Plate Tectonics Theory of Continental Drift Alfred Wegener suggested that continents had once been part of supercontinent named, that later broke up. The pieces moved apart over of years and formed the separate we know today. These ideas are known as the Theory of. Evidence of continental drift includes: in mountain ranges of eastern North America and western Europe are similar. found in South America and South Africa suggest these continents were once joined. and living only in South America, Africa and Australia suggest that these continents were once linked but moved apart. Theory of Plate Tectonics Tectonic Plates The lithosphere is made up of the and the upper layer of the ; It is and, and can fracture during earthquakes; The lithosphere is divided into pieces called plates; These plates float on the hot, plastic (lower region of the mantle), which is too hot to ever fracture (although it can be stretched); Tectonic plates can either contain both and crust, or only crust; There are a dozen plates and many plates.
Plate Movement Tectonic plates move because of currents in the mantle; Magma is heated up near the core and becomes less and ; Rising magma pushes plates apart at centres in oceans, called boundaries; Where oceanic plates collide with continental plates, the oceanic plate will under the continental plate and be into the mantle (subducted). Continental crust is less than oceanic crust and never. Continental crust is forever pushed around the of the earth, and consequently contains the rocks on earth. Oceanic crust is continually being and is much.
Video: Plate Tectonics 1. The theory is the theory that the Earth s outer layer is made up of plates that have moved throughout history. 2. Tectonics comes from the greek work one who. 3. About 250 million years ago, the Earth had one unified supercontinent (landmass) called. 4. Continental drift was first proposed by a scientist named. 5. Evidence for continental drift includes: a. common b. remains c. old belts d. and deposits 6. Submarines noticed a pattern of stripes on the ocean floor. These represent magnetic, which occur when the Earth s magnetic field flips. 7. spreading is when 2 plates move away from each other, allowing magma to rise from the Earth s interior and making new ocean floor. 8. In summary, 2 pieces of evidence that give rise to plate tectonics are: a. b. 9. The crust and upper mantle form a rigid outer shell called the.
10. The weak, mushy, partially melted layer beneath the lithosphere is called the. 11. The rigid floats on the. 12. The lithosphere is broken up into that slide about. 13. There are about major plates, and several minor ones. 14. Plates may contain both crust and crust. 15. The Earth s plates move at a rate of about per year. 16. We can measure plate movement directly using. 17. Inside the Earth, molten material is able to flow, causing. 18. Convection drives the of the plates.
Plate Boundaries Plate boundaries are marked by,, ranges and ocean. There are three main types of plate boundaries: 1) Boundaries (or Spreading Centres) Where plates are spreading apart; Huge mountain ranges found beneath the Earth s oceans known as midocean ; Basaltic pours out from the ridges and spreads out to form new oceanic crust. Boundaries Where two plates collide; When continental plates collide, neither plate is enough to be pushed down, so the land like a car hood in a car crash ( uplifting ), forming ranges; When continental plates collide with oceanic plates, occurs the oceanic plate sinks beneath the continental plate; are found beneath the ocean where the oceanic crust subducts; When two oceanic plates collide, usually one plate beneath the other. 3) Transform Boundaries: Where two plates by each other instead of subducting and uplifting; Results in frequent.
INSERT BOUNDARY MAP ACTIVITY
Continental Growth The ancient core of a continent is called the. The cratons are much smaller than the we see today. Growth material for the continents comes from: 1) deep sea (scraped off subducting plates) 2) rock 3) sediments deposited by that flow across the continent.
