Eosc 114 Final exam notes

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Earth and Ocean Sciences
EOSC 114
Deborah Giaschi

EOSC 114 – Final Review Notes Unit 1: A Fragile System  Explain what density is & how it relates to stratification. o Density = mass/volume; how much mass fits into a space. Unit: kg/m 3 o Stratification = less-dense materials float on top of denser materials  This is found in the atmosphere, the ocean, the earth, etc.  Explain why disaster scales are based on the Order-of-Magnitude concept, and interpret graphs with logarithmic scales. o Without using a log scale, sometimes a graph will be too large. o “Orders of magnitude” are powers of 10 – a logarithmic graph steps by powers of 10  Converting an exponential curve into a logarithmic graph will give a linear graph. o Many disaster scales use powers of 10: Richter, Fujita, Torino, Beaufort, etc.  Relate natural-disaster risk & intensity to frequency, return period, and consequences (costs). o Risk = probability severity * cost of damage ($ + human lives) o Intensity is inversely proportional to frequency. o Return period = average number of years between disaster events of the same magnitude  RP (M) = time span of data / # of cases of magnitude M.  Explain how some recent disasters were associated with concentration or dilution of energy. o Time scales for energy to build up and release Concentration of energy Dilution of energy  Earthquakes: years -> minutes  Tsunami: minutes -> hours  Volcanoes: decades -> days  Floods: hours -> days  Hurricanes: months -> days  Storms: hours -> minutes  Rogue waves: hours -> seconds  Get the disaster info you need from reliable sources.  Compare tectonic, rock, hydrologic, and biogeochemical cycles.  Tectonic Cycle o Involves the creation -> movement -> destruction of plates o One cycle can last more than 200 million years! o Types of plate boundaries  Divergent: two plates move away  Forms: large, underwater mid-ocean ridges  Rifts formed through seafloor spreading  Convergent: two plates collide  Subduction zone: one plate moves beneath another (usually ocean and continental)  At 100-120 km, melts and releases H2O and CO2 -> hot enough to cause lower crust to melt -> magma moves up -> reaches surface -> erupts  Transform boundary  Movement along a transform fault – most are beneath oceans but some are on continents  Rock Cycle o Rock: aggregate of one or more minerals. Mineral: naturally occurring crystalline substance w/ specific elemental composition o Rock Cycle: recycling of three major groups of rock  Crystallization of molten rock -> igneous rock beneath/on Earth’s Surface  Weathering -> sediment  Sediment is transported by wind/water/ice to depositional sites  Buried -> lithification -> sedimentary rock  Chemically active fluids + heat + pressure cause metamorphic rock to be formed  Eventually, temp high enough -> melt -> restart   Water Cycle o Cycling of water from oceans -> atmosphere -> continents -> back again o Driven by solar energy o Residence time: estimated avg time a drop of water spends in any part of the cycle  Only a tiny fraction of earth’s water is active at a certain time – often stored  Only ~.3% of all water important for life -> groundwater  Biogeochemical cycles o Cycling of an element/elements through atmosphere/lithosphere/hydrosphere/biosphere  Related to the other cycles  Tectonic provides water + gas, heat + energy. Rock and hydrological transfer and store.  Elements and chemicals are transferred via storage compartments/reservoirs  When a biogeochem cycle is understood, the rate of transfer (flux) among all components is known  List the 1st and 2nd most common elements in the earth, ocean, and atmosphere. Elements Earth Crust Ocean Atmosphere st 1 most common Fe O O N 2 most common O Si H O rd 3 most common Ni Al Cl Ar  Describe how viscosity and compressibility relate to the phase of matter. o Fluids: Easily flow, change shape easily = gases, liquids o Viscosity: measure of how much fluids resist flowing or changing their shape.  Greater viscosity, more resistance. Depends on temperature + chemical structure. o Compressibility: ability to be squeezed/expanded. Results in a change in density because of volume change. o Phases of matter  Solids: Not fluid, not very compressible.  Liquids: Very fluid, not very compressible.  