1.3.1.1. Physical Weathering

Physical weathering reduces the size of the parent rock material, without any change in the original composition of the parent rock.

Physical weathering refers to the process where large rock formations break down into smaller pieces without changing their chemical structure. This means that although the physical size of the rock alters, its mineral content remains the same. For example, if a large boulder splits into smaller fragments, those fragments are still made of the same materials as the original boulder.

Imagine a chocolate bar. If you break it into smaller pieces, the chocolate itself hasn’t changed—it’s just in smaller sizes. Similarly, in physical weathering, rocks break down but retain their original materials.

Physical or mechanical processes taking place on the earth's surface include the actions of water, frost, temperature changes, wind and ice. They cause disintegration and the products are mainly coarse soils.

Several processes facilitate physical weathering. Water can seep into cracks of rocks and freeze; the ice expands and causes the rock to crack further. Temperature changes cause rocks to expand when heated and contract when cooled, leading to stress and fractures. Wind can erode rock surfaces, and ice can grind against them. These actions produce smaller fragments, constituting coarse soils.

Consider a sponge left outside in the winter. When water seeps into its pores and freezes, it expands and can cause the sponge to crack. Each freeze-thaw cycle can wear it down, similar to how rocks are weathered by these natural processes.

The main processes involved are exfoliation, unloading, erosion, freezing, and thawing.

Exfoliation refers to the process where layers of rock peel away due to temperature changes causing expansion and contraction. Unloading occurs when overlying materials are removed, relieving pressure on deeper rocks, causing them to break apart. Erosion involves the removal of weathered material by natural forces such as water, wind, and ice, leading to further breakdown of rocks.

Think of an onion. The layers can be peeled away without destroying the onion itself. This is similar to how exfoliation removes layers from a rock. Meanwhile, consider how riverbanks erode through constant water flow—this constant action breaks down soil and rock over time.

The principal cause is climatic change. In exfoliation, the outer shell separates from the main rock. Heavy rain and wind cause erosion of the rock surface.

Climatic changes, such as variations in temperature and precipitation, significantly impact physical weathering. For instance, in a hot climate, rocks can heat up and, at night, cool down rapidly. This fluctuation can cause layers to crack off. Heavy rain and strong winds can exacerbate erosion by washing away and wearing down rock surfaces more swiftly.

Consider how your car's paint fades over time from sun exposure and rain. Similarly, rocks are affected by weather conditions; consistent temperature swings and rain can 'wear down' these surfaces over years, leading to more substantial weathering.

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