Disappearing sandcastles
Sand is made of tiny grains of rock. Long ago, they were part of bigger rocks that broke apart. That breaking is called weathering. When the grains are picked up and carried by water or wind, that is erosion. When they stop and settle in a new place, that is deposition. A sandcastle on the beach shows all this fast. Waves pull the grains away. The wind blows dry grains off the top. Rain flattens the walls. In an hour the castle is a low hump, and in a few years the sand has moved to other places along the shore. Rocks and canyons change in the same ways, only much more slowly. Pointed shapes with sloping sides, like a wrecked castle, can be made by water and wind on real rocks too.
| When | The castle |
|---|---|
| 20 minutes before | whole |
| 1 hour after | a low hump |
| 10 years after | flat sand |
| What happens | Process |
|---|---|
| waves pull sand away | erosion |
| sand settles in a pile | deposition |
| stone crumbles | weathering |
Tray sandcastle (a grown-up is near). Fill a baking tray with damp sand and build a small castle. Draw it. Now spray it gently with a water bottle like rain, then slowly pour a little water at one edge like a wave. Draw it again after one minute and after five minutes. Where did the sand go? Write which step was weathering, erosion or deposition. Wash your hands afterwards.