Geology lecture 14 and 15
Geology lecture 14 and 15 Geol101
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This 14 page Class Notes was uploaded by Shelby Green on Thursday April 7, 2016. The Class Notes belongs to Geol101 at Clemson University taught by Dr. Coulson in Spring 2016. Since its upload, it has received 23 views. For similar materials see Physical Geology in Geology at Clemson University.
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Date Created: 04/07/16
3/5/16 Geology Lecture 14 Coastlines Geology in the News: Fossil of rare Siberian rhinoceros found Why should we care? About 53% (> 3.5 billion) of the world population lives within 120 miles of a coastline Coasts Remember- still on continental crust! Several forces acting on these environments Coastlines are very complex systems. Several processes interact together to create this environment. If one element is changed, the entire system Coastal Processes Tides: water level changing every few hours (higher/lower) covering more land as it comes in, and exposing more land as it recedes o High tide: sides facing towards and away from the moon o Low tide: the in-between sides Tidal flats: when the water recedes for low tide, tidal flats exposed Tide height: Hawaii has a tidal range of 1-2 ft Bay of Fundy has a tidal range of about 40 ft o If your coastline is well connected to the ocean, the tidal ranges are very small (Hawaii surrounded entirely by water well connected) Waves: o Wavelength: how closely spaced are the waves Changes as wave gets closer to shore… Decreases speed: seafloor creates friction (occurs when water depth gets to about half the wavelength) Wavelength decreases: waves get closer together Waves get taller and starts to roll over and break Wave refraction: waves change direction as they move into shallower water o One side of wave gets to shallow depth earlier, slows down earlier other side catches up b/c its deeper and moving faster until it hits the same shallow depth Wave refraction Longshore current: water movement that moves parallel to the shoreline o moves on and off shore, being bushed back and forth by the waves Longshore drift: sediment movement with the longshore current Shoreline Features Shoreline features depend on: o Tectonics o Rock type o Sea level fluctuations Stack o Storm size/strength Types of Coastlines Emergent Coastlines: uplift occurring, so more areas are emerging above the sea level o Stacks: small islands that tend to be very steep a hill that has been submerged underwater, and its peak is exposed above water level o Terraces: wide flat areas that resemble stair cases (each stair is a different age as time goes by, sea level has changed) Emergent Coastline Submergent coastlines: most of the coastline is submerged appears to be flooded o Long, wide beaches and coast plains (SC coastline) o Spit: elongated sand body that is still attached to shore Lots of sediment deposition o Barrier Islands: elongated sand body that is not connected to shore Spit A lot of the southeast shore Move around/change frequently & rapidly bad for building Barrier Island Offshore Features Continental margin: edge of continent underwater Depends on whether or not it is near a plate o Active: continental margin is also edge of continental plate o Passive: continental margin that is not on the edge of continental plate Continental Shelf: landmass which extends from a continent, resulting in an area of relatively shallow water known as a shelf sea o Water is shallow/warm, sediment deposits from rivers, nutrient rich water, lots of biological activity (sea life) Economically important Best fishing (“all you can eat buffet for fish”) Oil and methane gas found on the continental shelf Continental Rise: the very end/edge of continental margin (could be several miles off shore) Coastal Erosion Can occur along any type of coasts Emergent and Submergent coasts o Threatening for construction along coastlines Erosion is a natural process so its not a bad thing it just becomes a hazard when people don't consider erosion occurring when they’re building CASE STUDY: Cape Hatteras The Outer Banks of NC o Strong longshore currents: a lot of sediment transported from one end to the other end of the coast The Cape Hatteras lighthouse o 1868: built 1500 ft. inland 1998: just 120 ft. from the ocean Q: