EESA06 Textbook Notes.docx

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Environmental Science
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Lisa Tutty

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EESA06 Textbook Notes Chapter 1: Introduction to Physical Geology and the Environment What is Geology? Geology – the study of earth Moving Continents 1.1 William Smith – Father of English Geology, first to publish a geological map 1.2 William Logan – first to systematically describe the geology of Canada (Candian) - Cross-section – a hypothetical vertical slice thru the land 1.3 Alfred Wegener – theory of continental drift in 1912 “The Origin of Continents and Oceans” - Pangea – continents has previously been clustered together in a large land mass 1.4 J. Tuzo Wilson – plate tectonics theory in the early 1970s (Canadian) - Transform faults – large-scale faults that offset the crust laterally but neither created nor destroyed material, now recognized as a major plate boundary type - Hot spots – active volcanoes, young volcanic islands stuck in the middle of the oceans - Volcanic islands chains (ex: Hawaiian Islands) resulted from a moving plate drifting over a stationary magma plume in the mantle – support for plate tectonic theory Time and Geology Deep time – vastly greater amounts of time (more than hours, years) Mid-ocean ridge – a giant mountain range that lies under the ocean Earth is estimated to be at least 4.55 Ga years old What do Geoscientists Do? 1.5 Exploration Geologists – looking for gold, diamonds and other metals Geoscientists – expand the scope and responsibilities of modern geologist into additional scientific fields - Geochemists – working in a ordered environment of the laboratory and use high-technology equipment to analyze the chemistry of rocks or minerals - Mineralogists – study minerals 1.6 Petrologists – study the makeup of rocks and how they form - Geophysicists – using high-tech equipment in the field, using boats, planes, or satellites to learn more of the nature of the physical conditions on or under the Earth’s surface - Petroleum/coal geologists – search for oil and gas and coal - Seismologists – study how to measure and mitigate earthquake activity - Paleontologist – studies the fossilized remains of ancient organisms - Glacial Geologists – study landforms and sediments left behind by ice sheets (glaciers) - Hydro-geologists – study and protect sediments that contain and transmit water 1.7 Environmental Geoscientists – finding and managing drinking water, dealing with a wide range of wastes ranging from radioactive waste to household (municipal) waste 1.8 Engineering Geologists – work with the challenges of engineering structures that form part of the human landscape, landscape stability problems. 1.9 Geomatician – collect, organize, analyze and create images from any spatial and geographical data available in digital form What is the Scientific Method? Scientific Method – the process by which scientists first identify a problem, then they select a methodology to collect data in order to help solve the problem, then they analyze and interpret the information, and come up with a hypothesis, after several test, form a theory Hypothesis – a theoretical explanation where the geologist How did the Earth form? - Nebula – a cloud of gas and dust particles - Bulbous core & flattened disc – created by gas and dust rotate and contract - Sun created from a nuclear fusion - Planets - dust in the outer disc condensed to form rocks and metals that combined to form large rounded planets and - Planetismals – much smaller, irregularly shaped planets - Accretion – the process of building large bodies of matter thru collisions and gravitational attraction - Terrestrial planets (ex: Mercury, Venus, Earth, Mars) – form close to the sun, small, dense, rocky - Jovian planets (ex: Jupiter, Saturn, Uranus and Neptune – low density, large, further from sun What was the early earth like? Differentiation – process of zonation of different materials within a planet - Heavier metals (iron and nickel) settle towards the center, lighter metals (silica and oxygen) rise towards Earth’s surface 1.10 Meteorites – small solid particles of rock, metal, and or ice/orbiting the Sun 1) iron (rare but look unique easily found) – iron mixed with small amount