Gases: Very fluid, very compressible.  Be able to diagnose the type of strain by the way a material deforms. o Strain: Change in shape or size of a solid object (deformation)  Elastic: Ability to change shape when forced but spring back to original shape when force lifted  Plastic: Ability to permanently change shape or deform when forced o Ductile = very plastic, Brittle = not very plastic, fractures instead of bending.  Explain how gravity affects motion and energy, list the 5 types of energy, and describe what causes them to vary. Force (F)  A push/pull  Unit: Newton = 1 (kg * m/s^2) -> F = ma  A 15 km/h breeze = 1 N Gravity (g)  Force that 2ttracts matter  G = 9.8 m/s = gravitational acceleration Types of Energy Work (W)  Work = force x distance in = Joules Potential Energy  Mass * gravity * height (distance against pull of gravity) Kinetic Energy  0.5 m V 2 Sensible Heat (QH)  Heat we can feel  ΔQ H m C ΔT o C = specific heat capacity Latent Heat (Q E  When solids melt/liquids evaporate – sensible heat becomes stored as latent heat o When they condense/freeze - > released  Q = LΔm E  Delta m = change in mass  Constants o Latent Heat of Vaporization: liquid -> gas,vL o Latent heat of fusion: liquid -> solidf L  Explain the 5 main concepts for understanding natural processes as hazards. 1. Hazards can be predicted through scientific analysis  Scientific method used  Predicted by  Identifying location, finding probability, looking for precursor events, forecasting, warning 2. Risk analysis is an important element in understand the effects of hazards  Risk = probability * consequences 3. Linkages among different hazards exist 4. Damage from natural disasters is increasing 5. 6. Damage and loss of life can be minimized  Explain (with examples) how energy conservation applies to natural disasters. o Energy is conserved when it changes form. o Most sources of energy are diffuse: weak, but cover a wide area o Disasters generally have a concentration of energy into a small area  Describe relationships between force, pressure, stress, strain, energy, and power.  Power: work/consuming energy per second = measured in watts o Pressure: force per unit surface area applied perpendicular to a surface o Stress: force per unit area applied parallel to a surface  Stress tends to strain deform objects  Describe population growth and explain why it is important for natural disasters. o Population growth was exponential over the past 12,000 years  Doubling time = 70/growth rate  Applies only to an exponentially growing pop o Carrying capacity + overpopulation limit the growth  Recent growth is linear -> growth limited? o With greater population = infrastructure is more important + sensitive  Transport, communication, utilities etc  Harder to evacuate + communicate if damaged by disaster Unit 2: Earthquakes  Describe the global distribution of earthquakes and how often quakes of various magnitudes occur o Earthquakes tend to happen near plate boundaries  Plate = lithosphere = crust + top of upper mantle. Strong layer, about 100 km thick.  Plates float on the asthenosphere  Oceanic plates: fast moving (cm’s/year), young (less than 200 MY), created at mid-ocean ridges, destroyed at subduction zones  Continental plates: old (buoyant, not subducted), slower moving (mm to cm)  Relative motion of these plates results in…  Mid-ocean ridge spreading center: tension    Transform fault: shearing , slide past  Collision boundaries/subduction zones: compression    Understand the different types of faulting at different plate boundaries, and which plate boundaries produce the largest quakes 1. Divergent plate boundaries: Plates move apart due to tension (stretching), small-ish earthquakes 2. Convergent plate boundaries: Due to compressive forces  Continental collision: Continental plates collide, tends to form mountains  Subduction zone:  Oceanic + continental: oceanic plate is subducted under continental -> volcanic activity  Oceanic + oceanic: once plate subducted under another  Convergent boundaries cause small to very large quakes.  Subduction zones cause the greatest quakes – located in Japan, Mexico, Alaska, etc 3. Transform plate boundaries: Plates move sideways past eachother, leads to shearing motion  Many moderate to large quakes, but not as large as convergent margins  San Andreas fault, Queen Charlotte fault 4. Intraplate earthquakes: not at plate boundaries, can be devastating  Occur along ancient fault lines/plate boundaries which have been reactivated  Waves can travel far without getting smaller.  