Weathering (teach)


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To help elementary students understand the process of weathering

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Weathering (teach)

  1. 1. WEATHERING Destructive Forces in Nature.. Those that destroy landforms.By Moira Whitehouse PhD
  2. 2. How are Landforms Made?• The forces that create the differentlandforms are, broadly speaking: • Constructive forces • Destructive forces
  3. 3. Constructive forces• Are those that build up the land.• Landforms such as mountains ranges,volcanoesand plateaus are built by themovement of the Earth’s plates• Landforms such as deltas, plains and sanddunes are created when rocks and soilresulting from weathering and erosion arecarried away and deposited in new areas.
  4. 4. Destructive forces• Those that wear down the land, like weatheringand erosion.(Don’t let the name “destructive forces” mislead you.Destructive forces create landforms like canyons,valleys, etc. but to do so they first had to destroysome other landforms, mountains, plateaus, etc.)
  5. 5. The two players in the destructive process are: Weathering and Erosion
  6. 6. All rocks do not weather at the same rate.Further we will find that parts of somerocks weather faster than other parts ofthe same rock. Why?Whatever the reason, one can find somevery odd looking weathered rock:
  7. 7. Why?Grand canyon Image courtesy of National Geographic
  8. 8. Yes, the rock on the bottom is softer than therock on top of this formation. The top rockweathers more slowly.
  9. 9. Why?Is it because therock on top isharder than therock below? Wolfgang Staudt
  10. 10. What causes weathering; that is, whatcauses rocks to break into smaller andsmaller pieces?
  11. 11. • Nonliving things and living things canbreak bigger rocks into smaller pieces.We will look first at non living things thatbreak up rock.
  12. 12. Nonliving things that break rocks into pieces. 1. Water running over the rock 2. Water freezing in cracks in the rocks 3. The temperature of rocks changing from hot to cold 4. The abrasion of rock by the blowing wind carrying sand 5. Water with acid in it
  13. 13. Running water
  14. 14. Rapidly moving water particularly high up inthe mountains or a canyon can break off piecesof rock.
  15. 15. Seen here, a small,fast runningstream of water isdramaticallycutting throughthe rock in the sideof this mountain.
  16. 16. Rocks carried by fast moving water hit other rocksbreaking them into pieces. Moving sand acts likesandpaper on the larger rocks in the river bedrubbing off pieces of rock. These smallerpieces are then carried downstream by thefast movingriver. kia4067
  17. 17. Here you can see pieces of rock created byfast moving water. Randy OHC
  18. 18. Rocks that have been tumbled for a long time in rivers and streams become smooth and rounded.
  19. 19. Freezing water
  20. 20. Here we can seecracks in largemountain rocks. Copyright 2004 by Andrew Alden,, reproduced under educational fair use
  21. 21. Rain fills these cracks with water.When the water freezes, it expands withinthe crack pushing the rock apart. Image courtesy of the geology department umd
  22. 22. As the ice melts, the water flowsdeeper into the crack.Then the water freezes again, furthercracking the rock.
  23. 23. This repeated offreezing andthawing forces thecrack open moreand more,eventuallyshattering the largerock into smallerpieces.
  24. 24. Changing temperature
  25. 25. 3. Changing temperature also causesweathering. As rocks heat up, they expand. As they cool,they contract.This process is repeated over and over againin nature. Eventually this process causes them tobreak apart.
  26. 26. Here we see large rock in a desert environment that has probably been exposed to the freeze- melt cycle. aka Hank Ashby aka Mr. Freshtags
  27. 27. Abrasion
  28. 28. 4. Abrasion by windblown sand alsoweathers rocks particularly in deserts. Itis similar to rubbing sandpaper over apiece of wood or sandblasting concrete. beige alert
  29. 29. Frequent sandstorms in the desertweather exposed rocks. nukeit1
  30. 30. The scouring of the rock by the windcarrying sand wears off fragments of rock.
  31. 31. Water with acid in it
  32. 32. Carbonic acid is very common in nature. It isproduced when carbon dioxide combineswith water.When this weak carbonic acid tricklesinto cracks in limestone, it dissolves therock and eats “holes” in it.
  33. 33. The mildly acidic rainwater flows intocracks in the ground.Sometimes it eatshuge holes in therock--caves.
  34. 34. The same acid that made this rock “holy”when it was buried in the ground, alsoworks to make caves
  35. 35. stalactites stalagmitesThis is a picture of a cave with stalactitesand stalagmites.
  36. 36. When the acid water dissolved the rockevaporates, crystals of calcite are left behind.When the water from many, many drips at thetop of a cave evaporates, a stalactite forms. (theone on the ceiling stuck tight ...stalactite)Drips that fall on the cave floor cause stalagmitesto grow. (The stalagmitesmight have stuck to theceiling but they didn’t.)
  37. 37. More pictures ofstalactites andstalagmites, doyou rememberwhich is which?
  38. 38. Sometime other minerals in rocks react withthe weak acid in water to form other weakersubstances.These weaker substances are then more easilyworn away by weathering. Feldspar changes to clay.
  39. 39. Living thingsthat causeweathering
  40. 40. These are some of the living thingsthat break rocks into smaller pieces:1. Plant roots—particularly tree roots2. Lichen growing on rocks3. Burrowing animals
  41. 41. Plant roots
  42. 42. The roots of plants, particularly tree roots,are amazingly strong. When they startgrowing as tiny root hairs they can fit intothe smallest of cracks.As these tree roots continue to grow,cause the cracks to get bigger and biggerbreaking the rock apart.
  43. 43. Here theroots of thetree aregrowing inthe cracks inthe rocksmaking thecracks larger. Chazz Layne
  44. 44. city bumpkins
  45. 45. Lichen growth
  46. 46. Lichens appear in the form of small patchy crusty colors of green, brown, and orange patches. They often grow on rocks and break them apart.
  47. 47. Burrowing animals
  48. 48. 3. Burrowing animalsWhen animals burrow in rocks or betweenthe rocks, they carry seeds which germinatein the cracks in the rocks.
  49. 49. How about a little review. Do you remember what the word weathering of rock means?Yes, it means breaking rock into smaller and smaller pieces.But, with weathering, it is not a hammer or man whobreaks the rock. It is forces in nature.
  50. 50. What are the main forces in nature that break rock intosmaller and smaller pieces? Yes, there is: • fast running water • wind carrying sand • water in the cracks freezing, melting and freezing • rocks heating up in daytime and cooling down at night • acid in water “eating” holes in rock and forming caves • plant roots • burrowing animals
  51. 51. What force in nature iscausing the rock toweather in the pictureson the left forming adeeper and deepervalley?
  52. 52. In the desert, thereis very little runningwater. What forcein nature causesrock formations likethe one seen in thepictures on theleft?
  53. 53. What force innature has causedthe rock in thepicture on the leftto break into twopieces?
  54. 54. What will happento this rock if watergets into the cracksand freezes, melts,freezes and meltsover and overagain?
  55. 55. After millions andmillions of yearsthe mountains onthe left will finallylook like the onesshown below.Weathering isconstantly changingthe surface of theEarth.