2240 Notes

EARTH SCIENCE 2240F NOTES UNIT ONE CHAPTER ONE- PHILOSOPHY OF GEOLOGY ● Charles Darwin- the father of evolution ○ Used geology to develop his principle ● Nicolaus Steno - the father of stratigraphy ○ Ended up renouncing his life’s work to join the church ○ Collected fossil evidence from the Italian highlands ○ His work was dumped on by scholars such as Issac Newton simply because he wrote in Italian rather than English. ● Thomas Burnet ○ Decided that all uneven features of the world were a cause of Noah’s flood ● Archbishop James Ussher ○ Was tasked with mathematically calculating the age of the earth. ○ Using the Bible he decided that the Earth was created on October 22nd, 4004 BC ● Catastrophism ○ Main belief are: ■ Earth was a record of unique events ■ There is no evolution (biological, geological, or otherwise) ■ No possible way to predict nature ○ Baron Georges Cuvier ■ Published a paper examining stratigraphy and sentiments of the Paris Basin, seeing unusual and repeating layers of fine sentiments and boulders ■ Determined that abnormal layers were due to unpredictable catastrophes ■ Disregarded finding that conflicted with the church and catastrophism. ○ If you were a believer of catastrophism, you would believe that: ■ The earth began as a molten ball ■ While it cooled and solidified, a few seizure-like convulsions whipped up the semi molten peaks and turned them into mountains. ■ Valley were eroded at one during Noah’s Flood ■ Fossils represent previous life forms that were fully erased from Earth by catastrophes ■ There is no biological connection between species. They're all a unique gift from god. ● Uniformitarianism ○ Formerly called gradualism.

○ Introduced in 1795 by James Hutton in his book “Theory of Geology”. He died two years later ○ Hutton theorized that landscapes change over time, not all at once through watching creeks pick up and move sentiment downstream. ○ Charles Lyell drew from Hutton in his book “Principles of Geology” (1830) ■ He threw away the age of the earth decided by Usser and proposed an unlimited geological time. ■ Bishop Cuvier died in 1830, so there was no one eloquent enough to oppose his claims. ■ Lyell changed geology and led the new revolution into Uniformatarianism. Thanks to him many other scholars ditched the Christian ‘earth age’ and were able to further his work. CHAPTER TWO- GEOLOGICAL AGE DATING ● The true age of the Earth is 4.54 billion years. The solar system was created approximately 4.567 billion years ago ● Earth ‘eats up’ and recycles old rocks– not many from the original crust exist anymore. ○ Oldest crustal fragments or earth are both found in Canada, yet none are as old as the original crust. ○ Many recycled rocks make up the grains within sedimentary rocks ● Relative Age Dating ○ Steno proposed three fundamental principles in geology that are the basis for current geological mapping. Also known as Steno’s Laws ■ Principle of Superposition: sedimentary rock layers are deposited onto one another ■ Principle of Original Horizontality: sedimentary rock layers are lain flat and horizontal when deposited ■ Principle of Original Lateral Continuity: sedimentary rock layers are deposited over large areas. ○ Steno’s Laws couldn’t explain igneous intrusions, or the relationship between eroded rock and the strata lain on-top. ○ James Hurron added his own Principle of Cross-Cutting Relationships, which tells us: ■ A fault is younger than the youngest rock it cuts ■ The strata above an unconformity are younger than the strata below ■ Any feature that cross-cuts a rock must be younger than the rock it cuts ○ The final price of Relative Age Dating is the application of Reference Horizons by William Smith. Other principles were able to date rocks relative to each other in a geographic region. But you could not date rocks region to region because there was no effective way to do so.

