GEOG 1113 Unit 1
GEOG 1113 Unit 1 GEOG 1113
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This 9 page Bundle was uploaded by Kevin Smith on Wednesday April 6, 2016. The Bundle belongs to GEOG 1113 at University of Georgia taught by Brooks in Fall 2015. Since its upload, it has received 11 views. For similar materials see Introduction to Landforms in Geography at University of Georgia.
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Date Created: 04/06/16
Introduction to Landforms Structure of the Earth Radius: 400 miles Gold mines: 2 mile o Get hotter as depth increases because rocks increase in temperature Oil wells: 4.5 miles Geothermal gradient: 1C / 50 m o Rate at which temperature increases as depth increases, moving closer towards the center of the earth Density of surface rocks: 2.8g / cc (cubic centimeter) o Average density of earth: 5.5g / cc Average for any given rock Density of rock increases as depth increases o Average density is 5.5g / cc, but surface average density is only 2.8g / cc Shock Waves / Seismic Waves produced by earthquakes Every time there is an earthquake, the whole world feels it When there is an earthquake, the energy moves out into the rock in all directions Epicenter: the point on the surface directly above an earthquake’s focus point, strongest and closest to focus Focus: the origin of the earthquake Anticenter: the point of the surface that is diametrically opposite to the epicenter Seismograph: instrument used to measure the strength of the earthquake o Milne-Shaw Seismograph Used around 1940s, but improved over time 1) Light reflected from mirror onto rotating drum (with light sensitive paper) 2) Light burns a line into paper 3) Measures time that displacement of beam occurred Seismogram: record of the measurement made by the seismograph John Milne & John Johnson Shaw created Milne-Shaw Seismograph Drum seismograph: displacement from side to side creates lines that measure the strength of the earthquake Types of Seismic Waves Primary (P) – 4.8 miles/sec Secondary (S) – 2.7 miles/sec Long (L) – 2.5 miles/sec P+S waves travel out from the focus deep within the earth L waves move slowly, often reflected / refracted, can cause most devastation because they can’t handle dense rocks and move through surface P waves travel in the same manner as sound waves o Push/pull in direction of energy movement S waves o Up/down movement o Vibration of particles o Horizontal side to side L waves (surface waves) o Orbital motion o Elliptical Locating an Earthquake’s Epicenter P wave energy is the fastest o About 2x fast as other waves L wave travels across surface P & S waves move directly from source to surface through earth P waves arrive sooner to seismograph than S waves o The larger time displacement between arrival of P and S waves, the farther away the earthquake is 1) Use seismograph to find the time between P and S waves 2) Use Time vs. Distance chart to find distance 3) Draw circles on a map radiating from seismocenters Shadow Zones P waves travel through solids, liquids, and gases S waves travel only through solids S-Wave Shadow Zone S wave shadow zone is located at 103 from epicenter around each side of the surface of the earth Since S wave don’t pass through liquids, energy is absorbed by the earth’s core (liquid), thus creating the shadow zone o Core is liquid because high heat and low pressure P-Wave Shadow Zone P wave energy refracted through core o Change in density of mantle->core causes angle refraction o Core is much denser than mantle P wave shadow zone ranges from 103 to 143 from the epicenter on each side of the earth’s surface Seismic Wave Travel Time It takes about 4 minutes to travel to the core’s edge and about 20 minutes to travel to the anticenter As focus depth changes, P-shadow zone’s position will also change Why are the wave paths curved? Energy is faster in denser rocks As the energy front enters the core from the mantle, energy is refracted and one edge refracts sooner than the other edge of the front o Mantle is solid – fast o Core is liquid – slow Internal Structure of the Earth Inner to Outer: Inner core, Outer core, Mantle, Asthenosphere, Lithosphere Asthenosphere: not a completely true liquid but it still mobile o Similar to glass in that it is a flexible solid o Flows more slowly than the mantle Outer core is a liquid because it is under high heat and lower pressure (ideal conditions for melting solids) Inner core is solid because it is under high heat and high pressure (ideal conditions for maintaining state) Temperature decreases closer towards surface o Pressure remains same, so levels solidify more and more closer to surface Zones within the Earth Interior of the Earth Earth’s Magnetic Field Produced by flow of electrically-charged particles in core Flow generates electrical current that produces magnetic field Flow in outer core is 1 million times faster than flow overlying mantle Dynamo: rotate a magnet inside a coil of copper wire to produce a current Electric motor: pass a current through a coil of wire to produce a magnetic field Earthquakes Richter Scale o Charles F. Richter, 1935 o Modified in 1965 and 1967 o “The log10 of the maximum seismic wave amplitude (measured in 1000ths mm) on a Wood-Anderson seismograph at 100 km from the epicenter” How Severe is an Earthquake 2.5 – large enough to be felt nearby st 5.0 – about the same severity as 1 atomic bomb detonated in New