Physical Geology Test 3 Study Guide
Physical Geology Test 3 Study Guide Geol101
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This 40 page Study Guide was uploaded by Shelby Green on Sunday March 20, 2016. The Study Guide belongs to Geol101 at Clemson University taught by Dr. Coulson in Spring 2016. Since its upload, it has received 218 views. For similar materials see Physical Geology in Geology at Clemson University.
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Date Created: 03/20/16
2/23/16 Geology Lecture 9a Climatology Intro to Climatology • Why do we care? • Climate change. If conditions are changing on earth, it may affect where we live, how much food and water are available, how severe natural hazards are, etc. • Why are we covering this in a geology class? • Geologists do a lot of climate research! Studying ancient climate helps predict future climate trends (remember uniformitarianism) Climate Basics • Climate: Average surface conditions over some long period of time – Ex: usually want at least a decade of data • Often confused with Weather- Average surface conditions over some short period of time – Ex: days-season – Ex: Temp in Clemson last February was often in the 30s, but that is not Clemson’s climate; that was just the weather during Feb 2015 • Why does climate vary so much around earth? i.e., why don’t we have a desert planet or an ice planet like in Star Wars? – Climate (cli) is determined by complex interactions among the lithosphere, atmosphere, biologic processes, ocean circulation, etc – It’s not just about atmospheric processes! System Interactions • Interactions among all these earth systems are complicated to untangle – Ex: how do the lithosphere and atmosphere interact to affect climate? • Some interactions create feedbacks- a change in one component of system affects other things that then eventually affect the original component – So you create a type of cycle Positive Feedback • Change in the 2nd component enhances the change in the 1st component When A increases… B changes... Which causes A to increase again…. – Ex: Increasing the amount of soil causes more weathering to occur, which creates even more soil, which again causes weathering to increase, which again creates more soil…etc, etc, etc Note: ‘A’ can decrease every time you come around the cycle too! This is still a positive feedback b/c you keep enhancing the initial change – Ex: When temp drops, glaciers can get larger, which makes the temp drop even lower, which allows the glaciers to grow even larger, causing another temp drop…etc Positive feedbacks can be problematic b/c it can be hard to break out of the cycle; they just keep going until one component cannot change anymore or something else affects the system – “Runaway train” effect Negative Feedback st • Change to 2nd component offsets the initial change in the 1 component. Steps in a negative feedback: 1. When A increases, B decreases 2. When B decreases, A decreases 3. When A decreases, B increases 4. When B increases, A increases (back to step 1) Each component goes through a ‘see-saw’ effect. o First A goes up, then it goes down, then it goes back up, then it comes back down, etc o Same for B. Negative feedbacks stabilize the two components; neither can get too high or too low. What Controls Climate? • Main energy source for earth’s surface is the Sun • Insolation- INcoming SOLar radiATION. Solar energy that reaches earth – Not insulation! • Vary insolation and you vary the climate • Several things affect how much insolation earth receives Orbital Parameters • Vary earth’s distance from the sun and you vary how much insolation we receive. • The Sun is not directly in the center of earth’s orbit • Aphelion- farthest orbital point from the Sun – 152 million km • Perihelion- closest orbital point to the sun – 147 million km • NOTE: the 5 million km difference has an effect on how much insolation reaches earth • NOTE: Aphelion & perihelion do NOT control summer versus winter • Milankovich cycles: cyclic changes in earth’s motions in space. 3 main ones: 1. Eccentricity: The shape of earth’s Orbital path is more ovate orbital path oscillates from more to less circular. • Affects earth’s distance from the Sun • It takes about 100,000 yrs for Orbital path is one full cycle more circular • 50,000 to go from max to min, then another 50,000 to go back to max • Influences warming-cooling trends during ice ages • It takes 50,000 years to change from one extreme to the other 2. Obliquity (Tilt): Earth is tilted on it’s axis and the tilt angle oscillates over time • It takes ~ 41,000 yrs for one full cycle • 20,500 years to go from min to max angle • Why does such a small change in the tilt angle affect climate? • Earth is large planet, so even a couple of degrees difference impacts how much insolation different areas receive. • Obliquity affects the seasons • Obliquity is why we have opposite seasons in the N and S hemispheres (NH & SH) • EX: December: NH is tilted away from the Sun, so it gets less insolation, = winter. SH is titled towards the sun, so it gets more insolation & experiences summer • Changing the obliquity angle changes the seasonal contrast- The temp contrast btwn summer & winter • Higher angle = each hemisphere is pointed more directly towards/away from the sun, so summer is really warm & winter is really cool, creating a high seasonal contrast • Lower angle = each hemisphere is pointed less directly towards/away from the sun, so