of nickel 2) stony-iron – iron-nickel alloy and silicate minerals in about equal parts 3) stony meteorites (most common, look like earth’s rocks) – silicate minerals (plagioclase, olivine, pyroxene) and may contain small amount of iron-nickel alloy o 90% are Chondrites – contain round silicate grains aka chondrules o 10% are Achondrites – lack chondrules o Carbonaceous chondrites – composed mostly of serpentine or pyroxene and contain up to 5% organic materials, believed to have same composition as the original material from which the solar system was formed o Achondrites – similar to terrestrial rocks in composition (basalt) and texture (igneous rocks) Internal Structure of the earth - Core – composed of iron alloy (iron + nickel +silicon) - Mantle – composed of Fe-Mg silicates (form a rock called peridotite) - Outer crust – composed of lighter rocks such as basalt and granite o Basalt – a fine-grained, mafic, igneous rock composed predominantly of ferromagnesian minerals and with lesser amounts of calcium rich plagioclase feldspar - Lithosphere plates – large pieces of crust and uppermost rigid mantle broken from mantle convection - Asthenosphere – the weak layer, more mobile Formation of the Early Atmosphere - Outgassing – water and gaseous elements released during volcanic eruptions Early Life Forms - Prokaryotes –microorganisms, earliest life forms preserved in the geological record - Stromatolites – organic structures grown by prokaryotes by trapping sediments What is the “Earth System”? Earth System – a small part of the larger solar system but also has its own component parts or subsystems (aka spheres) - include atmosphere (gases), hydrosphere (water) , biosphere(living) and geosphere (rock or other inorganic Earth materials) - External energy source – sun, drives atmosphere and hydrosphere - Internal energy source – geothermal heat, radioactive decay of minerals with Earth, drives plate movement, volcanic eruptions, and earthquakes Rock cycle – conceptual model that links rock-forming process that operate in Earth’s crust - Magma – molten rock - Igneous – when magma solidifies - Sedimentary – unconsolidated sediment becomes lithified (cemented/consolidated into rock) - Metamorphic - subjected to heat and pressure, if high enough temperature rock melts to become magma completing the cycle Chapter 2: Plate Tectonics What is Plate Tectonics? - Plate Tectonics – Earth’s surface is divided into a few large, thick plates that move slowly and change in size - Continental Drift – continents move freely over the Earth’s surface, changing positions relative to one another - Sea-floor spreading – hypothesis that the sea floor forms at the crest of mid-oceanic ridges, then moves horizontally away from the ridge crest toward and oceanic trench, two sides of the ridge are moving in opposite directions like slow conveyer belts How did the plate tectonics theory Evolve? The Early Case for Continental Drift: - Paleoclimatology – the study of ancient climates Wegener studied climates, rocks and fossil, magnetic poles – supported the continental drift Renewed Interest in Continental Drift Study of the Sea Floor - Multibeam sonar – measures water depth and draws profiles of submarine topography - Sidescan sonar – measures the intensity of sound reflected from the ocean floor and provides detailed images and information about sediments and bedforms on the sea floor - sub-bottom profilers - examine the strata (layers) beneath the floor of the lake/ocean - seismic reflection profiler – louder noise, lower frequency, reflects from layers within sediment and rock, records water depth and reveals internal structure of sea floor (Ex: faults, folds) - Rock dredge – an open steel container dragged over the ocean bottom - Rock corer – steel pipe dropped vertically into mud and sand of ocean floor - Sea-floor drilling – drilling derrick - Submersibles – small research submarines, observe, photograph and sample rock and sediment Geophysical Research - Polar wandering – an apparent movement of the Earth’s plates Recent Evidence for Continental Drift - Rocks in Brazil and African country Gabon are very similar - GPS allows us to watch continents move in real time 2.1 Measuring Plate Movement in Real Time - Space geodesy – a space-based technique for taking very precise measurements of points