Exogenic Processes-Weathering, Erosion and Deposition 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 pieces Decomposition of rocks w/o any alteration of its through chemical reactions that change the rock-forming composition 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? 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. Exogenic Processes Erosion and Deposition RECAP: TERMS TO KNOW Erosion Deposition Abrasion Weathering VS. Erosion Weathering: the disintegration and decomposition of rock at or near the Earth surface; occurs in situ Erosion: the incorporation and transportation of material by a mobile agent Occurs as the weathering product starts moving EROSION Agents of Erosion: 1. Running Water 2. Ocean or Sea Waves 3. Glaciers 4. Wind 5. Groundwater 6. Gravity 1. Running Water Encompass both overland flow and stream flow FACTORS THAT AFFECT STREAM EROSION AND DEPOSITION: Velocity; and Discharge  1. Running Water FACTORS THAT AFFECT STREAM EROSION AND DEPOSITION: Velocity-dictates the ability of stream to erode and transport Discharge-vol. of water passing through a cross-section of a stream during a given time 1. Running Water From a cross-section: ↑ discharge, ↑width of the channel, depth of flow and velocity From headwaters to mouth: ↓Channel slope, ↓channel roughness, ↑discharge, ↑channel size, ↓flow velocity  1. Running Water Streams transport their sediment load in three ways: 1. in solution (dissolved load); 2. in suspension (suspended load); and 3. sliding and rolling along the bottom (bed load) A stream’s ability to transport solid particles is described by competence and capacity. 1. Running Water (Hjulstrom curve) Deposition occurs when river loses energy and can no longer transport such a large load. The deposits are sorted by particle size. 2. Ocean and Sea Waves Waves are classified by the generation force: wind-generated waves, tsunami, tides, seiches 2. Ocean and Sea Waves The water’s wavelength depends on the depth of the water  2. Ocean and Sea Waves Factors that influence the height, length, and period of a wave: Wind speed; Wind duration; and Fetch  2. Ocean and Sea Waves How do waves erode and move sediment along the shore? Shoreline erosion processes: (1) Hydraulic action, (2) abrasion, and (3) corrosion Transport by waves and currents: (1) Longshore current, beach drift 2. Ocean and Sea Waves  2. Ocean and Sea Waves What are the features created by wave erosion and depletion? Erosional Features: wave-cut cliff, wave –cut platform, marine terrace, headland, stacks and sea arches Depositional Features: beach, spit, baymouth bar, tombolo, barrier island 2. Ocean and Sea Waves  3. Glaciers A moving body of ice on land that moves downslope or outward from an area of accumulation Types: (1) Valley or Alpine, (2) Ice sheets or Continental glaciers, and (3) Ice shelves  3. Glaciers All glacial deposits are called GLACIAL DRIFT, and comprised of 2 types: Till; and Stratified drift  3. Glaciers The processes responsible for glacial erosion are: Plucking (lifting pieces of bedrock beneath the glacier); and Abrasion (grinding and scraping by sediments that is already in the ice)  4. Wind Wind erodes by: Deflation; and Abrasion Wind can carry sediments as: Bed load; and Suspended load  4. Wind Types of wind deposits (2): 1. Dunes-hills or ridges of wind-blown sand; and 2. Loess-extensive blankets of silt that were once carried in suspension  5. Groundwater The main erosional process associated with groundwater is solution.  6. Gravity Erosion can be influenced by MASS WASTING PROCESSES Factors: Slope Angle; Role of water; Presence of clays; and Weak materials and structures