Understanding Earth Fifth Edition Grotzinger Jordan Press Siever Chapter 16: WEATHERING, EROSION, AND MASS WASTING Interface Between Climate and Tectonics Lecturer: H Mohammadzadeh Assistant professors, Department of Geology, FUM Copyright 2007 by W. H. Freeman and Company Chapter 16 Weathering, Erosion, and Mass Wasting (Landslide): Interface Between Climate and Tectonics 1
About Weathering, etc. Weathering produces all the soils, clays, sediments, and dissolved substances. Erosion is the removal of sediments by natural processes such as wind and rivers. Mass wasting is the downslope movement of masses of Earth materials. Lecture Outline 1. Weathering, erosion, mass wasting, and the rock cycle 2. Controls on weathering 3. Chemical weathering 4. Physical weathering 5. Soil: the residue of weathering 6. Mass Wasting 7. Classification of mass movements 2
1. Weathering, erosion, mass wasting, and the rock cycle Weathering is the process of converting rock into sediment and forming soils, a main process in the rock cycle. Erosion and mass wasting are the processes that loosen and transport soil and rock downhill. 2. Controls on weathering Properties of the parent rock various minerals weather at different rates a rock s structure affects its susceptibility to cracking and fragmentation Other important factors climate (rainfall and temperature) soil (presence or absence) time (length of exposure) 3
2. Controls on weathering 3. Chemical weathering Occurs when minerals react with air and water role of water (hydrolysis) carbon dioxide (carbonic acid) moist soils 4
Granite is made up of several minerals that decay at different rates. 3. Chemical weathering: the disintegration of granite Feldspar Magnetite Biotite Quartz 3. Chemical weathering: the disintegration of granite The decay progresses, Granite is made up and the rock weakens of several minerals and disintegrates. that decay at Cracks form along different rates. crystal boundaries. Feldspar Magnetite Biotite Quartz 5
3. Chemical weathering: the role of increasing surface area 2 cm 1 cm 2 cm 1 cm Large rocks have less surface area for chemical weathering than small rocks do, so smaller rocks weather more quickly. 6
3. Chemical weathering Chemical stability: a speed control for weathering solubility rate of dissolution relative stability of common rock-forming minerals 7
3. Chemical weathering: red means iron 4. Physical weathering What determines how rock breaks? natural zones of weakness activity of organisms frost wedging exfoliation 8
4. Physical weathering: joints in rocks 4. Physical weathering: tree roots 9
4. Physical weathering: frost wedging 4. Physical weathering: exfoliation 10
4. Physical weathering Physical weathering and erosion duration of weathering bedrock type climate topography 4. Physical weathering 11
5. Soil: the residue of weathering Soils as geosystems input material transformations and translocations output material The basic soil-forming processes result in losses (transformations) and additions (translocations). Losses Additions Organic material Water erosion Airborne dust Wind Leaching Chemicals and minerals from bedrock Minerals, grains, and aggregates may move through the soil. TRANSLOCATION TRANSFORMATION Transformation and translocation occur throughout the soil profile. Minerals are transformed into other minerals. Other minerals precipitate from fluids. 12
5. Soil: the residue of weathering Paleosols ancient soils climate history ancient atmosphere history of erosion 13
6. Mass wasting Mass wasting includes all processes by which masses of rock and soil move downslope. Mass movement occurs when the force of gravity exceeds the strength of the material and it moves downslope. Three primary factors 6. Mass wasting Nature of slope materials Unconsolidated materials sand and silt rock fragments, sand, silt, and clay Consolidated materials rock compacted (cohesive) sediments and soils Amount of water Steepness and stability angle of slope accumulation of rubble breakage into large blocks 14
6. Mass wasting 6. Mass wasting: the behavior of dry and wet sand 15
6. Mass wasting: the accumulation of rubble on a slope 16
Water content lubrication liquefaction 6. Mass wasting Triggers of mass movements earthquake vibrations rainfall and water infiltration overloading 6. Mass wasting 17
Mass wasting: after the earthquake 7. Classification of mass movements Three characteristics used nature of material (rock or unconsolidated) nature of movement (flow, slide, or fall) velocity of movement (slow, moderate, or fast) 18
Key terms and concepts Chemical weathering Consolidated material Creep Erosion Exfoliation Hematite Humus Joint Kaolinite Liquefaction Mass movement Mass wasting Physical weathering Soil Soil profile Unconsolidated material 19