Earth's Movements and Changing Landforms Chapter Notes | Footprints Class 7: Book Solutions, Notes & Worksheets PDF Download

Understanding Earth's Dynamic Nature and Landforms

The Dynamic Nature of Our Planet

• Earth is in a constant state of change and motion.
• Various processes, both internal and external, shape the features of our planet.
• These processes lead to the formation of different landforms that we observe.

Internal Processes

• Tectonic movements: The shifting of tectonic plates results in the formation of mountains, valleys, and earthquakes.
• Volcanic activities: Volcanoes create landforms such as mountains, craters, and lava plateaus.

External Processes

• Erosion: The wearing away of land by wind, water, or ice forms landforms like canyons, valleys, and deltas.
• Deposition: The process of depositing eroded material leads to the formation of beaches, sand dunes, and river deltas.

Examples of Landforms

• Mountains: Formed through tectonic plate movement and volcanic activity, examples include the Himalayas and the Andes.
• Valleys: Created by erosion from rivers or glaciers, such as the Grand Canyon and Yosemite Valley.
• Beaches: Result from the deposition of sand along coastlines, like Bondi Beach and Waikiki Beach.

Endogenic and Exogenic Forces

• Endogenic Forces:
  • Endogenic forces are those that originate within the Earth's crust.
  • These forces result in slow Earth movements that lead to the formation of continents, ocean beds, mountains, plateaus, and plains.
  • They also cause sudden Earth movements like volcanic eruptions, earthquakes, and landslides.
• Exogenic Forces:
  • Exogenic forces originate outside the Earth's crust.
  • These forces bring about changes on the Earth's surface.
  • Natural agents such as wind and water cause erosion and deposition on the Earth's surface.

Formation of Landforms by Internal Processes

• Theory of Plate Tectonics

  The Earth's lithosphere consists of various large and small plates known as lithospheric or tectonic plates. These plates are positioned atop the molten mantle or asthenosphere and are in continuous motion driven primarily by the heat from the Earth's interior.

• Movements of Lithospheric Plates

  The lithospheric plates' movements bring about alterations on the Earth's surface. When plates move apart or diverge, rifts are created, leading to the formation of continents and ocean basins through processes like sea floor spreading.

• Plate Collision

  When lithospheric plates collide, various landforms are produced, such as mountains, trenches, and areas with heightened volcanic or seismic activity.

• Formation of Mountains
  • Mountains Formed by Plate Movements
    • Mountains are created due to the horizontal movement of lithospheric plates on Earth's surface.
  • Old Fold Mountains
    • Characteristics of Old Fold Mountains
      • Examples include the Appalachians, the Urals, and the Aravallis.
      • Formed millions of years ago through horizontal plate movements.
      • Have rounded peaks, gradual slopes, and are shorter compared to young fold mountains.
  • New Fold Mountains
    • Characteristics of New Fold Mountains
      • Include the Himalayas, Rockies, Alps, and Andes.
      • Continuously rising due to ongoing horizontal plate movements.
      • Higher in elevation with pointed peaks and deep valleys.
  • Folding
    • Definition and Causes of Folding
      • Refers to the wrinkling of Earth's crust due to compression when lithospheric plates collide.
      • Results in the bending and deformation of rock layers.

Faulting and Types of Faults

• Faulting

  When the Earth's plates move, stress can cause cracks and fractures on the Earth's surface, a phenomenon known as faulting.

• Types of Faulting

  • Normal Faulting

    Normal faulting happens when rocks move horizontally in opposite directions, creating tension that leads to one block of rock moving down compared to the other side.

  • Reverse Faulting

    Reverse faulting occurs when rocks move horizontally in a compressional manner, pushing one block of rock strata up along the fault line while the other block hangs below.

  • Tear Faults

    Tear faults are formed when the rock structure is displaced laterally in opposite directions. An example is the San Andreas Fault in California.

• Block Mountains and Rift Valleys

  Faulting often leads to the creation of block mountains and rift valleys. The land between two parallel faults either rises or remains at the same level while surrounding areas sink.

  • Examples of block mountains include the Vindhya and Satpura ranges in India, the Vosges in France, and the Black Forest mountains in Germany.
  • Examples of rift valleys are Death Valley in the USA and East Africa.

