Transcript Weathering
Weathering http://amazingworld.5u.com/photo.html Objectives • Define weathering • Identify causes of weathering – Physical or Mechanical Weathering – Chemical Weathering – Biological Weathering •Discuss soil formation Weathering Weathering is a set of physical, chemical, and biological processes that alter the physical and chemical state of rocks and soil at or near the earth's surface. http://www.uh.edu/~jbutler/physical/chapter6.html Effects of Weathering • Loss of atoms and molecules from weathered surfaces. • Addition of specific atoms to the weathered surface. • Breakdown of one mass into two or more masses. Chemical Weathering • Involves the alteration of the chemical composition of weathered material. There are different process that result in chemical weathering including: – Hydrolysis – Oxidation – Carbonation Hydrolysis Chemical weathering is a process that involves the reaction between mineral ions and the ions of water (OH- and H+), and results in the decomposition of the rock surface by forming new compounds, and by increasing the pH of the solution through the release of the hydroxide ions. - Silicate minerals weather by hydrolysis to form clay. Oxidation Chemical attachment of free oxygen to other elements and compounds. Iron-bearing silicate minerals that undergo oxidation include the following: – pyroxene – amphibole http://wwwrses.anu.edu.au/research/annrep/ar2006/ee/index.php?p=pillans – biotite – olivine Rocks that contain these elements weather by oxidation into an orange color. Carbonation Dissolving of calcium carbonate (limestone) in acidic groundwater - similar to hydrolysis but all the products are ionic and there is no residue - produces bicarbonate (HCO3), a major part of the dissolved load of most rivers http://www.khaolaklanddiscovery.com/_images/tours/khao_sok/ old_coral_big.jpg - the carbonation of limestone results in karst topography: caves, sinkholes, etc. Physical Weathering • Breakdown of mineral or rock material by entirely mechanical methods brought about a variety of reasons. – Frost Wedging – Exfoliation or Unloading – Thermal Expansion – Plant Wedging http://members.aol.com/rhaberlin/mwstyg.htm Frost Wedging • Mechanical disintegration, splitting or break up of rock by the pressure of water freezing in cracks, crevices, pores, etc. • Caused by repeated freeze-thaw cycle of water in extreme http://regentsprep.org/Regents/earthsci/units/weathering/frostwedging.gif climates. Exfoliation or Unloading • Expansion of rock caused by lifting and erosion • Rock breaks off into sheets along joints that parallel surface. http://facstaff.gpc.edu/~pgore/Earth&Space/condestr.html Thermal Expansion • Repeated cooling and heating of rock. • Heat caused rock to expand and cooling causes rock to contract • Looks very similar to frost wedging and salt crystal growth, but typically occurs in climates of extreme weather changes. Thermal shattering of sandstone by forest fire. http://w3.salemstate.edu/~lhanson/gls210/gls210_weath1.htm Plant Wedging • Plant roots can wedge into cracks in rocks and produce enough pressure to split them • Chemicals produced by the roots of plants help in the chemical weathering, as enzymatic activity digest the rock as the plant searches for nutrients in the rock. http://facstaff.gpc.edu/~pgore/Earth&Space/condestr.html Biological Weathering • Animals and Plants can assist in breaking down rocks into sediment and soil. Biological Weathering can be caused by: • Roots of trees and other plants • Lichens, fungi, and other microorganisms. • animals http://w3.salemstate.edu/~lhanson/gls210/gls210_weath1.htm Soil Formation • Soil is formed from the weathering of rocks and minerals. • Surface rock breaks down by weathering and is mixed with organic material. Over time it creates a thin layer of soil. lh3.google.com/.../s800/IMG_1466-1.jpg Five Soil Forming Factors 1. 2. 3. 4. 5. Parent Material- The primary material from which rock is formed. Climate- Weathering forces including heat, rain, ice snow, wind, etc. Organism- all animals living in or on the soil. Ex: Animals living in the soil will affect how soil is moved around and decomposition of waste materials. Topography- the location of the soil on a landscape. Ex: Soil at the bottom of a hill will get more water than that on the slope. Time- The formation of soil takes years. Topography Image courtesy of the United States Department of Agriculture, Soil Conservation Service http://soil.gsfc.nasa.gov/soilform/parmat.htm References • • • • • • • http://uregina.ca/~sauchyn/geog221/wthrng.html http://www.physicalgeography.net/fundamentals/10r.html http://gpc.edu/~pgore/Earth&Space/condestr.html http://geosun.sjsu.edu/paula/134/pdf/lecture3.pdf http://library.thinkquest.org/J003195F/soil.htm http://soil.gsfc.nasa.gov/soilform/parmat.htm http://w3.salemstate.edu/~lhanson/gls210/gls210_weath1.htm