Weathering vs. Erosion

Weathering

• Definition: The breakup of rock due to exposure to processes that occur at Earth's surface.
• Types:
  1. Physical Weathering
  2. Chemical Weathering

Erosion

• Definition: The removal, transportation, and deposition of sediment.

Physical Weathering

• Definition: Splits or breaks rocks into smaller pieces of the same material without changing its composition.
• Creates Sediments: Boulder, Cobble, Pebble, Sand, Silt, Clay.
• Types of Physical Weathering:
  1. Frost Wedging: Water in cracks freezes and expands, breaking the rock.
     • Example: Potholes.
  2. Root Wedging: Roots grow into cracks, expanding and breaking the rock.
  3. Animal Burrowing: Animals dig and expose rock to elements, further breaking it apart.
  4. Abrasion: Moving sediment in ice, water, or wind scrapes against rocks.
     • Water Abrasion: Tumbling action rounds pebbles.
     • Ice Abrasion: Glaciers create striations on rocks.
     • Wind Abrasion: Creates ventifacts, smoothed rocks with several faces.
  5. Expansion Cracking: Due to wetting/drying, heating/cooling, pressure release/exfoliation.
     • Examples: Mud cracks, Columnar Joints (e.g., Giant's Causeway).
     • Exfoliation: Removal of outer rock layers.

Chemical Weathering

• Definition: Changes a rock's minerals into different substances through chemical reactions.
• Types of Chemical Weathering:
  1. Oxidation: Reaction with oxygen, especially effective on iron minerals (rust).
     • Example: Desert varnish.
  2. Hydrolysis: Water reacts with minerals, e.g., feldspar turning into clay.
  3. Dissolving: Leads to formations like sinkholes.
  4. Carbonic Acid: CO2 in rainwater creates acid that weathers rocks like marble and limestone.
     • Example: Acid rain affects trees and monuments.

Factors Affecting Weathering Rates

1. Climate: Hotter and wetter climates increase chemical weathering; colder climates increase physical weathering.
2. Composition of the Rock: Igneous/metamorphic rocks are generally tougher.
3. Surface Area/Exposure: More surface area leads to more weathering.

Case Study: Cleopatra's Needle (Granite)

• Based on its composition and the climate of NYC, specific types of weathering can be analyzed.