Geog 1113K Notes- Week 4 (Wed)
Geog 1113K Notes- Week 4 (Wed) GEOG 1113
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This 3 page Class Notes was uploaded by Victoria Koehl on Wednesday September 14, 2016. The Class Notes belongs to GEOG 1113 at Georgia State University taught by Larry Kleitches in Fall 2016. Since its upload, it has received 10 views.
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Date Created: 09/14/16
Geog 1113 Notes Braking Up is Hard to Do Part 2 Weathering is the breakdown and alteration of rocks and minerals at or near the Earth's surface by exogenic processes into products that are more in equilibrium with conditions found in this environment The exogenic system: external processes that set air, heat, and water into motion, powered by solar energy Most rocks and minerals are formed deep within the Earth's crust by endogenic processes (internal heat and plate tectonics), where temperatures and pressures differ greatly from the surface The physical and chemical nature of materials formed in the Earth's interior are characteristically in disequilibrium with conditions occurring on the surface Due to this disequilibrium, these materials are easily attacked, decomposed, and eroded by various chemical and physical surface processes Weathering works towards low relief (elevation), little change, and the stability of sequential landscapes Physical and chemical weathering processes are important to the overall reduction of the landscape and the release of essential minerals from bedrock Highways in cold climates appear rough and broken, older marble structures dissolved by rainwater, or the roundness of a rock formation A simple examination of soil gives evidence of weathered mineral grains from many diverse sources This leads to downslope movement of rock or soil as a more or less coherent gathering known as mass movement or mass wasting The erosional processes that reduce a landscape like the Grand Canyon are balanced against the resistance of the materials that make up the landscape Weathering and erosional forces naturally oscillate, especially in the desert, with high rainfall variability coming in episodic thunderstorms Denudation is a general term referring to all processes that cause reduction or rearrangement of landforms The principal denudation processes affecting surface materials include weathering, erosion, and deposition Weathering is greatly influenced by the character of the bedrock: hard or soft, soluble or insoluble, broken or unbroken; the differing resistance of rock result in differential weathering Interactions between the structural elements of the land and denudation processes are complex , and represent a constant struggle between internal and external processes The dynamic equilibrium model is a balancing act between tectonic uplift and reduction by weathering and erosion, between the resistance of crust materials and the work of denudation processes Landscapes evidence ongoing adaptation to rock structure, climate, local relief, and elevation A dynamic equilibrium demonstrates a trend over time Endogenic events (earthquakes/volcano eruptions), or exogenic events (forest fire/rainfall), may provide new sets of relationships for the landscape As changing conditions provide new sets of relationships for the landscape, the system eventually arrives at a geomorphic threshold That point at which the system breaks through to a new set of equilibrium relationships and rapidly realigns landscape materials accordingly A slope in disequilibrium goes through compensating adjustment Slopes, as parts of landscapes, are open systems and seek an angle of equilibrium among the forces described here Conflicting forces work together on slopes to establish an optimum compromise incline that balances these forces A geomorphic threshold is reached when any of the conditions in the balance is altered Many factors could alter a hillside's equilibrium such as an earthquake, or the building of a house or dam (adding mass); all the forces on the slope compensate by adjusting to a new dynamic equilibrium The relationship between rates of weathering and breakup of slope materials shapes slopes A slope is stable if its strength exceeds these denudation processes and unstable if materials are weaker than these processes Spheroidal weathering: Water penetrates joints and fractures and dissolves the rock's weaker minerals or cementing materials The resulting rounded edges are the basis for the name spheroidal weathering Spheroidal weathering is an example of the wat chemical weathering attacks rock The sharp edges of a rock are rounded as the alteration of minerals progresses through rock The joints in the rock thus offer more surfaces of opportunity for weathering Carbon compounds react with carbonic acid, created when water vapor dissolves carbon dioxide Carbonic acid is strong enough to react with many minerals, especially limestone, in a process known as carbonation When rainwater attacks formations of limestone, the constituent minerals are dissolved and wash away with the mildly acidic rainwater All mass movements occur on slopes, the steepness of a slope determines where loose material comes to rest depending on the size and texture of the grains; this is called the angle of repose, this angle represents a balance of driving and resisting forces The driving force in mass movements is gravity, working in conjunction with the weight, size, and shape of the grains or surface material, the degree to which the slope is oversteepened, and the amount and form of moisture available The greater the slope, the more susceptible the surface material is to mass movement 2 The resisting force is the shearing strength of slope material, its cohesiveness and internal friction working against mass movement To reduce shearing strength is to increase shearing stress, which eventually reaches the point at which gravity overcomes friction Four basic classifications of mass movement are used: fall, slide, flow, and creep Each involves the pull of gravity working on a mass until the critical shearing strength is reduced to the point that the mass falls, slides, flows, or creeps downward A rockfall is simply a quantity of rock that falls through air and hits a surface During a rockfall, individual pieces fall independently and characteristically form a pile of irregular broken rocks called a talus cone at the base of a steep cliff The hot eruption of Nevado del Ruiz liquefied mud and volcanic ash, sending a hot mudflow downslope Such a flow is called a lahar, an Indonesian word referring to flows of volcanic origin The lahar killed over 23,000 people in the village of Armero The last eruption occurred 140 years earlier Large openpit strip mines such as the Bingham Copper Mine and the Berkeley Pit, are examples of humaninduced mass movements, called scarification At the Bingham Copper Mine, a mountain was literally removed The disposal of tailings and waste material is a significant problem with such large excavations because the tailing piles prove unstable and susceptible to further weathering, mass wasting, or wind dispersal 3
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