summer is less warm & winter is less cool, creating a low seasonal contrast • Eccentricity also affects the seasonal contrast. o Obliquity: NH tilted away from sun = winter BUT… o Eccentricity: NH winter currently occurs near perihelion (see pic below) o SO the 2 cancel each other out some, & the seasonal contrast is relatively low • Remember: the cycles are changing over time o Eventually NH winter will occur @ aphelion • It can be difficult to track all 3 Milankovitch cycles at once to determine what their net affect on climate will be • 3. Precession: Earth not only ‘rocks’ on its axis, but it also ‘wobbles’. The wobble is called precession. • This causes the North Pole to point in different directions in space over time • Watch the animation at this link; note how the red line (indicating the N Pole) points in different directions as the video runs. That motion represents the ‘wobble’ of the planet on its axis • How is Precession different from obliquity? (Students often get these 2 confused) • Obliquity was a rocking motion; precession is a spinning motion • Ex: think of the difference between a rocking chair and spinning a toy top • Precession takes about 22,000 years per cycle (= one full ‘spin’ through a complete circle) • Precession affects climate because it determines which hemisphere is pointed towards the Sun at any given time of year (see pic on next slide) • Top: Earth’s orientation during January • NH points away from the Sun, so NH has winter • Bottom: 11,000 years from now, precession will have wobbled so that, during January, • NH is pointed towards the Sun, so January will be summer in the NH Atmosphere • First thing insolation encounters is the Atmosphere • Troposphere- the lowermost layer of the atmosphere • This is where most weather phenomena occur • Some insolation (ca 30%) is reflected back into space, so it provides little-no energy to earth. • Albedo- a measurement of reflectivity. Varies with material. • That 30% loss comes from reflection off 3 things (see pic on next slide): • Ground = 4% • Atmosphere = 6% • •Clouds = 20% Atmospheric Gases • Insolation also interacts w/ the different gases in the atmosphere • Atmospheric Composition: – Nitrogen- 78% – Oxygen- 21% – CO , 2 O,2and all others < 1% • Many gases are thus present in small amounts, but they are important as greenhouse gases • Greenhouse gases: they trap insolation close to earth’s surface for longer periods of time – When insolation reaches earth’s surface, some is absorbed as heat energy, the rest is re-radiated back into space. – Greenhouse gases prevent that re-radiated energy from leaving as quickly as it should – This allows earth to absorb more of the energy, making it warmer – This is the greenhouse effect- insolation comes in through the atmosphere, but can’t easily leave • Ex: this is why the inside of your car is much warmer than the outside air temp during a sunny day – Key point: even though greenhouse gases (GGs) make up a small % of the atmosphere, they trap a large amount of insolation • If you were to remove all GGs from the atmosphere, earth’s surface temp would be 33 C lower!! • This explains why scientists think that adding more GGs to the environment could cause Global Warming (we’ll come back to this in lecture 10) – Next point: Insolation Changes w/ latitude – At the equator: a given amount of insolation covers a relatively small area b/c it strikes the earth ~ perpendicular to the surface – But closer to the poles, the same amount of insolation gets spread over a larger area b/c it strikes a curved surface (see pic on next slide) – Explains why the poles are colder than the tropics- there’s less insolation per unit area Latitudinal Isolation Distribution • This means there’s an energy imbalance on earth (see graph on next slide): – Equator absorbs a lot, loses a little – Poles absorb little, lose a lot • Nature doesn’t like such gradients, so processes redistribute the energy • Otherwise the equator would get extremely hot and the poles would get extremely cold Heat Transfer in the Atmosphere • Several circulation cells help move heat energy away form the equator and towards the poles • Hadley cells: Transport heat from equator to 30 degrees lat Steps in the Hadley cells (starting at equator): 1. Insolation warms the air close to the ground a. Remember convection? When you heat something, its density decreases, causing it to rise 2. As it rises, it begins to cool and gets pushed aside by warmer air rising beneath it a. This creates low air pressure at the equator (Thus, Hadley cells work just like convection cells in the asthenosphere) 3. As the air mass cools down while rising, some water vapor cools into liquid water & falls as rain a. This is why the equator is associated with rainforests & lots of rain 4. Once pushed aside, some of the air moves N and some moves S 5. As it moves N or S, the air mass continues to cool, so more water vapor is lost as rain along the way 6. By the time the air mass reaches ~ 30 degrees latitude, it is cold enough that its density has increased, causing it to sink back to earth’s surface a. This creates high air press at the surface b. There is little water vapor left, so this area gets little rain 7. Once close to the surface, the air absorbs more insolation, heating it up as it moves across the surface as wind until it is warm enough to rise again a. Some of the wind blows N, moving the heat farther N b. Some of the wind blows S, completing the