on the earth’s surface (ex: very-long-baseline interferometry (VLBI), satellite laser ranging (SLR), GPS) - GPS is the most useful technique for studying earth’s movements What is Sea-Floor Spreading? Wegener – thought ocean floors remained stationary as continents moved Harry Hess 1962 at Princeton – suggest that sea floor might be moving too - Spreading axis (spreading center) – the ridge crest (MOR) with the sea floor moving away from it on either side - Subduction – the sliding of the sea floor beneath a continent or island arc - Convection – a very slow circulation of a substance driven by differences in temperature and density within that substance How Old is the Sea Floor? - Fairly young only 200 million years old What are plates and how do they move? - Plate – a large, mobile slab of rock making up part of the Earth’s surface - Lithosphere – the rigid outer shell of the Earth, 70 to 125 more kilometers thick, includes rocks of the crust and the uppermost mantle - Asthenosphere – a region of the Earth’s outer shell beneath the lithosphere, is of indeterminate thickness and behaves plastically - Divergent plate boundary – boundary separating two plates moving away from each other - Convergent boundary – a boundary between two plates that are moving toward each other - Transform plate boundary – boundary between two plates that are sliding past each other How do we know that plates move? Paleomagnetic Evidence - Magnetic reversals – a change in the Earth’s magnetic field between normal polarity and reversed polarity. - Normal polarity – compass points north, enters earth - Reversed polarity – periods when the lines of magnetic force run from the south pole to the north pole and compass needles point to the south, leaves earth - Paleomagnetism – a study of ancient magnetic fields - Magnetic polarity time scale – records the pattern of magnetic reversals over time - Anomaly – a deviation from average readings of magnetic strength - Magnetometer – an instrument that measures the strength of the Earth’s magnetic field Marine Magnet Anomalies The Morley-Vine-Matthews Hypothesis – pattern of magnetic anomalies on one side of the MOR was mirror image on the other side, magnetized dikes form parallel to rift valley = cause of anomalies - Predicts age of sea floor How fast do plates move? Predicting Sea-Floor Age - Similar to dating tree rings Another Test: Fracture Zones and Transform Faults - Transform fault (Tuzo Wilson) – the portion of a fracture zone between two offset portions of ridge crest (earthquakes occur at points where movement is opposite directions) What Happens at Plate Boundaries Divergent Plate Boundaries – to create or open new ocean basins - Graben – a down-dropped fault block - Ex: Red Sea – divergent margin - rifting before uplift, crust is thinned, fault break crust, shallow earthquakes, and basalt eruptions, high heat flow - Passive continental margin - transition between oceanic and continental crust, a thick sequence of marine sediment blankets the thinned continental rock Mid-Ocean Ridges – a giant mountain range that lies under the ocean and extends around the world - Rift valley – a tensional valley bounded by normal faults, are found at diverging plate boundaries on continents and along the crest of the mid-oceanic ridges Geologic Activity on Ridges - Shallow-focus earthquakes – from 0-20km below the sea floor - High heat flow – heat loss at the ridge crest is a lot higher - Basalt eruptions – occur in and near the rift valley on ridge crests (ex: Iceland) - FAMOUS ALVIN – French-American Mid-ocean Undersea Study – 40 submersible dives - Black smokers – chimney-like mounds around the hot spring Biological Activity on Ridges - Presence of exotic, bottom dwelling organisms - Thermophyllic – heat, sulphur loving bacteria - Geomicrobiology – bacteria’s role in the precipitation of minerals Ridges and Ore Deposits Transform Boundaries – where one plate slide horizontally past another plate - Marked by shallow-focus earthquakes Convergent Plate Boundaries Ocean-Ocean Convergence – two plates capped by sea floor converge, one plate subduct under another - Oceanic trench – a narrow, deep trough parallel to the edge of a continent or an island arc - Island arc – a curved line of islands - Accretionary wedge (subduction complex) – inner wall of a