Geography Notes Chapter 4 Exogenetic Processes Part-2 Class 9 Maharashtra Board

1. Introduction to Exogenetic Processes

What are Exogenetic Processes?

• These are processes that wear away, move, and deposit materials on the Earth’s surface.
• They include erosion, transportation, and deposition.
• Agents: rivers, glaciers, wind, sea waves, and groundwater.

How They Work:

• Erosion: Wears away rocks and soil.
• Transportation: Carries the eroded material.
• Deposition: Drops the material when the agent slows down.

Result: New landforms are created over time.

2. Work of Rivers and Landforms

What is a River?

• A river is a large flow of water formed when many small flows (rills, gullies, streams) join together.
• It flows downhill due to gravity.

Factors Affecting River Work:

• Slope of the land, type of rock, amount of water, length of flow, and sediments.

Erosional Work:

• Rivers start high in mountains, flow fast, and erode their beds and banks.

Landforms:

• Gorges (Canyons): Deep, narrow valleys.
• V-shaped Valleys: Valleys with steep sides shaped like a “V.”
• Waterfalls: Sudden drops where water falls over hard rocks.

Transportation and Deposition:

• As the slope gets gentler, rivers slow down and drop sediments.

Landforms:

• Alluvial Fans: Triangular deposits at foothills.
• Meanders: Bends or curves in the river’s path.
• Flood Levees: Raised banks along the river from sediment.
• Flood Plains: Flat areas near rivers covered with sediment.
• Deltas: Sediment deposits at the river’s mouth near the sea (Fig 4.1).

3. Work of Glaciers and Landforms

What is a Glacier?

• A glacier is a large mass of ice formed from piled-up snow in cold regions.
• It moves slowly downhill due to its weight.

Erosional Work:

• Glaciers erode by scraping their beds and banks with ice.

Landforms:

• Cirques: Bowl-shaped hollows where glaciers start.
• Arêtes: Sharp ridges between cirques.
• Horns: Pointed peaks from eroded cirques.
• U-shaped Valleys: Wide, U-shaped valleys.
• Hanging Valleys: Smaller valleys above the main valley.
• Rôche Moutonnées: Smooth, rounded rocks like sheepbacks.

Transportation and Deposition:

• Glaciers carry sediments called moraines.
• Types of Moraines: Ground (under glacier), Lateral (sides), Medial (middle), Terminal (end) (Fig 4.2).

Landforms:

• • Drumlins: Small, egg-shaped hills.
  • Eskers: Long ridges of sediment from melted glacier streams.

Fun Fact: The Jacobshavn Glacier in Greenland moves 46 meters per day!

4. Work of Wind and Landforms

What is Wind?

• Wind is moving air that erodes, transports, and deposits material.
• Works best in deserts and semi-arid areas with no plants.

Erosional Work:

• Wind carries sand and pebbles, scraping rocks.

Landforms:

• • Mushroom Rocks: Rocks with thin bases from wind erosion (Fig 4.3).
  • Deflation Hollows: Depressions from wind removing loose material.
  • Yardangs: Streamlined, wind-eroded rock shapes.

Depositional Work:

• Wind drops sand when it slows down.

Landforms:

• • Sand Dunes: Hills of sand.
  • Barchans: Crescent-shaped dunes.
  • Seifs: Long, straight dunes.
  • Ripple Marks: Small wave-like patterns in sand.
  • Loess Plains: Flat areas of fine wind-blown soil.

5. Work of Sea Waves and Landforms

How Sea Waves Work:

• Waves are caused by wind and tides hitting the coast.
• They erode, transport, and deposit materials.

Erosional Work:

• Waves hit rocks with water, stones, and pebbles, wearing them away.

Landforms:

• • Wave-cut Platforms: Flat areas at the base of cliffs.
  • Sea Caves: Hollows in cliffs from wave erosion.
  • Sea Arches: Natural bridges in rocks.
  • Sea Cliffs: Steep rock faces along the coast (Fig 4.4).

Depositional Work:

• Waves drop sand and pebbles where their force is weak.

Landforms:

• • Beaches: Sandy or pebbly shores.
  • Sand Bars: Long ridges of sand in the water.
  • Lagoons: Water bodies separated by sand bars.

6. Work of Groundwater and Landforms

What is Groundwater?

• Rainwater that seeps into the ground through cracks or porous rocks.
• Collects above non-porous layers.

Erosional Work:

• Groundwater dissolves minerals in soft rocks like limestone.

Landforms:

• Sinkholes: Holes in the ground from collapsed rock.
• Limestone Caves: Underground hollows from erosion.

Depositional Work:

• Minerals settle when water evaporates or can’t hold them.

Landforms:

• Stalactites: Icicle-like deposits hanging from cave ceilings.
• Stalagmites: Deposits rising from cave floors.

Water Table:

• The top level of groundwater.
• Higher in rainy seasons, lower in summer.