Variations in rock type greatly influence the rate and type of weathering in coastal environments. Different rocks possess distinct physical and chemical properties, making some more susceptible to certain weathering processes than others. For instance, limestone and chalk, being soluble, are highly susceptible to chemical weathering processes like carbonation. In contrast, granite, being more resistant, is less affected by chemical weathering but can be subject to physical weathering processes like freeze-thaw. Sedimentary rocks, often layered and less cohesive, can be prone to mechanical disintegration and biological weathering. The rate of weathering is also affected; softer rocks like chalk and sandstone weather more quickly compared to harder rocks like granite. These variations lead to diverse coastal landscapes, with different rock types giving rise to distinct coastal features such as cliffs, stacks, and wave-cut platforms, each shaped by the dominant weathering processes acting upon them.

Human activities can significantly affect sub-aerial processes in coastal areas. Urbanisation, construction, and coastal engineering projects can alter the natural landscape, impacting both weathering and mass movement processes. For instance, construction of buildings or roads on cliff tops can increase the weight on the land, exacerbating processes like soil creep, landslides, or rockfalls. Altering natural drainage patterns through construction can increase the risk of mudflows, especially during heavy rainfall. Additionally, removal of vegetation for urban development or agriculture can accelerate erosion and mass movement, as plant roots that bind the soil and rock are eliminated. Pollution can also impact chemical weathering rates, particularly in areas where acid rain is prevalent. Overall, human interventions in coastal areas can significantly disrupt the natural equilibrium of sub-aerial processes, often leading to increased rates of coastal erosion and landscape change.

Chemical and biological weathering, while distinct, often interact synergistically in coastal environments. Chemical weathering involves the breakdown of rocks through chemical reactions, such as hydrolysis, oxidation, and carbonation. For instance, carbonation occurs when carbon dioxide in rainwater reacts with calcium carbonate in limestone, leading to the rock's dissolution. On the other hand, biological weathering involves the physical or chemical breakdown of rocks by living organisms. Plant roots can grow into cracks and fissures in rocks, prying them apart (physical), and organic acids from plants or microorganisms can chemically alter the rock's composition.

In coastal environments, these processes often work together. For example, plant roots may penetrate rocks (biological weathering), creating pathways for water and chemicals to penetrate deeper and react with the rock (chemical weathering). This interaction accelerates the weathering process, leading to more rapid disintegration of coastal rocks and influencing the formation and evolution of coastal landforms.

Temperature variation significantly influences physical weathering, especially through processes like thermal expansion and contraction. In coastal environments where the temperature fluctuates dramatically between day and night, rocks undergo considerable stress. During the day, the outer layers of the rock expand due to the heat. At night, these layers contract as temperatures drop. This constant expansion and contraction leads to the formation of cracks and ultimately, the breaking away of rock fragments. In arid coastal regions, this process is particularly pronounced, leading to exfoliation or sunburst weathering. Over time, this contributes to the formation of distinct coastal features like smooth, rounded rock surfaces and the gradual retreat of cliffs. The intensity of this weathering process depends on the rock type, with some rocks being more susceptible to temperature changes than others.

Sub-aerial processes play a crucial role in the formation and evolution of specific coastal landforms like caves, arches, and stacks. While these features are initially formed by marine processes like erosion and wave action, sub-aerial processes like weathering and mass movement contribute significantly to their development and eventual disintegration.

For instance, once a cave is formed by wave action, weathering processes (especially chemical weathering in the case of limestone caves) can further enlarge the cave. Arches formed through the erosion of headlands are subject to intense weathering and mass movement at their tops, which can weaken the structure over time. The eventual collapse of an arch, leading to the formation of a stack, is often the result of these sub-aerial processes. Freeze-thaw action can cause fragmentation at the top of a stack, while wind erosion can further shape its appearance. Mass movement processes, such as rockfalls or slumps, can lead to the gradual breakdown of these features, continuously reshaping the coastal landscape. Therefore, while the initial formation of these landforms might be due to marine action, their ongoing change and eventual demise are largely influenced by sub-aerial processes, illustrating the dynamic interaction between various environmental forces in shaping coastal geographies.