1. © 2007, John Wiley and Sons, Inc. Physical Geography by Alan Arbogast Chapter 14 Weathering and Mass Movement Lawrence McGlinn Department of Geography State University of New York - New Paltz

2. © 2007, John Wiley and Sons, Inc.Weathering Process by which rocks break down into smaller pieces Two Primary Types: Mechanical (or physical) – cold, wet/dry environments Chemical – warm, moist environments

3. © 2007, John Wiley and Sons, Inc. Weathering Environments

4. © 2007, John Wiley and Sons, Inc. Mechanical Weathering Destruction of rock through physical stresses Rocks break into small pieces – surface area of rock increases – even greater weathering Types: Frost Wedging Impact of Roots Temperature Fluctuations Salt Crystal Growth Exfoliation

5. © 2007, John Wiley and Sons, Inc. Frost Wedging Most common form of mechanical weathering Water flows into joints (fractures) in rock Expands 9% when it freezes Stress cracks rock

6. © 2007, John Wiley and Sons, Inc. Impact of Roots Roots or trunks of vegetation, especially trees, can grow through & expand cracks in rocks

7. © 2007, John Wiley and Sons, Inc. Temperature Fluctuations- Temperature expansion Warming & cooling – rocks expand & contract – rocks break down – especially in arid regions Death Valley, CA

8. © 2007, John Wiley and Sons, Inc. Salt Crystal Growth Salt in rocks weakens mineral bonds, loosening sediments which erode through wind or water Arid climate in Southwestern US

9. © 2007, John Wiley and Sons, Inc.Exfoliation Deep rock slowly uncovered by erosion of overlying layers – pressure on rock reduced Under less pressure, rock layers flake off Most common in igneous or metamorphic rock

10. © 2007, John Wiley and Sons, Inc. Chemical Weathering Changes rock by altering its chemical composition – water particularly important Types: Hydrolysis Oxidation Carbonation Acid Rain

11. © 2007, John Wiley and Sons, Inc.Hydrolysis Decomposes silicate minerals in rocks Hydrogen & hydroxyl ions from water added to rock – silicate molecules split Rounds sharp edges and corners of rocks Spheroidal Weathering

12. © 2007, John Wiley and Sons, Inc. Oxidation Oxygen is added to chemical compounds, causing electrons in compounds to be lost Happens in rocks high in iron (rust) Oxidized Sandstone in southwest US

13. © 2007, John Wiley and Sons, Inc. Carbonation CO 2 dissolves in atmospheric water vapor, forming carbonic acid in precipitation This carbonic acid dissolves minerals, esp. limestone (calcium carbonate) Effects of Carbonation in limestone

14. © 2007, John Wiley and Sons, Inc. Acid Rain Coal-burning power plants in Midwest emit sulfur dioxide (SO 2 ) & nitrogen oxides (NO x ) SO 2 & NO x mix with water in clouds to form sulfuric or nitric acid Clouds move east where acid rain falls Acid rain accelerates chemical weathering Acid rain can also harm lakes & forests Regulation has cut acid emissions dramatically Weathering

15. © 2007, John Wiley and Sons, Inc. Mass Wasting Large volumes of sediment moving down hill slopes under force of gravity Types:

16. © 2007, John Wiley and Sons, Inc.Solifluction Form of soil creep in tundra landscapes Surface of permafrost melts & soil sags down slope in uneven lobes

17. © 2007, John Wiley and Sons, Inc. Earth Flow Slow-to-rapid movement of wet soil & other loose sediment over a broad surface One of 3 types of Flow – mass movement of wet sediment

18. © 2007, John Wiley and Sons, Inc. Mudflow Fine textured sediments that move very quickly down slope – occur after heavy rainfall Mudflow deposit Never-Sumner Range, Colorado

19. © 2007, John Wiley and Sons, Inc. Debris Flow Mud, boulders, trees, etc. flowing down slope after heavy rainfall – very dangerous La Conchita, CA Debris Flow

20. © 2007, John Wiley and Sons, Inc.Slump Slide where rock & sediment rotates & moves down slope along plane concave to surface Happens on slopes w/ soft deposits rich in clay and shale

21. © 2007, John Wiley and Sons, Inc. Debris Slide Type of Landslide – mass of rock, regolith & soil that flows downhill Slope failure along a plane roughly parallel to the slope Madison Slide, Montana

22. © 2007, John Wiley and Sons, Inc. Soil Creep Slowest mass wasting process Force of gravity slowly pulls soil particles down hill – features of hill shift down hill, as well

23. © 2007, John Wiley and Sons, Inc. Rockfall Process in which rocks break free from cliff faces & rapidly tumble into valley below

24. © 2007, John Wiley and Sons, Inc.Avalanche Large mass of snow or rock that suddenly slides down a mountainside Starting Zone Track Runout Weathering and Mass Movements