Samacheer Class 7 Social Science - Landforms

The process of breaking and crumbling of rocks is weathering, which occurs through physical, chemical, and biological processes that break down rock material without transportation. The place where the river joins a lake or a sea is known as a river mouth, which is the terminal point of a river system where it discharges its water into a larger body of water. Inselbergs are found in the Kalahari desert in South Africa, where they appear as isolated rocky hills rising abruptly from the surrounding flat terrain. A cirque is known as Kar in Germany, which is a bowl-shaped depression formed by glacial erosion at the head of a valley. The longest beach in the world is Miami Beach in the U.S.A., which extends for several miles along the Atlantic coast of Florida.

mountain, hill2. The raised river banks are called ………………..
Levees
3. An active agent of erosion and deposition in the deserts is ………………..
wind
4. An isolated residual hill, stand like a pillar with rounded tops are ………………..
Inselbergs
5. Northern China loess deposits are brought from the ……………….. Desert.
Gobi
6. A part of land adjoining near the sea is called ………………..
sea coast7. The boundary of the sea coast, where land meets water is ………………..
coastline
8. ………………..are steep rockfaces formed when the sea waves dash against them.
sea cliffs
9. The wall-like feature in the sea is ………………..
stacks
10. The second largest beach in the world is the ……………….. beach in Chennai.
Marina
11. Moraines are ………………..deposition.
glacial
12. ……………….is a stream or river that flow into and joins the main river.
Tributary13. The collection of sediments from all the months of river forms ………………..
Delta
14. ………………..is the armchair shaped depression formed by glacial erosion.
Cirque
15. The process of leveling of highlands is called ………………..
Gradation

A V-shaped valley is formed primarily through river erosion and vertical cutting action. As a river flows downward with considerable force, it erodes the riverbed more intensely than the banks, creating a steep-sided valley that resembles the letter V when viewed in cross-section. V-shaped valleys are characteristic of young rivers in their upper courses, where the river has high velocity and significant erosive power. In contrast, a U-shaped valley is formed by glacial erosion. Glaciers move slowly down mountain valleys, eroding both the valley floor and the sides through a combination of abrasion and plucking. This lateral and vertical erosion widens and deepens the valley, creating a broad, flat-bottomed valley with steep sides that resembles the letter U in cross-section. U-shaped valleys are characteristic features of glaciated mountain regions and indicate past or present glacial activity. The difference between these two valley shapes reflects the different erosional processes and agents involved in their formation.

Continental glaciers and mountain glaciers are two distinct types of glaciers that differ in their size, extent, and location. A continental glacier is an enormous sheet of ice that covers vast areas of a continent, extending over hundreds of thousands of square kilometers. Continental glaciers are characterized by their immense thickness and their ability to cover entire landscapes, including mountains and valleys. The major examples of continental glaciers are found in Antarctica and Greenland, where thick ice sheets persist due to extremely cold climatic conditions. These glaciers flow outward in all directions from their centers. A mountain glacier, also called a valley glacier, is a much smaller body of ice that flows along a mountain valley and is bounded by steep valley sides. Mountain glaciers are confined to specific valleys and move downslope under the influence of gravity. Examples of mountain glaciers are found in the Himalayan mountain range and the Alps. While continental glaciers are massive ice sheets covering entire regions, mountain glaciers are linear features flowing through valleys, making them distinctly different in scale and geographic distribution.

Flood plains are very fertile because of the continuous deposition of nutrient-rich sediments by rivers. When a river overflows its banks during the monsoon season or due to heavy rainfall, it spreads across the surrounding low-lying areas, depositing layers of fine soil and other organic materials called sediments along its banks and across the flood plain. These sediments are rich in nutrients and minerals that have been transported by the river from upstream areas. Over time, successive floods deposit multiple layers of these fertile sediments, building up a thick, nutrient-rich soil layer. This process of natural soil enrichment makes flood plains exceptionally fertile and suitable for agriculture. The flat topography of flood plains, combined with their fertile soil and access to water, makes them ideal for farming. Many of the world's most productive agricultural regions, such as the Indo-Gangetic Plain in India, are located on flood plains. Farmers have traditionally settled in these areas and developed irrigation systems to take advantage of the natural fertility and water availability provided by rivers and their flood plains.