trench toward the arc, thrust-faulted and folded marine sediment and pieces of oceanic crust - Forearc basin (trench side) – between accretionary wedge and the volcanic arc - Backarc region (other side of arc) Ocean-Continent Convergence - Active continential margin – when oceanic crust subduct under continental lithosphere - Magmatic arc – a line of batholiths or volcanoes, generally the line is curved Continent-Continent Convergence – close ocean basin - Suture zone – collisional margins, where two continental plates join or subduction zones 2.2 British Columbia and the Juan de Fuca Plate/Cascadia Subduction Zone - Subduction of Juan Plate beneath North America cause large and frequent earthquakes Backarc Spreading - Backarc oceanic crust if found in most ophiolites 2.3 Oceanic Crust and Ophiolites - Gabbro - dark, coarse-grained, intrusive mafic igneous rocks chemically equivalent to basalt Convergent Boundaries and Ore Deposits How do mountain ranges form? Orogenies and Plate Convergence - Orogeny – mountain building, an episode of intense deformation of the rocks in a region, generally accompanied by metamorphism and plutonic activity Ocean-Continent Convergence – (Ex: The Andes) Arc-Continent Convergence – intervening ocean is destroyed by subduction, flipping subduction zone Continent-Continent Convergence – (Ex: Appalachian Mountains) 2.4 Canadian Rocky Mountains – accretion of micro continents 2.5 Wilson Cycle (Tuzo Wilson) – continued opening and closing controlled by plate tectonics What Causes Plate Motions? 1) Mid-ocean ridge crests are hot and elevated while trenches are cold and deep 2) Ridge crests have tensional cracks 3) The edges of some plates are subducting sea floor, while the edges of other plates are continents (which cannot subduct) - Ridge-push and slab-pull (thought to cause rapid plate motion) and trench-suction How are mantle plumes and hot spots related? - Mantle plumes – narrow column of hot mantle rock that rises and spreads radially outward Seamounts, Guyots, and Aseismic Ridges - Seamounts – conical mountain rising 1,000 meters or more above sea floor, scattered along MOR, form islands - Guyots – eroded flat-topped seamount found mostly in western Pacific Ocean - Aseismic (locked) ridges – submarine ridge with which no earthquakes are associated 2.6 The Geological Significance of Aulacogens - Aulacogens – failed rifts, host to petroleum (ex: St. Lawrence rift) Why is it important to understand plate tectonics? 2.7 Plate Tectonics and Earthquake Risk in Southern Ontario - Earthquakes focused around suture zones or terrane boundaries - Plates move 2.7cm/year - Central Meta-sedimentary Belt Boundary Zone (CMBBZ) – seismogenic structure Pickering nuclear plant is built on top of it Chapter 3: Earthquakes What Causes Earthquakes? - Earthquake – a trembling or shaking of the ground caused by the sudden release of energy stored in the rocks beneath the surface - Seimic Waves – a wave of energy produced by an earthquake - Elastic rebound theory – the sudden release of progressively stored strain in rocks results in movement along a fault 3.1 Indonesia/Sumatra Earthquake and Tsunami, December 26, 2004 – largest earthquake 9.3 Why do Earthquakes cause so much damage? - Focus – the point within the earth from which seismic waves originate in an earthquake - Epicenter – the point on the earth’s surface directly above the focus of an earthquake Body waves – within earth - P wave – a compressional wave (seismic wave) in which rocks vibrate parallel to the direction of the direction of wave propagation - S wave – a seismic wave propagated by a shearing motion, which causes rock to vibrate perpendicular to the direction of wave propagation Surface waves – a seismic wave that travels on the Earth’s surface - Love waves – a type of surface wave that causes the ground to move side to side in a horizontal plane perpendicular to the direction the wave is travelling - Rayleigh waves – a type of surface wave that behaves like a rolling ocean wave and causes the ground to move in an elliptical path How do we know where earthquakes occur? - Seismograph – a seismometer recording device that produces a perm record of earth motion - Seismogram – paper record of earth vibration Determining the location of an earthquake - Travel-time curve – a plot of seismic-wave