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152 Cards in this Set
- Front
- Back
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Explain the Impact of Internal Processes on the Landscape.
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• Internal processes are the supreme builders of terrain
• Energized by forces within Earth, the internal processes actively reshape the crustal surface of Earth • Internal Processes have been taking place for billions of years • Some examples are earthquakes and volcanoes They are fundamentally responsible for the gross shape of the lithospheric landscape at any given time. The internal processes do not always act independently and separately from each other. |
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From Rigid Earth to Plate Tectonics
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• The shapes and positions of continents seem fixed from human perspective
Continents have moved, collided and merged, and then been torn apart again; ocean basins have formed, widened, only to be eventually closed off. • Until mid-twentieth century, scientists believed Earth’s continents were rigid • Continental drift—Pangaea |
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What is the notion of Continental Drift?
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Theory that proposed that the present continents were originally connected as one or two large landmasses that have broken up and drifted apart over the last several hundred million years.
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Who was Alfred Wegener?
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A German meteorologist and geophysicist that put together the first comprehensive theory to describe and partially explain the phenomenon of continental drift
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What is Pangaea?
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The massive supercontinent that Alfred Wegener first postulated to have existed about 200 million years ago. Pangaea broke apart into several large sections that have continually moved away from one another and that now comprise the present continents.
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Explain some of the Evidence to support Wegener's theory of Continental Drift and Pangaea.
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• Evidence includes similar geologic features on coasts of different continents
• Continents fit together with jigsaw puzzle like precision • Glaciated continents reconstructed made sense • Supported evidence also came from paleontology |
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LC 14-1
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Rejection of Continental Drift
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Explain the Evidence behind The Theory of Plate Tectonics.
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Plate boundaries
• Earthquakes occur along lines • Correspond with locations of trenches and ridges in the seafloor |
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What is Seafloor Spreading?
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The pulling apart of lithospheric plates to permit the rise of deep-seated magma to Earth’s surface in midocean ridges.
• Mid-ocean ridges formed by magma rising up from the mantle • New basaltic ocean floor created, moves away from ridge • At trenches, older lithosphere descends into the asthenosphere where it is recycled—subduction |
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Explain The Theory of Seafloor Spreading.
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• This theory stated that midocean ridges are formed by currents of magma rising up from the mantle
• Volcanic eruptions create new basaltic ocean floor that then spreads away laterally from the ridge. •Thus, the midocean ridges contain the newest crust formed on the planet. At other places in the ocean basin—at the oceanic trenches—older lithosphere descends into the asthenosphere in a process called subduction, where it is ultimately “recycled.” The amount of new seafloor created is compensated for by the amount lost at subduction zones. |
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What is Subduction?
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At other places in the ocean basin—at the oceanic trenches—older lithosphere descends into the asthenosphere in a process called subduction, where it is ultimately “recycled.”
Where denser ocean lithosphere converges with less dense continental lithosphere, the oceanic plate slides under the continental plate in a process called subduction. |
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Explain the Process of Seafloor Spreading.
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Seafloor spreading. Convection currents bring magma from the asthenosphere up through fissures in the oceanic lithosphere at the midocean ridge. The solidified magma becomes a new portion of ridge along the ocean floor and the two sides of the ridge spread away from each other. Where denser ocean lithosphere converges with less dense continental lithosphere, the oceanic plate slides under the continental plate in a process called subduction. Magma produced by this subduction rises to form volcanoes and igneous intrusions.
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LC 14-2
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What two lines of evidence confirmed the validity of Seafloor Spreading?
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1. Paleomagnetism
2. Ocean Floor Core Sampling |
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What is Paleomagnetism?
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When any rock containing iron is formed—such as iron-rich ocean floor basalt—it is magnetized so that the magnetic field within its iron-rich grains become aligned with Earth’s magnetic field. This orientation then becomes a permanent record of the polarity of Earth’s magnetic field at the time the rock solidified.
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What is Paleomagnetism?
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Paleomagnetism was used to test the theory of seafloor spreading by studying paleomagnetic data from a portion of the midocean ridge system.
If the seafloor has spread laterally by the addition of new crust at the oceanic ridges, there should be a relatively symmetrical pattern of magnetic orientation— normal polarity, reversed polarity, normal polarity, and so on—on both sides of the ridges. Such was found to be the case. |
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What is Paleomagnetism?
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• Iron in cooled magma orients itself with the magnetic poles of Earth
• Provides a record of past magnetic fields • Magnetic field has changed orientation at least 170 times over 100s of millions of years • Should be symmetry in magnetic orientation • Used to verify age of ocean floor rock and seafloor spreading |
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What is Ocean Floor Cores?
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What is Ocean Floor Cores?
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What is Ocean Floor Cores?
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What is Ocean Floor Cores?
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LC 14-3
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What is The Theory of Plate Tectonics?