cell • The Ferrel cells and polar cells operate in the same way, just at higher latitudes • The three interlock, like gears, to keep moving heat away from the equator and towards the poles • El Nino: periodic changes in wind strength over the Pacific Ocean during some winters • Affect global weather patterns • First, let’s look at normal conditions in the Pacific… • The map on the next slide is color-coded by water temperature. • Notice that, near the equator, water temp is much higher in the western pacific (near Australia) than in the eastern pacific (near Peru) • West Pacific Warm Pool (WPWP)- the area of warm water in the western Pacific Normal Winter Conditions: 1. Trade winds push water to the W 2. The ‘void’ left is filled by cool water upwelling in the E 3. WPWP heats the air above it, causing the air to rise • Creates low atmospheric pressure above it 4. The rising air cools, creating lots of rain • Just like the beginning of the Hadley cell So in the western Pacific during normal conditions it’s warm & wet In the Eastern Pacific it’s cool & dry El Nino Winter Conditions: 1. The trade winds weaken or even stop 2. This allows the WPWP to flow back to the east (remember, the winds were the only thing pushing the warm water west) 3. Eastern waters become warm, so upwelling stops 4. The low pressure area must follow the warm water b/c the warm water creates it • Southern Oscillation- the resulting flip-flop in air pressure between west & east 5. The rain must follow the low pressure area • So in the Western Pacific during El Nino conditions it becomes cool & dry • And in the Eastern Pacific it becomes warmer & wetter • Basically, everything switched NOTE: The El Nino cycle can be tricky to understand. • You have to keep in mind which location you are at, AND you have to determine whether normal or El Nino conditions are occurring • The animation is a good illustration of the entire process El Nino Effects • Why do these changes affect weather in other parts of the world? • The Pacific Ocean is huge. As the warm water & low pressure system move across the Pacific, they displace other air and water currents, like the Jet Stream • If the Jet Stream moves, it affects weather across N America • During El Nino: SC has a wet & cool winter, dry & warm summer • El Nino does not occur like clockwork • Quasi-periodicity of once every 4-7 years • Scientitsts know what happens during an El nino, but they still are not sure why the trade winds occasionally weaken and cause an El Nino What is La Nina? • In some years, the trade winds strengthen instead of weaken • This pushes the WPWP farther west • La Nina basically has the opposite effects from El Nino – Ex: The eastern Pacific gets even cooler & drier than usual – Ex: SC has a relatively warm & dry winter • Winter 2011-2012 was a La Nina winter, which explains why it was so warm around Clemson 3/1/16 Lecture 9b Climatology Geology in the News • New Study suggests oxygen buildup on earth might have started during the Archean eon instead of the Proterozoic eon • 1.8 billion years earlier What affects Climate? 1. The Hydrosphere: Water has a high heat capacity (heat energy store), the heat stored in the water moves north and south through currents to distribute the heat Gulf Stream: a stream of warm water that originates in the gulf of Mexico that supplies a warmer climate towards Europe, red in top photo Thermohaline Cirulation: the red pathway, shows how water moves at the surface of the ocean, and the blue shows how the water moves at the bottom of the ocean All one big current , moves like a conveyor belt moves warm salty water around. Key to keep belt moving: the water sinks in the north atlantic Ocean Heat Transport: why does water sink in the north Atlantic? o Water gets cooler/saltier/denser as it travels north and begins to sink. Ocean Heat Transport: o Slowing of ocean heat transport in recent decades because.. The oceans are warmer now days, so there isn’t much cooling in the process Glaciers are melting and adding fresh water into the ocean and dilutes the slat content Negative feedback loop: the area where warm water is being brought to has gotten warmer, causing belt to slow down, which brings less warm water in the area, that area then cools, so the belt speeds up again, and as it speeds up, warm water is brought to the area, then slows down again, repeat… 2. The Biosphere Plants o Draws down CO2 for photosynthesis which warms temp o Affects albedo or the measure of reflectivity (how much sunlight will be reflected vs. absorbed) Animals o Release CO2 and methane CO2/methane increase, temp increases Biological Pump o Interaction of biosphere, atmosphere, hydrosphere, and lithosphere Organisms in the ocean cause CO2 to be stored long term in the lithosphere (kinda like photosynthesis in the oceans) Crysphere o The amount of snow and ice o Ice covers ca ~9% of land surface Antarctica has more ice during winter than summer o Ice coverage albedo: reflects 40-90% of the sunlight Hard to warm area back up if its reflecting that much light o Land surfaces albedo: reflects 14-25% of the sunlight 3. The Lithosphere Tectonics affect climate in several ways o Continental position: whether its near/far from equator o Continental size: the bigger continents tend to have desert like interiors b/c they’re so far from coast line, smaller continents have more weather climates b/c they’re closer to coastline o Collision zone uplift: rain shadows, mountain