Physical Geology - Geo 303 Quiz

Physical Geology - Geo 303

• Course instructor: Dr. Fares Khedr
• Department: Geology, Faculty of Science

Geological Processes

• Epigene processes: Driven by air, wind, water, glaciers, organic activity
  • Examples: Denudation (weathering, erosion, transportation)
  • Examples: Sedimentation (mechanical, chemical, organic)
• Hypogene processes: Driven by internal Earth processes.
  • Examples: Earth movements (earthquakes, mountain building)
  • Examples: Magmatic activity (volcanic eruptions, lava flow)
  • Examples: Metamorphism (igneous and sedimentary rocks)

Weathering

• Definition: The decomposition and disintegration of rocks and minerals at the Earth's surface.
• Result: Formation of weathered material, which accumulates and overlies unweathered bedrock.

Erosion, Transportation, and Deposition

• Erosion: The removal of weathered rocks and minerals by moving water, wind, glaciers, and gravity.
• Transportation: The movement of eroded rock fragments from their source by flowing water, wind, ice, and gravity.
• Deposition: The settling of transported materials when the carrying agent (wind or water) slows down or loses energy, or when the agent melts (like glaciers).
• Processes discussed work together to modify the Earth's surface.

Weathering Types

• Mechanical weathering: Reduces solid rock to rubble but doesn't change the chemical composition of rocks and minerals.
  • Causes: Pressure-release fracturing, frost wedging, abrasion, thermal expansion/contraction, organic activity
• Chemical weathering: Occurs when air and water chemically react with rock, altering its composition and mineral content.
  • Causes: Dissolution, hydrolysis, oxidation

Mechanical Weathering Processes

• Pressure-release fracturing: Overlying rock erodes, decreasing pressure on buried rock, causing expansion and fracturing.
• Frost wedging: Water freezing in cracks expands, widening the cracks and breaking the rock apart.
• Abrasion: Mechanical wearing and grinding of rock surfaces by friction and impact (e.g., rocks tumbling in streams or glacial movement).
• Thermal expansion and contraction: Daily/yearly heating and cooling cycles cause rocks to expand and contract, leading to fracturing.
• Organic activity: Plant roots growing in cracks push rocks apart.

Chemical Weathering Processes

• Dissolution: Minerals dissolve in water, forming a solution.
  • Example: Halite (rock salt) dissolves readily in water.
  • Example: Calcite dissolves in carbonic acid, produced by carbon dioxide in water.
• Hydrolysis: Water reacts with a mineral to form a new mineral with water incorporated into its crystal structure.
  • Example: Feldspar weathering to form clay.
• Oxidation: Loss of electrons from a compound or element during a chemical reaction, often when the mineral reacts with oxygen.
  • Example: Iron oxides forming when iron-containing minerals react with oxygen.
  • Example: Sulfur reacting to form sulfuric acid.

Additional Concepts

• Spheroidal weathering: Mechanical and chemical weathering processes round boulders and other rocks.
• Salt cracking: Growth of dissolved salt crystals widens cracks and fractures rocks.
• Exfoliation: Large plates or shells of rock split away like the layers of an onion (a mechanical process often followed by chemical weathering).
• Acid rain: Sulfur dioxide reacts with water to create sulfuric acid, damaging structures and causing weathering.
• Water carries away dissolved ions, creating caves.