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A coherent theory of massive lithospheric rearrangement based on the movement of continent sized plates.
Plate tectonics provides a framework with which we can understand and relate a wide range of internal processes and topographic patterns around the world. – Theory behind motion of lithospheric plates The lithosphere is a mosaic of rigid plates floating over the underlying plastic asthenosphere – Plates “float” on asthenosphere – 7 major plates, 7 intermediate plates, 12 smaller plates |
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What is the Driving Mechanism for Plate Tectonics?
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The driving mechanism for plate tectonics is thought to be the slow convection within Earth’s mantle.
A slow, thermal convection system appears to be operating within the planet, bringing deep-seated hot, lower density rock slowly to the surface. Plates may be “pushed” away from midocean ridges to a certain extent, but it appears that much of the motion is a result of the plates being “pulled” along by the subduction of colder, dense oceanic lithosphere down into the asthenosphere. – Convection can push plates away from each other – Most motion results from plates pulled by subduction of dense oceanic lithosphere The complete details of thermal convection within the mantle and the ultimate fate of subducted plates remain to be confirmed. = Ongoing area of research These plates move slowly over the asthenosphere. |
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LC 14-4
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What are Plate Boundaries?
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Plates are relatively cold and rigid and therefore deformed significantly only at the edges and only where one plate interacts with another. Most of the “action” in plate tectonics takes place along such plate boundaries
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What are the Three (3) Types of Plate Boundaries?
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1. Divergent Boundaries
2. Convergent Boundaries 3. Transform Boundaries |
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What is a Divergent Boundary?
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Two plates may diverge (move) away from one another (divergent boundary)
At a divergent boundary, magma from the asthenosphere wells up in the opening between plates. This upward flow of molten material produces a line of volcanic vents that spill out basaltic lava onto the ocean floor, with the plutonic rock gabbro solidifying deeper below. A divergent boundary is usually represented by a midocean ridge. Associated with shallow-focus earthquakes and volcanic activity Divergent boundaries are “constructive” because material is being added to the crustal surface at such locations. Divergent boundaries can also develop within a continent, resulting in a continental rift valley or if the spreading has been great enough, can form a “proto-ocean.” |
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What is a Midocean Ridge?
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A lengthy system of deep-sea mountain ranges, generally located at some distance from any continent; formed by divergent plate boundaries on the ocean floor.
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Midocean ridge spreading center. Seafloor spreading involves the rise of magma from within Earth and the lateral movement of new ocean floor away from the zone of upwelling. This gradual process moves the older material farther away from the spreading center as it is replaced by newer material from below. Transform faults are found along the short offsets associated with slight bends in the ridge system.
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What is a Continental Rift Valley?
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Fault-produced valley resulting from spreading or rifting of continent
A continental rift valley develops where divergence takes place within a continent. As spreading proceeds, blocks of crust drop down to form a rift valley. |
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What is a Proto-Ocean?
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LC 14-5
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What is a Convergent Boundary?
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The collisions between plates
Two plates may converge (collide) toward one another Are sometimes called “destructive” boundaries because they result in removal or compression of the surface crust Convergent plate boundaries are responsible for some of the most massive and spectacular of earthly landforms: major mountain ranges, volcanoes, and oceanic trenches. There are three types of convergent boundaries. |
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What are the three (3) types of Convergent Boundaries?
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1. oceanic–continental convergence
2. oceanic–oceanic convergence 3. continental–continental convergence. |
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What is Oceanic–Continental Convergence?
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Where an oceanic plate (dense) converges with a continental plate, the oceanic plate is subducted (sinks) into the asthenosphere and an oceanic trench and coastal mountains with volcanoes are usually created.
Because oceanic lithosphere includes dense basaltic crust, it is denser than continental lithosphere, and so when it collides, the oceanic plate sinks into the asthenosphere in the process of subduction. The subducting slab pulls on the rest of the plate and is probably the main cause of most plate movement. Wherever such an oceanic–continental convergent boundary exists, a continental mountain range is formed on land (i.e., Cascades, Andes) and a parallel oceanic trench develops as the seafloor is pulled down by the subducting plate. – Earthquakes occur along margin – Volcano formation along the plates—continental volcanic arc |
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What is Subduction?
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Descent of the edge of an oceanic lithospheric plate under the edge of an adjoining plate.
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What is an Oceanic Trench (Deep Oceanic Trench?)
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Deep linear depression in the ocean floor where subduction is taking place.
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What is a Continental Volcanic Arc?
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The chain of volcanoes that develops in association with an oceanic–continental plate subduction zone is sometimes referred to as a continental volcanic arc.
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What is Oceanic–Oceanic Convergence?
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Where an oceanic plate subducts beneath another oceanic plate, an oceanic trench and volcanic island arc result.
