Study Guide for Midterm-1 GEL 105 Spring 2010 Be sure to look at all of your in-class exercises and to review your quiz. 01-Lecture: Introduction to Geologic Hazards Know the definition of science The systematic way of studying knowledge derived from observations and studies Know the correct order of steps taken in the scientific method Observe Hypothesis Test Theory (only after repeated positive tests) Why should ?natural hazards? really be called ?unnatural hazards?? Natural events become hazards only when people place themselves in harm?s way (UN Secretary General) What is the relationship between the size (magnitude) of a hazard and how often (frequency) that hazard occurs Magnitude is inversely proportional to frequency ( ) What does it mean to live ?sustainably?? Living off earth?s resources without depleting or degrading them; not using our resources faster than they can be replenished naturally What is the principle of uniformitarianism? Processes operating today are the same as those operated in the past; frequency, magnitude, and location may differ, but processes don?t 02, 03-Lecture: Plate Tectonics Know the supporting evidence that Wegner used for his concept of Continental Drift Continents fit together (Continents must have been joined at one time) Coastal geology (similar rock types) Glaciation in the tropics (direction of ice movement from glacial scour) Fossils (similar fossils found spread across continents; animals wouldn?t have been able to swim that far) Know the definition of ?lithospheric plate? and the difference between lithosphere and asthenosphere Lithosphere is the rock layer that is the uppermost part of the mantle and crust; it?s relatively cool and brittle and can break easily, forming plates Asthenosphere is the weak layer that is plastic, ductile, and flows easily Lithosphere floats on the asthenosphere because of isotacy (floating based on differences in density) What portions of the earth is the lithospheric plate made of? The crust (oceanic and continental) and the uppermost part of the mantle Know why subduction occurs Oceanic crust is more dense than continental crust, which causes it to subduct Know the cause (mechanism) for plate tectonics Plates are constantly in motion and float on top of the astenosphere, subducting and converging Know what modern evidence we have obtained to support the theory of plate tectonics Mid-ocean ridge system (ocean floor isn?t flat as was once assumed) Age of seafloor (seafloor never gets older than 200 million years, which means it must be constantly recycled; rocks found equally distant on either side of mid-ocean ridges are the same age) Thickness of sediment (sediment thickens away from ridges) Location of earthquakes and volcanoes (along plate lines) Magnetic reversals (paleomagnetism shows that the poles of earth?s magnetism are preserved in very old rocks) Hotspots and island chains (as plates move, volcanoes move along the surface; greater distance from a hotspot means that islands are older) How does the magnetism of ocean floor rocks and the ages of the rocks support the concept of sea-floor spreading? Iron minerals acquire orientation of Earth?s magnetic field, and rocks on the ocean floor have high solid iron content, so they preserve shifts in the magnetic field as the sea floor spreads Rocks that are equidistant on either side of a ridge are also equal in age, proving that the ocean floor is spreading at mid-ocean ridges Know the 5 types of plate boundaries, and be able to recognize them on a diagram. Be able to give a few geographic examples as well (ie. is an o.c.-o.c. convergent boundary) Ocean-ocean divergent characterized by mid-ocean ridges and magma flows, which create new ocean floor Ocean-continent convergent characterized by oceanic trenches, linear mountain chains, and volcanic activity along continental coasts (geographic example ? Andes Mountains) Ocean-ocean convergent characterized by oceanic crust and volcanic island arcs (geographic example ? Japan) Continent-continent convergent characterized by lots of earthquakes, no subduction, and very large mountains (geographic example ? Himalayas) Transform characterized by two plates rubbing against each other, creating many earthquakes, no magma production, and fault lines (geographic example ? San Andreas Boundary) What information do hotspot-produced island chains give us? (ans. = the direction and rate of plate motion) The progressive aging of island chains shows which direction plates are moving in and how fast they?re moving (example ? Hawaiian island arc) Be able to relate the earth?s surface features with the correct plate boundary (refer to the summary slides in the 03-plate tectonics lecture). Interior mountain chains (highest elevations, no volcanism) ? continent-continent convergent Coastal mountain chains (volcanically active) ? ocean-continent convergent Volcanically active island arcs (near a deep sea trench) ? ocean-ocean convergent Deep ocean trenches ? ocean-ocean and ocean-continent convergences Deep valleys (very thin continental crust) ? continent-continent divergence Mid-ocean mountain ranges (mid-ocean ridge) ? ocean-ocean divergent Earthquake prone regions ? all boundaries Magma production ? ocean-ocean divergent, ocean-continent