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Weathering and Erosion Earth Processes Hill Science 6 Weathering Weathering is the wearing or breaking of rocks into smaller pieces by water, temperature changes, wind, living things, or chemical changes. The fragments of rock stay in place. Weathering There are two types of weathering: Mechanical weathering and Chemical weathering Mechanical Weathering The physical breakdown of rocks into smaller pieces, gradually reducing them to the tiny particles that make up soil. Agents of Mechanical Weathering Wind, water, gravity, glaciers - Abrasion Ice – ice wedging Pressure change – inside earth to surface of earth - exfoliation Temperature change – alternating hot to cold - exfoliation Plants and animals – organic activity – root pry, animal burrowing Wind Arches National Park, Utah, USA These rocks have been blasted by wind and sand causing them to become rounded. Type of Weathering? WIND ABRASION Water The Grand Canyon created by the Colorado River Water Friction and Repeated Impact Type of weathering? Abrasion Glacial Action Glacial ice will scour and abrade the surface it slowly scraps over. Glaciers form broad U-shaped valleys in their wake. What type of weathering? Abrasion Exfoliation On Half Dome, the rock is peeling away from the mountain in layers just like an onion. This is called exfoliation which is caused by the change in pressure when a rock that was formed underground is thrust to the surface. Pressure Changes Peeling of the surface of a rock due to pressure change. What type of weathering? Exfoliation Temperature Changes Warm to cold and back again Splits rocks or peels off layers Temperature Change Repetition of cooling and heating over and over again. When might that happen? What type of weathering? Exfoliation Temperature Changes Water to Ice Ice Wedging Heaving Glaciers Ice Wedging Water fills a crack, freezes and expands making a larger crack. This process repeats over and over. Ice wedging slowly breaks up this sedimentary rock into unusual shapes. Frost Heaving Repetitious freezing and thawing of water under the patio causes the surface to heave when the ice expands under the patio and contracts when ice melts. Organic Activity Plants What do you see happening here? Root Pry Plant Roots The action of plant roots is called root pry Animal Activity- how does this cause weathering? Pictures of Mechanical Weathering Link to pictures Link to places Mechanical Weathering 1. Abrasion – the wearing away of solid particles; caused by wind, water, glacier ice, and gravity 2. Ice wedging - when water in a crack or hole in a rock freezes it expands making the opening larger. Melting moves it deeper into the opening and the process repeats; Caused by the repeated thawing and freezing of water. Mechanical Weathering 3. Organic activity – people, animals, or plants break up rock by digging or burrowing. Root pry the splitting of rock caused by the expanding root growing deeper. 4. Exfoliation – flaking off of the surface of the rock; caused by change in pressure from inside earth where formed to lower surface pressure or temperature change. 5. Heaving – rocks shift and crack; caused by repeated freezing and thawing Chemical Weathering Chemical weathering is the breaking down of rocks by changing their chemical composition. Agents of Chemical Weathering Acid precipitation - carbonation Acid from plants – humic acids Oxygen - oxidation Water Carbonation - Water weathers rock by dissolving it Carbon Dioxide CO2 dissolves in rain water and creates carbonic acid Carbonic acid easily weathers limestone and marble (CaCO3) A cave may result Type of weathering? carbonation Chemical Weathering Carbonation Sinkhole Karst terrain Stalactites and Stalagmites Result of Rainwater Weathering Type of Weathering? carbonation Humic Acids Acid from Lichens Weathering Rock Living Organisms Lichens that grow on rocks produce weak acids that chemically weather rock Type of weathering? Humic acids Oxygen Iron combines with oxygen in the presence of water in a process called oxidation The product of oxidation is rust Oxygen Caused Chemical Weathering Type of weathering? oxidation Chemical Weathering Carbonation-Acid precipitation - CO2 dissolves in rain water and creates carbonic acid which easily changes the chemical composition of certain rocks (limestone and marble) Humic Acids – lichens and moss produce acids that break down the minerals found in rocks they are growing on Oxidation – when oxygen combines with another substance to create an entirely new substance Fe + O produces iron oxide (rust) Weathering and Erosion Weathering and erosion are called external processes because they occur at or near Earth’s surface. Weathering and erosion are part of the rock cycle because they are responsible for transforming solid rock into sediment. So how do they differ? Weathering or Erosion? Weathering is the breaking of rocks into smaller pieces. Erosion is the moving of weathered sediments from one place to another. Erosion is the transportation of weathered material by the mobile agents of wind, water and glacial action (ice). Video Links Formation of the Grand Canyon Grand Canyon Lava Flows Ireland: Glaciated Landscape Principal of Uniformity Belief that the processes that changed our world in the past are still in existence today and continue to change the earth. Chemical Weathering Chemical weathering is the breaking down of rocks by changing their chemical composition. Chapter 10 Rates of Weathering Differential Weathering • What Is Differential Weathering? Differential weathering is a process by which softer, less weather resistant rock wear away and leave harder, more weather resistant rock. The image below is an example of differential weathering. Devil’s Tower, Wyoming Rates of Weathering What determines how quickly a rock will weather? Type of Rock (differential weathering) – some rocks weather more quickly than others, due to composition or condition Pollution – causes acid precipitation which will weather rocks more quickly Climate – tropical fastest due to more moisture and plant action, deserts slowest due to lack of humidity Size – smaller rock has more surface area to volume than a larger rock. More surface is exposed to weathering, so it will weather more quickly. Chapter 10 Rates of Weathering Chapter 10 Rates of Weathering Weathering and Elevation • High Elevations Rocks at higher elevations, as on a mountain, are exposed to more wind, rain, and ice than rocks at lower elevations. • Steep Slopes The steepness of mountain slopes increases the effects of mechanical and chemical weathering. Steep slopes cause water and sediments to quickly run down the side of the mountain. Weathering Website Weathering animation click here http://www.uky.edu/AS/Geology/howell/goodies/elearning/module07swf.swf