If the convergent boundary is between two oceanic plates, subduction takes place. As one of the oceanic plates subducts beneath the other, an oceanic trench is formed. Shallow and deep-focus earthquakes occur and a Volcanic Island Arc is eventually formed |
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What is Continental–Continental Convergence?
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Where a continental plate collides with a continental plate no subduction takes place, but mountains are generally thrust upward.
Where there is a convergent boundary between two continental plates, no subduction takes place because continental crust is too buoyant to subduct. Instead, huge mountain ranges, (i.e. the Alps and the Himalayas) are built up. – Volcanoes are rare – Shallow earthquakes are relatively common |
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LC 14-6
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What is a Transform Boundary?
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Two boundaries slip past each other laterally.
This slippage occurs along great vertical fractures called transform faults (a type of strike-slip fault) Because the plate movement is basically parallel to a transform boundary, these boundaries neither creates nor destroys lithosphere. Transform faults are associated with a great deal of seismic activity, commonly producing shallow-focus earthquakes. Most transform faults are found along the midocean ridge system, where they form short offsets in the ridge perpendicular to the spreading axis. However, in some places, transform faults extend for great distances, occasionally through continental lithosphere. – San Andreas fault (is on a transform boundary between the Pacific and North American plates) |
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Explain the Lithospheric Rearrangement.
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– 450 million years ago, one supercontinent existed
– Broke up 200 million years ago – Arrangement to the current continental configuration |
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LC 14-7
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What is the Pacific Ring of Fire?
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Name given to the rim of the Pacific Ocean basin due to widespread volcanic and seismic (earthquake) activity; associated with lithospheric plate boundaries.
Plate boundaries are found all of the way around the Pacific basin—primarily subduction zones, along with segments of transform and divergent boundaries. It is along these plate boundaries that the many volcanoes and earthquakes take place in what is now called the Pacific Ring of Fire 75% of all volcanoes lie in the Pacific Ring of Fire |
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What are two (2) examples of important additions to The Plate Tectonics Theory?
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1. Hot Spots
2. Accreted Terranes |
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What is a Hot Spot?
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There are many places on Earth where magma rising from the mantle comes either to or almost to the surface at locations that may not be anywhere near a plate boundary (in which case they would be volcanoes).
These locations of volcanic activity in the interior of a plate are referred to as hot spots |
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What model was proposed to explain the existence of Hot Spots?
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The Mantle Plume Model
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Explain the Mantle Plume Model.
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This explanation suggests that midplate volcanic activity develops over narrow plumes of heated material rising through the mantle—perhaps originating as deep as the core–mantle boundary. Such mantle
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Explain the Mantle Plume Model.
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A plume of heated material rises from deep within the mantle. When the large head of the plume reaches the surface, an outpouring of flood basalt results. Plate motion carries the flood basalts off the stationary plume and a new volcano or volcanic island forms. As the moving plate carries each volcano off the hot spot, it becomes extinct, resulting in a straight-line “hot spot trail.” As volcanic islands move off the hot spot, the plate cools, becomes denser, and subsides; some islands may eventually sink below the surface to become seamounts.
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What is a Mantle Plume?
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A plume of mantle magma that rises to, or almost to, Earth’s surface; not directly associated with most lithospheric plate boundaries, but associated with many hot spots.
• Localized hot areas not associated with plate boundaries |
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Hawaiian Island Hot Spots / Hot Spot Trail
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The most dramatic present day example of a hot spot is associated with the Hawaiian Islands.
The Hawaiian hot spot. A hot spot has persisted here for many millions of years. As the Pacific Plate moved northwest, a progression of volcanoes was created and then died as their source of magma was shut off. Among the oldest is Midway Island. Later volcanoes developed down the chain. The numbers on the main islands indicate the age of the basalt that formed the volcanoes, in millions of years before the present. |
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LC 14-8
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What is an Accreted Terrane?
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– Piece of lithosphere carried by a plate that eventually collides and fuses (accretes) with another plate
A terrane is a small-to-medium mass of lithosphere—bounded on all sides by faults—that may have been carried a long distance by a moving plate, eventually to converge with the edge of another plate. The terrane is too buoyant to be subducted in the collision and instead is fused (“accreted”) to the other plate, often being fragmented in the process. |
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Explain the formation of an Accreted Terrane.
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The origin of an accreted terrane in a convergent boundary. (a) A moving oceanic plate carries along an old island arc. (b) The oceanic plate converges with a continental plate. (c) The oceanic plate begins to subduct under the continental plate, but the island arc is too buoyant for subduction and so is accreted to the continental plate.
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What is a Terrane?
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LC 14-9
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What are some of the Remaining Questions about the Plate Tectonic Theory that have remained unanswered?
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– Why are there mid-continent mountain ranges (i.e., the Appalachians)?
