The Grand Canyon is more than a mile deep. A river did most of the digging, a grain at a time, over millions of years.
Key idea
Weathering breaks rock into smaller pieces. Erosion carries the pieces away. Deposition drops them somewhere else, where they build new land.
| What does it | How |
|---|---|
| Water | rivers and waves grind rock; rain wears it |
| Ice | water in cracks freezes, expands and splits rock |
| Wind | blows sand that scrapes rock |
| Plants | roots grow into cracks and pry them open |
| Gravity | pulls rocks and soil downhill in landslides |
Rivers drop their sand and mud where they slow down, often where they meet the sea. That builds a delta, like the Nile Delta or the Mississippi Delta.
Worked example: Which is it?
Rain washes soil off a bare hillside into a stream. Weathering or erosion?
- The soil was already in small pieces.
- It is being carried away.
Answer: Erosion.
Common mistake
Thinking weathering and erosion are the same. Weathering breaks; erosion moves.
Try it at home
- Outdoors or in a tray, build a small hill of sand or soil.
- Pour water slowly from a cup at the top. Watch where it carries the sand and where it drops it.
- Do it again with a few stones and leaves pressed into the hill. Do they slow the erosion?
Going further. Weathering and Erosion and Deposition in Earth Science.