow of snow, ice, and rocks down a mountain slope.
→ Bay: A broad inlet of the sea where the land curves inward.
→ Barchan Dune: A crescent-shaped sand dune formed by wind.
→ Biological Weathering: Breakdown of rocks caused by plants, animals, or microorganisms.
→ Bunding Building earthen embankments along contour lines to reduce soil erosion and conserve water.
→ Cave: A natural underground hollow formed by the erosion or dissolution of rocks.
→ Chemical Weathering: Breakdown of rocks through chemical reactions.
→ Cirque: A bowl-shaped hollow formed by glacial erosion.
→ Conduction: Transfer of heat through direct contact.
→ Continental Plate: A tectonic plate carrying continental landmass.
→ Continuous Contour Trench (CCT): Trenches dug along contour lines to conserve soil and water.
→ Contouring: Shaping or farming the land along its natural slopes and curves.
→ Convection Currents: Circular movement of hot and cool material inside the Earth’s mantle.
→ Convergent Boundary: A plate boundary where two tectonic plates move towards each other.
→ Coastal Erosion: Wearing away of the coastline by sea waves and currents.
→ Core: The innermost layer of the Earth.
→ Crust: The outermost solid layer of the Earth.
→ Deflation: Removal of loose soil and sand by wind.
→ Deflation Hollow: A depression formed when wind removes loose surface material.
→ Delta: A landform formed by the deposition of sediments at the mouth of a river.
→ Deposition: The process of laying down transported sediments.
→ Desertification: The process by which fertile land becomes desert.
→ Distributary: A branch of a river flowing away from the main channel.
→ Divergent Boundary: A plate boundary where two plates move apart.
→ Dune: A hill or ridge of sand formed by wind.
→ Dust Storm: Strong winds carrying large amounts of dust and sand.
→ Ecosystem: A community of living organisms interacting with their environment.
→ Erosion: Wearing away and transportation of rocks and soil by natural agents.
→ Fault: A crack in the Earth’s crust where movement occurs.
→ Fertile: Rich in nutrients and suitable for growing crops.
→ Fjord: A deep, narrow sea inlet formed by glacial erosion.
→ Floodplain: Flat land beside a river that is often flooded.
→ Fold Mountains: Mountains formed by the folding of rock layers due to plate collision.
→ GLOF (Glacial Lake Outburst Flood): A sudden flood caused by the bursting of a glacial lake.
→ Glacial Erosion: Wearing away of land by moving glaciers.
→ Glacier: A large, slow-moving mass of ice.
→ Gradation: The levelling of the Earth’s surface by erosion and deposition.
→ Groundwater Recharge: Refilling underground water supplies through rainwater infiltration.
→ Hanging Valley: A smaller valley joining a larger glacial valley.
→ Headland: A piece of land projecting into the sea.
→ Hydroelectric Power: Electricity generated using flowing water.
→ Infrastructure: Basic facilities such as roads, bridges, and buildings.
→ Inner Core: The solid, hottest, and densest part of the Earth.
→ Irrigation: Artificial supply of water to crops.
→ Karst Topography: Landscape formed by the dissolution of limestone.
→ Landform: Physical feature on Earth’s surface.
→ Landslide: Sudden movement of rocks, soil, and debris down a slope.
→ Lateral Moraine: Rock debris deposited along the sides of a glacier.
→ Levee: A raised riverbank formed naturally or artificially.
→ Limestone: A sedimentary rock that dissolves easily in acidic water.
→ Lithosphere: The rigid outer layer of the Earth consisting of the crust and upper mantle.
→ Livelihood: A means of earning a living.
→ Longitudinal Dune: A long sand ridge formed parallel to the prevailing wind.
→ Magma: Molten rock beneath the Earth’s surface.
→ Mantle: The thick layer of hot rock between the crust and the core.
→ Meander: A winding curve or bend in a river.
→ Medial Moraine: A moraine formed where two glaciers join.
→ Mid-Ocean Ridge: An underwater mountain range formed at divergent plate boundaries.
→ Molten: Melted by intense heat.
→ Moraine: Rock, soil, and debris deposited by glaciers.
→ Mud Volcano: A volcano that erupts mud, gases, and water instead of lava.
→ Navigation: The movement of ships and boats through waterways.
→ Oceanic Plate: A tectonic plate carrying ocean floor.
→ Outer Core: The liquid layer of the Earth’s core made mainly of iron and nickel.
→ Oasis: A fertile area in a desert where water is available.
→ Oxbow Lake: A crescent-shaped lake formed when a river meander is cut off.
→ Parabolic Dune: A U-shaped sand dune often stabilised by vegetation.
→ Physical Weathering: Breakdown of rocks without changing their chemical composition.
→ Plate Tectonics: The theory explaining the movement of the Earth’s tectonic plates.
→ Plunge Pool: A deep pool formed at the base of a waterfall.
→ Rapids: Fast-flowing, turbulent sections of a river.
→ Ring of Fire: A region around the Pacific Ocean with frequent earthquakes and volcanoes.
→ Sand Bar: A ridge of sand formed by waves or currents.
→ Sea Arch: A natural arch formed by wave erosion.
→ Sea Cave: A cave formed by the action of sea waves.
→ Sea Cliff: A steep rocky coast formed by wave erosion.
→ Sea Stack: An isolated pillar of rock left after a sea arch collapses.
→ Sediment: Small particles of rock, sand, or soil carried by natural agents.
→ Semi-arid: A region with low rainfall but not completely dry.
→ Semi-molten: Partially melted due to high temperature.
→ Sinkhole: A depression formed when the ground collapses into an underground cavity.
→ Stalactite: A mineral formation hanging from the roof of a cave.
→ Stalagmite: A mineral formation rising from the floor of a cave.
→ Subduction: The process in which one tectonic plate sinks beneath another.
→ Sustainable: Able to continue without harming the environment.
→ Tectonic Plates: Large pieces of the Earth’s lithosphere that move slowly.
→ Terminal Moraine: A moraine deposited at the farthest end of a glacier.
→ Terracing: Cutting hill slopes into steps for farming and soil conservation.
→ Transform Boundary: A plate boundary where plates slide past each other.
→ Transportation: The movement of weathered materials from one olace to another.
→ U-shaped Valley: A broad valley carved by glaciers.
→ Underground River: A river flowing beneath the Earth’s surface.
→ Ventifact: A rock shaped and polished by wind- driven sand.
→ Volcanic Activity: The movement and eruption of magma from the Earth’s interior.
→ Waterfall: A place where a river drops vertically over a steep rock face.
→ Wave-cut Platform: A flat rocky surface left behind as sea cliffs retreat.
→ Weathering: The breaking down of rocks into smaller pieces without movement.
→ Yardang: A streamlined rock ridge carved by wind erosion.