Many found in Ontario and Quebec.  Plate Boundaries near UBC 1. Queen Charlotte fault – north, near Vancouver island 2. Cascadia subduction zone: Juan de Fuca plate and North American plate  Divergent margin formed between Juan de Fuca and Pacific Plate 3. San Andreas fault much further, south.  Fastest plate on earth = Nazca plate 1. Creates mostly shallow quakes, biggest magnitudes are deep  In BC, most earthquakes (minor) happen around Vancouver and Queen Charlotte Islands. Some intraplates near Alberta.  Quakes follow factor of 10 rule -> minor ones common, occur 10 times as less for every increase in magnitude  Describe how the Earth builds, stores, and releases energy in earthquakes (elastic rebound) o Types of stress: compressional, tensional, shear = depends on direction of force and orientation of surface  Pressure: compressional stress that is the same in all directions (Cup example). NOT STRAIN.  Changes an object’s volume, not its shape  Stress can involve forces with different magnitudes -> changes shape. Force per area.  Change of shape under stress = strain  Understand concepts of (1) stress causing strain and (2) plastic versus brittle deformation o Responses to stress  Elastic deformation: relatively small stress, smalls trains but not permanent since material bounces back. Energy can pass as waves.  Plastic deformation: like putty, material strains but does not bounce back  Brittle deformation: material stores elastic energy but will eventually break. Catastrophic release. o Cold rock is brittle = upper crust. Can break if stress is large. o Hot rock is ductile = most of Earth’s interior  Elastic Rebound Theory o A pre-existing fault is locked by friction  BUT, elastic plates (“block”) on each side move slowly relative to each other (mm to cm per year)  This leads to the deformation of the blocks  Since they are elastic, shear stress gradually builds up  Earthquake starts at hypocenter/focus. At this points, two blocks slide past  In most cases, sliding stops and earthquake is tiny  Rupture occurs when elastic stresses exceed friction  However, in a large quake, a large part of the fault breaks and the blocks move relative to each other. Elastic strain and shear stress decrease. o At a depth, fault zones are ductile and not brittle. Relative motion of plates here is steady, so no quakes.  Describe how the rupture propagates from the focus and why shaking and damage are not necessarily greatest at the epicenter  Faults are weak surfaces, weaker than surrounding rock o They break repeatedly and may accumulate 100s of km of “slip” over millions of years o Rupture begins at hypocenter and travels two ways  Maximum slip is usually NOT at the hypocenter  The rupture propagates away at 2-3 km/sec  Shaking is greatest in the direction the rupture travels!  Foreshocks sometimes formed, aftershocks always, aftershocks decrease as 1/time o Biggest is usually 1 magnitude smaller than mainshock, however, distribution of SIZE does not vary o Aftershocks form because earthquake stress changes can affect probability on nearby faults  Describe the different types of seismic waves and how they move through the Earth o When elastic energy of rocks is released, energy goes to breaking rocks, generating heat o A tiny fraction of total energy causes seismic waves which can travel far from the hypocenter  Body waves: travel inside the Earth o P wave (Primary)  Compression and extension of a solid – like a sound wave.  Fastest type of seismic wave, about 6 km/s in continental crust. o S wave (Secondary)  Shearing distortion of the solid  Particle moves perpendicular to direction that the wave propagates  Slower than P wave, about 3.5 km/s. Cannot pass through fluids.  Surface waves: require an interface – ground-air, water-air, mantle-liquid outer core… o Slower than body waves o Rayleigh wave: vertical and horizontal motion parallel to wave direction like a rolling ocean wave o Love wave: Horizontal movement, perpendicular to wave travel direction. Like a snake.  