blocks one side of mountain from getting rain Land Bridges o Control where the ocean currents can move which play a big role in heat energy Land bridge formed between north and south America keeping the current from going between them and changed the climate o Land bridge broke down between south America and Antarctica and changed the Antarctic climate Recording Climate Instrument and historical records only go back so far **Studying previous climates and comparing it to our climate now, helps us understand how climate can change in the future 1. Air trapped in glacial ice: o Air bubbles are pockets of atmosphere that has been preserved since the was ice formed (so it could be over 50 thousand years old) Can see how much CO2 was in the atmosphere at that time vs. now ** Note: NOT A PROXY actually studying samples from ancient atmosphere so there is no substation involved o Ice cores Like an oil rig for ice (digging for old ice in ice cores to study the air bubbles) Ice cores in Greenland and Antarctica >2 miles (3300 m) Scientists haven’t even reached the bottom of these cores yet and they already represent >1 million years 2. Proxies: Substitute to get the info you want o Lots of things that form in nature are sensitive to different aspects of climate that can be studied to tell us about those parts in the climate o Can also tell us different time scales o Always consider the nature of proxy Tree Rings: Tree ring width tells us how healthy that tree was during that year (healthy=good climate) Hard to decide what made the tree unhealthy/healthy though between the diff aspects of climate Biogeography: The study of where different plants and animals live (species distributions) Many species only live in different climate conditions Fossils of those organism tells us about the climate at different points in the path o Not going to find crocodile fossils in a cold climate area Crocodile fossils from 90 million yrs ago found in Canada climate in Canada must have been warm 90 million year ago Stable Isotopes Measure as ratio: ex) 1O/ O6 Diff atomic weights = diff amounts of each isotope get incorporated into molecules Ratio: always bigger #/smaller # Key: the ratio in some materials changes with climate variables Ex: at one temperature, you add a certain ration of 1O/ O to a growing shell…. …But at a different temperature, you add a different 18 16 ratio of O/ O Stable Oxygen Isotopes Ex: many invertebrate & plankton shells Can provide quantitative paleotemperature data Oxygen in shells can be used to calculate the water temp when that animal was alive Ex: 1O/ O (stable isotopes of oxygen) in fish bone reflects water temperature when the fish was alive T = 111.4 – 4.3*(Df – Dw) Df = ratio in fish bone Dw = ratio in seawater (assume= 1.0) T = water temp (Celsius) Measured ratio in a fossil fish is 20.1, what was the water temp? T= 111.4-4.3*(20.1-1)=29.27 Other Temp Proxies Some Trace Metals in Shells Ex: Magnesium/Calcium in shells also tell what temp the ocean was at that point Q: Why do we want multiple temp proxies? The more ways to find temp, the more accurate the guess If same answer found of water temp with three different proxies proves it is an accurate reading Stable Carbon Isotopes 1C/ C both stable isotopes of carbon Both isotopes form CO in the atmosphere 13 12 2 Ex: CO 2 , CO 2 Plants take in both types of CO fo2 photosynthesis The 13C/ C ratio in each plant depends on the plant’s photosynthetic style C3 plants vs C4 plants **Note: the names ‘C3’ and ‘C4’ do not refer to carbon isotopes; they refer to types of plants Groups of plants that photosynthesis with slightly different weights (Like a Ford vs. Chevy truck: same type of car, different parts) Each type of plant represents two diff types of habitats 13 12 • The C/ C ratio in animals’ skeletons thus reflects the type of plants in the ecosystem • Provides clues to climate 3/3/16 Lecture 10 Global Warming Global Warming (GW) • This is a big topic in society, and debates can get quite heated – Sorry, bad pun intended J • Everyone has an opinion, but remember the difference between opinions & hypotheses? – Hypotheses require facts to support them – Opinions do not (Ex:) IMO sushi is terrible. • This is just my opinion, and it’s not even based on many facts: • I’ve only tried sushi 1-2x • There are a lot of types I’ve never tried • So why should you believe me if I tell you sushi is yucky? • Remember: – People are always trying to convince you to agree with their opinion • “Vote for this candidate, he/she’s the best!” • “Buy this product, it’s better than other products!” – But what are their opinions based on? – Think about the issue for yourself & develop your own, informed opinion One big source of confusion w/ GW is that there are 2 separate questions: 1. Is the Earth warming up? 2. If so, why is it warming up? **We have to address these issues separately. o If Earth is not warming up, we don’t even have to worry about #2 Is Earth Warming up? • It sounds simple, but temp calculations can get confusing – You have to consider different locations, whether you’re measuring daily, weekly, monthly, or seasonal temp, are you going by daytime highs or daytime lows, what statistical and graphing methods to use….yikes! • Instead, let’s use a simple proxy glaciers – If Earth is warming up, then glaciers should be getting smaller. That’s a simple hypothesis to test… • To test the hypothesis, all we have to do is see if glaciers are getting smaller. • All pictures on the next pg show the same location in the same season Based on Glaciers shrinking, we must conclude that yes, lots of places are getting warmer over the past several decades So now we can start to figure out WHY the Earth is warming up…. Why is Earth Warming? 