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General Geology: Weathering and Soil. Instructor: Prof. Dr. Boris Natalin. Principle processes. Weathering – disintegration and decomposition of rocks at or near the Earth’s surface Mass wasting – the transfer of rock fragments downslope under influence of gravity
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General Geology: Weathering and Soil Instructor: Prof. Dr. Boris Natalin
Principle processes • Weathering – disintegration and decomposition of rocks at or near the Earth’s surface • Mass wasting – the transfer of rock fragments downslope under influence of gravity • Erosion – the incorporation and transportation of material by mobile agents as water, wind, or ice
Types of weathering: - Mechanical weathering - Chemical weathering
Fragmentation of rocks • Frost wedging • Expansion resulting from unloading • Thermal expansion • Organic activity
Frost wedging Water expands about 9% upon freezing Ice Broken fragments fall to the base of the cliff and create talus Talus
Thermal expansion Rounded pebble disintegrated due to the rapid cooling
Organic activity Weathering is accomplished by: • Plants • Burrowing animals • Human beings
Chemical weathering Water is a good solvent
Acid increases the corrosive force of water • Transformation of solid into soluble • H+ is active ion • Formation of carbonic acid: • Water is a weak acid
Oxidation • 4Fe + 3O2 → 2Fe2O3 • Hematite (Fe2O3) and limonite [Fe2O3(OH)] • Mine acid Hydrolysis
Alteration caused by chemical weathering • Physical change of outcrops - Sharp corners are attacked more readily - Spheroidal weathering
Rates of weathering • Rock characteristics • Climate • Topography
Rock characteristics granite marble
Climate 3500 years in Egypt 75 years in New York
Topography • Humid regions • Arid regions • Differential weathering
Soil • Regolith – • Soil – • Humus –
Soil formation • Parent material • Time • Climate • Plants and animals • Slope
Time in soil formation • Short time – parent material • Long time – other factors, especially climate
Climate in soil formation • Wet and hot climate • Dry climate • Precipitation leach various material from soil
Plants and animals • Main function is to furnish organic matter to the soil • Soil fertility depends on amount of organic matter • Organic decay creates organic acids • Microorganisms and humus • Earthworms mix the soil
Slope in soil formation • Steep slope • Bottomlands and valleys • Flat-to-undulating upland surfaces • Slope orientation
Soil profile A soil profile is a vertical cross-section from the surface down to the parent rocks
Soil profile humus Topsoil 30% humus True soil (solum) subsoil Time span of soil formation Layer A needs many hundreds to several hundreds years Layer B needs 10,000 to 100,000 years
Soil erosion • It is a natural process • Human being can increase the fertility of soil • Human being can damage or destroy soil
Soil erosion • Sheet erosion • Rills • Gullies
Soil erosion • 9 billion metric tons per year • 24 billion metric tons per year • Wind erosion • Filling water reservoirs with sediments • Filling water reservoirs with pesticides and nutrients