Physical Weathering | Second Quarter | Lesson 1 | Earth Science

Summary

This video lesson covers the concept of physical weathering, explaining how rocks and minerals break down without changing their chemical composition. It details various types of physical weathering, including frost wedging, salt crystal growth, abrasion, biological activity, exfoliation, and heat-cold cycles. Each type is described with examples, such as how water expansion causes frost wedging or how roots of plants can break rocks. The lesson highlights how different natural forces and organisms contribute to the physical breakdown of rocks, setting the stage for deeper understanding in future discussions.

Takeaways

• 🌍 There are two main types of weathering: physical (also called mechanical) and chemical.
• 🪨 Physical weathering involves the breakdown of rocks and minerals without changing their chemical composition.
• ❄️ Frost wedging occurs when water fills cracks in rocks, freezes, expands, and breaks the rock apart through pressure.
• 💧 Freeze-thaw cycles continuously break rocks as water freezes, expands, and thaws repeatedly.
• 🧂 Salt crystal growth causes physical weathering as salt crystals precipitate in cracks and exert pressure, leading to rock disintegration.
• 💨 Abrasion happens when rocks or sediments bump into each other, causing friction that breaks them down. It can be caused by wind, water, or gravity.
• 🐾 Biological activity, such as animals digging or plant roots growing, can physically break down rocks.
• 🐚 Certain organisms, like bivalves, can also contribute to the breakdown of rocks through physical processes.
• 🪨 Exfoliation occurs when pressure is reduced on rocks, often due to erosion, causing the outer layers to peel off.
• 🌡️ Heat and cold cycles cause the expansion and contraction of rocks, leading to their breakdown over time.

Q & A

What is physical weathering?

Physical weathering is the process of breaking down rocks and minerals into smaller pieces without changing their chemical composition. It is also known as mechanical weathering.

What is frost wedging and how does it contribute to physical weathering?

Frost wedging occurs when water fills cracks in rocks, freezes, and expands. This expansion exerts pressure on the rock, causing it to break into smaller pieces over time, especially during repeated freeze-thaw cycles.

How does salt crystal growth cause physical weathering?

Salt crystal growth happens when salt crystals precipitate from water and grow within the cracks of rocks. As the crystals expand, they exert pressure on the rock, eventually causing it to break apart.

What is abrasion, and how does it lead to the breakdown of rocks?

Abrasion occurs when rocks or sediments bump into each other due to forces like wind, water, or gravity. This constant friction causes the rocks to break down into smaller particles over time.

How can biological activity contribute to physical weathering?

Biological activity, such as animals digging or plants growing roots into cracks, can break rocks apart. This activity exerts physical pressure, causing the rocks to fragment.

What is exfoliation, and what causes it?

Exfoliation is the process where the outer layers of rock peel off due to a reduction in pressure. This happens when overlying materials are removed, exposing the rock beneath and causing it to break down due to the release of pressure.

How do heat and cold cycles contribute to physical weathering?

Heat and cold cycles cause rocks to expand and contract. This repeated expansion and contraction weakens the structure of the rock, leading to its breakdown over time.

What is the difference between physical and chemical weathering?

Physical weathering involves breaking down rocks without altering their chemical composition, while chemical weathering involves changes to the rock’s chemical structure due to reactions with water, air, or other substances.

Can flowing water cause physical weathering through abrasion?

Yes, flowing water can cause physical weathering by carrying sediments that abrade the surface of rocks, causing them to wear down and break apart.

What role does pressure play in the exfoliation process?

Pressure plays a key role in exfoliation. When the pressure on a rock is reduced, such as when overlying layers are eroded, the rock expands and its outer layers peel off, leading to weathering.