Weathering

Rocks do not stay the same forever. They get worn away slowly. Rain, wind, frost and temperature changes can all wear away rocks.

When rocks are worn away by these things we call it weathering.

Chemical weathering

Rainwater is slightly acidic. When rainwater attacks limestone a chemical reaction takes place. This is an example of chemical weathering.

Limestone is made of calcium carbonate. When acid reacts with it, carbon dioxide gas, water and a salt are produced. 

The carbon dioxide gas goes into the air and the other products are washed away by the rain.

Rain is a very weak acid so the reaction is only very slight. It takes many years to notice the differences caused by the limestone.

Physical weathering

Water gets into the spaces and cracks in rocks. When this water freezes, it expands. 

This makes the cracks larger. When the water melts the larger cracks are left.

When this happens many times the rocks are broken up. This is an example of physical weathering.

The heat of the Sun can make rocks expand. At night the temperature falls and the rock contracts.

When this happens over and over again the rocks can crack.

Wind and running water can wear away rocks. Rocks are made smooth by water running over them.

Biotic weathering

Living organism can cause rocks to break apart. This is called biotic weathering.

Plants can grow in the cracks in rocks. The growth of the plant’s roots causes cracks and damage to the rocks.