Chapters 4 & 5 Weathering and Erosion Weathering • Weathering is the breaking down of rocks and other materials • 2 types of weathering – Mechanical – Chemical Mechanical/Physical Weathering • Mechanical Weathering occurs when rocks are broken down into smaller pieces, but the chemical composition is not changed • Examples: temperature, frost, tree roots, gravity (abrasion) Physical Weathering QuickTime™ and a Sorenson Video decompressor are needed to see this picture. Mechanical Weathering • Temperature - rocks expand when they are heated up, and contract when they are cooled. This process breaks rock. • Frost Action- water gets into cracks of rock and freezes when it gets cold. Crack expands • Organic Activity - roots of trees break rocks • Gravity - rocks are pulled downward by gravity • Abrasion - wind blown sand wears away rocks (also water running over rocks) Chemical Weathering • Chemical weathering occurs when rocks are broken down and their chemical composition is changed • Examples: water, carbon dioxide, oxygen, plants Chemical Weathering QuickTime™ and a Sorenson Video decompressor are needed to see this picture. Chemical Weathering • Water - most chemical weathering occurs w/ water/CO2. Water dissolves minerals. • Oxidation - process in which oxygen chemically combines with another substance. (iron in rocks can rust) • Carbonation - occurs when CO2 dissolves in water and forms carbonic acid. • Plant Acids - moss and lichens produce weak acids that dissolve minerals in rocks Soil Formation • Soil is formed when rocks are continuously broken down by weathering. • Soil that stay close is called residual, soil that is moved is called transported. • Bedrock is the layer of rock beneath the soil Erosion • Erosion is the process by which weathered rock is moved. • Grand Canyon was formed by erosion. • Causes of erosion: gravity, wind, running water, glaciers, and waves. • Deposition is the process by which sediments are laid down in a new place. Erosion QuickTime™ and a Sorenson Video decompressor are needed to see this picture. Erosion • Gravity pulls rocks and soil down slopes. Examples: landslide or mudflow • Wind is most active agent of erosion in deserts and on beaches. Wind erosion can form dunes or caves. • Running water is the major cause of erosion. Examples: rivers, streams, and runoff. • Glaciers ice erodes rocks beneath it by abrasion. • Waves erode and shape shorelines. Erosion Caused by Wind QuickTime™ and a Sorenson Video decompressor are needed to see this picture. Humans Impact Erosion QuickTime™ and a Sorenson Video decompressor are needed to see this picture.