9.2 Rates Of Weathering
Pick a chore that you have to do. Explain two different ways to perform the same chore. How much time will it take? Why do the times vary?
Differential Weathering The process by which softer, less weather resistant rocks wear away and leave harder, more weather resistant rocks behind. Devils Tower in Wyoming
How does the composition of a rock relate to differential weathering? Softer rocks weather more completely than hard rocks do in the same amount of time.
Surface Area of Rocks The greater the proportion of a rock that is exposed to weathering the faster the rock will wear down. Weathering takes place only on the outer surface of rock.
Climate The average weather conditions of an area over a long period of time. Warmer wet climates weather faster.
Temperature Major factor in weathering Higher temperatures cause faster chemical reactions. Temperature using infrared wavelengths
Moisture The rate of chemical reactions and mechanical weathering increase when water is present.
High Elevation Has high winds and temperature extremes. Exposed to large amounts of precipitation. Cause rocks to weather fast.
Steep Slope Increase the speed of water running downhill. Has more energy to break down rock.
Biological Factors Organisms can produce acid in soil that speeds chemical weathering. Burrowing animals and plant roots speed mechanical weathering.
Review Questions 1. How does climate affect rates of weathering? Rocks in areas that have warm, humid climates will weather faster than rocks in areas that have cold, dry climates will. 2. Name two ways in which water may increase the rate of weathering. Water can increase the rate of chemical weathering because weathering reactions like oxidation happen faster in the presence of water. Water can also increase the rate of mechanical weathering by causing abrasion or by causing ice wedging.
How can the process of chemical weathering be influenced by mechanical weathering? When a rock is mechanically weathered, the surface area of the rock increases. Therefore, more of the rock is exposed to chemical weathering, and the rate of chemical weathering increases. What factors would cause the rate of mechanical weathering to differ for different rocks? Rock hardness, surface area, climate, elevation, slope, and biological factors.
Chapter 9 Review Mechanical weathering Chemical weathering Ice wedging Abrasion Plant growth Oxidation Acid precipitation Rates of weathering: Climate Temperature High elevation Differential weathering