○ Currents within Earth’s liquid outer core coming into contact with the solid inner core produce the magnetic field, according the the Dynamo Theory ■ Electric currents generated by enormous ‘dynamos’ are driven by circulating hot currents in the liquid metal outer core and magnetic fields surrounding those electric currents. ■ Earth's flow is not always stable, as liquid outer core currents periodically change orientation. If many dynamos change orientation it can result in the reversal of our magnetic poles. ○ Paleomagnetism is the study of the intensity and orientation of magnetic fields and poles of earth, which have inverted many times throughout history. ○ Magnetic field is anything but stable. Intensity and polarity change chaotically. ○ Magnetite is a common igneous mineral found in many volcanic rocks and is known for its strong magnetism. ■ The crystals, when within a lava, will orient themselves to the earth's magnetic field. Once cooled their position is locked until the rock is melted and recycled. ■ By measuring the orientation of magnetite grains on the ocean floor we have found an intact record of the Earth’s paleomagnetic field and polarity. ● Developing Plate Tectonics ○ After the discovery that continents were moving, interest piqued in Plate Tectonics. Here is what we knew at this time so far: ■ Continents were previously assembled into the supercontinent Pangaea ■ Large volcanic change up middle of oceans are where new oceanic crust is being produced ■ New oceanic crust moves away from spreading centres, forcing continental landmasses to move. ○ Spreading centres are traceable around the world ■ Deep Oceanic trenches because the obvious place where crust was being forced down into the earth, through a process called subduction ■ Subduction Zones were traced around the globe, mirroring areas noted for significant earthquakes ○ Hugo Benioff and Charles Richter worked to develop earthquake monitoring or measuring equipment. ■ Benioff used new equipment to measure seismicity near ocean trenches and found that earthquake foci followed the subducting tectonic plate ■ Three classes of earthquakes were cited with in the Hugo-Benioff Zone : shallow, intermediate, and deep focus earthquakes ■ With modern instruments we can actually track the downward motion of the slab by temperature– the cold oceanic slab stands out through the hot asthenosphere.

● Plate Boundaries ○ Convergent Boundary : tectonic plates are colliding, forcing more dense crust underneath less dense crust, reflects compressional stress of crustal rocks ○ Divergent Boundary : tectonic plates are moving apart with new Basaltic crust morning at mid-ocean ridges, creating extensional stress ○ Transform Boundary: tectonic plates are moving laterally past each other, creating shearing stress. (result of strike-slip faults rather than normal/reverse faults) ● What drives plate motion? Convection within the currents in the asthenosphere ● Mantle Plumes ○ Very hot partially-melted material moves up through the Earth ○ Difference with mantle plumes is plumes produce discrete spots of volcanism, rather than chains of volcanism. ○ Due to decreasing density towards the surface, mantle plumes move upwards as they differentiate– molten rock almost always has a lower density than solid rock ○ There is strong evidence that mantle plumes can interact with and begin rifting of the crust to the surface, leading to the entire separation of continents ● When a hotspot initiates rifting, a characteristic triple-junction with form containing two main branches and one failed branch, known as the aulacogen – which will produce a region of high tectonic/crustal instability ● The convection model of motion within the Earth is not simple, as calls are easily interrupted by subducting slabs and mantle plumes that cut near-vertically through the Earth ○ Two main processes for driving plate motion ■ Slab Push : erupted lavas work to push material away from the speaking centre, forcing the entire tectonic plate away ■ Slab Pull : gravity drags the subducting plate down further into the trench, pulling the length of the tectonic plate behind it. CHAPTER FOUR- EARTHQUAKE BASICS ● Faults and Seismicity ○ Faults are breaks in the rock where it has been broken apart by applied stress ■ Normal faults ■ Reverse faults ■ Strike slip faults ○ We explain earthquakes using the Elastic Rebound Theory, which has four steps ■ a) baseline ■ b) building stress ■ c) rock breaks, fault forms ■ d) new baseline, cycle repeats

