Physical Geology Notes Essays - Environmental Soil Science

Physical Geology Notes Chapter Seven 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, & subdivision Factors of Weathering * rock type/structure- minerals: quarts & granite resistant -differential weathering based on composition & structure * slope- steep =* rapid, gradual =* slow * climate- moisture and heat promote reactions (chem. react. prev. @ =* eq.) -carbonate rocks (calcite diss.) in different regions * time- hundreds/thousands years for a few mm Soils: The part of the regolith that can support rooted plants. Formed by the weathering of bedrock: mineral component mixed with organic material. * soil horizons: identifiable succession of subhorizontal weathered zones * distinct physical, chemical, and biological characteristics * collectively known as soil profile (parent material =* surface) * O- surface organic debris * A- humus, chemical leaching * E- gray/white, present in evergreen forests (acidic soil) * B- enriched in clay produced by weathering within the horizon * K- only in arid zones (rich in calcium carbonate) * C- deepest, slight weathered parent material, lacks distinct properties, yel/brn oxidation * soil forming factors: * time * climate- rain & temperature * composition of parent material * vegetation cover * soil organisms * topography Soil Types (influence the process, classified by chem/phys properties) * polar soils- well drained, lack well-developed horizons, weak oxidation -wetter env'ts: tundra causes water-logged, organic rich soil, A not B * temperature-latitude soils- well-developed horizons, unique to env't -deciduous Affisols, evergreen Spodosols, mountainous Entisols and Inceptisols, prairie Mollisols * desert soils- no leaching produces solid, impervious layer of caliche * tropical soils- heavy weathering, leaching produces iron-rich laterite Environmental Aspects of Soils * rate of soil production: dependent on climate (in regolith, not bedrock (cw) * mod. T. & high R.- rapid, within 100s years * mod. T. & avg. R.- 100,000 years * low. T. & low. R.- millions of years * paleosols are ancient soils recorded in rock as unconformities Soil Erosion * indirect effects- lake infilling behind dams * rate of soil loss- 7% of soil lost each decade * control of erosion- soil conserving farming practices, terracing, tree planting * the world economy- soil is nonrenewable resource Chapter Eight Mass Wasting: The movement of regolith and masses of rock down slope under the pull of gravity. -No Carrier: Gravity is the primary force for mass movement. Requires slope. * role of gravity * shear stress (as slope +, tc +) -perpendicular component of gravity (perpendicular to inclined surface) holds in place -tangential component of gravity (parallel to inclined surface) causes to move * shear strength: internal resistance to movement -particle cohesion and plant roots govern * role of water -capillary attraction is cohesive until saturated (failure) Mass Wasting Processes -landslides = down slope movement of rock and/or regolith. * types of mast wasting * slope failure- sudden down slope movement of coherent masses (rocks) (dry) * sediment flows- down slope flow of mixtures (sediment, water, and air) Slope Failure * slump- down/out rotational movement on tilted concave up surface -can be annual event, associated w/ heavy rains or shock (earthquakes) * falls -rockfall- sudden free falling of detached bedrock from a steep slope -debris fall- accompanying regolith and vegetation * slides -rockslide- sudden