Understanding Earthquakes

• Definition: Earthquakes are natural phenomena that result in vibrations or tremors on the Earth's surface.
• Causes: Earthquakes can be triggered by the collision or rubbing of lithospheric plates, volcanic eruptions, landslides, and faulting.
• Study of Earthquakes:
  • Seismology: This field focuses on analyzing earthquake waves, and experts studying earthquakes are known as seismologists.
  • Instrumentation: A seismometer or seismograph is a device designed to detect and measure the vibrations generated by earthquakes.
• Measuring Earthquake Strength:
  • Richter Scale: The Richter Scale, ranging from 0 to over 9, is commonly used to quantify earthquake intensity.
  • Impact: Earthquakes measuring 6 or higher on the Richter Scale can result in severe devastation, causing extensive damage to life and property.
• Volcanoes:
  • A volcano forms at the boundary where two tectonic plates collide, with one plate sliding beneath the other. This collision triggers volcanic activity.
  • Defined as an opening in the Earth's crust, a volcano allows the escape of hot magma, volcanic ash, steam, rock particles, and gases from beneath the surface.
  • Different parts of a volcano include the vent, which is the opening through which volcanic materials erupt, and the crater, the bowl-shaped depression at the top.
  • Volcanoes are categorized based on their eruption frequency as active (currently erupting), dormant (inactive currently but may erupt again), or extinct (no longer capable of erupting).
• Formation of Landforms by External Forces:
  • Landforms on Earth's surface are shaped by processes such as weathering, erosion, and deposition.
  • Weathering breaks down rocks into smaller particles, erosion transports these particles, and deposition deposits them in new locations, contributing to landform creation.
  • Natural agents like running water, glaciers, wind, groundwater, and sea waves play crucial roles in forming landforms through these processes.

Geological Processes

Weathering

• Weathering refers to the gradual breakdown and decay of rocks in their original position due to atmospheric conditions. This process does not involve the movement of rock fragments through external agents.
• Weathering can be caused by chemical, physical, and biological processes, all of which contribute to altering landscapes and are essential for soil formation.

Example:

An example of physical weathering is freeze-thaw action, where water seeps into the cracks of rocks, freezes, expands, and eventually causes the rock to break apart.

Erosion

• Erosion is the process of wearing down the Earth's surface and transporting the eroded material through natural agents like water, ice, wind, and waves.

Example:

Wind erosion in deserts can lead to the formation of unique landforms like sand dunes through the constant movement of sand particles.

Deposition

• Deposition involves the settling and accumulation of rock debris, which has been weathered and eroded, in different parts of the Earth by natural forces.
• Over time, the deposited debris can build up to form new rocks through processes like compaction and cementation.

Example:

When a river floods, it carries sediment downstream. As the flow slows, the sediment is deposited along the riverbanks, contributing to the formation of river deltas.

This HTML structure provides a detailed and organized summary of riverine landforms, including their formation processes and key characteristics across the river's journey from its source to the mouth.

Glacial Landforms

• Formation of Glaciers

  Glaciers are formed when accumulated snow in valleys slowly moves down mountain slopes due to gravity, forming a river of ice.

• Valley Formation

  As glaciers move, they carry rocks and gravel, simultaneously eroding the bed and sides of the valley. This process creates V-shaped valleys with flat bases and steep sides.

• Mountain Features

  In mountains, glaciers carve deep hollows, creating bowl-shaped depressions known as corries (Scotland), cirques (France), or cwms (Wales). These features are prevalent in the Scottish and Welsh highlands.

• Corrie Formation

  After ice melts in a corrie, it forms a lake called a corrie lake or tarn.

• Erosion and Deposition

  Glaciers act as immense plows, eroding the land underneath. They transport sand, gravel, clay, and boulders, depositing these materials as moraines when the ice melts.

• Glacier Termination

  Sometimes, glaciers reach the sea without melting, breaking up to form floating masses of ice known as icebergs.

• Wind Landforms
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  • The impact of winds on shaping landscapes is most evident in deserts characterized by sandy, dry, and loose soil. In these areas, winds transport loose sand particles, which serve as tools to abrade and smooth rocks, resulting in various land formations.
  • When wind erosion is most pronounced at the base of rocks due to the inability of the wind to carry sand higher, mushroom rocks or gaur formations can emerge as a result.
  • As wind speed decreases, it deposits the sand and particles it carries, leading to the accumulation of sand that forms structures like sand dunes. These dunes are dynamic, moving in the direction of the prevailing wind.
  • Occasionally, fine sand can be transported over significant distances and deposited in areas beyond desert boundaries, creating deposits known as loess, which can cover existing landforms extensively.
  • In situations where wind removes sand to form depressions and groundwater emerges, an oasis is formed, providing a fertile and lush area amidst arid surroundings.

Marine Landforms

• Sea waves, currents, and tides shape and transform coastal landforms.
• Wave action primarily affects a narrow coastal zone, leading to the creation of various features:
  • Sea cliffs and vertical rocks facing the ocean are sculpted by waves, forming wave-cut terraces or platforms.
  • Caves develop as headlands recede, gradually evolving into arches that may collapse, forming island stacks and slumps over time.
  • Wave deposits of sand and eroded materials along the shoreline contribute to the formation of beaches.
  • Deposition of sand and pebbles can create a low-lying ridge known as a spit, typically connected at one end to the mainland.
    • With continued growth, a spit extending across the coast may transform into a sandbar.
    • Sandbars can isolate sections of the sea, leading to the formation of lagoons or backwaters.