– Why are there earthquakes in the middle of continental plates? – Have the number of plates and plate sizes changed over Earth’s history? – Why are plates different sizes? |
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What is Volcanism?
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A general term that refers to all the phenomena connected with the origin and movement of molten rock.
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What is Extrusive (Volcanic) Volcanism?
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When magma is expelled onto Earth’s surface while still molten, the activity is extrusive and is called volcanism
• Extrusive volcanism—occurs on Earth’s surface, often shortened to volcanism |
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What is Intrusive (Plutonic) Volcanism?
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When magma solidifies below the surface it is referred to as intrusive or plutonic activity and results in intrusive igneous features.
• Intrusive volcanism—occurs below surface, plutonic activity |
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Volcano Distribution
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Areas of volcanism are widespread over the world, but their distribution is uneven. Volcanic activity is primarily associated with plate boundaries.
The most notable area of volcanism in the world is around the margin of the Pacific Ocean in the Pacific Ring of Fire— also called the Andesite Line because the volcanoes consist primarily of the volcanic rock andesite. About 75% of the world’s volcanoes, both active and inactive, are associated with the Pacific Rim. |
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What does it mean for a volcano to be considered "Active"?
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A volcano is considered active if it has erupted at least once within historical times and is considered likely to do so again.
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Volcanic Activity
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Active volcanoes are relatively temporary features of the landscape. Some may have an active life of only a few years, whereas others are sporadically active for thousands of years
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Explain some of beneficial services to the planet that result from Volcanic Eruptions.
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Despite the destruction they cause, volcanoes do provide vital services to the planet.
Much of the water on Earth today was originally released as water vapor during volcanic eruptions during the early history of our planet. *Soil Fertility Magma also contains elements such as phosphorus, potassium, calcium, magnesium, and sulfur required for plant growth. When this magma is extruded as lava that hardens into rock, the weathering that releases the nutrients into soil may require decades or centuries. When the magma is ejected as ash, however, nutrients can be leached into the soil within months. = Soil Fertility |
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Magma vs. Lava: What is Magma?
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molten mineral material below the surface
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Magma vs. Lava: What is Lava?
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magma (molten mineral material below the surface) extruded onto Earth’s surface
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Violent Eruptions vs. Gentle Eruptions
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The ejection of lava into the open air is sometimes volatile and explosive, devastating the area for many kilometers around; in other cases, it is gentle and quiet, affecting the landscape more gradually.
All eruptions, however, alter the landscape because they add new material to Earth’s surface. The nature of a volcanic eruption is determined largely by the chemistry of the magma that feeds it, although the relative strength of the surface crust and the degree of confining pressure to which the magma is subjected may also be important |
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Explain some related aspects of Violent (Explosive) Eruptions.
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During an explosive volcanic eruption, solid rock fragments, solidified lava blobs, cinders, and dust— collectively called pyroclastic material—as well as gas and steam, may be hurled upward in extraordinary quantities.
In some cases, the volcano literally explodes, disintegrating in an enormous self-destructive blast. |
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What are Pyroclastic Materials?
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Solid rock fragments thrown into the air by volcanic explosions
Solid rock fragments, solidified lava blobs, cinders, and dust— are collectively called pyroclastic material |
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What is an example of a volcano that had a self destructing blast?
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The supreme example of such self-destruction within historic times was the final eruption of Krakatau
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Discuss High Silica Felsic Magma and High Silica Eruptions
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which produces the volcanic rock rhyolite and the plutonic rock granite
pyroclastic / explosive eruptions A high silica content also usually indicates cooler magma Some of the heavier minerals have already crystallized and a considerable amount of gas has already separated. Some of this gas is trapped in pockets in the magma under great pressure. As the magma approaches the surface, the confining pressure is diminished and the pent-up gases are released explosively, generating an eruption in which large quantities of pyroclastic material are ejected from the volcano. Any lava flows are likely to be very thick and slow moving. |
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Discuss Intermediate Silica Andesitic Magma and Intermediate Eruptions
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which produces the volcanic rock andesite and the plutonic rock diorite
Volcanoes with intermediate silica content andesitic magmas erupt in a style somewhat between that of felsic and mafic magmas: periodically venting fairly fluid andesitic lava flows and periodically having explosive eruptions of pyroclastic material. |
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Discuss Relatively Low Silica Mafic Magma and Low Silica Eruptions
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which produces the volcanic rock basalt and the plutonic rock gabbro
quiet, nonexplosive eruptions Mafic magma is likely to be hotter and considerably more fluid because of its lower silica content. The resulting eruptions usually yield a great outpouring of lava, quietly and without explosions or large quantities of pyroclastic material. (Quietly is a descriptive term that is relative and refers to the nonexplosive flow of fluid lava.) The highly active volcanoes of Hawai‘i erupt in this fashion. |
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How does Lava Flow?
