Weathering and Erosion

1. Weathering and Erosion

2. Objectives • Identify the cause of rock shaping due to weathering and erosion • Explain how chemical weather forms caves • Describe how acid rain affects the landscape

3. Two Types of Weathering • Physical or Mechanical – breaking rock into smaller pieces • Chemical – breaks down the rock into something else

4. Ice can break Rocks • When water freezes it expands and gets less dense (this is why ice cubes float) • Frost Wedging is when water enters a crack in a rock, freezes and expands, and pushes the rock apart • Frost wedging is why there are more rocks on the roads next to cliffs after winter months

5. Example of Frost Wedging • Frost wedging has broken the rock into layers and pushed them in many directions

8. Plant roots break rocks • Plant roots enter a crack when they are small • As they grow, they expand and crack the rock

9. Bryce Canyon National Park

10. HooDoos Form In Bryce Canyon • The HooDoos form from a combination of Frost Wedging and Chemical Weathering • 200 days a year, the temperature in Bryce Canyon fluctuates both above freezing and below freezing • That’s 200 days a year for frost wedging to occur • The chemical weathering is both oxygen and acid rain

11. HooDoos in Bryce Canyon

12. Arches National Park • Arches also form from Frost Wedging, wind erosion, and Chemical Weathering

13. Fins form when cracks in sandstone are eroded

14. Double Arch has been used in movies (Raiders of the Lost Arc)

15. Weathering continues on fins, some fins collapse, others form spires and arches

16. Glaciers also erode rocks • Glaciers are large rivers of ice • They flow, slowly, down slopes • As they flow, they carve the rocks underneath them and take large amounts of rocks and boulders with them as they move • They also grind some of the rocks into small particles called Glacial Silt

17. Yosemite Valley

18. Glacial Silt • Glacial silt is common in Alaska and extremely dangerous • Tourists walk out onto the beaches of Alaska, only to realize it is like quicksand • They get stuck and the tide comes in

19. Glacial Silt • The murky looking water is caused by fine Glacial silt floating in the water

20. Lake Louise, CanadaThe water color is from Glacial Silt

21. Yosemite Valley • Yosemite is formed from mostly Granite • Granite takes longer to erode than the sandstone of Bryce Canyon and Arches National Park • The major shapes in Yosemite were weathered by Glaciers moving through the valley • Frost Wedging does still occur today

23. Half Dome was cut by a Glacier

24. Chemical Weathering • Things as basic as Oxygen, Carbon Dioxide, and acid cause chemical changes in rocks

25. Oxidation • Oxygen is a very reactive element • Oxygen combines with many elements • The Red Rocks seen around the Rocky Mountains (Grand Junction, New Mexico..) are Hematite • Hematite forms when iron reacts with oxygen • The red color is an indication of old rocks and old soils

26. Grand Junction, Colorado

27. Chemical Weathering by Carbon Dioxide • Carbon Dioxide gets dissolved in rainwater • Carbonic Acid, H2CO3 • Although this is a weak acid, it is strong enough to weather rocks both above ground (acid rain) and below ground (caves)

28. Cave Formations • We talked about cave formation yesterday • Caves are usually in limestone • Limestone reacts with Carbonic Acid in the water and “dissolves” and is carried away

29. pH measures acid • Neutral water has a pH of 7.0 and has the same amount of hydrogen ions (H+) as hydroxide ions (OH-) • Hydrogen ions are acidic • Hydroxide ions are basic • Many things you drink are acidic (they can cause damage to your insides) like Coffee, Soft drinks, Orange Juice • Milk is a basic drink (does not cause damage)

31. Acids • Numbers below 7 are acidic • Lower numbers are more acidic • Coffee and many soft drinks have pHs around 2-3, they are very acidic, they eat the enamel of you teeth

32. Bases • pHs above 7 are considered Bases • These do not have the reactive hydrogen ions in them and do not cause damage like acids do • There is research that indicated many diseases could be prevented or reversed if our bodies pH were kept more basic, this includes cancer and many viruses

33. Mountain Dew Mouth • It’s acidic dude • This person is 15!

35. Acid Rain • Rain water is naturally acidic in many parts of the country • Rain water below a pH of 5.7 is acidic enough to damage forests, streams, living organisms, and rocks • Because humans continue to burn fossil fuel, our rain is becoming more acidic • Fossil fuel increases the amount of Nitrous acid and sulfuric acid in our rain water

36. Coal Fired plants release nitrogen and sulfur dioxide

37. Effect of acid rain on forests

38. Effect of acid rain on statuesThese are not old statues

39. Erosion • Erosion is the removal and transport of weathered and non-weathered material • Can be from running water, wind, waves, ice, gravity • Water is the most effective agent of weathering and erosion (we’ve already discussed glaciers, cave formation, acid rain)

40. Streams move more than water • Have you seen the Rio Grande in Spring? • It’s muddy, it’s carrying with it soil, rock, and organic material (leaves, branches, dead animals…) • Streams can carry material when they are moving fast • When water slows down, it drops much of what it was carrying

42. Deposition • Sediment is laid down

44. Rocky Mountain National Park Water flowing down steep hill slowed and deposited mud

45. Ocean’s move sediments • Wave action - Ocean waves can erode coastline. In many areas where people own coastline, they can lose property to the ocean. • You can lose 40 feet in one storm

46. The coastline is eroding

47. Erosion removes sand from beaches • Waves erode beaches • Miami Beach is losing beachfront property every year • Cape Cod, Mass. Also loses beachfront property – some people have to move their houses so the house is protected from the eroding coastline

48. Things communities do to save their beaches • Build retaining walls • Bull dose more sand in to beaches