Chapt 15-Preliminaries to Erosion

Chapt 15-Preliminaries to Erosion - Chapter 15...

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Chapter 15: Preliminaries to Erosion: Weathering and Mass Wasting I. The Impact of Weathering and Mass Wasting on the Landscape A. denudation : overall effect of disintegration, wearing away, and removal of rock material lowering of continental surfaces B. denudation accomplished by the interaction of 1. weathering 2. mass wasting 3. erosion C. weathering and mass wasting often de-emphasized, but they play a critical role in landform modification: most of what one sees in the Grand Canyon are forms produced by weathering and mass wasting II. Weathering A. intro 1. weathering : mechanical disintegration and/or chemical decomposition that destroys the coherence of bedrock and begins to fragment rock masses into progressively smaller components a. 1 st step in shaping Earth’s surface by external forces b. occurs wherever the lithosphere and atmosphere meet c. wherever bedrock is exposed, it weathers 1) changes in color and texture 2) looser and less coherent than the underlying rock 2. 5 types of openings in rock that provide avenues for penetration by weathering agents: a. microscopic spaces b. joints 1) cracks that develop as a result of stress 2) show no appreciable rock displacement 3) most important of all rock openings in facilitating weathering c. faults 1) cracks in bedrock along which there is relative movement 2) allow easy penetration of weathering agents d. lava vesicles: holes that develop in cooling lava when gas is unable to escape as the lava solidifies e. solution cavities: holes formed in calcareous rocks (particularly limestone) as the soluble minerals are dissolved and carried away by percolating water B. Jointing 1. almost all lithospheric bedrock is jointed 2. causes: a. contractive cooling of molten material b. contraction of sedimentary strata as they dry c. diastrophic tension 3. usually arranged in sets of parallel fractures C. Weathering Agents 1. intro – weathering agents: Chapter 15: Preliminaries to Erosion: Weathering and Mass Wasting – p. 1 of 5
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a. most weathering agents are atmospheric: 1) gases easily penetrate cracks and crevices 2) oxygen, carbon dioxide, and water vapor b. temperature changes are a second important weathering agent c. water d. biotic agents (burrowing, roots) 2. 3 categories of weathering (usually acting in concert): a. Mechanical Weathering 1) physical disintegration of rock material without any change in its
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Chapt 15-Preliminaries to Erosion - Chapter 15...

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