1. Earth is currently naturally warming after coming out of the most recent ice age – Natural processes (ex- Milankovich cycles) account for ~ 50% of warming over the past few centuries 2. Unusual Warming Pattern: – But the warming is occurring faster and has a greater magnitude than other warming trends we have data for in recent history – The temps are higher now than at any time within the past 2,000 years and they’ve risen very quickly since ~1850 Greenhouse Gases and Global Warming • Humans have added a lot of greenhouse gases (GGs) to the atmosphere since the Industrial Revolution began in the 1800s • Remember: – Greenhouse Effect: GGs trap insolation, keeping more heat energy at Earth’s surface Question: Is the amount of GG in the atmosphere increasing? These 3 GGs have become much more abundant in the atmosphere, and the timing coincides with the Industrial Revolution Question: Are the GGs really decreasing the amount of insolation that escapes from Earth? Yes. Satellites measure exiting insolation. o It’s been steadily decreasing for decades. o The energy wavelengths that GGs trap are exactly the wavelengths that are escaping less and less easily. Conclusion: Based on these facts, scientists calculate that ~ 50% of the temp increase of the last ~ 200 years is due to greenhouse gas buildup. Humans and Greenhouse Gases Are human-made GGs responsible, for the warming? i.e., is the GG buildup anthropogenic (man-made)? • World population is now > 7 billion – Up almost 3 billion since 1970 – That’s a lot of people emitting a lot of GGs, but is it really enough to alter global climate? • Let’s look at the atmospheric GG buildup closer… – This data (the Mauna Loa Curve) clearly shows that carbon dioxide levels in the atmosphere have been rising – Levels are higher now than any time for the past 1,000 years – But neither graph can tell us where the CO2 coming from CO2 Buildup (400k yr record) **Modern Levels have no equal in the past 400,000 years, still haven’t proved where CO2 came from The CO2 Buildup • So we have plenty of data demonstrating that CO levels 2re higher now than at any point in the past 400,000 years • Next, we need a way to figure out where all this extra CO h2s come from • For that, we’ll examine carbon isotopes again 12 – Note: C-12 and C mean exactly the same thing; the notations are used interchangeably in this lecture Finding the Carbon Source • Different sources produce diff isotopic mixes of carbon – Ex: volcanoes release C-13, forest fires release C-12 & C-14, etc 14 12 • Seuss Effect: a decline in the atmospheric C / C ratio – Why would that ratio decrease? • There are two ways to make a ratio smaller: • 1: make the numerator smaller to decrease the amount of C-14 in the air • 2: make the denominator bigger to increase the amount of C-12 in the air – Think of the isotope ratio like a mixed drink… • C-14 = rum and C-12 = Coke • You put one shot of rum in each glass, so they have the same amount (= the numerator is the same) • Next, fill the glasses with Coke. • The small glass has a higher rum/coke ratio than the big glass b/c the big glass has more Coke (the denominator is larger) – So which happened, less C-14 or more C-12? • Remember that C-14 is created in the atmosphere (we covered this during lecture 8) at a pretty constant rate • Thus, the amount of C-14 in the atmosphere has not significantly changed • So there must be more C-12 in the air than they’re used to be – So what can add C-12 to the air without adding any C-14 or C-13? • It wasn’t discussed herein, but the amount of C-13 has not changed • Volcanoes would add C-13 to the atmosphere • Other sources (ex- forest fires, cellular respiration) would add some C-14 • Fossil fuel burning adds lots of 12C to atmosphere and adds no 14C – Why doesn’t fossil fuel burning produce C-14? • Remember: It takes ~ 57,300 yrs for all the 1C to decay after an organism dies • But It takes millions of years for organic remains to become fossil fuels • So, fossil fuels contain no C-14, just C-12 – Thus, the Seuss Effect strongly supports the anthropogenic hypothesis b/c burning fossil fuels is the only thing that accounts for the drop in the 14/12 ratio. • Note: it’s fine if people want to challenge the GW hypothesis, but that requires finding a better explanation for the Suess Effect, which GW skeptics have not been able to do. • Remember: to challenge scientific ideas, you have to work with facts, not just some group’s opinion • Fact: humans are increasing atmospheric CO 2 • Fact: CO 2elps increase temperature • Conclusion: humans are responsible for some of the current warming • Even if someone remains unconvinced that humans are the cause of GW, remember that we have to deal with the changes GW causes regardless of what’s causing it – Possible effects of GW: • Ice sheet melting • Rising sea levels • Aridity in mid latitudes • Stronger hurricanes and El Ninos • Extinctions due to ecosystem changes – These are all things that will adversely affect our society Seven Global Warming Myths ***Both sides exaggerate & twist the facts 1. “The Coasts are about to flood!” a. As glaciers melt, much of the water will flow into the oceans, so sea level will