convergent, ocean-ocean convergent 04-Lecture: Minerals What are ions, cations, anions? Ions are negatively or positively charged atoms Cations are positively charged atoms because they have given off one or more electrons Anions are negatively charged atoms because they have accepted one or more electrons What are the bond types discussed in class? (which of these is the weakest?) Ionic ? electron transfer (weakest ? NaCl can be broken by water) Covalent ? electron sharing Metallic ? extreme sharing of numerous electrons Know the two most common elements in the whole earth, and in the crust. Whole earth ? Iron (Fe) and Oxygen (O) Crust ? Oxygen (O) and Silicon (Si) Know the definition of a mineral (5 criteria) Naturally occurring (not man-made) Inorganic (don?t contain living or previously-living materials) Solid Somewhat specific chemical composition (minerals made naturally are never pure) Characteristic crystalline structure (repeating chemical pattern) Know why ice is a mineral, but glass is not Ice is a solid, naturally occurring, crystalline structure that is inorganic with a somewhat definite chemical composition Glass, by definition, has no crystal structure (created from chaos) Know what the mineral?s hardness represents Chemical bond strength Know the most common mineral group in the crust and mantle Silicates (SiO?) Know why silicates are the most common mineral group Silicates are composed of the elements Silicon and Oxygen, which are the two most abundant elements in the earth?s crust What is a cleavage plane? Line along which a mineral breaks (examples ? 1 plane, 2 at 90º, 3 at 90º, 3 not at 90º, 4) How do we identify a mineral? (What are the tests used? Example: What is the streak?) Hardness scale, cleavage breaks, streaks (color of mineral in powdered form), luster (how a mineral appears when it reflects light), and color 05-Lecture: Igneous, Sedimentary, and Metamorphic Rocks How are igneous rocks formed? Crystallization of magma or lava Know the difference between plutonic and volcanic (intrusive and extrusive) igneous rocks Plutonic rocks are cooled slowly at a depth because the rocks underground provide an insulation against rapid heat loss Volcanic rocks are erupted and quickly cooled Know how igneous rocks are classified Color (composition) and texture (size of crystals) Know the difference between basalt and gabbro Basalt is a mafic-rich magma that has cooled quickly above the surface Gabbro is a mafic-rich magma that cools slowly and forms large crystals underground Know the difference between rhyolite and granite Rhyolite is felsic-rich magma that cooled quickly above the surface Granite is a felsic-rich magma that crystallizes at depths and cools slowly underground What do the terms felsic and mafic mean? (How do their compositions differ?) Felsic is magma that is poor in Fe and Mg, but rich in Si (opposite of mafic) Mafic magma is rich in Fe and Mg, but poor in Si (opposite of felsic) What is texture, and what is the relationship between texture and crystal size? Used to describe the overall appearance of a rock based on the size, shape, and arrangement of minerals Crystals are formed from minerals that are cooled at different rates, creating different textures How are scoria and pumice different from the other types of igneous rocks? They both have a glassy texture, although pumice does float and scoria doesn?t How are sedimentary rocks formed? Lithification of sediment How is sediment formed? What are physical and chemical weathering? (know the different types of each). Sediment formed through either physical or chemical weathering Physical weathering is done through fracturing (pressure release and exfoliation), frost and mineral wedging, and roots and other biologic activity Chemical weathering is done through dissolution and oxidation How are sediments transported (the mechanisms of sediment transport) Water, wind, ice, animal activity, and human activity What is the relationship between transport distance and grain size, shape, and sorting? Sediment transported farther from the source is rounder, smaller, and very well sorted (such as a desert) What is sorting (what is the difference between a well-sorted and a poorly-sorted sediment)? The process of sediment being transported through various means into similarly-sized selections (poorly sorted sediment is angular and has a large variation in size; well-sorted sediment is very rounded, very similar in size, and so small that you can?t select a single grain from the rest) What are the clastic sediment sizes (ranging from largest to smallest?boulders to clay) Largest (boulders, cobble, pebbles), Sand (coarse, medium, fine), and Clay and silt (so small you can?t select a single grain) What rocks are made up of clastic sediments? What is the correct order of events prior to the formation of a sedimentary rock? Uplift, weathering, transportation, deposition, lithification What rocks form from the precipitation of minerals? Limestone and Rock Salt What is coal? Compressed plant remains How do metamorphic rocks form? Transformation (recrystallization) of pre-existing rocks by heat, pressure, and (chemically active) fluids over time What is the difference between confining pressure and differential pressure? Which