Mexico ( July 16, 1945) 8.6 – releases about 3 million times the energy of a 5.0, or 3 million atomic bombs Largest Earthquakes Scale is logarithmic, so 5.0 is 10x larger than 4.0, and 6.0 is 100x larger than 4.0 o 33x the energy released for each unit of scale San Francisco – 1989 – 7.1 Alaska – 1899 – 8.6 On average, we receive 2 earthquakes measuring about 7.8-8.6 Continental Drift Early on, geologists found marine shells and corals in rocks that are thousands of feet above sea level o This suggested either that sea level was once much higher than now, or that the rocks had somehow been pushed upward to higher elevations In 1915, Alfred Wegoner, a German meteorologist, suggested that not only had the rocks been pushed up, but that the continents had also moved horizontally o In 1930, he proposed that at one time, all the continents formed one super- continent, called “Pangaea” (“all earth”) Can we prove Wegoner is correct? A) The Jigsaw Problem 1) Do the pieces fit? We should be bale to fit the continents together if Pangaea were true 2) If pieces fit, is the picture correct? Sometimes, jigsaws fit but color and picture do not match up We can test this by looking at the patterns and ages of rock by examining evidence of ancient glaciation B) Paleomagnetism 1) Does evidence show that the continents were joined? Ancient magnetism is used to determine past position of continents 2) If continents did drift, when did Pangaea exist and how did the continents drift? The problem of Shape: Where is the edge of the continent? Shoreline is not always in the same position o Varies due to ever-changing sea level The edge is probably somewhere on the continental slope Sire Edward Bullard Bullard’s Fit During the 1960s, Bullard and his associates used a compass to try to fit all the continents together Instead of using shorelines, like other geophysicists had done, he used a depth of 500 fathoms (3000 feet) (1 fathom = 6 feet) below sea level Bullard created an almost near perfect match of continental positions of Pangaea Evidence of Ancient Glaciations Glacial striations are scratch marks on rocks A pebble frozen into basal glacial ice gorges a furrow in bedrock over which the ice is moving Eventually, the pebble starts to loosen and roll and then is carried upwards into the ice and stops making striations o Sharp end of striation is the final position of the pebble o Striation also gets shallower towards the end Glacial Till Fabric Tillites are indurated, or cemented, glacial tills Common cements are calcite and silica An example of a tillite is the Dwyka tillite in Southern Africa Evidence of Permo-Carboniferous glaciation 300 million years ago o In many areas, the evidence suggested ice flow from the sea to land, which does not make sense o It makes sense when we reassemble Pangaea o South pole was close to where Johannesburg in South Africa is today Paleoclimate Evidence of Continental Drift If Pangaea really existed, evidence of past climates should make sense across the super-continent…and it does o Coal o Ice-rafted boulders o Coral o Evaporate deposits o Desert dune deposits Paleontological Evidence of Continental Drift If Pangaea existed, plants and animals in South America, Africa, Madagascar, India, Antarctica, and Australia should show some resemblance…THEY DO! o Anacondas in Madagascar and South America (extinct in South Africa, replaced by python) Paleomagnetism (Ancient Magnetism) Remanent Magnetism o Eiter thermal remanent magnetism (TRM) or depositional remanent magnetism (DRM) Magnetism in rocks o Curie temperature: 700C Heat at which magnetism is lost o Lava (molten rock) has a temperature of about 900-1200C o As lava cools, it acquires magnetic properties known as remanent magnetism Estimating the Latitudes of continents in the Past Latitudes can be calculated using knowledge of the magnetic lines of force in the area Equation: tan(m) = 2 tan(L) o m = inclination of magnetic lines of force o L = latitude of location Example 1: Age: 200 Ma Inclination: 45 o Estimated latitude: 26.6N Example 2: Age: 300 Ma Inclination: 0 (the equator) o Estimated latitude: Northern Europe is now at 50N, but 300 Ma it was close to the equator o As a result, carboniferous coal deposits are common in Northern Europe, which fuled the Industrial Revolution A Wandering Magnetic Pole Remanent magnetism in rocks suggest that the magnetic pole has migrated in a sinuous path over the last 520 Ma In fact, the magnetic pole was fixed. It was the continents that moved. o If continents are positioned correctly, and the subsequent magnetism is recorded, the pole appears to stay stationary Discovering Magnetic Reversals Reverse magnetization: the north pole and south pole switch locations Scientists test different levels of cooled lava and find readings of alternating reversed polarity of the remanent magnetism o Drill out samples from known varied levels of rock to test magnetism Normal: from core, down to south pole, around earth up to north pole Reversed: from core, up to north ole, around earth down to south pole Without a magnetic field, earth’s organisms would suffer greatly from UV rays and other harmful elements o During magnetic reversals, magnetic fields weaken Allows for opportunity of rays and other elements to reach earth Foreign elements can cause birth defects o Birth defects and mutations signify the start of a new era of evolution Suggests that evolution