Geology Week 3 Notes
Geology Week 3 Notes 80176 - GEOL 1010 - 001
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80176 - GEOL 1010 - 001
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This 8 page Class Notes was uploaded by Sarah Canterbury on Monday February 1, 2016. The Class Notes belongs to 80176 - GEOL 1010 - 001 at Clemson University taught by Alan B Coulson in Fall 2015. Since its upload, it has received 45 views. For similar materials see Physical Geology in Environmental Science at Clemson University.
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Date Created: 02/01/16
Lecture 5—1/26/16 Geology in the News Volcanic glass ‘egg’ found after Kilauea (Hawaii) eruption last week Geologists have never found anything like this before Part 3- Volcanoes Misconception- The US doesn’t have to worry about volcanoes Japan and Indonesia are the only countries with more volcanoes than the US Active Volcanoes: Hawaii-7; Alaska-41 Case Study: Krakatoa Indonesian island volcano Aug 26, 1883 200 million tons TNT = 13000x the yield of Hiroshima A-bomb 25 cubic km of ejecta Heard>3000 mi away Air pressure waves circled the globe for 5 days, caused waves in the English channel Over 30,000 dead, several languages and cultures went extinct 2/3 of island was destroyed, new volcano built up since Explosiveness Volcano Explosivity Index (VEI) Ranks how explosiveness of volcanoes Explosive vs. Non-Explosive Magma Properties Viscosity- measure of thickness, how difficult it is to flow (low viscosity means easy to flow) Viscosity controlled by 2 main things: 1- Temp: increase temp means decrease viscosity 2- Silica content: increase silica content means increase viscosity Viscosity controls gas content If low viscosity, gas can escape easily If viscosity high, gas can’t escape easily; explosive eruption Non-explosive Features Pahoehoe: (Hawaiian word) has a smooth streaky lava; cooling on the surface, but still flowing and under the crust is still very hot Aa: the lava looks more broken and like solid rock; lost the soft ropey texture of pahoehoe; very brittle, almost all the way cool Vesicles- Explosive Features How fast does lava flow? ‘Fast’= 16km/hr Several hazards beyond lava Lahar: mudslide associated with volcanic eruption Magma works its way up, warming the ground, melting ice/snow on the ground, making it very unstable Pyroclasts: chunks of rock being ejected with lava Divided by size: Bombs > 64mm Lapilli > 62-2mm Ash < 2mm Many people don’t think is too dangerous Can fall in tremendous amounts, sometimes able to bury cars, collapse rooves, get trapped in engines, can turn into cement-like material in your lungs Thrown out of volcano- it’s not made of burnt material Pyroclastic Flow: solid debris trapped in a cloud of gas that can move down the mountain very fast because the gas cloud is typically more dense than air around it Can’t escape it Volcanoes Tend to form layer by layer with different eruptions Different types based on types of eruption and erupted material Shield Volcano: look like a shield; very broad with a very gentle slope up to the top Very common Erupts basaltic magma Explains shape of volcano- low viscosity, flows easily, doesn’t get thrown into the air, spreads out very thin Tephra (cinder) Cone: much steeper volcano; very small; will typically form around larger volcanoes Erupts more pyroclastic material Explains why not so big- not a lot of lava, pyroclasts will just roll down Stratocones: (composite volcano, stratovolcano) tend to have more explosive eruptions Lava has high viscosity Explains steepness- isn’t liquidy enough to flow all the way down the slope Supervolcanic Eruptions These eruptions have a widespread global impact 3 Tambora (1815) 100 km ejecta So much material was ejected, it changed climate patterns Ex) climate too cool for crops in Ireland- famine th Ex) New England had frost on the 4 of July Yellowstone Huckleberry Ridge eruption (2 mya) 2500 km ejecta 3 Covered almost half the country Drives entire species into extinction Hot Spots: over time, the plate above it is going to move, but hot spot won’t move Explains how Hawaii has 7 active volcanoes but not near any plate edges Lecture 6—1/28/16 Sedimentary Processes Why do we care? Type of rock we encounter the most Most common rock type of earths surface Landslides, agriculture, construction, oil, where we find fossils Part 1- Forming Sedimentary