Spheroidal weathering, also known as “balls and bowls” or “onion skin” weathering, is a type of breakdown process that occurs in rocks that are composed of layered minerals or that have a layered structure.
It is characterized by the formation of small, spherical or ellipsoidal pits or depressions on the surface of the rock, which are surrounded by concentric layers or rings.
How does spheroidal weathering occur?
It is most commonly found in humid, temperate regions where there are large fluctuations in temperature and moisture levels. It can also occur in other climates, but it is less common in dry or arid regions.
Therefore, it is thought to be caused by the expansion and contraction of the rock layers due to changes in temperature and moisture levels. It occurs when the corners and edges of rocks become rounded over time.
As the rock expands and contracts, the outer layers are subjected to stresses that can cause them to crack and peel away from the underlying layers. This process creates the characteristic pits and layers that are characteristic of this type of weathering.
It is commonly observed in sedimentary rocks such as sandstone and shale, and it is most commonly found in humid, temperate regions where there are large fluctuations in temperature and moisture levels. It can also be found in some metamorphic rocks, such as slate, and in some volcanic rocks, such as basalt.
It can have important implications for the stability and strength of rock structures, as the pits and layers that are formed can weaken the rock and make it more prone to erosion and collapse.
It can also play a role in the supply of nutrients to ecosystems, as this process can release minerals and other nutrients that are essential for plant growth and other biological processes.
What is the difference between spheroidal and exfoliation weathering?
This and exfoliation weathering are both types of breakdown processes that occur in rocks that are composed of layered minerals or that have a layered structure. However, they are distinct processes with different characteristics and effects.
Exfoliation weathering, also known as “sheet” weathering, is a type of process that is characterized by the peeling or flaking away of the outer layers of rock.
This process is caused by the expansion and contraction of the rock layers due to changes in temperature and moisture levels, and it results in the formation of thin, flat sheets or layers on the surface of the rock.
It is most commonly found in regions with high temperatures and low humidity, where there are large fluctuations in temperature and relatively little moisture.
Overall, the main difference between spheroidal and exfoliation weathering is the shape and size of the features that are formed on the surface of the rock.
Spheroidal weathering is characterized by the formation of small, spherical or ellipsoidal pits, while exfoliation is characterized by the formation of thin, flat sheets or layers.
Both processes can weaken the rock and make it more prone to erosion and collapse, and they can also release minerals and other nutrients that are essential for plant growth and other biological processes.
Frequently Asked Questions
1. What is onion skin weathering? What is it also known?
It, also known as spheroidal or concentric weathering, refers to a specific type of physical breakdown. It occurs when the outer layers of rocks peel or flake off, resembling the layers of an onion.
This process is typically driven by temperature changes, especially in arid or desert environments, where intense heating during the day and rapid cooling at night cause the outer layers of the rock to expand and contract.
Over time, this repeated expansion and contraction lead to the detachment of thin layers, resulting in the characteristic layered appearance.
2. How can a large block of granite form layers like an onion?
A large block of granite can develop layers that resemble an onion through a geological process known as exfoliation. It occurs when pressure is released from the underlying rock layers, causing the outer layers of the granite to expand and crack.
Over time, these cracks propagate inward, leading to the peeling or flaking of successive layers, creating the appearance of concentric layers akin to an onion.
3. What formed the “pits” in the rock?
The “pits” in the rock can be formed by various natural processes. One common cause is erosion, where wind, water, or ice gradually wear down the surface of the rock, creating hollows or depressions.
Another factor is chemical weathering, where substances like water or acids dissolve certain minerals within the rock, leaving behind pits or cavities.
Biological activity, such as the action of burrowing animals or the growth of plant roots, can also contribute to the formation of pits in the rock.