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– Lava generally flows horizontally
– Uniform cooling results in hexagonal structure |
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One of the most distinctive of all volcanic landscape features commonly develops from flows of fluid lava such as basalt. When such a lava flow cools uniformly, it contracts and forms a distinctive pattern of vertical joints (cracks in the rock), leaving prominent hexagonal columns known as columnar basalt
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What is Flood Basalt?
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Many of the world’s most extensive lava flows were not extruded from volcanic peaks but rather issued from fissures associated with hot spots. The lava that flows out of these vents is nearly always basaltic and frequently comes forth in great volume.
The term flood basalt is applied to the vast accumulations of lava that build up, layer upon layer. Correlated with mass extinctions, due to atmospheric emissions altering climate |
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What is Flood Basalt?
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The term flood basalt is applied to the vast accumulations of lava that build up, layer upon layer
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What are Volcanoes?
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Volcanoes are surface expressions of sub-surface igneous activity.
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What are Shield Volcanoes?
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Broad, low-lying volcanoes that are built up of layer upon layer of solidified lava flows
Little pyroclastic material. Some shield volcanoes are massive and very high, but they are never steep-sided and have gentle slopes. Shield volcanoes, such as those on the Big Island of Hawai‘i, have gentle slopes and consist of layer after layer of solidified lava flows with little pyroclastic material. Volcanoes built up in a lengthy outpouring of very fluid basaltic lava. Shield volcanoes are broad mountains with gentle slopes. |
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What are Composite (Stratovolcanoes) Volcanoes?
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Volcanoes that emit higher silica “intermediate” lavas such as andesite often erupt explosively and tend to develop into symmetrical, steep-sided volcanoes known as composite volcanoes (ex. Mt. Fuji)
Composite volcanoes consist of layers of pyroclastic material and solidified lava flows. • Composite volcano Volcanoes with the classic symmetrical, cone shaped peak, produced by a mixture of lava outpouring and pyroclastic explosion; also stratovolcano. • Emit higher silica lavas (andesite lava) • Form symmetric, steep sided volcanoes • Pyroclastics from explosive lava flows alternate with nonexplosive flows • Pyroclastic flows produce steep slopes, lava holds it together |
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What are Lava Dome (Plug Dome) Volcanoes?
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• Masses of very viscous lava that do not flow far
• Lava bulges from the vent, dome grows by expansion from below and lava within • Some lava domes form inside of composite volcanoes Lava domes (plug domes) develop when viscous lava (commonly rhyolite or dacite) is “squeezed” up into a volcanic vent. The plug of lava may be mantled or surrounded by explosively ejected pyroclastic material. |
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What are Cinder Cone Volcanoes?
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Small, common volcano that is composed primarily of pyroclastic material blasted out from a vent in small but intense explosions. The structure of the volcano is usually a conical hill of loose material.
• Smallest volcanic mountains • Basaltic magma is most common • Slopes form from pyroclastic materials |
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What is a Caldera?
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A Large, steep-sided, roughly circular depression resulting from the explosion and/or collapse of a large volcano (uncommon occurrence)
• Results from a volcano that explodes, collapses, or both • The result is an immense, basin-shaped depression (generally circular) that is larger than original crater • Example: Crater Lake in Oregon |
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Calderas formed from Shield Volcanoes
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Shield volcanoes may develop summit calderas in a different way. When large quantities of fluid lava are vented from rift zones along the sides of a volcano, the magma chamber below the summit can empty and collapse, forming a relatively shallow caldera. Both Mauna Loa and Kˉılauea on the Big Island of Hawai‘i have calderas that formed in this way
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What is a Volcanic Neck?
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Pipe or throat of an old volcano that filled with solid lava
A small, sharp spire that rises abruptly above the surrounding land. It represents the pipe, or throat, of an old volcano that filled with solidified lava after its final eruption. |
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Explain some of the Volcanic Hazards.
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–Volcanic gases—mainly water vapor, but can cause acid rain, alter global climate and kill local residents
–Lava flows—cause immense property damage –Eruption clouds—gas and ash material clouds that extend up to 16 km into the atmosphere, drop large rock fragments called “bombs” –Pyroclastic flows— avalanche of hot gases and material, up to 100 mph –Volcanic mud flows (lahars)—result from heavy rain and/or snow melt during an eruption |
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Volcanic Hazards: Volcanic Gases?
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mainly water vapor, but can cause acid rain (sulfur dioxide emissions released during an eruption), alter global climate and kill local residents
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Volcanic Hazards: Lava Flows?
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cause immense property damage
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Volcanic Hazards: Pyroclastic Flows?
