Exogenic Processes - Weathering PDF

Exogenic Processes Weathering Recap: What are the possible natural agents and/or processes that can break down rocks into smaller pieces? Weathering is the breakdown of rocks at the Earth's surface, by the action of rainwater, extremes of temperature, and biological activity; it do...

Exogenic Processes Weathering Recap: What are the possible natural agents and/or processes that can break down rocks into smaller pieces? Weathering is the breakdown of rocks at the Earth's surface, by the action of rainwater, extremes of temperature, and biological activity; it does not involve the removal of rock material. Main Categories of Weathering Processes 1. Physical; and 2. Chemical Weathering usually occurs in situ (in place). Main Categories of Weathering Processes Broken into several Decomposition of rocks pieces w/o any through chemical reactions that change the rock- alteration of its forming minerals 1. Physical Weathering Processes a) Frost wedging- when water gets inside the joints, alternate freezing and thawing episodes pry the rock apart b) Salt crystal growth- force exerted by salt crystal that formed as water evaporates from pores/cracks in rocks can cause the rock to fall apart 1. Physical Weathering Processes c) Abrasion- wearing away of rocks by constant collision of loose particles d)Biological activity- plants and animals (including humans) as agents of mechanical weathering 1. Physical Weathering Processes 1. Physical Weathering Processes  Major Processes of Chemical Weathering 1. Dissolution- Dissociation of molecules into ions; example: dissol’n of salt 2. Oxidation- Reaction between minerals and oxygen dissolved in water 3. Hydrolysis- Change in the composition of minerals when they react with water Question: Is it possible for physical and chemical weathering occur simultaneously? Will it produce a synergistic effect? What are the different factors that may affect weathering? FACTORS: 1. Climate; 2. Rock type; 3. Rock structure; 4. Topography; and 5. Time 1. Climate Cold and dry=slow rate of chemical weathering High temperature and high rainfall=high rate of chemical weathering 2. Rock type Weathering rates roughly follow the inverse of the order of crystallization of minerals in the Bowen’s reaction series Therefore, the mineral/rock that crystallizes first is the less resistant, v.v 3. Rock Structure The presence of cracks where agents of weathering (water, plant roots, etc.) enter can enhance weathering 4. Topography Physical weathering occurs more quickly on a steep slope than on a gentle one (due to mass wasting) 5. Time Longer time of exposure to agents of weathering means higher rate of weathering The rock has been weakened, therefore easier to break.