Weathering Chapter 7.1 Earth-Environmental WZPP

WZPP ees 7.12 Introduction Read page 153 on Cleopatra’s needle and see figure 7-1

WZPP ees 7.13 Weathering of Cleopatra’s needle. The photograph taken to the left in Egypt before 1880, on the right was taken in New York in 1918 (courtesy of the Metropolitan Museum of Art)

WZPP ees 7.14 Introduction Weathering  Is the process by which rocks near the earth’s surface break down and change Erosion  The removal and transport of weathered material These processes have been going on for a long time

WZPP ees 7.15 Mechanical Weathering Materials change size or shape Breakdown of material into smaller pieces Holly Lake Tetons NP J B Photos Backcountry lake Tetons NP J B Photos

WZPP ees 7.16 Mechanical Weathering Temperature  Water freezes and expands by 9%  Exerts pressure on the rock  Frost wedging Causes potholes

WZPP ees 7.17 Mechanical Weathering Pressure  When rock is deep underground and is exposed at the surface, the pressure of the rock is reduced Rocks break apart like layers in an onion (exfoliation)  Example: Half Dome in Yosemite NP 7.1a ws

WZPP ees 7.18 Mechanical Weathering Pressure  Roots wedge themselves into cracks and exert pressure as they grow

WZPP ees 7.19 Chemical Weathering Rocks and minerals undergo changes due to chemical reactions Chemical reactions form new minerals and release dissolved substances

WZPP ees Chemical Weathering Composition of the rock determines the effects of chemical weathering

WZPP ees Chemical Weathering Temperature determines the rate of chemical weathering  Increase temperature means increased chemical weathering

WZPP ees Chemical Weathering Agents of erosion:  Water  Oxygen  Carbon dioxide  Acids

WZPP ees Chemical Weathering Water  Dissolves many kinds of minerals and rock  Serves as a medium through which other reactions occurs

WZPP ees Chemical Weathering Oxygen  Combines with other substances  Iron (& other minerals) readily combine with atmospheric O 2

WZPP ees Chemical Weathering Carbon Dioxide  CO 2 + H 2 O  weak carbonic acid  Reacts with minerals (like calcite) in limestone, marble to dissolve rock 7.1b ws

WZPP ees Chemical Weathering Acid precipitation  Caused mainly by oxidation of sulfur dioxide and nitrogen oxide in atmosphere due to human activities  Is precipitation below 5.5 pH  Is harmful to living organisms

WZPP ees Rate of Weathering Climate has a major influence  Variables include Precipitation Temperature Evaporation  Interaction between temperature and precipitation is the greatest effect

WZPP ees Rate of Weathering Chemical weathering occurs readily in areas that have warm temperatures, abundant rainfall and lush vegetation

WZPP ees Rate of Weathering Physical weathering occurs readily in cool, dry climates  Is highest where water undergoes repeated freezing and thawing Remember, cool temperatures inhibit (slows) chemical reactions

WZPP ees Rate of Weathering Harder rock is going to be more resistant to weathering than soft rock  This depends type of rock and their composition (what they are made of) Sedimentary rock is generally going to be more easily weathered than igneous or metamorphic

WZPP ees Rate of Weathering Surface area  Increased surface area equals increased weathering Both physical and chemical

WZPP ees Rate of Weathering Topography  The steeper the slope, the greater tendency for a material to move downhill Indian Paint brush canyon Tetons NP J B Photos

WZPP ees Rate of Weathering Organisms  Decaying organic matter and plant roots release carbon dioxide for chemical weathering 7.1c ws