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avalanche of hot gases and material, up to 100 mph
High-speed avalanche of hot gases, ash, and rock fragments emitted from a volcano during an explosive eruption; also known as a nuée ardente. A pyroclastic flow can develop when an eruption column collapses, sending a surge of hot gases and pyroclastic material down the side of a volcano. The photograph shows a pyroclastic flow heading down the flank of Mount St. Helens |
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Volcanic Hazards: Volcanic Mudflows (Lahars)?
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result from heavy rain and/or snow melt during an eruption
A fast-moving, muddy flow of volcanic ash and rock fragments; also called a lahar. A loose mantle of ash and pyroclastic flow deposits on the slopes of a volcano can be mobilized easily by heavy rain or by the melting of snow and glaciers during an eruption. The water mixes with unconsolidated pyroclastic material to produce a fast-moving—and sometimes hot—slurry of mud and boulders, flowing with the consistency of wet concrete. Lahars typically flow down stream valleys off the slopes of a volcano, leaving the valley floor buried in thick mud and debris |
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Volcanic Hazards: Eruption Clouds:
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The violent ejection of pyroclastic material and gases from a volcano can form an eruption column
gas and ash material clouds that extend up to 16 km into the atmosphere, drop large rock fragments called “bombs” smaller fragments of volcanic ash and dust form an enormous eruption cloud from which great quantities of ash may fall. A heavy covering of ash can damage crops and even cause the collapse of buildings. |
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Monitoring Volcanic Hazards?
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– Research to locate previous pyroclastic flows and lahars
– Tiltmeters, measure the slope of a volcano to look for swelling – Monitor earthquake activity The monitoring of active volcanoes includes measuring slight changes in the slope of a mountain using sensitive “tiltmeters” that can detect swelling of a volcano with magma, measuring variations in gas composition and quantity vented from a volcano that may indicate changes in magma, and monitoring earthquake activity below a volcano—swarms of small earthquakes may indicate the filling of the magma chamber below a volcanic peak. |
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When magma solidifies below Earth’s surface it produces plutonic igneous rock. In general, these types of igneous rocks form structures called igneous intrusions.
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What is an Igneous Intrusion?
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rock formed beneath the Earth’s surface within the crust
Features formed by the emplacement and cooling of magma below the surface. |
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What is a Pluton?
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A large, intrusive igneous body.
A general term used to refer to intrusive igneous bodies of nearly any size. |
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The formation of common types of igneous intrusions. (a) Volcanic eruptions and intrusion of magma. (b) After erosion.
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Scheme for Classifying Igneous Intrusions?
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Batholith?
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The largest and most amorphous of igneous intrusions.
Which is a large, subterranean body of great/unknown depth; important in mountain building |
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Laccolith?
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A specialized form of intrusion which is produced when slow-flowing, usually viscous felsic magma, is forced between horizontal layers of preexisting rock forming a mushroom-shaped mass that domes the overlying strata.
slow-moving, viscous magma forced between horizontal layers of rock; builds up a mushroom shaped mass Many laccoliths are small, but some are so large as to form the cores of hills or mountains in much the same fashion as batholiths. |
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Dikes?
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One of the most widespread of all intrusive forms formed by the intrusion of a vertical or nearly vertical sheet of magma into preexisting rock, sometimes forcing its way into vertical fractures and sometimes melting its way upward.
Dikes are notable because they are vertical, narrow, and usually quite resistant to erosion. A vertical sheet of magma that is thrust upward into preexisting rock. Dikes are often found in association with volcanoes, occurring as radial walls extending outward from the volcano like spokes of a wheel. |
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Sills?
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A sill is also a long, thin intrusive body, but its orientation is determined by the structure of the preexisting rocks. It is formed when magma, typically basaltic, is forced between strata that are already in place; the result is often a horizontal igneous sheet between horizontal sedimentary layers.
long, thin body whose orientation is determined by preexisting rocks |
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Veins?
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Least prominent among igneous intrusions but widespread in occurrence are thin veins of igneous rock that may occur individually or in profusion. They are commonly formed when hydrothermal fluids are forced into small fractures in the preexisting rocks.
Molten material forces itself into smaller fractures in preexisting rock, takes irregular shapes |
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What is Diastrophism (Tectonism)?
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Refers to the deformation of Earth’s crust
Two primary types of diastrophism, folding and faulting |
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What are the Two (2) primary types of Diastrophism?
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1. folding
2. faulting |
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What is Folding?
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The bending of crustal rocks by compression and/or uplift.
When crustal rocks are subjected to stress, particularly lateral compression, they are often deformed by being bent. • Results when rock is subjected to lateral compression • Can take place on any scale • Can vary in complexity • Two types |
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What are the two (2) types of Folding?
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– Anticline/upfold, can be forced to have reverse orientation, an overturned fold
– Anticline A simple symmetrical upfold in the rock structure. – Syncline/downfold— overthrust fold – Syncline A simple downfold in the rock structure. |
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What is an Anticline?
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A simple symmetrical upfold.