occurred in short bursts over time with each pole reversal, rather than over a long period of time as Darwin proposed We are currently in Bruhnes Normal Remanent Magnetism The Breakup of Pangaea Laurasia – Northern Hemisphere continents Gondwanaland – Southern Hemisphere continents Tethys sea Iapetus Ocean – pre-Atlantic Ocean o Pushed up into Appalachian Mountains Sutured: two land masses collide o India and Asia, creating the Himalayas Plate Tectonics Mid-ocean ridges o More than 27,000 feet hi goon ocean floor Deep-ocean trenches o More than 23,000 feet deep Magnetic Lineations on ocean floor Earthquakes / Volcanoes occur in narrow belts Guyots Continental rocks o Continental rocks are more than 550 Ma, but oceanic crust is only 65-190 Ma o Older rocks continually get destroyed in zone of subduction, so the only rock left in he oceanic plate is more recent Magnetic Lineations Plane equipped with magnometer to measure strength of the magnetic field flies over area of ocean Resulting map shows linear bands of strong and weak magnetization What the magnometer measures As the plane flies over positively magnetized rock, the remanent magnetism is added to earth’s magnetic field when strength of field is measured When the rock is reversely magnetized, the remanent magnetism is opposite of earth’s field and remanent magnetism is subtracted from earth’s magnetic field Guyots Mountain on the deep ocean floor o rounded tops: seamounts o flat tops: guyots shallow marine sediments have been dredged from the top Model of Plate Tectonics a) four plates – two continental, two oceanic b) plates are driven by convection currents in the mantle plates are pulled away from each other by opposing convection currents o cracks form o molten lava fills in the gaps of the plates molten lava remains in liquid form pressure drops closer to surface, but temperature stays the same c) earthquake / volcanic activity at sea floor spreading zones of subduction d) deep ocean trenches at subduction zones plate is pushed down into mantle by convection current plate is melted due to high temperature of mantle molten lava rises up to the surface and creates volcanoes e) high mountains on ocean floor at mid-ocean ridges plutons – large bodies of molten rock that cooled below the surface of the ocean o i.e. Stone Mountain Structure of the Upper mantle and Crust Lithosphere plate contains continental crust, oceanic crust, and upper portion of mantle o continental crust: 35km thick SIAL Density at top: 2.7 g/cc Density at discontinuity: 2.9 g/cc o Oceanic crust: 5-6km thick SIMA Density at discontinuity: 3.31 g/cc Discontinuity at bottom: 3.34 g/cc o Upper colder portion of mantle: 60km thick SIMA o Mohorovicic discontinuity between continental crust and upper portion of mantle Lower hotter portion of mantle: starts about 70-80km below earth’s surface Sea floor Spreading Worldwide spreading rates 1.5-15.7 cm/year Atlantic Ocean floor is spreading 2.5-5.0 cm/year o i.e. Mid-Atlantic ridge down splitting, causing Iceland to grow larger Mountain Building 1) Volcanic mountains 2) Large scale mountain ranges Volcanoes Manua Loa volcano o Main island of Hawaii o 120km diameter o 9km from base to summit Olympus Mons o Volcano on Mars o More than 700km in diameter o 25km from base to summit Why are volcanoes on Mars larger than those on Earth? Plates on Earth move o Subduction zone is not permanent Plates on Mars do not move o Subduction zones are permanent Only melt plates in same spot over and over again Allowing for uninterrupted growth where volcanoes are located (places where there are no subduction zones, so plates do not get melted) Types of Eruptions Effusive: lava has low silica content o Mainly found in oceanic areas o Quiet eruptions Explosive: lava has high silica content o Usually found on continents Central-vent volcanoes Fissure eruptions and flood basalts o Lava seeps up through cracks in crust Kimberlite pipes: feeder pipes deep in the earth, leading to surface o High heat and high pressure are ideal for creating diamonds from coal Continental Volcanoes Kilauea is a parasite cone (secondary escape point – usually on edge of volcano) of Manua Loa, Hawaii Mt. Etna (Sicily) is about 10,900 feet high and it has more than 200 parasite cones Products of Vulcanism Gases Pyroclastic material (Tephra) Lava that becomes basalt Gases Less than 1% of products by weight, but take up a lot of volume Most abundant: steam (water), carbon dioxide, nitrogen, sulfur dioxide Lesser amounts: hydrogen, carbon monoxide, sulphur, chloride The Primordial Atmoshphere The earth’s original atmosphere is believed to have been much like the suite of gases given off by volcanic eruptions today Simple experiments to simulate early conditions with an ocean (salt water), an atmosphere, and lightning (spark of energy) have produced organic molecules (proteins) Pyroclastic material (Tephra) Three different types: o Essential o Accessory o Accidental Volcanic bombs o Surtsey off the coast of Iceland, 1964 Lapilli: lead shot-sized or pea-sized fragments Dust: volcanic veil theory o Mt. St. Helen, March 1980 o Krakatau in Sumatra and Java, 1883 o Volcanic Veil Theory Environment and climate change due to lack of sun’s rays Rays are blocked by clouds of volcanic ash in the sky Look at ice to identify acid layers of previous dust in order to date and count old eruptions
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