Overview
This lecture introduces weathering, focusing on physical (mechanical) weathering, its processes, causes, and the key role it plays in shaping landscapes and forming soil.
Introduction to Weathering
- Weathering is the breakdown of rocks and minerals at the Earth's surface into smaller pieces in situ (without movement).
- It occurs due to natural forces like wind, water, temperature changes, and biological activity.
- Weathering is a slow process that shapes landscapes, forms soil, and exposes minerals.
- Weathering is different from erosion; erosion involves movement of broken material, while weathering does not.
Types of Weathering
- There are three main types: physical (mechanical), chemical, and biological weathering.
- This lesson focuses on physical weathering.
Physical Weathering (Mechanical Weathering)
- Physical weathering breaks rocks into smaller pieces without altering their chemical composition.
- Main physical weathering agents are temperature changes, water, wind, pressure, and living things.
Types of Physical Weathering
- Freeze-thaw (Frost Wedging): Water enters rock cracks, freezes, expands, and splits the rock; common in climates with temperature fluctuations above and below freezing.
- Exfoliation (Onion Skin Weathering): Temperature-driven expansion and contraction causes outer rock layers to peel away, mostly in hot, dry regions.
- Pressure Release (Unloading): Rocks formerly buried under pressure crack and expand when exposed at the surface as overlying material is removed.
- Salt Crystal Growth (Salt Wedging): Saltwater enters rock pores, evaporates, and leaves salt crystals that grow and force the rock apart, typical in coastal and desert areas.
- Abrasion: Rocks are broken down by friction and collision with other rocks moved by water, wind, or gravity, leading to smoother, rounded shapes.
Key Terms & Definitions
- Weathering — the breakdown of rocks and minerals into smaller pieces at their original location.
- Physical Weathering — breaking rocks into smaller fragments without chemical changes.
- Freeze-thaw (Frost Wedging) — water freezing in cracks expands and splits rocks.
- Exfoliation — process where outer rock layers peel due to temperature fluctuations.
- Pressure Release — cracking of rocks after removal of overlying pressure.
- Salt Crystal Growth — salt crystals forming in rocks' pores, causing breakage.
- Abrasion — wearing down rocks by friction from particles in wind, water, or gravity.
Action Items / Next Steps
- Test your understanding by answering the quick questions provided at the end of the lesson.
- Watch the next video on chemical weathering for further learning.