Weathering: Chemical alteration and mechanical breakdown of rock and sediment. * depth of air/water penetration * as distance of formation from surface rises, so does susceptibility to weathering * physical weathering: The physical breakup of rocks. * chemical weathering: The decomposition of rocks and minerals caused by stability-increasing chemical reactions. -rate of weathering positively linked to presence or absence of high mountains, and thus to plate tectonics Physical Weathering-Mechanical Processes (water, fire, roots) * development of joints- rock moved upward after erosion, causes fractures -columnar joints in igneous rock * crystal growth- salts precipitated from seeping groundwater * frost wedging- frozen seeping water * effects of heat- rocks don't conduct, spall (outer shell) breaks away * plant roots- seeds germinate in cracks Chemical Weathering-Chemical Reactions (stabilize to surface temp) * carbonic acid- rain + CO2 makes carbonic acid, frees H+ (comp. chg.)* hydrolysis- water ions replace mineral ions -decomposed potassium feldspar, kaolinite replaced* leaching- water removes soluble materials from bedrock/regolith-seeps into water, bad taste* oxidation- post-weathering iron release, goethite prod w/ hydration (O)-hematite produced w/ dehydration-intensity of color tells time/severity of weathering* dissolution- carbonic acid dissolves calcite (previously unsoluble)Results of Weathering* common rocks- granite's high silica hydrolysis=* clays & soluble min.-basalt oxidizes, limestone dissolves* conc of stable minerals- resistant to attack, @ streambeds/beaches b/c spec. grav. (cw)* weathering rinds- light colored rind surrounding a darker core of rock-composed of solid byproduct of chemical weathering* exfoliation- spalling off of outer rock shells caused by stress during weathering* spheroidal weathering- rock tendency to be rounded by weathering-weathering most effective w/ *surface area, & subdivisionFactors of ...