○ Transform boundaries ■ Crust moves in opposite directions, causing shearing friction ■ Example: San Andreas Fault in California ● Measuring and Forecasting earthquakes: when measured earthquakes have two features of location and magnitude ○ Based on location , we can determine which settlements are at risk of violent earthquake shaking,and what fault the earthquake accrued on and whether other damaging effects like mudslides or tsunamis may occur ○ Based on magnitude , we can determine how much energy was released by the earthquake, how much damage we can expect, how far the shaking reaches, and how violent the shaking from the earthquake is expected to be. ● Magnitude is the most defining feature of an earthquake. We’ve tried different ways of measuring magnitude over the years. Currently we try to always use Moment Magnitude, that standard in seismology ○ Moment Magnitude is a logarithmic scale, meaning that each step in the scale is 10X greater than the last. (for example, a 7.0M earthquake is 10x larger than a 6.0M one ● Earthquake forecasters use three main criteria for defining an effect prediction ○ 1) geographic location of the event ○ 2) amount of time the earthquake produces strong shaking ○ 3) probable magnitude\ ■ Forecasting earthquakes is one of the hardest jobs a Geoscientist can have. Sometimes, strange behaviour by animals or smaller foreshocks cna indicate an earthquake is imminent- though most often earthquakes are essentially randomly-occurring, in that predicting when an earthquake will happen is nearly impossible. ● There are two main seismic zones in Canada ○ Pacific Seismic Zone: western margin of North America follows a convergent plate boundary, causing minor volcanism and major seismicity ○ Charlevoix Seismic Zone: along the St. Lawrence River in QC, a cluster of earthquakes occur around Charlevoix (the site of a meteor impact that disturbed the plate’s stability) CHAPTER FIVE- MEGATHRUST EARTHQUAKES AND TSUNAMIS ● Megathrust are a special type of convergent boundary earthquakes where the fault plane is almost horizontal ○ Defined as, occurring at an inter-plate zone, where one plate is subducting under another, occurring upon the sudden release of a locked/stuck section, and has a magnitude greater than 7.0. ● Indicators of past earthquakes:

○ Tsunami evidence: finding geology that has been affected by a tsunami is a strong indicator of a nearby earthquake source ○ Submerged Coastlines: drowned forests are a common feature of plates that show a loss of stored stress, where the plate is allowed to un-deform and flatten to its original position, sometimes lowering the elevation of land. ○ Large Underwater Landslides : underwater landslides are often strong indications of these hugely powerful events and the amount of shaking they produce. ● Tsunami : a set of ocean waves caused by a large, abrupt displacement of water ○ Can be produced through earthquakes, eruptions, meteorite impacts, landslides, etc ○ Waves can travel up to 700 km/h in the open ocean ○ When a tsunami reaches shore, the deeper part of the wave is forced up, making the waves much taller. ● Tsunami Vocab: ○ Imamura-lida scale : the tsunami magnitude scale used in this course, based on the max wave height in the open ocean ranging from -1 to 4 ○ Shoaling effect: reduction in the water depth increases friction under the tsunami wave, causing the waves to grow in height ○ Draw-down: the dramatic sea level drop along a coast prior to tsunami triking ○ Run-up: max vertical height of the tsunami wave above shore level ○ PTWC (Pacific Tsunami Warning Center): international response center that issues tsunami warnings and watches for at-risk areas after M6.5+ earthquakes occur in or around the Pacific basin. ● Case Study #1: The Cascadia Subduction Zone ○ A sucdection occurs along the Cascadia Subduction zone, wher ethe Juan de Fuca plate moves under the North American Plate. Strike-Slip occurs along the San Andreas and the Queen Charlotte Faults ○ The spreading centre is so close to the subducting edge of the Juan de Fuca plate, the plate remains hot and buoyant, causing it to subduct at a very shallow andle and setting the stage for a megathrust environment ○ The Juan de Fuca plate continues to move northeast at a rate of 4cm a year, increasing the tectonic stress levels along the boundary with the North Ameirican Plate ○ The North American Plate is locked, and once it slips and releases all the built up energy, a megathrust earthquake will occur. ○ 1700 Cascadia Megathrust Earthquake (M9.0) ■ Earthquake was a full rupture, breaking the entire 1100km long Cascadia caused a vertical displacement of around 20m. This lead to drowned forests and the production of a very large tsunami event.