Rock Step 1- Parent rock is weathered down to rubble, break down the rock Physical vs Chemical weathering Physical weathering: physically breaking down the rock Ex) plant roots breaking through rock, frost wedging: water fills crack and freezes to ice, but because water expands when freezes, over time and repetition of this process, rock will break Chemical Weathering: more common in many environments As rock types get more unstable, they chemically weather faster More unstable rocks were formed in an environment much different than earth’s surface Chemical weathering with water Saprolite: rock that appears stable, but when hold it or poke it, it will crumble Step 2- Erosion Picking up the weathered particles and moving it somewhere else Requires a lot of energy Eroding agents- water, gravity, wind, glacial ice (least obvious) Step 3- Deposition Putting the rock down Basin- any place where you can deposit cells Accommodation space- how much sediment you can fit into the basin Subsidence- lowering og ground level in basin Caused by: Many basins have huge accommodation space, filled with a lot of sediment that weighs down the floor, allowing for more accommodation space Forms layers (strata, beds) of sedimentary rock Step 4- Lithification Compaction- want to compact the sediments together Want to add more and more layers, which will cause the bottom layers to compact Cementation- as you compact sediments, water will leave the empty spaces, and water will leave behind dissolved materials that will help the sediments cement together Part 2- Classification 1- Detrital (clastic) sediment: formed going through steps we just learned, but usually formed by physical weathering Traits: Sorting- measure of uniformity If grains are all the same size, well sorted; if grains are different sizes, not well sorted Rounding- measure of how smooth the rock is If rock has many corners and jagged, not well rounded; if smooth, well rounded As you transport rock farther and farther, rock gets more rounded Identifying Detrital: Grain size is key 2- Chemical Sediments: formed by chemical reactions, instead of physical Dissolution and re-precipitation Usually comprised of just 1 major mineral Ex) halite=rock salt; quartz=chert Sorting and rounding don’t really apply to chemical sediments Economically viable: ex) mining, because it’s mostly formed of what you’re looking for, so less money on processing 3- Biogenic Sediments: used to be parts of plants or animals, such as shells Ex) chalk, limestone, coal Part 3- Mass Wasting (landslides) Why do we care? Poses hazards, causes delays Slope Destabilization Angle of Repose: maximum angle where a slope is stable; max steepness ~35˚ is pretty average Lack of Moisture: it’s very hard to pile up dry sediments Excessive moisture: creates mud, and mud flows very easily Lack of Vegetation: plant roots are very good at holding sediments in place Excessive vegetation: more roots = pathways where water can get through; also, more plants means more mass, which can be very difficult on steep slope Types of Mass Wasting Categories are based on: material, type of movement, speed Ex) Rockslide: block of solid rock sliding down a slope; because or friction, not going to be as fast as other types of mass wasting Ex) Creep- over time, because the ground is unstable, the sediment is creeping down very slowly Causes of Mass Wasting Unstable slopes do not automatically have a landslide occur Need energy to cause mass wasting Ex) Storms, earthquakes (can also cause secondary hazards), humans and landscaping, clearing out trees Risk Assessment Risk Assessment Maps: color coded maps that display where the biggest hazards are, such as highest risks for landslides Have to be updated fairly regularly Prevention Can often prevent mass wasting, but just need to know the causes Drainage control- add a drainage system to help prevent excess water Decrease slope grades- sometimes slopes are too steep Building codes: make sure people aren’t building in really high risk places Retaining walls Rock bolts: anchors the surface area into layers behind it Prevention: Costs Expensive to implement changes, but damage is more costly Est return is $10-$2000 per $1 spent on prevention Ex) Thistle, UT: 1983 slide caused $200 million in damage, but deemed preventable if $0.5 million had been spent on drainage systems
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