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WEATHERING AND EROSION CHAPTERS 14 & 18 WEATHERING WATCH BRAIN POP • The breaking down of rock • 2 types: mechanical and chemical MECHANICAL WEATHERING • Rock is broken down by physical means • Types: – Ice wedging (freezing and expansion) – Abrasion (collision of rocks by wind, water, or gravity) – Organic activity (plant roots, digging of animals) ABRASION CHEMICAL WEATHERING • Rock is broken down due to chemical interaction with the environment TYPES OF CHEMICAL WEATHERING • Oxidationelements in rock combine with oxygen, mostly in rocks with iron (rusting) TYPES OF CHEMICAL WEATHERING • Hydrolysisreaction of minerals in rock to water, turns rock into clay TYPES OF CHEMICAL WEATHERING • Carbonation-carbon dioxide dissolves in water and creates carbonic acid (like in your soda!) • This acid causes slow break down of rock TYPES OF CHEMICAL WEATHERING • Acid precipitationwater mixes with carbon dioxide and other air pollutants • Weathers rock • Air pollutants are often from burning fossil fuels RATES OF WEATHERING DIFFERENTIAL WEATHERING: PROCESS BY WHICH SOFTER, LESS WEATHER-RESISTANT ROCK WEARS AWAY AND LEAVES HARDER, MORE WEATHER RESISTANT ROCK. • Weathering occurs very slowly • Rates depends on many factors: – Rock composition – Amount of exposure – Climate – Topography and elevation – Human activities – Plant and animal activities ROCK COMPOSITION • Rocks containing calcite weather the quickest • Rate is determined by what material holds the sedimentary grains together AMOUNT OF EXPOSURE • More exposure=faster weathering • Larger surface area exposed=faster weathering • Fractures and joints create channels for more exposure CLIMATE • Areas with alternating hot and cold seasons have fastest rate of weathering • Areas that are hot and dry have the slowest rate of weathering SOIL WATCH BRAIN POP: SOIL • Mixture of minerals, gases, water, remains of dead organisms (humus) • Soil profiles show layers of soil called horizons • Humus • Climate determines soil formation SOIL PROFILE EROSION WATCH BRAIN POP • Products of weathering are transported • Soil erosion is caused by both natural and human activities (such as some farming) • Erosion keeps crops from growing and can cause famine • Roots of plants hold the soil in place • Agents of erosion include: wind, water, gravity, glaciers GRAVITY AND EROSION Mass movements caused by gravity: rockfalls and landslides-very fast mvmt mudflows and slumps-rapid mvmt solifluction-slow, in cold regions creep-very slow mvmt LANDSLIDES SLUMP Large block of soil and rock becomes unstable and moves downhill in one piece-occurs on very steep slopes EROSION FROM WIND • Sand grains get moved by a process called saltation (bouncing of grains by wind or water). EFFECTS OF WIND EROSION • Deflation-removal of top soil and rocks • Deflation hollows-holes left from deflation • Ventifacts-rocks with smooth surfaces from wind abrasion WIND DEPOSITION • Dunes are formed when the wind slows down and drops the sand it is carrying WAVE EROSION • As wind moves over the ocean, wind produces waves and currents that erode the coastline. STRUCTURES FORMED FROM WAVE EROSION • Sea cliffs • Sea caves, arches, stacks • Terraces See pgs 452-453 STACKS SHORELINE EROSION • Force of waves will break off rock and throw the pieces back on the shore creating abrasion (mechanical weathering) • Shoreline is also chemically weathered-air and salt water are forced into cracks in the rock BEACHES • A deposit of sediment along the shore • More sediment is deposited than removed FARMING AND EROSION PREVENTION • Contour Plowing • Strip Cropping • Terracing • Crop Rotation These techniques help reduce the erosion caused by water flowing over the land. CONTOUR PLOWING TERRACING