rise b. Some GW advocates claim coastal cities and beaches thus are in imminent danger of flooding c. Consider the timescale of the change i. Significant sea level will occur, but on decadal-century timescale ii. Thus, the threat is Not imminent 2. “The Planet is burning up!” a. The map below was included in Al Gore’s movie, An Inconvenient Truth, to make people realize how much GW is occurring b. The data is real, but about that map has some issues… i. When you project a 3-D world onto a flat map, things can get distorted. ii. This type of map makes things near the poles look really big iii. Thus, the worst warming appears to cover a bigger area iv. Also, the color scheme intentionally uses colors that we associate with danger signs/warnings c. This map shows the same type of data in a less alarming manner d. Earth tone color scheme e. Different type of map that doesn’t stretch the area near the poles i. Again, the data on the other map is fine, but that map was designed specifically to get you to agree with their message 3. “Record Low temps disprove GW” a. GW skeptics often make statements like this one: i. “1,100 record low temperatures were recorded in the US during summer ‘09… so much for Global Warming!” b. Many people listen to this point b/c it sounds like a fact with lots of data supporting it… but often these people are talking about weather, not climate c. The data are accurate, but the data do not support the conclusion i. The temps may be from just one small area ii. They may reflect only one small length of time d. Data on record highs and norms is lacking e. We don’t base climate trends on data from just one area (Ex) Spring semester 2011 was very cold around Clemson i. We even missed the first day of class due to snow! 1. GW skeptics were quick to use this as anti-GW fodder, 2. But it was just one cold month in one place- that’s not a global climate trend, that’s just unusual local weather ii. Spring semester 2012 we had unusually WARM conditions all semester J 4. “It’s only 3 degrees, who cares?” a. Skeptics dismiss GW b/c scientists predict global temps will increase about 3 over the next century, and that seems like a tiny temp change b. Scientists use Celsius, but most people use Fahrenheit i. 3 C = ~ 5.4 F, that’s a bigger change ii. ****Always check your units! c. That number is a global average; temps will vary a lot form place to place i. During the last Ice Age: global average temp was only ~ 4.5o C lower than today d. So drop the temp 4.5o C and we get an ice age, so what will a 3o C increase do? L i. Many organisms can’t tolerate temp shifts of even a few degrees ii. We rely on many species for food, medicine, etc. 5. “Scientists Can’t Decide between Global Warming and Cooling!” a. This point goes back to 1975… i. National Academy of Science Report stated that global warming or cooling was possible ii. Data was inconclusive, so they could not determine how temperature would change b. Also published in 1975: i. Newsweek- "The evidence in support [of global cooling] has now begun to accumulate so massively that meteorologists are hard-pressed to keep up with it.” ii. Reporters often make mistakes when trying to explain scientific studies iii. Skeptics still use this 37 year-old Newsweek issue to try and discredit scientists, even though it is clearly outdated AND make a huge reporting error in the first place c. Lesson: Always consider the source & check the date! i. We often get our ‘facts’ from unreliable sources ii. Ex: I can post a blog on the internet describing my life as a roadie for Metallica who has 3 arms… but that’s not even remotely true d. If you want reliable info, talk to experts… e. Tooth aches? Talk to a dentist. Car won’t start? Talk to a mechanic. Unsure about GW? Talk to scientists. Bloggers post anything to get your attention Politicians say anything to get your vote. 6. “Scientists Profit from Global Warming a. Scientists are telling us climate is changing just so they can have “lavish laboratories“ and fund their “Arctic vacations” (quotes from a Senator speaking out against global warming research a couple of years ago) i. When a scientist gets a grant, it does NOT go into their pockets. ii. The money is closely controlled by the university/company they work for. iii. They must justify and document every expense they want to make 7. Professionals a. Many anti-global warming politicians have recently started using this tactic: “I’m not a scientist.... but I don’t trust what climate scientists tell me because they are paid to study climate for a living”. b. Think about that… they’re saying you shouldn’t listen to the professionals who know the most about the subject c. So who would they recommend we listen to…. amateurs who don’t really know much about the subject? That doesn’t make any sense 3/8/16 Lecture 11 Deserts Geology in the News • Cores being taken from the Atlantis massif • Providing insight into the origins of life on Earth and perhaps on other planets • Former Clemson geology student is one of the researchers (Class of 2014) Why do we care? • Cover extensive areas, and are growing – 20% of all land is desert – Another 15% is semi-arid (semi-desert) What is a desert? – Temp does not define a desert some deserts are actually very cold regions – Lack of rainfall is the key to defining a desert (less than 10 in/yr qualifies a desert) • Semi-arid is a little more than that, but not much more • The 10 Largest Deserts (km²) – Antarctic (Antarctica) 