5.7.2 Erosion

What is Erosion?

It means the moving of broken-down rocks, soil, and sediments from one place to another.

The moving is done by natural forces — mainly flowing water and wind .

Example

• Have you noticed fine sand on riverbeds or in lakes?
• This sand did not appear by accident.
• It was formed elsewhere and then moved here by flowing water.
• The whole process is called erosion .

Why Erosion is a Physical Change

During erosion, no new substance is formed .

The rocks and soil only move from one place to another.

Their shape may also wear down.

So erosion is a physical change .

Examples of erosion

• A landslide
  • Soil and rocks slide down a hill in a single moment.
  • This is a dramatic example of erosion.
• Smooth river pebbles
  • Pebbles in a river look smooth and rounded.
  • Flowing water keeps rubbing them against each other.
  • Rough edges slowly wear off over years.
• Sand on beaches
  • Wind and waves carry sand grains and deposit them along coasts.

How Erosion Eventually Forms New Rocks

The journey of broken-down material has many steps.

Step-by-step process

• Step 1 — Wind or water slows down.
  • For example, where a river meets the sea, the water slows.
  • Where wind speed drops, the wind also slows.
• Step 2 — The carried material settles.
  • Sand, soil, and small pebbles drop to the bottom.
  • This is called deposition .
• Step 3 — The settled sediments harden.
  • Over thousands of years, layers pile up.
  • The pressure from the layers above compresses the lower layers.
• Step 4 — New rocks are formed.
  • The hardened sediments slowly become new rocks.

The full cycle

• Weathering → Erosion → Deposition → New rocks.
• The full cycle takes millions of years .
• It cannot be reversed at any human timescale.