Understand the principle behind early warning systems (such as the one in Japan) and how much warning time they can give o Recording seismic waves at the earth’s surface allows us to locate earthquakes, find their magnitude and maybe provide early warning.  Can tell us about earth’s interior: where are interfaces btw different materials, which parts are liquid?  Japan: The alarm goes out when P-waves are detected by seismometers near the epicenter. Warning time = difference between P and S wave arrival times (seconds to minutes).  Describe how an earthquake is recorded and how to locate the epicenter o Seismographs: heavy mass suspended by a spring. Seismograph moves with ground but the mass stays put - relative motion causes pen to trace ground displacement over time. o Geophones similar: use a magnet instead of mass, generates current when ground moves. Records velocity vs time, but can be converted to displacement vs time.  Best = broadband seismometer, but $$$  Seismic waves o Waves contain many different frequencies jumped together, but one can be dominant o Analyzing S and P llag time tells us distance to quake since P wave arrives first o Can find distance to earthquake using 3 seismometers  Calculate distance D to quake at 3 different seismographs  Draw a circle of radius D  EPICENTER IS WHERE THE 3 INTERSECT  Global Seismic Network: detects M4+ events worldwide. 150 stations. Also detects nukes.  Local: Canadian National Seismograph Network – detects small quakes in lower mainland. ~1600 per year  Understand how local ground conditions can affect the duration and amplitude of shaking o Earthquakes don’t kill. Collapsing buildings do.  Compare and contrast the meanings and uses of earthquake magnitude and intensity scales o Magnitude: how much energy was released o Intensity: how strong ground motion was felt at a location  A bulb has fixed magnitude, but different intensities depending on where you are.  Explain the different magnitude scales, which one is best for large quakes, and why  Must be estimated indirectly since we can’t monitor the focus. o Use seismic amplitude + distance to focus o Can look at Richter (local) magnitude, surface wave magnitude, body wave magnitude or find energy released and convert (moment mag)  Richter Magnitude M L o Based on largest amplitude of shaking for high-frequency body waves (1 hz)  Logarithmic  Energy increases 32 fold  Shaking increases 10 fold  Calculated using biggest amplitude and S-P lag time  Problem: most shaking from quakes is low frequency, as a result, Richter underestimates o Moment magnitude M is most common for large quakes w  Explain factors that determine earthquake intensity o Distant quakes: small amplitude, lower frequency recorded o Large: all frequencies  Close earthquakes feel like a jolt, far ones feel like a rolling o Larger quakes: shaking amplitude is greater, shaking lasts longer, dominant frequencies are lower. o Intensity is measured using Modified Mercalli index or instrumentally  Rated from I to XII (1 to 12)  Factor 1: Magnitude o Maximum intensity correlates with magnitude but o Smaller earthquakes can be devastating due to bad construction + after effects (landslides, fires etc)  Factor 2: Ground type o Hard rocks do not amplify – mixture of frequencies o Soft rocks amplify shaking – low-frequency waves may reverberate in basins  High frequencies absorbed o Hard rock = north van, soft rock = Richmond. Waves trapped + amplify  Factor 3: distance from epicenter  Building height o Large quakes produce low frequency shaking -> shakes tall buildings o Small quakes produce more high frequencies -> small buildings shake  Different heights -> buildings can move and crash  Soft story buildings can collapse  Improperly reinforced concrete also collapses  Be aware of how earthquakes can be the cause of other natural disasters (e.g., tsunamis, liquefaction, landslides) o Liquefaction:  Soil grains may be loosely packed and saturated.  Ground motion can increase pore fluid pressure.  Soil temporarily loses strength and flows like a liquid.  Understand the basics of how buildings can be designed or retrofitted to better resist earthquakes (and reduce casualties) o Base isolation: allow the ground to move under the building with isolators o Dampers: absorb energy from the building fame transmitted from moving ground. o Moment resisting frame of beams and columns with strengthened connections allows building to move and evenly distributes load o Retrofitting: fixing old buildings  Add sheer walls, base isolators, dampers, reinforce walls, etc  Connecting a building to foundation is important  Identify fault zones that could produce an earthquake damaging to Vancouver. o Queen Charlotte: M8 o Cascadia: M9?  