type of pressure causes foliation? Know that foliation develops perpendicular to the pressure. Confining pressure is equal in all directions Differential pressure is not equal in all directions and causes foliation Foliation is the pattern in metamorphic rock that is caused by differential pressure; the pattern is perpendicular to the pressure applied What is a protolith? What is the protolith for marble? For quartzite? Protolith is a pre-existing rock Marble?s protolith is limestone Quartzite?s protolith is quartz sandstone Know that shale recrystallizes into slate, phyllite, schist, and gneiss and that these are arranged in order from low to high grade metamorphic rocks. Describe the foliation pattern seen in gneiss Gneissic banding is the foliation described by alternating light and dark minerals What is contact metamorphism? Why are these rocks not foliated? Metamorphism due to increased temperature Rocks not foliated because there is equal temperature increases from all around Be able to complete a rock cycle diagram like the one done as an in-class exercise 06-Lecture: Mineral Resources Know the definition of a mineral resource and the definition of ore. Mineral resources are concentrations of minerals that can be extracted and processed into useful materials at an affordable cost Ore is a rock containing enough of one or more metallic minerals to be mined profitably Know that the size and depth of the ore deposit determines how it is mined (surface vs. subsurface) Surface mining used for ore deposits found at shallow depths Sub-surface mining used for ore deposits found deep underground What is a kimberlite pipe? What precious mineral can be found in this structure? Kimberlite pipes are formed by violent degassing from at least 200 km below the earth?s surface Diamonds are found in Kimberlite pipes Why are gold and silver found in ?veins? in a rock Gold and silver are found in areas with faults associated with superheated water (contact metamorphism); superheated groundwater can dissolve gold and silver and other precious elements in a process called leaching. Gold and silver are then taken out of their solid form, dissolved into water, and once the water cools, precipitated back out into veins of cooled rock Know the relationship between gold, silver and copper deposits and plate boundary type Gold and silver found along convergent boundaries Copper found along convergent and divergent boundaries What is leaching? How can it create an ore deposit? Leaching is the process of superheating water to dissolve minerals into it, then once the water cools, mineral resources are precipitated out and left behind as ore deposits What are overburden and spoils? Overburden is the soil and rock above the ore deposit Spoils is the name given to the overburden that is removed and discarded as waste Know the different types of surface mining Open-pit mining Area strip mining Contour strip mining Mountaintop removal What is gangue? Gangue is waste material created by the separation of ores from rocks What are some of the harmful effects of mining? Disruption of land surfaces Subsidence Toxic-laced mining wastes Acid mine drainage Air pollution 07, 08-Lecture: Earthquakes Know the stress/strain graph What is the Wadati-Benioff zone? Explain the distribution of focal point depths in this zone Focal points are relative to how deep the subduction of the oceanic plate is underneath the younger oceanic plate (ocean-ocean convergent boundary) Where do earthquakes occur? Mostly along plate boundaries, or anywhere there is a fault line Know the difference between the focus and epicenter of an earthquake Focus is the origination point of the earthquake underground, where the plates move or slip past each other Epicenter is the point on the surface directly above the focal point Know how seismic waves travel through the earth (ie. How fast, how do the waves move through material, why are some called body waves) Surface waves ? most dangerous; slowest velocity and great amplitude; complex motions of scissors/shearing and rolling; found only on the surface of the earth Body waves ? P waves push and pull (compress and expand) the subsurface, changing the volume of the intervening material; fastest wave; can travel through any material Body waves ? S waves shear the subsurface; travel slower than P waves, but faster than surface waves because energy is spent going up and down instead of directly outwards; can only travel through solids What wave type cannot pass through liquid? S-waves What does the time lag between P and S arrival times allow us to determine? Lag time allows us to determine where the earthquake originated at What do we need to know in order to find the Richter Magnitude of an earthquake? Amplitude height and difference in arrival times of wave types What materials slow down the seismic waves, and in the case of S-waves, stop them? Liquids and gases Why are surface waves so destructive? High amplitude and slow velocity Know how to read a seismogram Know how to read a P and S travel time curve How do we find the epicenter of an earthquake? Triangulate the location using differences in arrival times from at least 3 different locations What are the building codes that help mitigate (reduce) the