Warm-up: What has occurred in these pictures? Please write a brief description. Weathering Types of Weathering Mechanical or Physical Chemical Weathering is the process that . . __________________________ __________________________ _____ Mechanical Weathering Definition: Mechanical weathering breaks apart rocks without changing the chemical structure. Types of Mechanical Weathering 1) Frost wedging 2) Exfoliation 3) Thermal expansion Mechanical Weathering Expansion and Contractions water expands when it freezes and causes rock to break Mechanical Weathering Freeze/thaw cycles break down rock as water enters cracks and widens them Mechanical Weathering: Exfoliation rock breaks off into sheets, which is caused by the – Expansion of the rock due to erosion – Pressure from the earth’s surface Mechanical Weathering: Thermal Expansion Chemical Weathering Types: Chemical weathering occurs when water, air, and other substances react with minerals in the rocks and it’s chemically changed. 1) Dissolution 2) Oxidation Chemical Weathering: Dissolution – Can dissolve rock – Can form acids as they react with rocks and atmosphere – The gravestone shown here is chemically changed from London’s pollution, vehicle exhaust fumes that contain sulfur and nitrogen. Chemical Weathering: Oxidation – Oxygen combines with elements in the rock – Often rocks become discolored Some types of rock are easily weathered by chemicals. – For example, limestone and chalk are made of a mineral called calcium carbonate. – When acidic rainwater falls on limestone or chalk, a chemical reaction happens. – New substances are formed in the reaction. These are washed away and the rock is weathered. – Chemical weathering can make caves form and cliffs fall away. Chemical Weathering – Carbon dioxide with water creates carbonic acid that eats away rock. Carbonic acid is the same weak acid that makes soft drinks fizzy. Chemical Weathering – Several caves around the world are examples of chemical weathering What did we learn? What is mechanical weathering? What is chemical weathering? Do they work together? Now, let’s take a weathering walk and find what kind of weathering takes place in our backyard!!