Biological weathering also means organic weathering. It is the disintegration of rocks as a result of the action by living organisms. Plant and animals have a significant effect on the rocks as they penetrate or burrow into the soil respectively. Biological weathering can work hand in hand with physical weathering by weakening rock or exposing it to the forces of physical or chemical weathering.
For instance, some plants and trees grow within the fractures in the rock formation. As they penetrate into the soil, and their roots get bigger, they exert pressure on rocks and make the cracks wider, and deeper that weaken and eventually disintegrate the rocks. Microscopic organisms can also produce organic chemicals that can contribute to the rock’s mineral weathering.
Biological weathering is a very common type of weathering that we see around us. There are many small animals that bore hole in the rock and live inside it. Over the time, they burrow and widen cracks and end up breaking rocks apart. Then there are bacteria, algae and lichens produce chemicals that help break down the rock on which they survive, so they can get the nutrients they need. They produce weak acids which convert some of the minerals to clay. We, humans, are also responsible for biological weathering. As we construct more homes, industries, dams, power plants, roads, we rip the rocks apart.
According to NPS,
“Biological weathering is weathering caused by plants and animals. Plants and animals release acid forming chemicals that cause weathering and also contribute to the breaking down of rocks and landforms.“
Process and Types of Biological Weathering
Bio-chemical processes, root penetration, and animal burrowing are some of the processes determining biological weathering. Bio-chemical action plays an important role by emitting organic compounds. The organic compounds have acidifying molecules that corrode rock minerals and as such, makes them weak and prone to disintegration.
This biological action usually results in chemical weathering. The process of root penetration during plant growth exerts pressure on the rocks that subsequently breaks them apart. On the other hand, burrowing animals can break down rocks while some eats away the rock’s minerals.
Here are the three main types of biological weathering
- Growing Plant Roots
It is common to see some roots growing within the face of a rock. Well, such plant activity contributes to biological weathering. The roots of plants and trees penetrate into the soil in search of nutrients and water. As the roots penetrate the soil, they go through cracks or joints in the rocks and as they grow they progressively crack the rock apart. Bigger growing roots can also exert pressure on the adjacent rocks. Some plant roots also emit organic acids that aid to dissolve the rock’s minerals.
- Microbial Activity
Some plant microbial activity releases organic acidic compounds. These compounds can break down iron and aluminum minerals in the rocks. Microscopic organisms like algae, moss, lichens and bacteria are such kind of plants. They grow on the surface of the rocks and produce organic chemicals that are capable of breaking down the outer layer of the rock by altering the rock’s chemical composition. They release what are termed as acidifying molecules (organic acids and protons) and chelating compounds (siderophores and organic acids). The amount of biological activity that breaks down minerals depends on how much life is in that area.
As much as these compounds are produced through biological process, they arise out of bio-chemical reactions which accelerate chemical and physical weathering. Nonetheless, the process is categorized as biological weathering since it is biological in nature. Besides, these microscopic organisms also bring about moist chemical micro-environments which encourage the chemical and physical breakdown of the rock surfaces.
- Burrowing Animals
Burrowing animals such as moles, squirrels and rabbits can speed up the development of fissures. Many animals such as the Piddock shells drill into rocks for protection either by releasing acids to dissolve the rocks or fragment away the rock grains. These animal activities can create fissures in the rocks and also eats away the rock’s minerals.
As this process continues, gaps and holes develop within the rock, further exposing the rocks to chemical, biological and physical weathering. Burrowing animals can as well move the broken rock pieces to the surface and so indirectly increasing the processes of rock weathering.
- Human Activities
Human activities equally dig, crash, and widen the cracks and wind up fragmenting the rocks apart. These activities include mining, road construction, and housing developments.