Elastic stresses gradually building up as crust is strained (compressed). Causes uplift, can be measured. o Shallow crustal faults: big one will happen later o Conventional forecast: based on recurrence interval. CONSTANT LINE.  However, over time elastic stress builds up. Chance of stress exceeding friction builds too. o Renewal forecasts show increasing probability . We have these for Cascadia.  Recurrence time + standard deviation estimates required. o Big quakes can trigger other quakes, so earthquake Interaction can be included. Rises temporarily. Unit 3: Landslides  Explain how the impact of landslides depends on 1) population density, 2) economic infrastructure, and 3) population preparedness. o As population density increases, increasing damage. o Most fatalities from a slides are under-reported as they accompany major disasters  Japan has the most deaths from landslides per year, but highest pop density as well o Largest landslides in Canada happen on West coast (here), between BC and Alberta and in Quebec + Ontario  Explain why British Columbia has the highest frequency of landslides in Canada and what we should expect as our population expands into the mountains. o Mountainous terrain, lots of rain, complex geology (unconsolidated glacial sediments) and many possible triggers  South BC: return period is 25 – 70 years for large slides  Distinguish between the 3 main failure modes (falls, flows, and slides) and how they are influenced by geology. o Falls: very fast.  Occur on very steep slopes (usually rock)  Material detaches because of weakness – falls very fast due to gravity o Slides – cohesive block moves on a surface  Vary from slow to fast. Usually soil, rock or debris  Curved/bowl shaped surface: Rotational slide (slump)  Usually weak material (sediment). Characterized by scarp above slide.  Flat/planar surface: Translational slide  Usually strong material. Cohesive block slides down. o Flows – fluid motion (Chaotic)  Very fast – mudflows can be up to 80 km/h  Soil, mud, wet debris, rock. Water usually involved o Complex movements (combination of above)  Categorize, identify, and name a variety of different landslides o Landslides classified mainly by type of material and type of movement. Rate of movement also important.  Materials: Rock, Soil/Earth, Mud, Debris  Define Angle of repose o Steepest angle a slope can maintain without collapsing. Depends on material.  Assess the balance between the strength of the slope and the destabilizing forces acting on it (Factor of Safety) o Stability of a slope depends on  Driving forces: Gravity  Gravity is manifested as Shear stress “T”  Gravity force is parallel to the slope, moving downwards  Resisting forces (Shear strength) – “f”  Friction – resistance to sliding  Cohesion – material holding together  Normal stress – perpendicular to slope o Factor of Safety (Fs) = (Tf/T) = (Shear strength / Shear Stress) = (Strength / Stress)  FS >> 1, stable slope  FS < 1, unstable – failure may occur  At angle of repose, FoS = 1 or just above.  Compare and contrast landslide causes and landslide triggers. o Causes – usually long term factors that lead to instability of slope  Reduce shear strength of a slope o Triggers – translate instability into motion. Usually short term events. o There can be many causes, but only one trigger.  List and describe several external causes of landslides o Factors outside of slope that affect stability o High slope angle o Undercutting of a slope (removal of bottom) by roads, rivers, buildings o Overloading a slope with excess weight o Vegetation is weird…  Roots bind loose materials = good  Overloading by tress = bad o Climate  Avg temp and rainfall high = more water = increased weathering  Around 0 = frost wedging  List and describe several internal causes of landslides o Water content  Present in all slopes. Adds weight (overloading)  Decreases normal foce/normal stress, which creases Tf  Increases weathering  Medium for flows  In sediment (lose rocks, sand, silt), water can help or hinder cohesion depending on amount  No water = low angle of repose. Some water = high angle. Too much very low angle  In solid rock, reduces shear strength along planes of weakness and causes frost wedging o Inherently weak materials - silt, sand, clay  Clay is so small that Van Der Walls force has an effect  When deposited in salt water, clay is attracted to other clay particles.  