Can be forced to have reverse orientation, - an overturned fold |
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What is a Syncline?
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A simple downfold in the rock structure - overthrust fold
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What is a Monocline?
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A one sided fold—a slope connecting two horizontal or gently inclined strata.
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What is an Overturned Fold?
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Also relatively common is an upfold that has been pushed so extensively from one side that it becomes oversteepened enough to have a reverse orientation on the other side; such a structure is referred to as an overturned fold.
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What is an Overthrust Fold?
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If the pressure is enough to break the oversteepened fold and cause a shearing movement, the result is an overthrust fold, which causes older rock to ride above younger rock.
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??
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The development of folded structures. (a) Compressive stresses cause sedimentary strata that are initially horizontal to fold. (b) The basic types of folds.
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What is Faulting?
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The breaking apart of rock structures accompanied by displacement (movement of the crust on one or both sides of the break)
The displacement can be vertical or horizontal or a combination of both. Faulting usually takes place along zones of weakness in the crust; such an area is referred to as a fault zone, and the intersection of that zone with Earth’s surface is called a fault line. Movement of crust along a fault zone is sometimes very slow, but it commonly occurs as a sudden rupture resulting in large (hundreds of km) faults over millions of year |
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Where does Faulting usually take place?
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Faulting usually takes place along zones of weakness in the crust; such an area is referred to as a fault zone
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What is a Fault Zone?
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Zones of weakness in the crust
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What is a Fault Line?
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The intersection of the fault zone with Earth’s surface is called a fault line.
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??
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Major faults penetrate many kilometers into Earth’s crust. Indeed, the deeper fault zones can serve as conduits to allow both water and magma from inside Earth to approach the surface.
Frequently springs are found along fault lines, sometimes with hot water gushing forth. Volcanic activity is also associated with some fault zones as magma forces its way upward in the zone of weakness. |
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What is a Fault Scarp?
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Cliff formed by faulting
Steep cliffs that represent the edge of a vertically displaced block Fault lines are often marked by prominent topographic features. Most obvious perhaps are fault scarps. Although most commonly associated with normal faulting, slight amounts of vertical displacement along strike-slip faults may also leave a scarp. |
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What are the four (4) primary types of faults?
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1. Normal Fault
2. Reverse Fault 3. Thrust Fault 4. Strike-Slip Fault |
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What is a Normal Fault?
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A normal fault results from tension stresses (pulling apart or extension) in the crust. It produces a very steeply inclined fault zone, where the upper block slides down the fault plane “normal” to the sense of gravity. A prominent fault scarp is usually formed.
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What is a Reverse Fault?
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A reverse fault is produced from compression stresses (pushing together), where the upper block slides up the incline of the fault plane in “reverse” of the sense of gravity, so that the fault scarp would be severely oversteepened if erosion did not act to smooth the slope somewhat.
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What is a Thrust Fault?
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More complicated in structure and
more impressive in their dynamics are thrust faults (or overthrust faults), in which compression forces the upthrown block to override the downthrown block at a relatively low angle, sometimes for many kilometers. Overthrusting occurs frequently in mountain building, resulting in unusual geologic relationships such as older strata being piled on top of younger rocks. Both thrust faults and reverse faults are commonly associated with subduction zones and continental collision zones. |
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What is a Strike-Slip Fault?
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In a strike-slip fault the movement is horizontal (side-to-side), with the adjacent blocks being displaced laterally relative to each other. Strike-slip faults are a consequence of shear stresses (stress causing two parallel surfaces to slide past one another). Transform faults are one variety of strike-slip fault.
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What is a Tilted Fault-Block Mountain?
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Under extensional stresses, a surface block may be faulted along one side without any faulting or uplift on the other. When this happens, the block is tilted asymmetrically, producing a steep slope along the fault scarp and a relatively gentle slope on the other side of the block.
One side of the fault block is tilted steeply relative to the other |
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What is a Horst?
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A relatively uplifted block of land between two parallel faults.
Frequently such horsts are the result of the land on both sides being downthrown rather than the block itself being uplifted. In either case, the horst may take the form of a plateau or a mountain mass with two steep, straight sides. |
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What is a Graben?
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A block of land bounded by parallel faults in which the block has been downthrown, producing a distinctive structural valley with a straight, steep-sided fault scarp on either side.
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What are Rift Valleys?
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Where a divergent plate boundary develops within a continent, the resulting downfaulted grabens occasionally extend for extraordinary distances as linear valleys enclosed between steep fault scarps. Such lengthy troughs are called rift valleys
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Landforms associated with Strike-Slip Faulting?
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Linear Fault Trough
Offset Stream Shutter Ridge |
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What is a Linear Fault Trough?
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The surface trace of a large strike-slip fault may be marked by a linear fault trough or valley, formed by repeated movement and fracturing of rock within the fault zone.