What was the average rate of erosion in this area from 1868-1998? o 10.6 ft./yr To save the lighthouse, in 1999-2000 it was moved 2900 ft. inland over the course of 23 days o Cost: $15 million How to deal with coastal erosion… o Zoning: Build farther inland Setback distance: how far away from the shoreline is it considered safe to build Erosion lines (aka E lines): line along the coast marking where erosion will move the shoreline to in the future Formula: erosion rate x interval = E-line distance EX: you want to know where the coastline will be 10 years from now o Given: erosion rate = 10 ft/yr o 10 ft/yr * 10 yrs = 100 feet How far inland should the setback distance be in order to keep buildings safe? National: E-60 line (most construction current day is expected to last 50 yrs) SC: E-40 Why doesn't SC use the E-60 line? o Tourism: the #1 revenue source for SC 2010: ~$18 billion for SC b/c of tourism o Barriers Protect the shore in one of two ways… Weakens Waves Keeps sand from moving away Types of Barriers: Seawalls: takes the blunt of the waves hits o Very effective soak up wave energy o Expensive to build/repair o Not very scenic Groins: walls build perpendicular to shore built to mess up the longshore drift so the sediment stays o Expensive to build o Need a series of groins, not just one o Hard to get permission to build b/c the problems they cause o Beach (Re)nourishment Replace the eroded sediment Some wildlife issues o Natural beach sand is ideal (light and fluffy) for wildlife to move through it o Added beach sand tends to be more compact and makes it harder for wildlife to move through Ex: turtles have a hard time digging down in the sand either give up, or burry their eggs to shallow CASE STUDY: Miami 1950s: erosion washed out the sand and the water was coming up right next to the buildings 1980s: replenished beach with beach nourishment o Expensive but tourism made up for the cost New Jersey 1980s: tried to copy Miami o 5 million dollars of sand added to their coast o A few years later, all the added sand was gone New Jersey had diff environment than Miami Geologist studied these differences With geologists help, New Jersey tried again and was successful 3/7/16 Geol Lecture 15 Nonrenewable energy Geology in the News Archean Eon glaciation (3.5 Ga) may have been greater than previously thought Why do we care? Everything we use almost requires a source of energy Effects our economy, politics, etc Energy Sources 1. Renewable: replenish themselves fast enough for human consumption a. Ex: sunlight 2. Nonrenewable: either do not replace themselves or replace themselves slowly on geologic time scales Fossil Fuels • ~ 82% of energy consumption in the US and globally (by far the most important source we have) – Coal = 22.6% – Oil = 36.8% – Nat gas = 22.9% – Hydroelectric = 6.3% – Nuclear = 6.0% – All others = ~ 1.4% • Reserve: the amount of the material you have for immediate use • Resource: the total amount of material whether you can use it or not • General Advantages – Historically, cheap & abundant – Technology (techniques) well developed – Infrastructure built to run on them • General Disadvantages – Nonrenewable – Deposits not uniformly distributed • Some countries have huge amounts of fossils fuels while other ones have none – Costs going up – Environmental damage • Climatology/global warming/health issues • Hydrocarbons: things you can combust/break down/burn – Combustible H-C compounds – Requires: • Area of high biological productivity (plankton type creatures) • Relatively low oxygen in waters/sediments (just deep enough) • Ex) continental shelves 1. Methane aka Natural Gas – Advantages Resources growing in recent years Don't have access to many of these deposits right now Burns much cleaner than other FFs 30% less CO emitted per unit energy compared to oil 2 Price often cheaper than oil – Disadvantages Safety issues. Sour gas (contains H S or dihedron sulfide) that you 2 don't want to burn NG heat system malfunctions can create CO as a byproduct CO build up is deadly) Still contributes to atmospheric C0 buildup 2 2. Oil – Oil Window (ideal oil conditions) Hard to form needs to be 2- 5 km down and < 150°C – 62% is in the Middle East 22% in Saudi Arabia alone 2.5% in the US (enough to sustain us??) – The US uses 7.5 billion barrels each yr 2010: US had to