Weathering and Erosion Weathering the disintegration and decomposition of material at the surface Erosion the transportation of weathered material by water, wind, or ice
Weathering Two kinds of weathering Mechanical weathering Chemical weathering
Weathering along joints Balanced Rock, Joshua Tree National Monument
Weathering along joints Balanced Rock, Joshua Tree National Monument
Unloading and exfoliation of igneous rocks
Exfoliation joints Tioga Road, Yosemite National Park
Exfoliation joints Yosemite National Park: Half Dome
Ice wedging expansion of water due to freezing
Salt weathering growth of salt crystals due to evaporation of water
Prying apart of rocks due to growth of tree roots along joints and fractures
Water transport
Wind transport
Ice transport
Weathering Chemical weathering Dissolution of minerals Chemical alteration of minerals by removal/addition of elements
Acids: chemical solutions in which hydrogen ions (H + ) are released
Formation of carbonic acid CO 2 + H 2 O water and carbon dioxide
Formation of carbonic acid CO 2 + H 2 O water and carbon dioxide H 2 CO 3 carbonic acid
Formation of carbonic acid CO 2 + H 2 O water and carbon dioxide H 2 CO 3 carbonic acid H + + HCO 3 - hydrogen ion + bicarbonate ion
Formation of carbonic acid CO 2 + H 2 O water and carbon dioxide H 2 CO 3 carbonic acid H + + HCO 3 - hydrogen ion + bicarbonate ion 2H + + CO 3 2-2 hydrogen ions + carbonate ion
Carbonic acid in the ocean
Chemical weathering -- dissolution of calcite Granite Limestone
Chemical weathering dissolution of limestone or marble
Weathering Chemical weathering of silicate minerals Goldich s stability series Stability of silicate minerals increases with the percentage of Si-O bonds: Quartz all Si-O bonds, most stable Feldspars Micas Hornblende Augite Olivine fewest Si-O bonds, least stable
Weathering Chemical weathering of silicate minerals Weathering of mafic minerals produces insoluble iron oxides and clay minerals
Weathering Chemical weathering of silicate minerals Weathering of mafic minerals produces insoluble iron oxides and clay minerals Weathering of feldspars produces clay minerals and silica in solution
Weathering Chemical weathering of silicate minerals Weathering of mafic minerals produces insoluble iron oxides and clay minerals Weathering of feldspars produces clay minerals and silica in solution Quartz remains substantially unaltered
Formation of Kaolinite, a clay mineral, from the weathering of Orthoclase 2KAlSi 3 O 8 orthoclase
Formation of Kaolinite, a clay mineral, from the weathering of Orthoclase 2KAlSi 3 O 8 + 2H 2 O orthoclase water
Formation of Kaolinite, a clay mineral, from the weathering of Orthoclase 2KAlSi 3 O 8 + 2H 2 O + 2H + orthoclase water hydrogen ions
Formation of Kaolinite, a clay mineral, from the weathering of Orthoclase 2KAlSi 3 O 8 + 2H 2 O + 2H + orthoclase water hydrogen ions 2K + potassium ions
Formation of Kaolinite, a clay mineral, from the weathering of Orthoclase 2KAlSi 3 O 8 + 2H 2 O + 2H + orthoclase water hydrogen ions Al 2 Si 2 O 5 (OH) + 2K + kaolinite potassium ions
Formation of Kaolinite, a clay mineral, from the weathering of Orthoclase 2KAlSi 3 O 8 + 2H 2 O + 2H + orthoclase water hydrogen ions Al 2 Si 2 O 5 (OH) + 2K + + 2SiO 2 0 kaolinite potassium ions silica in solution
Clay crystals have a charge separation, with positive charges sandwiched between layers of negative charge, making them attractive to water molecules 10 microns = 0.01 mm
Spheroidal weathering chemical weathering along surfaces and joint planes
Sandcastles collapse when sand dries (pores contain only air) or when sand is saturated (pores contain only water)
Sand grains stick together while damp, due to surface tension -- when pores contain water and air, water molecules stick to each other and to sand grains
When dry, clay holds about 20% water -- sculptures thus hold their shape through the firing process
Rates of weathering Advanced mechanical weathering aids chemical weathering by increasing the surface area Important factors Rock characteristics Mineral composition and solubility Physical features such as joints
Rates of weathering Important factors Climate Temperature and moisture are the most crucial factors Chemical weathering is most effective in areas of warm temperatures and abundant moisture