arrival time against distance - Depth of focus – distance between the focus and the epicenter of an earthquake o Shallow focus : 0-70km deep o Intermediate focus: 70-350km deep o Deep focus: 350-670km deep Measuring the size of an earthquake - Intensity – a measure of an earthquake’s size by its effect on people and buildings - Modified Mercalli scale – scale expressing intensities of earthquakes (judged on amount of damage done) in Roman numerals ranging from I to XII - Magnitude – a measure of the energy released during an earthquake - Richter scale – a numerical scale of earthquake magnitudes - Moment magnitude – an earthquake magnitude calculated from the strength of the rock, surface area of the fault rupture and the amount of rock displacement along the fault What kinds of damage can earthquakes cause? - Ground motion – trembling and shaking of land can cause buildings to vibrate - Fire – broken gas and water mains - Landslides & Liquefaction - Aftershock – small earthquakes that follow a main shock - Permanent displacement of the land surface – scarp (low cliff, tear in ground) Tsunami (seismic sea waves) – huge ocean wave produced by displacement of the seafloor - most are associated with subduction zone earthquakes – which tend to be some of the strongest 3.2 Earthquakes in Canada Eh? - most earthquakes occur in Cascadia subduction zone off western coast of BC, St Lawrence and Ottawa river valleys 3.3 Earthquake Engineering - building on solid bedrock, using flexible wood, steel and reinforced concrete Where do earthquakes occur on a global scale? - Circum-Pacific Belt – major belt around the edge of the Pacific Ocean on which most composite volcanoes are located and where many earthquakes occur – ocean trenches, - Mediterranean-Himalayan Belt – a major concentration of earthquakes and composite volcanoes that runs thru the Mediterranean Sea, crosses the Mideast and the Himalaya, and passes thru the East Indies - Benioff zones – distinct earthquake zone that begins at an oceanic trench and slopes landward and downward into Earth at an angle of about 30-60 degrees - Island arc – Benioff zones slope under curved line of islands - Shallow focus – crest of MOR, near basaltic volcanoes What is the relationships b/w earthquakes and plate tectonics? Earthquakes at plate boundaries Divergent boundaries (ex: African Rift Valleys) – shallow earthquakes Transform boundaries (ex: San Andres Fault) – shallow earthquakes, strike-slip motion Convergent Boundaries (ex: Himalayas) - Collision quakes – two continents – shallow quakes (ex: Himalayas) - Subduction quakes – ocean and continent – underthrusting 3.4 Waiting for the Bid One in British Columbia - Crustal earthquakes – North American plate - Intraplate earthquakes - Juan de Fuca plate - Subduction earthquakes – plate boundary Subduction Angle - steeper when colder and denser oceanic plates subduct, shallow when younger and warmer oceanic plates subduct - faster rate of convergence = shallower angle Earthquakes away from plate boundaries - intraplate – within plate quakes, areas of thinned or weakened crust Can we predict when earthquakes will occur? - properties of rock, water levels in wells, interval between eruptions of Old Faithful, surface of Earth tilts and changes in elevation, animal behavior, foreshocks, 3.5 What to do before, during, and after an earthquake 3.6 Waiting for the Big One in California – San Andres Fault 3.7 Measuring Ground Displacement Caused by Earthquakes – InSAR using electromagnetic radiation Chapter 4: The Earth’s Interior 4.1 Deep Drilling on Continents 4.2 Canadian Lithoprobe Project -“dancing elephants” What can we learn from the study of seismic waves? - Geophysics – the application of physical laws and principles to a study of the Earth - Seismic reflection – the return of part of the energy of seismic waves to the Earth’s surface after the waves bounce off a rock boundary - Seismic refraction – the bending of seismic waves as they pass from one material to another What is inside the earth? Crust – the outer layer of rock, forming a thin skin over the Earth’s surface - Felsic – rocks high in feldspar and Silicon – continental crust - Mafic – rocks high in magnesium and iron (ferric) – oceanic crust - Mohorovicic discontinuity (Moho) – the boundary separating the crust from the