Biological Weathering

1. Biological Weathering Presented to you by: Amelia Lau, Brillia Soh, Sara Ang & Claudia Cheng

2. Definition • RBiological Weathering involves the disintegration of rock and mineral due to the chemical and/or physical agents of an organism. The types of organisms that can cause weathering range from bacteria to plants to animals. • For example, burrowing animals dig tunnels which allow both water and gases to enter, attack rocks and expand existing cracks. • Organisms in the soil such as earthworms and other insects respire, during which carbon dioxide is given out. When they die and decompose, carbon dioxide and organic compounds are released. These gases dissolve in the water present in the soil to form weak acids, which weaken and break rocks down b chemical processes.

3. Definition In short, The breaking down of rocks by living organisms

4. Factors affecting the type of weathering • Rock strength and hardness • Minerals formed under high temperature and pressure weather most quickly because they are ‘furthest’ from the conditions in which they were formed. Some rocks are ‘harder’ than others. • Chemical composition • The presence of silicate minerals is important. More stable minerals tend to be lighter in colour. • Rock texture • ie. coarse grained or fine grained. In finer grained rocks, the bonding is stronger, but the boundaries between crystals form lines of potential weakness or cleavage. Fine grained rocks often weather quicker.

5. Joints and bedding planes • : allow access by water: limestone is said to have a massive structure. Vegetation type • Topography • : slope angles, and aspect

6. Example of locations where Biological Weathering is found  Biological weathering of lava by lichen La Palma

7. Limpets and barnacles eroding limestone • Biological weathering is an important form of rock breakdown on rocky coasts. • Many organisms, such as barnacles and limpets, secrete organic acids that help to dissolve the rock. • This is especially important in rock pools, where there is only a small amount of water. • This means that the water can become quite acidic and break down the rock. • It most commonly affects limestone and chalk, although it is also important for its effects on granite.

8. Piddock shells • Many animals, such as these Piddock shells, bore into rocks for protection either by scraping away the grains or secreting acid to dissolve the rock.

9. Trees put down roots through joints or cracks in the rock in order to find moisture. As the tree grows, the roots widen and deepen the cracks and gradually prize the rock apart. As roots grow in size, they Eventually, the roots physically break the rocks apart.

10. Even the tiniest bacteria, algae and lichens produce chemicals that help break down the rock on which they live, so they can get the nutrients they need.

11. Photographs!