Geological Society - Erosion and Transport
Weathering describes the chemical and physical decomposition of rocks and minerals In contrast, erosion involves the entrainment and transport of rock and evolved view of the relationship between these processes and the concept of the. Erosion involves removal of solid material by a transporting agent. Weathering is the breakdown of rock into fragments at the Earth's surface. No movement is. Geomorphology is the study of the nature and origin of landforms, particularly of the formative processes of weathering and erosion that occur in the atmosphere.
Generally, higher, or tectonically active areas with steeper slopes have more dynamic weathering systems, whereas flat plains have slower weathering systems. Weathering Products Weathering gradually weakens rocks, and eventually produces new geological materials rock fragments, sands, silts and clays that are more stable in the new environment.
Weathering generally produces finer and less dense rock materials, and weaker, more porous and permeable rock masses. In the tropics and subtropics, intense weathering in the hot and humid conditions produces thick weathered profiles, which may be up to metres, or more, thick. Weathering processes penetrate down discontinuities planes of weaknesssuch as faults and joints, in the rock mass and then attack the faces of the joint-bounded blocks, penetrating the solid blocks Figure 3.
Weathering preferentially attacks the corners and edges of the joint blocks, causing them to become rounded. This action is assisted by stress release, which causes the rock to flake into curved shells in a process termed exfoliation Figure 4.
Weathering vs. Erosion
Rounded corestones with curved exfoliation shells in a weathered quartz monzonite. Vertical joints in granite widened by weathering. Weathering of tuff highlighting the joint pattern. Differential weathering of a volcanic rock, emphasising the joint pattern and components.
Weathering of some rock types, such as the granitic rocks and the coarse ash tuffs, results in the development of thick weathered profiles that are characterised by rounded boulders corestones set in a matrix of weak, silty, clayey, sandy material.
These corestone-bearing profiles are a distinctive feature of many cut-slopes in the urban areas of Hong Kong Island and Kowloon Figure 5. The downward limit of weathering may be irregular and diffuse, but in many cases terminates abruptly at a well-defined horizon Figure 6. This boundary is termed the weathering front by geomorphologists, or rockhead by engineers Figure 7.
The components of a typical corestone-bearing weathered profile in granitic rocks. Tabular corestones in a weathered profile in medium-grained granite. An abrupt, planar weathering front in volcanic rock. Erosion Erosion is the removal transport of weathered rock materials downslope, and away, from their original site of weathering. Erosion processes are driven primarily by the force of gravity, which may be aided by a flowing medium such as water e.
Wind can also remove weathered materials e. During transportation of the weathered rock materials, the angular particles commonly abrade rub or scour the surfaces over which they pass, wearing away and lowering the rocks. Thus, landslide debris may erode the slope or channel along its course, the sediments in rivers erode the rocky sections of their beds, and the rock fragments in glaciers erode the valley floor.
Erosion Processes Erosion processes are usually considered under four distinct categories: Mass wasting, or landsliding see belowprocesses are very important in Hong Kong Figure 8. Fluvial processes are very important in Hong Kong. The erosional effects of wind play only a small role in Hong Kong.
Glacial processes do not directly affect Hong Kong.
What Are The Differences Between Weathering And Erosion?
Erosion Controls The type and magnitude of erosion depends upon several factors including: This, combined with the steeper slope angles, results in more dynamic erosion in upland areas than on the surrounding plains. Within the same climatic regime, each rock type responds differently to weathering and erosion, exhibiting a characteristic resistance or weakness to the prevailing conditions.
Thus, some rocks are relatively resistant and form higher ground, whereas others are less-resistant and form valleys and lowlands. Consequently, these softer weathered materials are more easily eroded out, with the result that river valleys are usually located along the line of a major fault or joint set.
Channelised debris flows confined to steep and narrow seasonal stream channels. Deep erosion gullies dissecting narrow ridges in deeply weathered granite.
Weathering, Erosion, and Deposition
Erosion Products The rock and soil materials transported by erosion processes are eventually deposited in the sea, although they may be temporarily deposited in other locations such as below cliff faces e. Over the millennia, the topography of an area is sculptured by the processes of erosion, from an original mass of folded or uplifted rocks into a complex of mountain summits, intervening valleys, and surrounding plains.
Gravity causes landslides on hillsides, flowing water erodes gullies and shallow stream courses Figure 11and joint-bounded blocks of rock fall from cliff faces building up screes. On lower ground, rivers carve valleys and deposit floodplain sediments.
Below the ground surface, in soluble rocks such as limestone, water erodes passages, caves and shafts. The process of erosion has four major stages: Detachment, where the rocks break into small particles.
Entrainment, where the rock sediments mix with water, air or melting ice. Transportation through one of the forces of nature. Deposition, which means where the particles settle. Relationship Between Weathering And Erosion In looking at the differences between weathering and erosion, it is imperative to understand that weathering can be chemical, physical or biological while erosion is purely the movement of sediments from one place to another, evidently, weathering usually leads to erosion as it breaks down rock particles to sizes that natural forces can transport.
Weathering is unstoppable, but humans have since found ways to reduce erosion through mitigation by building gabions or planting trees. Advantages Of Weathering And Erosion Both weathering and erosion lead to the formation of new geological features through surface reshaping.
Weathering provides particles that eventually form sedimentary rocks like limestone and sandstone, plus, chemical weathering helps in reducing atmospheric carbon dioxide. If weathering did not exist, the earth would consist of bare rocks unable to support flora and fauna.
Most of the fertile soils are products of weathering process. Soil erosion deposits soil rich in minerals to places that were not fertile, making them agriculturally productive.
- Weathering vs. Erosion
- Erosion and Transport
- Weathering & Erosion - Introduction to Geomorphological Processes
Disadvantages Of Weathering And Erosion Weathering is a leading cause of breaking down of human-made structures like roads, bridges, and houses. Chemical weathering also results to a process called oxidation which is responsible for rusting.
Weathering and erosion may cause natural disasters through mass wasting like rockslides and mudslides that kill hundreds of people annually. The same weathering and erosion processes that are responsible for creation and deposition of fertile soils are also responsible for removing fertile soils from an area leaving the area agriculturally crippled.
This page was last updated on August 28, By Benjamin Elisha Sawe.