mantle beneath Mantle (670km) – a thick shell of rock that separates the Earth’s crust above from the core below - Upper mantle – diff from continental and oceanic crust, is most likely ultramafic rock (dense igneous rock, lack felderspar ex: periodite) - Lithosphere – the strong and brittle outer shell of the Earth, 70 to 125 more kilometers thick - Asthenosphere – a region of the Earth’s outer shell beneath the lithosphere, is of indeterminate thickness and behaves plastically – low velocity zone 4.3 A CAT scan of the mantle – seismic tomography uses earthquake waves, 4.4 Diamonds – A window into the mantle – diamond bearing igneous rocks - kimberlite pipes - Diamonds eventually breakdown to for graphite - First diamond mine in North America = Ekati mine near Yellowknife in NWT Core – the central zone of the Earth - P-wave shadow zone – the region on the Earth’s surface, 103-142 degrees away from an earthquake epicenter, in which P-waves from the earthquake are absent - S-wave shadow zone – the region on the Earth’s surface, any distance that is more than 103 degrees from the earthquake’s epicenter, in which S-waves are absent Composition of the core – core is made of metal not silicate, most likely iron (studying meteorites) The Core-Mantle Boundary – ultra-low velocity zone (ULVZ) – P wave velocities dramatically decrease - Convection – a circulation pattern in which low density materials rise and high density sinks How does the elevation of continents change? - Isostasy – the equilibrium between adjacent blocks of crust resting on a plastic mantle - Isostatic adjustment – concept of vertical movement of sections of the Earth’s crust to achieve equilibrium - Crustal rebound – the rise of the Earth’s crust after the removal of glacial ice What can gravity tell us about the earth’s crust? - Gravity meter – an instrument that measures the gravitational attraction between the Earth and a mass within the instrument - Positive gravity anomaly – greater than normal gravitational attraction, over an area underlain by denser rocks than those of the surrounding region (ex: a granite pluton) - Negative gravity anomaly – less than normal gravitational attraction How does the earth’s magnetic field change through time? - Magnetic field – region of magnetic force that surrounds the Earth - Magnetic poles – an area where the strength of the magnetic fields is greatest and where the magnetic lines of force appear to leave or enter the earth Magnetic Reversals - Curie point (580 for magnetite) – the temperature below which a material becomes magnetized - Paleomagnetism – a study of ancient magnetic fields 4.4 Earth’s Spinning Inner Core Magnetic Anomalies - Magnetometer – an instrument that measures the strength of the Earth’s magnetic field - Positive magnetic anomaly – greater than average strength of the Earth’s magnetic field - Negative magnetic anomaly – less than average strength of the Earth’s magnetic field 4.6 Magnetotellurics: New Tool for Investigating the Earth’s Interior - Magnetotellurics – a new geophysical approach being used in remote regions of the Canadian Arctic to investigate and map structures within the underlying crust and mantle How hot is the earth’s core? What is the origin of the earth’s heat? Geothermal Gradient – rate of temperature increase associated with increasing depth beneath the surface of the Earth (normally about 25 C/km) Heat Flow – gradual loss of heat (per unit of surface area) from the Earth’s interior out into space Chapter 19: Time and geology What is Uniformitarianism? - Uniformitarianism – principle that geologic processes operating at the present are the same processes that operated in the past. “The present is the key to the past” (uniform rate) - Actualism – physical laws are independent of time and location (same meaning as uniformitar..) Geological Time Scale – a sort of calander to which events and rock units can be referred - Earth was only 6,000 years old – biblical chronology, Noah’s flood - features we observed in rocks and landscapes where supernaturally and catastrophically James Hutton – “father of modern day geology” Charles Lyell – Principles of Geology book o geological features could be explained by present-day processes How can the Sequence of Past Geological ev
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