14 000 000 – Sahara (Africa) 9 000 000 almost same size as the US – Greenland (Arctic) 2 000 000 – Gobi desert (Asia) 1 125 000 – Empty Quarter (Middle East) 650 000 – Kalahari desert (Africa) 580 000 Compare: – Great Sandy Desert (Australia) 414 South Carolina: 82,000 000 – Karakum (Asia) 350 000 – Taklamakan desert (Asia) 344 000 Texas: 678,000 – Namib desert (Africa) 310 000 USA: 9,800,000 Distribution of Deserts • Found in certain latitudes – Red areas: 30 degrees N/S latitudes (Hadley Cells cause cold dry air here) – Yellow areas: rain shadow effect causes desert in left upper US, tectonic influence in middle Asia, Mongolia area center is far from coastline (continental size effect) causes desert here – Polar regions: Antarctica gets very little snowfall each yr Weathering in Deserts • Little water = little chemical weathering **Water important for weathering reactions • Weathering in deserts rely on oxygen & iron oxides • Slow chemical weathering b/c it relies on “ Desert Erosion • Water still an important player • Big Storm events—rare but do occur • No vegetation to constrain it • Arroyo-shallow/dry stream beds • Do not hike in arroyo flashfloods are a real threat Wind Erosion • Wind can only move relatively small particles • Wind has low density and low viscosity • Particles > than 0.06 mm in diameter hard to erode • All the small particles eroded by sand can still add up to a huge volume eroded • Ex: Sahara Desert • 250-500 million tons of dust are transported to the Atlantic every yr • Can be seen by space (example to right) • • Deflation-the process of moving the finest grain sediment • Pavements-surface of desert looks more and more cobble-y as a result of deflation (the bigger particles left behind) • Only about 20% of all desert areas are covered in sand! Desert Features • Ventifacts: any object that has been significantly reshaped by wind o Little particles hit bigger objects the more the impacts occur, the more reshaped the bigger object becomes (slow process) One side will be drastically different than the other Can happen to plants (cacti) or rocks, etc • Alluvial Fans: sediment fan that form at the end of arroyo o Sediment carried through arroyo until it gets deposited at the end • Playa lakes (aka playas): isolated lakes in desert regions that aren’t attached by any creeks and rivers o Form in any kind of depression (kind of like a runoff pond) o Rings of material forms around edges Mineral material that precipices out of the water as if evaporates Useful when searching for small mineral deposits • Inselberg: big bodies of rock that tend to be out in flat/featureless areas o Note: the iceburg of the desert o Igneous rocks formed below the surface as a pluton the sediment around the pluton eroded away, and left the massive rock behind • Arches (natural bridges) o Result of localized erosion o Arches Natl. Park (Utah) has over 2,000 arches Formation o Weathering/erosion attacked the weak cracks o Localized erosion Dunes • Wind deposits of sand • Initiated by surface irregularities that disrupt wind flow • Saltation-all the sand is jumping/skimming along the surface of the ground o Originates from Spanish word “saltar” which means “to jump” Types of Dunes • 5 different types • Important factors: – Variance in wind direction: – Sand availability – Vegetation 1. Barchan dunes • Standard/most common type of dune • Strong crescent shape o Two ends up the crescent called the horns Horns always pointing downward / direction the wind is going 2. Transverse Dunes • Merges Barchan dunes o Need a ton of sand supply o Wind direction is perpendicular to the crests 3. Linear Dunes (Aka longitundinal) • Long but relatively straight o Wind direction can change slightly • Not a lot of sand availability 4. Star Dune • Wind direction varies a lot • Look like a star 5. Parabolic Dune • U or V shaped (steep curve) • Vegetation • Horns point the direction the wind is coming from o Vegetation prevents the wind from blowing the horns faster Summary Desertification • Process of an area becoming a desert • Sahara expanding south about 30 mi/yr • 1 billion people in at-risk areas (1 in 7 people) • Risk assessment map below Why is it occurring? 1. Tectonics: • 3o degrees latitude touches a lot of land areas 2. Climate Change • Temp increasing so evaporation rate is higher • Water levels drop 3. Human Activity • Over grazing of livestock • Cutting trees down What can we do about it? 1. Change livestock practices move herds around more frequently 3/10/16 Lecture 12 Glaciers Geology in the News The amount of water flowing into Earth’s interior found to strongly correlate to active faults Effects of Glaciers As glaciers have been melting, other species are being affected o Ex: polar bears are losing their habitat • Sea level change • Melt all glaciers = sea level rise of ~ 65 m (about 200 ft) • In the diagram, all the hot colors are at risk of being flooded • Glaciers trap huge amounts of water Coastline during Ice Age Light blue = above water ------------> • Isostatic depression: the crust underneath the glacier warps downward due to glaciers weight • Some places like in E. Antarctic, ice sheet has caused up to 2.5 km of isostatic depression • As the crust is adjusted, the mantle has to adjust beneath it • Isostatic rebound: when the glacier is gone, the crust and the mantle will readjust to try and flatten back out • Affects weathering processes and what not at the surface • Alte rs thermohaline