import 61% of the oil we needed – Cost of that 61% = $337 billion $640,000 per MINUTE $48 million during this class – US Oil Production and Consumption The gap has grown for decades… 1973: importing ~50% 2007: importing ~75% 2004: importing ~66% 2010: importing ~61% – Fracking: Uses pressurized fluids to shatter rock below ground (creates permeability for oil to be pumped out) We’re seeing a boost in production in the past couple of years due to fracking. Advantage: o Gets oil out of areas where traditional drilling cannot Disadvantage: o Contamination: fluids used for fracking are not pure H2O May 2015: water supplies in PA contaminated with fracking fluids Fights over regulating the industry (regulations will prolong the process) o Seismic Activity: increases earth quake activity (magnitudes 4 and 5) Oklahoma looking at putting restrictions on fracking b/c of the amount of issues/seismic activity in their state – How much oil is left? Debatable o Lots! Find new deposits Improve technology to get more out of deposits o Little! Existing fields producing less New oil fields being found less often – CASE STUDY: ANWR Arctic National Wildlife Reserve Resource estimated to be = 20-30 bbls (billion barrels) Reserve estimated to be = 4-12 bbls (billion barrels) Q: Should we drill for oil in ANWR? PRO-drilling o 30 bbls = enough to last the US 60 years! o US free us from foreign oil o Lower gas prices o Tiny area affected ANTI-drilling o Only 12 bbls…that’s not even enough to fuel the US for even 2 years! o Spills devastate the environment Problems with pro-drilling side… “30 bbls = enough to last for about 60 yrs” assumes all 30 billion barrels are available “Would free us from using foreign oil” o By their numbers, ANWR would produce… o 30 billion barrels / 60 years = 500 million barrels/yr o The US imports ~ 5 billion barrels/yr o 5 billion – 500 million = 4.5 billion barrels still have to be imported o Cuts imports by only 10% improvement, but does not make US free from foreign oil by any means “Drilling will keep gas prices low” o OPEC production drives gas prices OPEC: made of group of countries in middle east o Not all ANWR oil would be used by the US o Ex: In 2008, the US EXPORTED > 500 mbls “Tiny area drilled” o That ‘point’ on the map doesn’t include infrastructure Roads Pipelines Power lines Tankers Problems with anti-drilling side “Spills devastate the environment” o Exxon-Valdez clean-up cost > $2 billion o 20 years later oil was still on the beaches o Gulf spill est cost $40 billion This point is a legitimate concern, BUT a major spill may never occur “12 billion barrels = enough to only last ~ 2 yrs” o Assumes 12 billion barrels available o The US uses ~ 15 bbls in 2 years o 12 billion < 15 billion TRUE o BUT: this does not mean ANWR would be pumped dry within 2 years! Production Rate: 12 bbls/2 yrs = 6 bbls / yr o Impossible to pump the oil that quickly – Other Oil Sources Oil Shales (OS) & Tar Sands (TS) o Shales /sands have high organic content Problem: oil not fully formed o Can mine the rock/sed & ‘cook’ it Specific Advantages: o Extensive deposits o Estimated OS resource has 4x more oil than Saudi Arabia o Estimated TS resource is 2x the global oil resource Disadvantages o Produce more GGs than other fossil fuels 25-50% more CO pro2uced than normal oil o Not profitable at low oil prices High production cost o Cooking = use energy to make energy?? o Extensive mining operations 13 million tons of OS to fuel the US for 1 day o Uses lots of water > 2 billion gallons of water to pro 3. Coal – Not a hydrocarbon o Similar requirements for formation swamps and bogs (vegetation/plants) – Stages of Coal Formation o Peat (50% C) o Lignite (70% C) o Bituminous coal (70-90% C) o Anthractie coal (90+% C) – Advantages o US coal reserve big enough to last 100+ yrs at current rate of use (= 1 billion tons/yr – Disadvantages o Creates more pollution than other fossil fuels Produces 25% more CO than2oil Mercury, arsenic, etc produced during mining & burning Ash disposal: 130 million tons/yr in the US o Acid Rain Coal burning releases sulfur from pyrite (FeS ) 2O + 3 H O = H S0 which leads to acid rain 2 2 4 Effects of Acid Rain 1. Weathering damage 2. pH changes in aqueous habitats (ponds/lakes) 3. Leaches nutrients out of soil
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