VOLCANOLOGY THE STUDY OF VOLCANOES Magma forms wherever and are high enough to melt rock. Some magma forms at the Magma also forms at plate, where intense heat and pressure develops from between the plates. Volcanoes Melted rock as it heats up, becoming less dense than surrounding rock. Magma moves upwards through ; If magma reaches the surface, it erupts through an opening called a. Magmas Felsic magmas: high, thick, -coloured, slow-moving Mafic magmas: low, thinner, -coloured, flow more easily Volcanic Eruptions Magmas contain gases (i.e., water vapour, carbon dioxide) As magma reaches the surface, is reduced and dissolved gas comes out of solution as of gas. Bubbles expand and therefore LOTS OF GAS = MORE EXPLOSIVE ERUPTIONS! Mafic magmas are more and let gases escape more easily than felsic magmas MAFIC MAGMAS = LESS EXPLOSIVE FELSIC MAGMAS = MORE EXPLOSIVE
Lava and Lava Fragments If magma reaches the surface of the earth, it is called Explosive eruptions produce lava fragments called TEPHRA CLASSIFICATION: < 2mm 2 mm 64 mm >64 mm FLOW: in explosive eruptions, tephra combines with gases to form a dense, superheated traveling at very high speeds (> 100 km/h) Volcano Hazards 1. Ash Gritty -sized particles blasted from erupting volcano Can reach very high. Large amounts can block sunlight, causing world to drop. Can destroy,, clog, damage. 2. Lava Molten rock may over large areas, destroying everything in its path. 3. Pyroclastic flow Destructive mix of gas, ash and debris, which can move > 100 km/h. 4. Lahar Flow of mud, water, ash and debris that can result when - covered volcanoes erupt.
Mount Baker Living with an Active Volcano 1. a) Name and briefly describe the four possible volcano hazards at Mt. Baker. b) Which hazard is considered to be of greatest concern? Why? 2. Describe the two ways that lahars can form. 3. When did volcanic activity begin in the Mt. Baker area? 4. In recent Mt. Baker history, when did: a) Lava flow from the summit vent? b) Pyroclastic flows pour down its side? c) Mt. Baker have its last major eruption? d) Mt. Baker have its last lahar flow? 5. What observations had scientists worried that Mt. Baker might erupt in 1975? 6. What signs did scientists look for that would have confirmed that magma was rising under the volcano? 7. What monitoring is currently being done at Mt. Baker?
TYPES OF VOLCANOES There are three main ways volcanoes are formed: 1. boundaries (composite volcanoes): As ocean plate sinks beneath the plate, increasing heat melts the rock, forming magma. Magma is lighter than the surrounding solid rock, so it rises up through the edge of the continental plate to form a. Form classic, -shaped volcanoes that erupt and Cone shape results from of ash and lava building up over time Magma is usually (very thick), and traps gas producing eruptions i.e, Mt. Baker 2. Divergent boundaries (rift eruptions): Magma flows out of volcanoes at ridges; occasionally, volcanoes grow high enough to rise above the of the ocean and produce i.e, Iceland 3. Hot Spots (shield volcanoes): Sometimes extremely high temperatures are found beneath the of oceanic plates, in areas called. At these locations, the melting of crustal rock produces magma that rises up to form a volcano. As the plate moves, it carries the hot spot with it, so that of volcanic islands are formed Magma is usually, so eruptions are not and volano s sides have a slope. i.e., Hawaii
Plutons and Volcanism Magma squeezes through and rock as it rises. Igneous rock masses that form inside other rocks are called. Structures are named according to their and. sheets of igneous rock that cut across the rock layers they intrude (usually mafic) sheets of igneous rock that are parallel to the rock layers they intrude (also usually mafic) dome-like masses of igneous rock formed by stiff magma which, spreading, bulges upwards (usually felsic). instead of plug of magma that hardened inside the vent of a volcano largest of intrusions; forms the core of many mountain ranges (usually felsic) small batholith ( < 100 square kilometers exposed at the surface).