circulation: • Density decreased, speed of process slowed down, (discussed in precious lecture) • Drinking water and irrigation: • Many places us glaciers as a water source • Ex) Washington gets ~470 billion gallons of water from a glacier per yr • NOTE: Melting glaciers do not provide MORE drinking water… The glacier gets smaller every year, so there is less and less ice to melt Glacier Basics • Glacier: Ice has to pile extremely thick (at least 50 meters of ~150 ft) and begin moving downhill due to the pull of gravity • Ice on Earth • Currently covers ~9% of Earth’s land area • Antarctica (85%) • Greenland (10%) • Ice on Antarctica exceeds 4,200 m (2.5 miles) in max thickness amount of weight of the ice is tremendous • Forming a Glacier • Granular snow: dense/more compact snow • Firn (denser) : denser pelets of snow build up • Glacial ice: firn slowly compacts into • Denser than ice from a freezer • Requires time to allow the build up to happen, cold enough that the snow/ice stays around yr round so that the glacier can accumulate over the years, & precipitation required to add more material Types of Glaciers 1. Valley Glaciers (aka Mountain, Alpine) Glaciers that will form/fill in valleys o Not exclusive to polar regions Ex: Mt Kilimanjaro (Africa; about 20,000 ft) 2. Continental Glacier (ice sheets) Covers entire landscapes o Exclusive to polar regions (Greenland and Antarctica) Glacial Advance and Retreat • Accumulation: the part of the glacier that is getting bigger • Makes the glacier appear to be advancing b/c its adding material • Ablation: the glacier is melting faster than its adding • Makes the glacier appears to be retreating b/c its losing material • Firn Line: the melting and adding balance out no change Glacial Movement Speed varies: o Center of the glacier moves faster than the sides The ice closer to the wall of the valley is affected by friction o Anything you stick in the ice is going to move along with the ice Explorers trying to mark their territories during exploration of Antarctica had to learn the hard way lol Type of Movement 1. Plastic flow: a. (>50 m thick) ice at the base of the glacier becomes more ductile b. Each individual ice crystal is being squeezed downhill i. Slow process 2. Basal slip: a. A little film of liquid water accumulated in-between the glacier and the ground i. Liquid forms because of the pressure its under has nothing to do with temp b. Liquid minimizes friction and glacier moves faster i. (Like a slip and slide) Glacier Feature Crevasse: massive cracks seen at the surface of a glacier o Surface cracks as its base moves ductile- like, and it moves more brittle-like Glacial Erosion Abrasion: sediment gets picked up and carried within the glacier, so when the glacier comes to a stop and melts, the sediment gets deposited o Glaciers often full of dirt and rock Plucking: big chunks of sediment that glaciers transport o Water under glacier, gets caught in cracks of crust, freezes, and breaks pieces of crust off of one side of hill Erosive Features Striations: thin/straight lines that have been carved into the surface of bedrock o Carved from glaciers U-shaped Valleys: steep walls but round valley Hanging Valley: little U-shaped valley that is elevated with in another valley **look for waterfall feature/rapids to identify hanging valley Cirque Valley: big bowl shaped valley o Tarns: lake trapped in the middle of a cirque Horn: sharp point shaped by multiple valley glaciers carving down all sides of the mountain Arete: ridge of rock coming down the side of mountain o Wall left in-between two valley glaciers Roche Mountonnee: big body of rock that appears to be a small cliff/hill o Asymmetrical occurring from plucking o Gentle side, steep side o Ex: glacier coming from SE to NW Glacial Sediment Deposits Erratics: o Boulders deposited by glacier Often out in the middle of no where Till: o Poorly sorted pile of sediment Rocks/ boulders/sand/gravel combined Outwash: o Sediment that has been carried by the melted water of glacier and gets sorted as it flows Better sorted Loess: o Smallest particles, best sorted, sediment from glaciers that have been eroded by wind Tend to make up soil great for agriculture Ex: Indiana NOTE: Make sure to keep the depositional features and erosional features separate in your mind Depositional Features Moraines: ridge of sediment that extends along one edge of glacier o As ice melts around its edges, sediment falls out and forms ridge along the glacier o Can sometimes form in the middle of glacier Tend to be more straight and narrows o Made out of till deposits poorly sorted Eskers: ridge of sediment formed under the glacier where the flowing water underneath has deposited some of the sediment o More wavy than moraines o Made out of outwash deposits better sorted Drumlin: looks similar to a mountanee (an erosional feature made of solid rock), but drumlin is a depositional feature that is merely a pile of loose sediment o The glacier moved toward the gentle slope, and came from the side of the steep slope (opposite Drumlin movement than a mountanee Kames: small hills/mounds of sediment Kame s o Usually form as glaciers breaks up, and smaller blocks of ice are left behind, and as that block melts, it forms its own hill of sediment Kettle lakes: melted water from ice blocks that were left behind is trapped in impressions of the surface o Minnesota is the “land of the kettle lakes”
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