However, when salt content is lowered by percolating groundwater, “house of cards” structure is broken and quake clay slide can occur. o Adverse geological tructures can occur as well  Unfortunate bedding or fractures.  List several landslide triggers o Earthquakes, snowmelt, rain, loud noises, jumping up and down, skiing, excavation, etc.  Compare and contrast several key triggers and causes of landslides and how they affect the force balance equation (i.e. Factor of Safety)  Explain how liquefaction landslides develop in sensitive marine clays  List and describe the site conditions (Causes and Trigger) that lead to the development of the Rissa quick clay slide in Norway. o Melting water from glaciers caused clay deposits. Following withdrawal of glaciers, marine clay deposits rose. Some of the best farm land in Norway.  Rain + surface water erode clay and upward flow of fresh ground water leaches salt out of water  Slide initiated by overloading.  Quick clay was liquefied.  Relate the type of landslide damage expected as a function of its velocity. o Faster - > stronger.  Identify tell-tale signs of an unstable slope.  Compare and contrast avoidance, prevention, and protection strategies for dealing with landslide hazards.  List the mitigation techniques commonly used for avoidance, prevention and protection strategies. o Once we identify a hazard, we move on to trying to mitigate it. o Start with investigating: will the slope fail or not? If so, where will it go?  Geological mapping, frequency + magnitude relationship.  Avoidance: move to a different area and avoid the problem o Can map hazards and move things out of the away. Can also use modeling  Prevention o Can remove material – very simple. However, very expensive. o Can add anchors – increase resisting forces by tightening cables. o Drainage – remove water o Add material at bottom of slope increases resisting forces.  Protection o Add barriers / netting to control rock falls  Mitigation o Debris flow protection: separate water and debris by removing debris (barriers) o Prevent more debris from being added – concrete lined channel o Slow down debris flow and reduce erosive capabilities – boulder embedded channel  Identify the appropriate mitigation strategy for a variety of risk situations. Unit 4: Volcanoes  Explain what magma density and magma viscosity are o Magma: mixture of molten rock, crystals and gas below the earth’s surface o Created by the melting of pre-existing rock in Earth’s interior (mantle + crust).  Reaches the surface through fractures, erupts as lava or pyroclastic material (tephra) o In order for magma to rise, it must be  List the different categories of volcanic rocks and Less dense than crust  Runny enough to flow  Hot enough to stay liquid o Main gases: H2O< Co2, SO2, Cl2  At a depth, <10% gas content. This decreases viscosity and density  As pressure decreases, the gases become less soluble and bubbles form o Viscosity = runninses, resistance to flow.  Explain the differences between the magmas they came from  Igneous rocks come from solidifying magma Mafic Rock Felsic Rock  Rich in denser minerals (olivine, pyroxene), darker in  Rich in low density minerals (quartz, feldspar) ls, light colour colour  Mafic rocks  Felsic rocks  Basalt (extrusive), Gabbro (intrusive)  Rhyolite (extrusive), Granite (intrusive)  Dacite (extrusive), Tonalite (intrusive) Intrusive Extrusive  Big crystals = intrusive aka plutonic (Granite, Gabbro). Small crystals = extrusive Freezes in crust, never erupted. Cools slowly.  Rapidly cooled Intermediate rocks: Dacite (ext), Tonalite (int) Andesite (ext), Diorite (int)  Explain why some magmas erupt explosively (as pyroclastic material) and some magmas erupt effusively (as lava) Basalt Andesite Dacite Rhyolite Mafic (less silica) Felsic (more silica) Hot (1200-1400 C) Intermediate Cool (600-1000 C) Low viscosity (RUNNY
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