Sea caves are formed when waves continuously strike the coastal rocks and create cavities through erosion. As these cavities become larger and deeper, only the roof of the cave remains standing, which forms a sea arch. When wave erosion continues to act on the sea arch, the roof further weakens and eventually breaks or collapses. Once the roof is completely removed or destroyed, only the vertical walls of rock remain standing isolated from the mainland. These isolated vertical rock walls or pillars are called stacks. Stacks are therefore the final stage in the erosion of sea caves, representing the remnants of what was once a larger rock formation that has been progressively worn away by the relentless action of waves and water.

Rivers are powerful agents of erosion that shape the landscape by flowing water cutting through rocks and soil. The running water in rivers erodes the landscape and creates different types of landforms. A V-shaped valley is formed when river erosion creates a steep-sided valley that resembles the letter V, with the river continuously deepening and widening its channel. Waterfalls are created when soft rocks are removed by river erosion, exposing harder rock layers that cause water to fall vertically. A plunge pool is a hollow or depression formed at the base of a waterfall through a process called cavitation, where water swirling with rocks creates a deep basin. An oxbow lake is formed due to continuous erosion along the sides of a meander, which is a curved bend in the river. As erosion progresses, the loop of the meander eventually cuts off from the main river channel, creating a cutoff lake called an oxbow lake. These various landforms demonstrate how river erosion gradually transforms the terrain over time.

Wind is an important natural agent that shapes landscapes through both erosion and deposition, particularly in desert regions. Mushroom rocks are distinctive rock formations found in deserts where wind erosion has shaped rocks into unusual shapes resembling mushrooms, with a wider top and narrower base. Inselbergs are eroded hills that stand isolated like pillars with rounded tops, formed when surrounding rock is worn away by wind and weathering while harder rock remains. Sand dunes are low hill-like structures formed when wind blows and transports sand, depositing it in accumulations across large areas. Barchans are crescent-shaped sand dunes that form in desert regions where wind direction is consistent, with the curved shape pointing in the direction the wind is blowing. Loess is very fine and light sand that is transported by wind over long distances and deposited in large areas, creating fertile plains in some regions. All these landforms result from the combined processes of wind erosion removing material and wind deposition accumulating sediment in new locations.

Aretes are distinctive landforms created through glacial erosion in mountainous regions. When two adjacent cirques, which are bowl-shaped depressions carved by glaciers, erode towards each other over time, the ridge of rock that separates them becomes progressively narrower and sharper. As glacial erosion continues from both sides, the previously rounded landscape is transformed into narrow, rocky, steep-sided ridges called aretes. These sharp ridges stand out prominently in glaciated mountain regions and represent the dividing line between two glacier-carved valleys. The formation of aretes demonstrates how glacial erosion is a powerful process that can dramatically reshape mountain topography, creating distinctive sharp features that are characteristic of areas that have experienced significant glaciation.

S.No Natural Agents Landforms Erosion Deposition 1. River V-Shaped Valley Alluvial Fan 2. Glacier Arete Moraine 3. Wind Inselberg Barchan 4. Sea wave Cliff Lagoon. These landforms are created by various natural agents through processes of erosion and deposition. Rivers, for instance, carve out V-shaped valleys through erosion and deposit sediments to form alluvial fans. Glaciers, powerful agents of erosion, create sharp, knife-edged ridges called aretes and deposit glacial till to form moraines. Wind, particularly in arid regions, erodes softer rock to leave behind isolated, steep-sided hills known as inselbergs, and deposits sand to form crescent-shaped dunes called barchans. Sea waves continuously reshape coastlines, eroding cliffs and depositing sediments to form features like lagoons.

Landforms are natural features of the Earth's surface that can be observed in various locations. Hills are elevated areas of land composed of rocks and mountains from which rivers often originate, providing water sources for surrounding regions. Waterfalls are dramatic features where water falls over a vertical step or cliff in the river bed, usually formed when softer rocks are eroded away exposing harder rock layers below. Rivers and streams are bodies of water that flow in a definite course across the landscape, serving as important sources of water for human use and habitats for aquatic life. Beaches are coastal landforms created when sea waves deposit sediments such as sand and gravel along the shores, forming sandy or pebbly areas where land meets the ocean. These features can be identified and studied in many regions, and each represents the work of natural agents like water, wind, and waves in shaping the Earth's surface over time.