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Weathering

Learn about the processes of weathering, erosion by rivers and glaciers, types of glaciers, and how natural elements shape the Earth's landforms. Gain insights into the impact of weathering factors and river systems on landscapes.

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Weathering

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  1. Weathering Erosion, Rivers and Glaciers

  2. Weathering • The breakup of rock due to exposure to the atmosphere • Can be Physical/Mechanical or Chemical

  3. I. Physical/Mechanical Weathering • When rocks are split or broken into smaller pieces of the same material without changing the composition • EXAMPLES: • Ice/frost wedging causes potholes • Root wedging lifts up sidewalks • Wetting and drying

  4. Ice/Frost Wedging

  5. Root Wedging

  6. II. Chemical Weathering • Decomposition of rock that takes place when the rock’s minerals are changed into new substances • EXAMPLES: • Hydrolysis is the chemical reaction of water with rocks • Oxidation is the reaction of oxygen and other substances: causes rusting • Carbonic Acid: dissolved carbon dioxide in water, changes minerals into clay minerals

  7. III. Acid Precipitation • Rain, snow, or sleet mixes with sulfuric and/or nitrogen compounds in pollution • Results in sulfuric and/or carbonic acid • Natural rain has a pH of about 5.7 due to natural CO2 in the atmosphere • Acid rain has a pH of between 4 and 5

  8. III. Acid Precipitation Cleopatra’s Needle, Central Park NYC

  9. Do Now: • What is it called when oxygen reacts with elements of rocks? • What is carbonic acid? • Obj: LWBAT continue your understanding of the processes of weathering.

  10. IV. Erosion • The removal and transportation of weathered materials by running water/waves, wind and ice (glaciers) • Carries and deposits sediment • Can form structures such as deltas, fins, and sandstone arches

  11. IV. Erosion Sandstone Arches, Arches National Park, UT Sandstone Fins, Arches National Park, UT

  12. V. Rate of Weathering • Weathering is affected by: • Amount of rock exposed at the surface • Type of rock • Igneous & Metamorphic – more resistant • Sedimentary – least resistant • Climate • Hot/Cold and dry – more physical weathering • Warm and moist – more chemical weathering

  13. VI. RIVERS • Running water • Comes from water cycle (precipitation to runoff) • Moves downhill from force of gravity • Breaking down of sediment and rock • Mechanical • Abrasion – rubbing of rocks against stream bed • Chemical • Rain and spring melt lowers pH of lakes – “Acid Shock” • Can be neutralized by dissolving soluble carbonate rocks (ex. Limestone)

  14. VI. RIVERS (con’t) • Erosion – water carries rock and sediment downstream • Solution – minerals dissolved in water • Suspension – small particles carried in water flow (“muddy water”) • Bed load – boulders and pebbles pushed along bottom of stream • Delta – fan shaped deposit of silt and sand at end of river

  15. Deltaand not the force

  16. VI. RIVERS (con’t) • Carrying Power • Amount of sediment and size of particles • Depends on speed and discharge • Increases as speed and discharge increase • Discharge – volume of water flowing past a certain point • Speed of stream • Depends on steepness of stream bed • Steeper = faster • “Graded River” – even/consistent slope

  17. E. Stages of Stream Development • Youth Stage • Steep V-shaped valley • Lowest discharge • Greatest speed

  18. E. Stages of Stream Development • Mature Stage • Wide valley • Erosion of valley walls • Floodplain developing

  19. E. Stages of Stream Development • Old-age Stage • Valley walls completely eroded • Large flat floodplain • Meanders and oxbow lakes • Maximum discharge floodplain Oxbow lake Meanders Tributary streams

  20. Colorado River, Grand Canyon, AZ

  21. F. Watersheds • Watershed – the entire land area drained by a river and its tributaries • Largest watershed in the US is the Mississippi

  22. VII. Glaciers • 2 types: • Valley aka Alpine Glacier • Long, slow-moving wedge-shaped stream of ice • Continental Glacier • Large sheets of ice covering a large part of a continent Ice Sheet on Ellesmere Island, Canada

  23. VII. Glaciers • Largest Glaciers • Antarctica • Continental Glacier • Last ice age • ~18,000 years ago • Ice covered Great Lakes and reached to IN, OH and NJ • Sea levels drop Great Lakes NJ

  24. C. Glacial Features Firn – granular snow atop a glacier Crevasses – deep cracks in the ice Snow line – lowest level of snow in summer Ice front – edge of a glacier **glaciers carve U-Shaped valleys**

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