Chapter 14 Review Volcanoes Name: 1. For each of the following, choose the phrase in Column B that best describes the term in Column A, and mark its letter in the blank space. 1. Magma a. rock mass crystallized within another rock 2. Lava b. large piece of solid rock thrown into the air during an explosion 3. Felsic c. largest of all igneous intrusions 4. Mafic d. solid fragments of lava produced in explosive eruptions 5. Ash e. flat sheet of igneous rock that cuts across rock layers. 6. Tephra f. Molten rock within the Earth 7. Sill g. Type of molten rock on Earth s surface that is thick and stiff 8. Lapilli h. Fragment of lava that solidifies in the air 9. Dike i. Flat sheet of igneous rock parallel to the intruded rock layer 10. Block j. Sill that forms a domelike mass 11. Neck k. Molten rock on Earth s surface 12. Stock l. The smallest piece of tephra 13. Batholith m. Pluton whose exposed area is less than 100 sq. km 14. Bomb n. Piece of tephra between 2 and 64 mm 15. Laccolith o. Type of molten rock on Earth s surface that is thin and fluid 16. pluton p. Hardened lava in the vent of an eroded volcano 2. What are the names of the three types of volcanoes? a) b) c) 3. Explain what a Hot Spot is, and give an example: 4. a) Which type of magma is the explosive type? b) What makes this type of magma so explosive? _ 5. During eruptions, many different types of lava fragments occur: a) The general term for the fragments is. b) Name the different types of fragments: - less than 2 mm in diameter: - up to 64 mm in diameter: - more than 65 mm in diameter:
6. Fill in the blanks with the most correct response. Each word may only be used once. Less dense felsic subduction zones Gases tephra composite Lava rifts mafic Aesthenosphere magma silica a) Volcanoes are caused by a surge of to the Earth s surface. b) Melted rock that comes to the surface is called. c) The magma rises because the liquid is than the surrounding rock. d) Magma is formed both in the, and at. e) Fast-flowing magma is made of a type of molten rock, while a slowflowing magma is made of a type of molten rock. f) Felsic magma contains a lot of, while mafic magma contains little. g) Violent eruptions are mostly due to inside the liquid rock. h) The most common type of volcano, the type, form at subduction zones. i) The type of volcanoes that occur at are shield type. j) are the solid rock fragments that are released from volcanoes. 7. Name and describe the four main hazards of a volcanic eruption: 1) 2) 3) 4) 8. Sketch a composite volcano, and label its parts. 9. Sketch and label the different plutonic structures that form within the Earth.
Seismology The Study of Earthquakes Earthquakes occur when rock masses in the Earth s outer layer move along lines. Focus the location on a fault where there is the amount of movement, the surface of the earth. Epicentre point on the that is directly the focus. Causes of Earthquakes: Rock masses on either side of a are pushing past one another. Rock masses and until there is enough stored energy to overcome between the rock masses; this energy is then is quickly released as kinetic during an earthquake Elastic Rebound Theory.
Earthquake Waves P waves longitudinal wave; S waves transverse wave; - particles move to the direction of the wave. - Almost twice as as S waves. - Travel through and (crust, mantle and core) - particles move to the direction of the wave. - Travel than P waves. - Travel only through (lithosphere) Love waves - Surface waves: - ground motion is a action, like ripples on a pond. - Travels along of the Earth. IMPORTANT: P Waves almost as fast as S Waves
Locating an Earthquake: The seismometer Instrument used to measure the ground resulting from earthquakes. Produces a tracing on a paper by a pen Tracing is called a Determining the Distance to the Epicentre P waves are than S waves; therefore, P waves arrive at a seismograph station the S waves. The time interval between the of P and S waves at a seismograph is used to determine the to epicenter. Time-distance graph is used as a tool to calculate distance to epicenter (p. 235, text) Locating the Epicentre Need different locations using the time-distance graph to calculate the epicenter. Draw a around each seismograph with a equal to the distance to the epicenter. The location where the three circles is the epicenter.
