Grade 9 Geography Term 3: Weathering

Weathering

• Weathering is the breakdown of rocks and soil caused by water, wind, temperature changes, and biological factors.
• Three main types of weathering: Physical, Chemical, Biological.

Physical Weathering

• Freeze and Thaw: Water expands when frozen, leading to rock fragmentation.
• Exfoliation: Outer rock layers peel away due to temperature fluctuations causing expansion and contraction.

Chemical Weathering

• Carbonation: Carbon dioxide in water forms carbonic acid, which dissolves rocks like limestone and dolomite.
• Oxidation: Iron-containing rocks react with oxygen, leading to rust formation.
• Hydrolysis: Hard rocks, such as granite, absorb water and convert to clay, facilitating weathering.

Biological Weathering

• Plant growth and animal activities (e.g., burrowing by worms and moles) expose rocks to weathering.
• Lichens produce acids that chemically weaken rocks.

Erosion and Deposition

• Erosion involves the removal of weathered material by water, wind, or animals.
• Deposition refers to the accumulation of this material in new locations.

River Systems

• Source: The origin of a river.
• Tributaries: Smaller streams that feed into a larger river.
• Confluence: The junction where tributaries meet.
• River Mouth: The endpoint of a river where it meets a larger body of water.
• Interfluve: High land between rivers and tributaries.

Fluvial Landforms

• Formed through erosion and deposition by river flow:
  • Rapids, Waterfalls, Meanders, Oxbow Lakes, Braided Streams, Flood Plains, Natural Levees.

Meanders

• Bends in rivers happen when water erodes one bank while depositing sediment on the opposite side, forming river cliffs and inside bends.

Oxbow Lakes

• Formed when a meander loop is cut off from the main river body.

Desert Erosion and Deposition

• Abrasion: Scraping away of material, common in low-vegetation areas.
• Erosional features include Mushroom Rocks and Yardangs.
• Depositional features include Barchan Sand Dunes, Sief Dunes, and Transverse Dunes.

Impact of Human Activities on Soil

• Deforestation, agriculture, construction, desertification, and mining significantly disturb soil, leading to erosion.
• Overgrazing jeopardizes the stability of soil structures.
• Monoculture farming depletes vital minerals, unlike crop rotation which maintains soil health.

River Depositional Features

• Braided Streams: Characterized by intertwining shallow channels.
• Flood Plains: Level areas alongside rivers formed by sediment deposits during floods.
• Natural Levees: Raised banks formed by sediment buildup after repeated flooding.
• Deltas: Formed where a river enters a larger body of water, resulting in branched distributaries.

Types of Deltas

• Arcuate Delta: Curved, arc-shaped channels (e.g., Okavango Delta, Niger Delta).
• Bird’s Foot Delta: Shaped like a bird’s claws.
• Estuarine Delta: Wide, shallow river mouth.
• Cuspate Delta: Triangular shape with few distributaries.

Coastal Erosion

• Hard rocks form headlands; softer rocks erode into bays.
• Erosion due to wave action can create caves, arches, stacks, and stumps.

Glaciation

• Glaciation is the movement of ice downhill due to gravity, producing features such as moraines and eskers.
• Lateral Moraines: Rock deposits on valley sides.
• Terminal Moraines: Deposits at the valley's end.
• Eskers: Ridges formed in glacial channels.