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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)
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Weathering and Erosion Chapters 14 & 18
WeatheringWatch 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)
Chemical Weathering • Rock is broken down due to chemical interaction with the environment
Types of Chemical Weathering • Oxidation-elements in rock combine with oxygen, mostly in rocks with iron (rusting)
Types of Chemical Weathering • Hydrolysis-reaction 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 precipitation-water mixes with carbon dioxide and other air pollutants • Weathers rock • Air pollutants are often from burning fossil fuels
Rates of WeatheringDifferential 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
SoilWatch 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
ErosionWatch 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
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
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.
