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GEO 110 (47)
Chapter 9


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Ryerson University
GEO 110
David Atkinson

CHAPTER 13 LANDMASS DENUDATION • Geomorphology- science of landforms (study of orgin, evolution,form and spatial distributions) • Denudation – any process that wears away landforms or rearranges the landform materials. Ie., weathering, mass movement, erosion, transportation, deposition • Endogenic processes build initial landscapes & exogenic sequential DYNAMIC EQUILIBRIUMAPPROACH • Uplift creates the potential energy of position above sea level and therefore disequilibrium between RELIEF and ENERGY • As physical factors fluctuate in an area the surface responds in search of an equilibrium • Dynamic equilibrium – increasing or decreasing operations in a system demonstrate a trend over time a change in average conditions • Dynamic equilibrium model – the balancing act between tectonic uplift 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 • Following destabilizing events (ie.heavy rainfall) landform arrives at a geomorphic threshold • Geomorphic threshold – the point at which energy overcomes resistance against movement  system then forms new equilibrium relationships with landform • Sequence - equilibrium stability destabilizing event period of adjustment development of a new and different condion of equilibrium safety SLOPES • Material loosened by weathering is susceptible to eriosion and transportation • Gravity wants to move this material downslope erosion must overcome the forces of friction, inertia (resistance to move) and cohesion of particles to each other • Slopes – inclined surfaces • Components  waxing slope near top (convex surface curving down) free face (resistant rock that froms a steep scarp or cliff) debris slope (receives rock fragments… condition reflects climate .. lower slope=humid climate cuz water carries it away)waning slope (concave gently erosive surface) WEATHERING PROCESSES • Weathering: breaking down of rocks at earths surface and to some depth below the surface, either diintegraitng them into mineral particles or dissolive it with water • Physical OR chemical • Does not transport but just generates minerals for erosion • Upper surface of bedock undergoes continuous weathering create broken rock = regolith • Regolith continues to weather or is transported/deposited, loose surface material is formed • Bedrock – parent rock which regolith and soil develops FACTORS INFLUENCE WEATHERING PROCESS 1. Rock composition and jointing: character of bedrock? Hard, soluble, broken? Joints: fractures or separations in rock that occur without displacement of the sides increases the surface area of rock exposed to both physical and chemical weathering 2. Climate precipitation, freeze thaw cycles 3. Subsurface water- position of water table and water movement in soils 4. Slope orientation- geographic orientation- facing the sun = cooler moist slope 5. Vegetation- produces organic acids from partial decay –contribute to chemical weathering PHYSICALWEATHERING PROCESS • Rock is broken and disintegrated without any chemical alteration 1. FROSTACTION (freeze-expand-thaw-contract- action) - freezing water expandscan exceed tensional strength of rock -joint block separation caused by frost action and uses frost wedging **water filled joint water freezes expands -.=. - areas of permafrost exposed bedrock surfaces covered iwht mounds of heavy rock called rock blisters broken along joint planes into equally sized blocks 2. CRYSTALLIZATION (salt weathering) -dry weather draws moisture to the surface of rocks -water evaporates dissolved minerals in the water grow crystals -crystals grow and exert a force great enough to spread apart individual mineral grains and start breaking up the rock 3. PRESSURE RELEASE JOINTING -rising magma high pressure intrusive igneious rocks plutons -plutons cool slowly produce coarse grai
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