Small depressions known as sags develop through the settling of rock within the fault zone, and may become filled with water to form sag ponds. |
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Offset Stream?
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A stream course displaced by lateral movement along a fault.
Streams flowing across the fault are displaced by periodic fault movement or diverted when a shutter ridge is faulted in front of a drainage channel, closing off a valley. |
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What is an Earthquake?
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Usually, but not exclusively, associated with faulting is the abrupt shaking of the crust known as an earthquake.
A vibration in Earth produced by shock waves resulting from a sudden displacement along a fault (earthquakes may also develop from the movement of magma or sudden ground subsidence). |
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What are Seismic Waves? Explain.
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The energy released in an earthquake moves through Earth in several different kinds of seismic waves that originate at the center of fault motion, called the focus
of the earthquake These waves travel outward in widening circles, like the ripples produced when a rock is thrown into a pond, gradually diminishing in amplitude with increasing distance from the focus. |
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Where are the strongest shocks of an Earthquake felt?
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The strongest shocks, and greatest crustal vibration, are often felt on the ground directly above the focus, at the location known as the epicenter of the earthquake.
Ground above origin experiences strongest jolt, the epicenter |
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What is the Epicenter?
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Location on the surface directly above the center of fault rupture during an earthquake.
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P-Waves vs. S-Waves: What are P-Waves?
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The fastest moving seismic waves, and the first to be felt during an earthquake, are known as P or primary waves.
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P-Waves vs. S-Waves: What are S-Waves?
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The strong side-to-side and up-and-down shearing motion of the slower-moving S or secondary waves that follows the initial jolt of the P-Waves.
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P-Waves vs. S-Waves.
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Both P waves and S waves travel through the body of Earth (so they are also known as body waves)
P waves and S waves travel at different speeds (P Waves are Faster than S-Waves) |
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What are Surface Waves?
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the motion of a third type of seismic wave is limited to the surface: These surface waves typically arrive immediately after the S waves and produce strong side- to-side movement as well as the up-and-down “rolling” motion often experienced during a large earthquake.
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How to determine the distance and focus of an Earthquake?
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The farther away an earthquake, the greater the time lag between the arrival of the P waves and the S waves.
By using a network of seismographs and comparing arrival times of the seismic waves, seismologists can pinpoint the focus of an earthquake with great precision. |
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What are Seismographs?
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instruments used to record earthquakes
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What is Earthquake Magnitude?
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The relative amount of energy released during an earthquake.
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How is the Magnitude of an Earthquake calculated?
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Magnitudes are calculated on a logarithmic scale, with an energy increase from one magnitude to the next of about 32 times.
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Richter Scale?
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??
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What is Shaking Intensity?
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Even though each earthquake can be assigned a single magnitude number to describe its relative size, every earthquake generates a wide range of local ground shaking intensities—and it is the strength of local ground shaking that directly influences the amount of damage that results from an earthquake.
Intensity of ground shaking not consistent during an earthquake Generally, the strength of ground shaking decreases with increasing distance from the epicenter of the earthquake, but this pattern can be significantly modi- fied by the local geology. |
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What is The Modified Mercalli Intensity Scale?
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the modified Mercalli intensity scale assigns the strength of local shaking to 1 of 12 categories, based on the observed effects and damage (Table 14-3). The modified Mercalli scale is also used by seismologists to describe the anticipated intensity of ground shaking that may occur during future earthquakes in a region.
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Explain Earthquake Hazards.
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Most of the damage from an earthquake is due to ground shaking.
Liquefaction Landslides are often triggered by earthquakes. Another kind of hazard associated with earthquakes involves water movements in lakes and oceans. Abrupt crustal movement can set great waves (known as seiches) in motion in lakes and reservoirs, causing them to overflow shorelines or dams in the same fashion that water can be sloshed out of a dishpan. Much more significant, however, are great seismic sea waves called tsunamis, which are sometimes generated by undersea earthquakes or landslides. |
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What is Liquefaction?
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Phenomenon observed during an earthquake when water saturated soil or sediments become soft or even fluid during the time of strong ground shaking.
A Hazard of Earthquakes |
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Plate Tectonics & New Jersey?
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• Compressional orogenies: Appalachian etc...
• Extensional events: Triassic rift valley • Atlantic Ocean • Passive continental margin • Triassic Rift Valley |
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The Complexities of Crustal Configuration?
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All these processes are interrelated
An example: Glacier National Park Was below sea level for millions of years Vast amounts of sedimentary rock Igneous activity added variety to the sedimentary rock Igneous intrusions created a sill and numerous dikes Tremendous mountain building and associated uplift combined with lateral pressure from the west resulted in a vast rupture and faulting Whole block moved by Lewis Overthrust Had Precambrian sedimentary rock over Cretaceous strata |
