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Surface Processes

Surface Processes. That affect the Geosphere: Weathering and Erosion. Weathering. Weathering describes the breaking down or dissolving of rocks and minerals on the surface of the Earth. Water, ice, acids, salts, plants, animals, and changes in temperature are all agents of weathering.

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Surface Processes

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  1. Surface Processes That affect the Geosphere: Weathering and Erosion

  2. Weathering • Weathering describes the breaking down or dissolving of rocks and minerals on the surface of the Earth. • Water, ice, acids, salts, plants, animals, and changes in temperature are all agents of weathering. • There are two main types of weathering.

  3. Mechanical Weathering • Breaks rocks down into smaller and smaller pieces through physical means • Minerals remain unchanged. • Fracturing (frost-, salt-, root-wedging) and • Abrasion- scraping of rock on rock • Plants • Water

  4. Plants • Lichen and mosses wedge tiny roots into pores and crevices of rocks • Tree roots

  5. Mechanical weathering by water/ice • Water takes up 10% more space when frozen • Water seeps into porous rock, freezes, pushes rock apart • waves force rocks to crash together or crack apart • Clay swells when wet, shrinks when dry

  6. Chemical Weathering (Decomposition) • Chemical weathering: molecular structure of existing minerals/rock are changed, forming new minerals and dissolved ions. • Agents of Chemical Weathering: Water, oxygen, carbon dioxide, acids of plant decay

  7. Reaction with Water • New Substances are formed when chemicals in rock react with water. • Hydration:  new substance created when water is absorbed (water molecule used to form a bond). • Eg. as the mineral anhydrite reacts with groundwater, it transforms into gypsum, one of the most common minerals on Earth. • Hydrolysis: Water molecule cleaves (breaks) chemical bond • Eg. feldspar in granite rocks changing to clay. 

  8. Carbonation: Reaction with Carbon Dioxide • Carbon dioxide from the air or soil can combine with water to form carbonic acid,that can dissolve rock. • Carbonic acid is especially effective at dissolving limestone.

  9. Chemical Weathering: Carbonation • When carbonic acid seeps through limestone underground, it can open up huge cracks or hollow out vast networks of caves. 

  10. Chemical Weathering: Carbonation • Carlsbad Caverns National Park, New Mexico, includes more than 119 limestone caves created by weathering and erosion. • The largest is called the Big Room. It is the size of six football fields.

  11. Chemical Weathering: Dissolution • Excess rain may carry away soluble rocks such as limestone, dolomite, and gypsum, leaving behind huge land forms called Karst. • The surface rock is pockmarked with holes, sinkholes, and caves.

  12. Chemical Weathering: Dissolution • One of the world’s most spectacular examples of karst is Shilin, or the Stone Forest, near Kunming, China. • Hundreds of slender, sharp towers of weathered limestone rise from the landscape. 

  13. Chemical Weathering: Oxidation • Eg.Rust in iron-containing rocks. • As rust expands, it weakens rock and helps break it apart.

  14. Erosion • Erosion is the removal and transport of earth materials by natural agents. • Agents of Erosion: Wind and Water (liquid and solid)

  15. Liquid Water and Ice • Rain, rivers, floods, lakes, and the ocean carry away bits of soil and sand, and slowly wash away the sediment.

  16. Erosion by Ice • As glaciers move, they transport everything in their path, from tiny grains of sand to huge boulders. • Deposits are called moraine

  17. Erosion by Ice Moving glaciers gouge out basins and form steep-sided mountain valleys. • Eroded sediment called moraine is often visible on and around glaciers.

  18. Erosion by Wind • Aeolian (wind-driven) processes constantly transport dust, sand, and ash from one place to another. • Wind can sometimes blow sand into towering dunes. • Eg. Sand dunes of Badain Jaran section of the Gobi Desert in China, reach more than 400 m high.

  19. Erosion by Wind • Windblown sand can blast against rock with tremendous force, polishing the rock until smooth—giving the stone a so-called “desert varnish.” • Eg. Arches National Park, Utah

  20. Ventifacts – stones shaped by wind

  21. Erosion by Gravity • Landslides and other forms of mass wasting • These processes cause rocks to dislodge from hillsides and crumble as they tumble down a slope. 

  22. Frank Slide 1903 It is the deadliest landslide in Canadian history and was the largest until the Hope Slide in 1965.

  23. What is the difference between Weathering and Erosion?

  24. What is the difference between Weathering and Erosion • Weathering is the breakdown or dissolving of rock but does not involve movement. • Erosion is the transport of material

  25. Which Rocks and Minerals Resist Most? • Quartz • Hard, no cleavage makes it resistant mechanical weathering • resists chemical weathering (water, oxygen, or acids) • Feldspar, hornblende, biotite mica, augite calcite and gypsum are all affected by chemical and mechanical weathering

  26. Which Rocks and Minerals Resist Most? • Most igneous rocks and many metamorphic rocks weather more rapidly in wet climates than in dry ones. • They often have cracks that are widened by mechanical weathering, contain minerals that are easily affected by chemical weathering

  27. Which Rocks and Minerals Resist Most? • Sedimentary rocks are only as strong as their cement holding them together. • Those with silica or quartzite as a cement are more durable. • Shale is weakest of all sedimentary rocks, easily split. • Marbles and limestones are fairly resistant to mechanical weathering (except calcite often found in marble reacts to acid). • Limestones last longer in dry climates because where there is very little dissolved acid.

  28. Check in • Which rocks are most resistant to chemical and physical weathering? • Why? • Which are most susceptible? • What kind of climate promotes weathering? • What types of rocks are susceptible to chemical weathering?

  29. Check in • Which rocks are most resistant to chemical and physical weathering? • Quarts • Why? Hard, no cleavage • Which are most susceptible? Shale is weakest – splits easily, • What kind of climate promotes weathering? Warm, damp • What types of rocks are susceptible to chemical weathering? Those containing calcite are susceptible to acid.

  30. Factors Affecting Rates of Weathering • Rocks themselves – how resistant they are • Amount of surface area exposed • Climate – warm, wet climates favor chemical weathering - Cold, dry climates favor mechanical weathering

  31. Homework • Read pages 131-136 • Answer #1-6 p 137 • Next Class: Lab from text p144-145

  32. MASS MOVEMENTS • Mass Movement – • Creep • Landslide

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