1) Phenomena Contributing to Physical Weathering
a) Freeze-Thaw Cycle (Frost Wedging):
This process occurs when water seeps into cracks in rocks and subsequently freezes. As water freezes, it expands by about 9%, exerting significant pressure on the surrounding rock. This pressure can cause the rock to fracture and break apart over time. With repeated freeze-thaw cycles, the cracks can become larger, leading to the disintegration of the rock into smaller clasts.
b) Thermal Expansion and Contraction:
Rocks can also weather physically through thermal expansion and contraction. When rocks are heated (for example, by the sun during the day), they expand; when they cool down (at night), they contract. This repeated cycle of heating and cooling can induce stress in the rock, leading to the formation of cracks and eventual fragmentation.
2) Common Reactions in Chemical Weathering
a) Hydrolysis:
Hydrolysis is a chemical reaction where minerals react with water to form new minerals and soluble ions. An example is the reaction of feldspar (a common mineral in granite) with water, resulting in the formation of clay minerals and dissolved ions. This process alters the original mineral structure and contributes to the breakdown of the rock.
b) Oxidation:
Oxidation occurs when minerals, particularly those that contain iron, react with oxygen in the presence of water. This process leads to the formation of oxides and hydroxides, which can weaken the structural integrity of the original minerals. For example, iron-bearing minerals can oxidize to form rust (iron oxide), resulting in the reddish-brown color seen on weathered rocks and contributing to their deterioration.
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