○ As more of the Juan de Fuca plate is subducted, the San Andreas fault grows to the north. ○ 1906 Earthquake ■ A locked section ruptured resulting in a M7.8 earthquake ■ Caused collapse of many new high rise towers ■ Shaking caused gas lines to break, resulting in widespread fire ■ 700 confirmed died, estimates are placed in 2,100-2,800 ○ 1989 Earthquake ■ M6.9 earthquake ruptured a fault connected to San Francisco ■ Death toll was lower than expected cause everyone was at home watching the World Series ■ Parts of the city were built on soft sud sediments, so they broke down in Oakland ○ We can certainly expect another huge earthquake in the Bay Area through the next few years, as many locked downed of the SAF show stresses far beyond previous ruptures ○ LA hasn’t seen an major earthquake since 1690. The accumulated stress is expected a M8 earthquake and up to 10m offset ○ California coast a currently an extremely dangerous place to live considering an immense seismic risk ● Intraplate Fault Earthquakes ○ Not all earthquake take place at plate boundaries. Although they cause small events, intraplate faults have the potential to generate devastating events ○ Transform, normal, and reverse faults are all possible in intraplate settings. ○ The seismic period on many intraplate faults is in the scale of thousands of years, so are relatively ‘rare’ ○ The study of Paleoseismology examines historical earthquakes of M6.5+. This is. Because smaller earthquakes don’t leave much long-standing geological evidence ○ New Madrid, MO ■ Through 1811-1812, the Missouri Bootheel experienced a very strong Seward of earthquakes on a failed rift under the town of New Madrid. ■ On Dec 16, 1811, a strong M8+ occurred, releasing many surface waves. The Mississippi River began flowing backwards as a result of the sudden rupture, permanently alert Erin waterways and flooding many settlements. ■ Shaking was felt as far as Boston ■ Then in January they felt a M8+, and in February there was a M9+ quake ■ Ruptured at a shallow depth ○ Another intraplate region, or an active auto open is the Charleroi Region in Quebec

CHAPTER SEVEN- VOLCANO BASICS ● Volcanos are usually found along plate boundaries– the type of boundary determines the type of volcano ● Most are found on the Ring of Fire ● Volcanos and Magmas: ○ Magna : molten rock inside the volcano ○ Lava : molten rock outside of volcano ○ Pyroclastic Material: molten rock violently ejected from the volcano, containing bombs, ash, and noxious ○ Bombs : blobs of molten rock thrown into the air ○ Ash : finely pulveized rock, made up of fragments of the volcano walls: very light and can travel hundreds to thousands of km’s. ● Igneous Rocks and Magma ○ Basaltic - low viscosity magma containing 45-55% solica, cooling to a black to dark-grey rock called Basalt ○ Andesitic - intermediate viscosity magma containing 55-65% silica, cooling to a medium to light-grey rock called Andesite . ○ Rhyolitic - high viscosity magma containing 65-75% silica, cooling to a white, pink, or light-coloured rock called Rhyolite . ● Silica : ○ Physical properties of magma are reflected in what type of volcano forms and what rocks are erupoted. ○ The chemical composition of many magmas are based on one mineral class: Silicates . ○ Silicates are made of the elements Solicon and Oxygen, and because of this chemistry are shaped like a tetrahedron. ● Temperature ○ Another factor controlling what a magna cools to is the rock’s formation temperature. As temp increases, chemical bonsa relax and allow the connected ions to vibrate faster, looseded bonds make chemical reactions in teh magma more likely, where minerals may be removed from a magma changing the composition. ○ Temp comprols viscosity, which plays a big role in teh explosiveness of volcanic eruptions. ■ High temp = low viscosity = very fluid ■ Low temp = high viscosity = stiff ● Crystals: As magma cool sand mineral crystals start to form, the chemical composition of the magma changes ● Volatiles : gasses that are dissolves in a magma ○ Water is the most common and important volatile in volcanology