Transcript Weathering
Weathering of Rocks Hoodoos More Resistant layer Breaking and Removing rock 1. Weathering - the disintegration and decomposition of rock at or near the surface. 2. Erosion – the transport of weathered material by water, wind, ice and gravity. Weathering in the Rock Cycle And Sedimentary Rocks Metamorphic Rocks Weathering and Erosion Heat and Pressure Magma Sediment Igneous Rocks *Types of Weathering Mechanical – physical breakdown of rocks with NO change in composition. Chemical – chemical alteration and decomposition of rocks by chemical reactions. Mechanical Weathering makes smaller pieces and exposes more surface area to weathering processes *Types of Mechanical Weathering 1. Ice Wedging – water freezes in cracks and expands them causing rocks to break apart. Ice Wedging *Types of Mechanical Weathering 2. Organic Activity – roots break apart rocks. Organic Activity Tree along 460 near Princeton that was saved by building a huge cement wall with drainage *Types of Mechanical Weathering 3. Exfoliation and Jointing because of pressure release also break apart rocks. Exfoliation Exfoliation Results of Jointing *Types of Mechanical Weathering 4. Abrasion –rounding or smoothing by water, wind, or glaciers Wind, water and glaciers also erode/deposit sediments. Glaciers smooth and/or scratch rocks. Examples: Glacial Striations Glacial Polish *Water transport in rivers smooths and rounds rocks. *Wind creates ventifacts (smoothed surfaces and erosion) Wind and water work together *Wind Deposition creates Dunes *Types of Chemical Weathering Hydrolysis - any reaction in which water participates. Also includes acid. *Types of Chemical Weathering 1. Rust (oxidation) – caused by water and oxygen 2. Carbonation (caves) – KARST topography forms when carbonic acid (formed by water and carbon dioxide) reacts with limestone (Calcium Carbonate) and converts it to soluble Calcium Bicarbonate. *2a. Stalactites and stalagmites form from carbonate deposits from dripping water in caves. *2b. Sinkholes can also cause pollution problems if they connect directly to the water table. Typical Sinkhole Not a Typical Sinkhole… *Types of Chemical Weathering 3. Acids in mosses and roots can react with minerals in rocks and dissolve them. 4. Changing of feldspar into clay (kaolin) by hydrolysis. 5. Dissolving by water. *Factors influencing Weathering Rates 1.Rock Composition – sedimentary rocks weather more rapidly than metamorphic or igneous. Also, quartz is resistant to weathering. 2.Rock Surface area – more surface exposed, more rapidly weathered. 3.Topography – high elevation and steep slopes weather more rapidly. 4.Climate – variable (freezes and thaws) and hot/ humid cause rapid weathering. Benefits of Weathering • Produces regolith (rock fragments) clay, sand, and gravel • Produces minerals • Creates soil Soil is made of loose, weathered rock, minerals, air and organic material (humus). Soil Profile(fill in the blanks) 0- Leaf Litter A-Humus B- Clay and Leached Minerals C- Partially Weathered Bedrock R R-Bedrock or Parent Rock Soil Profile In a crosssection of soil, various horizons are formed. A Horizon: Topsoil This layer is usually loose and crumbly with a significant amount of organic matter (HUMUS). (O is leaf litter) A Horizon: Topsoil Most productive layer of soil. Conservation efforts are focused here! B Horizon: Subsoils Subsoils are usually light, dense, clay-rich with some organic matter. This is where minerals leached from the A horizon accumulate. C Horizon: Transition Partially weathered parent material with little/no humus. Bedrock Below the C horizon the unweathered bedrock will be found. Climate and Soil Tropics – thick, unfertile soils called laterites. Arctic or Desert – thin, made mostly of regolith Topography and Soil Slopes – thin and dry topsoil Lowlands – thick, wet soils with humus Erosion Control Creating a soil condition that is resistant to erosion Control Practices and Structures for Farms Terracing, Crop rotation and Wind Breaks Wind Erosion Factors that Decrease Wind Erosion Cloddiness Crop residue Ridges Barriers Mass Wasting The downslope movement of unconsolidated Earth material due to gravity. Increasing Severity of Mass Wasting Slump- quick downward movement of a block of soil. Rock Slides Creep-slow movement of soil down a slope due to expansion and freezing. Creep Mudflows-very fast downward movement of water and mud The Stability of soil is reduced by: 1. Adding water to the material of a slope 2. Increasing the steepness of the slope 3. Removing material from the lower part of the slope 4. Earthquakes 5. Removal of vegetation (increases runoff) Erosion Created Landforms Mountains erode to peneplains Sometimes monadnocks (resistant knobs of rock) are exposed. Mountains erode finally to plains Plateaus (large high flat areas) erode to form mesas (smaller high table-like structures) and buttes (small narrow columns) Engineering Solutions Rock Nets Soil Nailing Avalanche Barriers (Switzerland)