Presentation on theme: "Weathering of Rocks. Exam 1 Why we see weathering 1.Most minerals are not stable at the Earth’s surface 2.The Earth wants to be flat – lowest energy."— Presentation transcript:
Weathering of Rocks
Why we see weathering 1.Most minerals are not stable at the Earth’s surface 2.The Earth wants to be flat – lowest energy state Topography provides energy
Bowen’s Reaction Series and Weathering
IgneousSedimentary Metamorphic Melting Erosion + Deposition Melting Erosion + Deposition Burial + Heating Weathering in the Rock Cycle
Three Dynamic Processes of Breaking and Removing rock 1.Weathering - the disintegration and decomposition of rock at or near the surface 2.Erosion 3.Mass wasting
Types of Weathering Physical (Mechanical) –breakdown of rocks into smaller pieces. Chemical – decomposition of rocks by chemical reactions.
Daily Questions Examine the five World Heritage Sites in Figure 9.1 (pg. 244) 1)Which site is at the greatest risk from physical weathering? Why? 2)Which site is at the greatest risk from chemical weathering? Why?
Mechanical Weathering Mechanical weathering breaks down rocks/minerals Smaller particles increases the amount of exposed surface area Does not change the chemical composition of the minerals\
Frost wedging – water penetrates into cracks, expands when it freezes. Must have: Adequate moisture Cracks in rocks Freeze/thaw cycles Types of Mechanical Weathering
Removal of overlying material allows rock to expands Top layers expand more than deeper layers Causes sheeting or exfoliation Unloading
Chemical Weathering Chemical alteration of minerals. Results in new minerals and ions in solution. Water and acid are essential.
Types of Chemical Weathering 1.Hydrolysis - any reaction in which water participates. a)Ion exchange – H+ replaces other cations. b)Dissolution - mineral completely dissolves, leaving only ions in solution. c)Oxidation - reaction in which elements gain or lose electrons (example: rust).
Dissolution Minerals dissolve in water For example: salts
Carbon Dioxide + Rain Becomes Acid Dissolves Minerals (i.e. carbonates such as calcite) Carries away---Ions Acid Hydrolysis - Dissolution H 2 O + CO 2 H 2 CO 3 CaCO 3 + H 2 CO3 Ca HCO 3 -
Oxidation 1.Iron silicate dissolves 2.Iron oxidizes 3.Oxidized iron combines with water 4.Leaves iron oxide
Results of Weathering 1.Water moves through joints a.Frost wedging b.Chemical dissolution – get clays 2.Joints enlarge 3.Corners are attacked more aggressively – get rounding of the material 4.Fines (clays and silts) wash out of rock
Weathering Products Regolith – a loose layer of broken rock and mineral fragments. Sediments Dissolved Ions