Exogenic Processes and Weathering

Exogenic Processes

• Exogenic processes are surface-level processes that wear away Earth's surface.
• They are very destructive, responsible for shaping and degrading landscapes.

Weathering

• Weathering is the disintegration or chemical alteration of rocks near Earth's surface.
• It involves the physical breakdown of rocks into smaller pieces without changing their composition (physical weathering).
• It also includes the chemical alteration of the minerals in the rocks (chemical weathering).
• It is also affected by biological activity (biological weathering).

Types of Weathering

Physical Weathering

• Rocks break down into smaller pieces without changing their composition.
• Examples include:
  • Exfoliation: The removal of outer rock layers, caused by pressure release from underground removal of rock. This causes the rock to expand and crack.
  • Ice wedging/Frost action: Water seeps into cracks, freezes and expands, widening the cracks until the rock breaks apart.
  • Temperature changes/Thermal expansion: Repeated heating and cooling causes rocks to expand and contract, creating cracks. These are usually faster changes in temperature, like daily changes.
  • Abrasion: Rocks hitting each other or material carried by wind, water or ice wearing away a surface.

Chemical Weathering

• Rocks break down as their minerals change composition.
• Common types include:
  • Hydrolysis: A new solution is formed as chemicals in the rock interact with water. Example - sodium minerals interact with water and create saltwater solution.
  • Hydration: Minerals absorb water, causing them to expand and create stress which causes disintegration of rocks.
  • Oxidation: Oxygen combines with other substances called oxides. Example, rust is iron oxide. Rusting can occur very quickly with water mixed with vinegar and salt.
  • Carbonation: Water combines with carbon dioxide to make carbonic acid. This is important in the formation of caves. Acid slowly eats away at the bedrock.

Biological Weathering

• The disintegration or decay of rocks caused by organisms.
• Examples include:
  • Roots of plants: Roots grow in cracks and joints, exerting pressure that causes the rocks to break and erode gradually.
  • Microbial activity: Bacteria, moss, lichen and organic acids breakdown rocks.
  • Animal burrowing: Animals dig burrows and creating fissures in rocks. It also progressively separates the rocks into pieces by taking nutrients from it.

Erosion

• Erosion is the removal of surface materials (like soil, rock debris) from the Earth's crust.
• Eroded materials are transported by natural processes.

Agents of Erosion

• Water: Rain, rivers, floods, lakes, ocean currents all wash away sediments. Erosion is even more intense when water moves faster, potentially carrying bigger or even larger objects like boulders and cars.
• Ice: Glaciers grind up rocks and scrape away the soil because of their weight and movement.
• Wind: Wind (especially strong, dry winds like in desert areas) transports dust, sand, and ash from place to place.
• Gravity: Gravity pulls everything towards the center of the Earth. The result is mixed piles of sediments that usually occur below slumps in the land.

Mass Wasting

• A rapid form of erosion that is primarily influenced by gravity, working in combination with other erosional agents.

Types of Mass Wasting

• Rock falls
• Landslides
• Debris and mudflows
• Slumps
• Creep

Deposition

• Deposition is the laying down of sediments transported and eroded by an erosional agent (moving water, wind, ice)
• Sedimentation adds sediments, soil and rock to a landform or landmass.