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UI CEE 1030 - Earth Science

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CEE 1030 1st Edition Lecture 4 Review Question: Which was the largest, explosive volcanic eruption of historic time?1. Laki, Iceland, 1783 AD2. Mt St Helens, USA, 1980 AD3. Mt Pinatubo, Philippines, 1991 AD4. Tambora, Indonesia, 1815 AD5. Krakatoa, Indonesia, 1883 ADWhich one of the following factors is more likely to lead to highly explosive eruptions?1. Low gas content 2. High temperature (~1200 C)3. Low SiO2 content (~50%)4. High viscosity 5. Basaltic compositionJune 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 rocksex. 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 silicatesex. 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 sideRates 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  moistureChemical weathering is most effective in areas of warm, moist climatesRates of chemical reactions double for 10oC increaseReview QuestionsWhich of the following statements about mechanical weathering NOT true?1. is important in the formation of talus slopes. 2. Allows for faster rates of weathering 3. Can occur due to expansion of water when it freezes in rock fractures4. Involves a major change in the mineral composition of weathered material 5. Reduces the grain of shared minerals Review QuestionUnder 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


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