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Deposition, Weathering, and Erosion Weathering What Caused This? http://commons.wikimedia.org/wiki/File:Toad_Rock_-_geograph.org.uk__767454.jpg http://en.wikipedia.org/wiki/File:KharazaArch.jpg Effects of Weathering • Weathering is a process that breaks down rock and other substances at Earth’s surface – creates soil – softer rock weathers faster – weathering is fastest in hot and wet climates Types of Weathering • Mechanical Weathering • Chemical Weathering What is Mechanical Weathering? • Breakdown of rock into smaller pieces without any change in the chemical composition of its minerals. – Sometimes called “physical” weathering – Rock is torn apart by physical force, rather than by chemical breakdown. Mechanical Weathering • Works very slowly • There are different types – ice wedging – exfoliation – thermal – biotic Mechanical - Ice Wedging Ice Wedging – Water fills joints of rocks and freezes – Freezing expands the water by 10% – Repeated freeze and thaw cycles over the years causes rock to break along joint Mechanical - Exfoliation • Exfoliation or unloading –Rock breaks off into leaves or sheets along joints which are parallel to the ground surface Mechanical - Thermal • Thermal expansion – Repeated daily heating and cooling of rock – Different minerals expand and contract at different rates causing the rock to split Mechanical - Biotic • Biotic – means life – Weathering caused by living organisms – Plant roots, digging animals, microscopic plants and animals, algae and fungi. Mechanical Weathering What is Chemical Weathering? • Breakdown of rock into smaller pieces because of change in the chemical composition of its minerals. – Chemical reactions break down the bonds holding the rocks together, causing them to fall apart. – Chemical weathering occurs in all types of rock but smaller rocks are more susceptible because they have a greater amount of surface area. Chemical Weathering • Types of chemical weathering • • • • • Oxidation (oxygen) Hydrolysis (water) Carbonation (carbon dioxide) Biotic (living organisms) Acid rain Chemical - Oxidation • Oxidation - oxygen combines with other elements in rocks to form new types of rock. – Causes a “rusting” of the rock, often causes a color change in the rock Chemical - Hydrolysis • Hydrolysis - water combines with the substances in rocks to form new types of rock – New substances are softer than the original rock types Chemical - Carbonation • Carbonation – Carbon dioxide is dissolved in water making carbonic acid, which eats away at the rock – Weak acid is formed when carbon dioxide in the air mixes with rain. This is the same acid found in soft drinks. Chemical - Biotic • Organisms - living organisms can cause changes in the chemistry of rock – Plants lower the local pH to make it more acidic – Bacteria act as catalysts in various geochemical processes Chemical Weathering Weathering by Water • Most important agent of chemical weathering • It can dissolve rock and minerals in rock Weathering by Waves • Waves weather the land: – Mechanical weathering • Broken down into smaller pieces – Chemical weathering • Dissolved in water Weathering by Waves Weathering by Wind • Wind weathers the land by mechanical means – Abrasion • Very slow process Weathering by Wind weathering The breaking down of rock into smaller pieces that remain next to each other. Weathering forms sediments mechanical weathering chemical weathering Physical breaking of rock without any change in the chemical composition of the rock. biotic force ice wedging exfoliation thermal The breaking down of rock into smaller pieces because of chemical changes within the rock. biotic oxidation hydrolysis carbonation Erosion What Caused This? http://commons.wikimedia.org/wiki/File:Water_erosion_ below_Hay_Bluff_-_geograph.org.uk_-_1074175.jpg http://commons.wikimedia.org/wiki/File:Wind_erosion_ Seminole_Canyon.JPG http://commons.wikimedia.org/wiki/File:Bave ntian_Clay_Beds_-_geograph.org.uk__1776748.jpg Erosion • Movement of weathered rock and soil to a new location. – gravity – water – glaciers – waves – wind What Is Gravitational Erosion? • downward movement of rock and sediments, mainly due to the force of gravity. Erosion by Gravity • Gravity can erode landscapes – – – – Landslides Mudflow Slump Creep Erosion by Water • Moving water is the strongest agent of erosion that has shaped Earth’s land surface • Erosion by water starts with rain. As the rain runs downhill, it carries soil rock and other material with it Erosion by Water • The rate depends on amount of rain, vegetation, type of soil, shape of land, and how people use the land • As water moves fast, it picks up sediment • As water slows down, it drops sediment Water What Is Glacial Erosion? • moves and carries rocks, grinding the rocks beneath the glacier – Glaciers pluck and abrade to cause erosion Erosion by Glaciers What Is Wave Erosion? • Waves - relentless pounding of waves that erodes the weaker, softer rock – Can take over 100 years to erode a rock to sand Erosion by Waves • When waves hit rocky coastlines, the impact can break off pieces of the rock • The sand and sediment in the waves can also act like sandpaper and wear away rock Waves What Is Wind Erosion? • wind picks up surface material and moves it, weakest agent of erosion – responsible for creating great deserts like the Sahara Desert and Gobi Wind erosion Movement of sediments from one place to another. wind glaciers water gravity waves Deposition Deposition • laying down (dropping) of sediment carried by wind, water, or ice Deposition by Water • Water is the strongest agent of deposition. • Rivers deposit soil and sediment on their flood plains and deltas • Good farmland is usually based on land where sediment was deposited by water Deposition by Water Water Deposition Deposition by Glaciers • When a glacier melts, it deposits the sediment it eroded from the land • This deposition can create new landforms and deposit sediment in new areas – Till – material deposited on the land’s surface – Moraine – ridge at the edge of a glacier Glacier Deposition Deposition by Waves • Waves shape coastlines by depositing sand on the beach • The type of sand is determined by the sediment on the ocean floor – White sand – Black sand Deposition by Waves Deposition by Wind • Wind is the weakest agent of deposition • When it drops the sediment it is carrying, it can form dunes or mounds Deposition by Wind deposition Laying down of sediment that was carried in from another place. wind water glacier waves • Wind, water, and waves work together in the processes of deposition, weathering, and erosion What’s the Difference? • WEATHERING - think weather wearing rock down • EROSION - think of a road and traveling • DEPOSITION – think of depositing money in a bank
