CEE 1030 1st Edition Lecture 4 Review Question Which was the largest explosive volcanic eruption of historic time 1 2 3 4 5 Laki Iceland 1783 AD Mt St Helens USA 1980 AD Mt Pinatubo Philippines 1991 AD Tambora Indonesia 1815 AD Krakatoa Indonesia 1883 AD Which one of the following factors is more likely to lead to highly explosive eruptions 1 2 3 4 5 Low gas content High temperature 1200 C Low SiO2 content 50 High viscosity Basaltic composition June 24th 1982 British Airways Flight 009 Boeing 747 London to Auckland Kuala Lumpur to Perth leg plane flew straight through eruption happening in Indonesia December 15th 1989 KLM Flight 867 Boeing 747 400 Amsterdam to Tokyo via Anchorage Alaska plane flew into ash cloud from Mt Redoubt that had started erupting 10 hours before after two crashes airlines started looking up what they can do to avoid these volcanic incidents International Symposium on Volcanic Ash and Aviation Safety Seattle 1991 Establishment of volcanic ash advisory center European airspace closed from 15th to 20th April also no Trans Atlantic flights Pacific completely surrounded by volcanoes planes know now to go right above the volcanoes Natural Processes of Change Sedimentary rocks formed from the breaking down of other rocks ex The Old Man of the Mountain New Hampshire Arches National Park near Moab Utah Earth s external Processes Weathering breakdown of rocks at the earth s surface These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Erosion physical removal of material by mobile agents ex water wind ice gravity Exposes fresh unaltered rock to weathering taking the material and putting it somewhere else lead to formation of sedimentary rocks release important nutrient elements into surface water some mineral weather very easily some do not Two types of weathering process mechanical weathering disintegration breakings rocks into smaller pieces without changing their chemical composition chemical weathering decomposition chemical reactions between rock minerals and air water 1 form new minerals 2 release ions into solutions Mechanical Weathering 1 Frost Wedging exerts immense pressure occurs as the result of 9 expansion of water when it is converted to ice 2 Root Wedging rocks on tree roots tree will still grow but begin lean slowly fall 3 Salt Wedging evaporation of water rich in dissolved species will lead to growth of crystals in cracks exerts force calcite gypsum halite 4 Thermal expansion large daily temperature changes cause thermal strain 5 Unloading uplift and erosion reduces pressure Chemical Weathering dissolution promoted by acidic water hydrolysis reaction of mineral with water Hydrogen ion attacks and replaces other ions oxidation exposure to atmospheric oxygen Chemical Weathering Dissolution rain water reacts with atmospheric gases to form weak acids H acidic water corrosive to minerals calcite a solid mineral is completely dissolved releasing calcium and Bicarbonate ions into the water Chemical Weathering Acid Rain burning of fossil fuels produces sulfur dioxide and nitrogen oxides these gases react with rain water to form sulfuric acid and nitric acid results in environmental damage Chemical Weathering Hydrolysis hydrogen ions replaces other cations in mineral structure producing new minerals solid potassium and feldspar acidic water solid residual Kaolinite clay solution containing dissolved potassium ions bicarbonate ions and silica Chemical Weathering Oxidation iron released from ferromagnesian silicates ex olivine pyroxene amphibole biotite mica Chemical Weathering Products breaking down chemical of rocks is a way to find different elements placer deposits resistant economic minerals ex gold diamonds Released from rock during weathering but resistant like quartz can be found in location such as Southern Africa mainly over to the eastern side Rates of Chemical Weathering surface area same volume of rock but smaller particles have greater total surface area rock type rocks containing calcite marble and limestone readily dissolve in weakly acidic solutions caves Silicate minerals weather in the same order as their order of crystallization High T minerals Less stable at Earth s surface often find fossilization in minerals during this weathering very important control is the climate temperature moisture Chemical weathering is most effective in areas of warm moist climates Rates of chemical reactions double for 10oC increase Review Questions Which of the following statements about mechanical weathering NOT true 1 2 3 4 5 is important in the formation of talus slopes Allows for faster rates of weathering Can occur due to expansion of water when it freezes in rock fractures Involves a major change in the mineral composition of weathered material Reduces the grain of shared minerals Review Question Under similar climate conditions why would basalt gabbro generally have higher chemical weathering rates than rhyolite granite 1 olivine pyroxene in the basalt and gabbro are subjected to oxidation and chemical breakdown 2 olivine and pyroxene in the rhyolite and granite are resistant to chemical weathering 3 quartz in the basalt and gabbro decomposes very quickly 4 quartz in the rhyolite and granite decomposes rapidly to clay minerals Physical Effects of Chemical Weathering spheroidal weathering gradual rounding of edges and corners of angular fragments can get differential weathering regolith layer of weathering products at the earth s surface rock and mineral fragments soil combination of mineral and organic matter plus water and air The portion of the regolith that can support the growth of plants humus decayed remains of animal and plant life organic matter essential part of soil Soil formation parent material Residual soil developed on bedrock Transported soil on unconsolidated deposits Factors controlling soil formation Climate most influential control Key factors are temperature and precipitation Time amount of time for soil formation varies for different soils depending on geologic and climate conditions Plants and animals influence soil physical and chemical properties Microorganisms worms Topography steep vs gentile slopes Tropical Soils Laterites highly leached soils laterites Mainly Fe and Al Nutrient poor soil Nutrients stored in plants and surface humus layer Tropical Soils Bauxite more intense weather good drainage bauxite Contains Gibbsite Al OH