Measuring an Earthquake - Earthquake Magnitude The Richter Scale is a standardized scale of earthquake (amount of shaking) Each point represents vibrations that are times greater than the point below it. Each tenfold increase in vibrations means times more energy released. Richter Magnitude Earthquake Effects Estimated no. per year <2.5 Generally not felt, but recorded 900 000 2.5 5.4 Often felt, but only minor damage detected 30 000 5.5 6.0 Slight damage to structures 500 6.1 6.9 Can be destructive in populous regions 100 7.0 7.9 Major earthquakes. Inflict serious damage >8.0 Great earthquakes. Produce total destruction to nearby communities 20 One every 5-10 years
Earthquake Damage The Mercalli Scale is used to estimate the of an earthquake by comparing amount of damage Damage done is not always an adequate means for comparison depends on: o from epicenter o Nature of materials o Building Modified Mercalli Intensity Scale I II III IV V VI VII VIII IX X XI XII Not Felt Felt only be persons at rest Felt by persons indoors only Felt by all, some damage to plaster, chimneys People run outdoors, damage to poorly built structures Well-built structures slightly damaged; poorly-built structures suffer major damage Buildings shifted off foundations Some well-built structures destroyed Few masonry structures remain standing; bridges destroyed Few masonry structures remain standing; bridges destroyed
Earthquake Hazards 1. Ground shaking The result of the waves set in by the earthquake Some move up and down while others move side to side Most buildings can withstand large -and- vibrations, but not -to- (cause collapse) 2. Liquifaction Vibrations cause to rise, turning solid ground into a liquidlike material. Buildings built on solid rock experience little damage; buildings located on bog muds or soft fill suffer severe damage 3. Tsunamis Large sea waves produced when earthquakes occur under. Caused by a large in the water column
Earthquake Waves inside the Earth As waves travel through earth, P- and S- waves change velocity, bend, or get reflected At 2900 km: Boundary between mantle ( ) and outer core ( ) P-waves down S-waves (don t travel through liquids) At 5200 km: P-wave velocity (approaches inner core ) Mohorovicic Discontinuity (The Moho) Another abrupt change in P - and S-wave velocities occurs at the boundary between the and the Discovered in 1909 by Andrija Mohorovicic : Found that seismograms showed distinct groups of P- and S-waves One of the groups traveled at an average velocity of km/s The other group of waves traveled at km/s Mohorovicic reasoned that the faster wave group had one through material below the crust This is the boundary between the crust and the mantle named The The Moho is about 32km deep under but only 8km deep below the
Shadow Zone Even though an earthquake sends waves throughout Earth s, not all seismograph stations receive information. Seismic stations that don t receive P or S-waves are said to be in the zone Caused by Earth s core P-waves refract ( ) when they pass through the mantle S-waves cannot travel through the outer core ( ) Vancouver s Next Big Earthquake The Juan de Fuca Plate, Explorer Plate, and Gorda Plate are all under the North American Plate Each of the three plates have fault lines Will most likely be produced by and generated at a transform fault or along a subduction zone
Mountain Building Mountain ranges form wherever tectonic plates. Where oceanic crust under continental crust, magma deforms the continental crust forming mountains and volcanoes. Where two continental tectonic plates collide, the plates like car hoods in a crash, forming vast mountain ranges. Faults Faults are or cracks in the Earth s crust along which movement has occurred. The surface that separates two moving pieces of crust is called the fault. Three types of Faults: 1) : rocks on one side of fault plane drop down below rocks on the other side. 2) : rocks on one side are driven up over the other side. 3) : rocks on opposite sides of fault plane move horizontally past each other. Folds During plate collisions, rock layers along continental margins sometimes crumple into folds: Anticlines: in the rock layers Synclines: in the rock layers Uplifting At some plate boundaries, sedimentary layers are to high levels with little deformation end up with aquatic fossils and beaches at high. Tilting/Overturning Most sedimentary rocks are formed in layers Folding and uplifting may result in layers being Sometimes rocks are tilted over on themselves and end up overturned.
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