damages to structures? Securing furniture and other items to the walls, placing steel brackets on exterior features (chimneys, pipes, etc), metal ?L? braces, diagonal wood bracing, plywood sheeting to reinforce buildings, tall buildings must be equal heights when built next to each other to reduce building sways, rubber bases and lead plugs to isolate ground shaking What are seiches and tsunamis, and how are they different from one another? Seiches are the rhythmic sloshing of water in lakes, reservoirs, and other enclosed basins that weaken the walls and can cause destruction because of seismic waves Tsunamis result from vertical displacement of water long a fault located on the ocean floor or a large undersea landslide triggered by an earthquake How do anticlines and synclines cause variations in building damage during earthquakes? Anticlines are the crests of earthquake s-waves; synclines are the troughs of earthquake s-waves; they focus energy in certain directions (along anticlines) which can cause significant damage to one building and little to no damage to another What are seismic gaps? Areas along faults that haven?t had earthquakes in awhile; greater lapse in time between earthquakes means greater magnitude of energy being stored that will be released in the next earthquake 09-Lecture: Mass Wasting (Landslides) Know the definition of mass wasting Down slope movement of rock and regolith near the Earth?s surface mainly due to the force of gravity What is the primary cause of mass wasting? Gravity Know what effects slope stability (we covered 8 in lecture) Know how they work Geology and slope steepness (angle) ? gravity, shear strength, shear stress, friction, angle of repose Fluid ? buildup of water can reduce friction, frost heaving and wedging, erosion of slope Vegetation ? usually strengthens slopes unless root systems are weak, absorbs water, softens the impact of rain on the soil Earthquakes ? fractures rock, loosens fractured rock and soil, loss of friction Volcanoes ? eruptions melt snow, which causes a loss of friction (can also cause earthquakes) Quick Clays ? clays that spontaneously liquefy and flow when disturbed Overloading ? can increase the water pressure within the slope material Climate and weathering of rock ? mass wasting more likely to occur in loose or poorly consolidated slope material than in solid bedrock What is the angle of repose? Maximum angle material can have and still be stable (dependent upon material) What are shear strength and shear stress? Know also the components of both Shear strength is a the force that helps maintain slope stability; combination of material?s strength and cohesion, plus perpendicular gravity; internal friction between grains; and any external support of the slope (usually man-made) Shear stress is the component of gravity acting parallel to the slope that opposes shear strength A safety factor of less than 1 means what? Slope failure is possible Be familiar with the diagrams showing a rock on a slope, and the components of gravity acting on it. What orientation of rock layering in relationship to the slope is unstable? Parallel; rocks dipping in same direction as slope What are the frost wedging and frost heaving? Frost wedging is the saturation of water into sediment that freezes (expands), and cracks the rock base underneath Frost heaving is the constant expansion and contraction of water that forces larger sediment particles up in the soil Be able to describe how liquefaction of sediment occurs. Loosely packed grains provide large pore spaces for water. If the grains collapse to a tighter arrangement, much of the water must be squeezed out, causing excess pore water to carry loads of overburden down a slope What are the 2 most common triggering mechanisms for mass wasting events? Earthquakes and excessive amounts of water What are the types of mass wasting and how are they classified? Flows ? creep, mudflows, debris flows (slowest movement) Falls ? rock falls (fastest movement) Slides ? rock slides, slumps (intermediate movement) Which is the slowest form of mass wasting? The fastest? Slowest is creep Fastest is rock falls What is the difference between a mudflow and a debris flow? Mudflows consist mainly of clay and silt-sized particles, have more than 30% water, and generally follow pre-existing channels Debris flows contain less water than mudflows and are composed of larger particles; more viscous, move more slowly What is the difference between a slump and a slide? Slumps are rotational slides in which material moves down a curved surface, usually involve poorly consolidated materials Slides take place on planar slopes and usually involve solid pieces of rock What are the indicators of creep? Bent trees, retaining walls flexing or broken, leaning man-made structures (telephone poles, tombstones, etc) Be able to identify a picture of these mass wasting events Creep Mudflow Debris flow Rock fall Slump Slide What are the possible preventative measures used to increase slope stability? Slope reduction (slope regarding) Retention structures (netting, fencing, retaining walls) Planting vegetation Fluid removal (drainage pipes) Recognizing the hazards (geologic mapping)
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