Earth Science with Lab

1 Weathering, Erosion, and Deposition Weathering refers to the chemical, physical or biological processes through which rocks are broken down into smaller fragments. Weathering occurs on rocks that are exposed to the atmosphere, water, or chemical substances. Physical weathering is associated with various factors including frost action, which is the freezing and melting of water, plan action whereby large roots form cracks on rocks causing them to disintegrate, and exfoliation whereby the pressure of overlying rocks and other materials is removed (National Geographic, 2020).

Temperature gradient has been cited as a significant contributor to rock weathering. Huissteden (2020) noted that low soil temperatures in conjunction with the repeated formation of ice influence the weathering of rocks. Temperature changes lead to the contraction and expansion of rocks which eventually disintegrate into tiny pieces (National Geographic, 2020). The image below represents weathering contributed by frost action.

Fig 1: Weathering due to frost action (National Geographic, 2020).

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2 Swiftly moving water in streams can also cause the weathering of rocks. In such cases, rapidly moving water lifts rocks that drop on other rocks and break into smaller pieces. Chemical weathering is associated with the changes in the chemical composition of rocks leading to the weakening of these rocks (Perdrial, Dere, West & Sullivan, 2020). This form of weathering usually occurs when water, oxygen, and carbonic acid react with the minerals in rocks. The key environmental implication of rock weathering is the change in the rocky landscape of the earth.

Weathering has resulted in the formation of the Grand Canyon in Arizona (National Geographic, 2020).

Erosion differs from weathering since it describes the process through which natural forces such as wind, water gravity, and ice transport soil and rocky fragments from one location to another (Perdrial, Dere, West & Sullivan, 2020). Erosion takes lace at the earth’s surface and does not lead to physical or chemical changes of the materials transported. Unlike, weathering where materials remain at the point of disintegration, eroded materials are displaced from their original location to other places. The five main agents of erosion are mass wasting, wind erosion, ocean erosion, glacial erosion, and water erosion (Slaymaker, 2020). In mass wasting, sediments move downhill under the influence of gravity. The main environmental implications of soil erosion include the loss of topsoil, formation of huge gullies, land degradation due to reduced organic matter, increased soil acidity and soil compaction (Huissteden, 2020). Erosion has played a huge role in the formation of the Grand Canyon in the United States.

Fig 2: Erosion leading to gullies (New South Wales gov, 2019).

3 Deposition, on the other hand, describes the process by which rocky materials, soil, and other sediments are released from an erosional system (Kanji, He & Sousa, 2019). The sediments usually settle on flatter surfaces where the influence of the factors contributing to erosion has minimal effect. This implies that deposition occurs once the velocity of the transporting agent decreases. The deposition process is influenced by several factors including the size, shape, and density of the sediments (Kanji, He & Sousa, 2019). Larger materials are likely to settle faster than smaller materials. Sediments that have a higher density and are spherical are also likely to have a faster settling rate. The image below shows the deposition of materials along the banks of a stream.

Fig 3: Alluvium Deposited in a Stream (American Geosciences Institute, 2020).

The deposition has significant effects on the environment. For instance, it leads to the loss of important aquatic habitats (Slaymaker, 2020). Deposition of soil, debris and rocky materials in rivers and lakes may also raise the water levels causing flooding in low-lying regions.

4 References American Geosciences Institute (2020). What is river and stream erosion? https://www.americangeosciences.org/education/k5geosource/content/rocks/what-isriver-and-stream-erosion Huissteden, J., (2020). Thawing Permafrost: Permafrost Carbon in a Warming Arctic. Springer Nature.

Kanji, M., He, M., & e Sousa, L. R. (Eds.). (2019). Soft Rock Mechanics and Engineering.

Springer Nature.

National Geographic (2020). Weathering. https://www.nationalgeographic.org/encyclopedia/weathering/ New South Wales gov. (2019). Gully erosion. https://www.environment.nsw.gov.au/topics/landand-soil/soil-degradation/gully-erosion Perdrial, J., Dere, A., West, N., & Sullivan, P. L. (Eds.). (2020). Critical Zone (CZ) Export to Streams as Indicator for CZ Structure and Function. Frontiers Media SA. Slaymaker, O. (2020). Landscapes and Landforms of Eastern Canada. Springer Nature.