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ES 3.6 PPT

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  • 1.  Mountain ranges provide us with continuous evidence that the Earth’s surface is constantly changing shape. › These changes result from deformation, or the bending, tilting, and breaking of Earth’s crust.  Happens when the lithosphere thickens or thins out.
  • 2.  Vertical movement of the lithosphere depends on two opposing forces: › Gravitational Force  Weight of the lithosphere pressing down on the asthenosphere. › Buoyant Force  The asthenosphere pressing up on the lithosphere. A condition of gravitational and buoyant equilibrium between Earth’s lithosphere and asthenosphere is called isostasy.
  • 3.  As Earth’s lithosphere moves, the rock in the crust is squeezes, stretched, and twisted. › The amount of force per unit area that acts on a rock is called stress. 3 types include: 1. Compression 2. Tension 3. Shear Stress
  • 4.  The type of stress that squeezes and shortens a body of rock. Common along convergent plate boundaries where tectonic plates collide with one another.
  • 5.  The type of stress that stretches and pulls a body of rock apart. Common along divergent plate boundaries where tectonic plates are being pulled apart.
  • 6.  The type of stress distorting a body of rock by pushing parts of the body in opposite directions. Common along transform plate boundaries where tectonic plates slide horizontally past one another.
  • 7.  A bend in rock layers resulting from stress is known as a fold. › The sloping sides of a fold are called limbs. › The limbs meet at the bend in the rock layers, which is called the hinge. › If the fold’s structure is such that a plane could slice the fold into two symmetrical halves, the fold is symmetrical and the plane is called the axial plane.
  • 8.  Upward-arching folds are called anticlines.
  • 9.  Downward trough-like folds are called synclines.
  • 10.  Folds where rock layers are folded so both ends of the fold are horizontal are called monoclines.
  • 11.  Recall, a fault is a break in the Earth’s crust along which blocks of the crust slide relative to one another.
  • 12.  A normal fault occurs when the hanging wall moves down relative to the footwall. › Results from tension.
  • 13.  A reverse fault occurs when the hanging wall moves up relative to the footwall. › Results from compression.
  • 14.  Faults that occur when opposing forces cause rock to break and move horizontally are called strike-slip faults. › Results from shear stress.
  • 15.  An earthquake is the movement or trembling of the ground caused by a sudden release of energy when rocks along a fault move. › Each year, over 30,000 earthquakes occur worldwide strong enough to be felt. › However, only about 100 major earthquakes take place each year.
  • 16.  Earthquakes are a result of elastic rebound, which is the sudden return of elastically deformed rock to its un-deformed shape.
  • 17.  The location within the Earth along a fault at which the first motion of an earthquake occurs is called the focus. › By the time vibrations from an earthquake having a deeper foci reach the surface, much of their energy has dissipated. › Therefore, earthquakes causing the most damage tend to have shallow foci. The point on Earth’s surface directly above the focus is called the epicenter.
  • 18.  As rocks along a fault slip into new positions, the rocks release energy in the form of vibrations called seismic waves. Two main types of seismic waves: › Body – seismic waves traveling through the body of a medium (fastest-moving seismic wave category).  P waves  S waves › Surface – seismic waves traveling along the surface of a body rather than through the middle of it (slowest- moving seismic wave category; most destructive).  Rayleigh waves  Love waves
  • 19.  Body waves traveling through solids and liquids are called P waves.  “Primary” waves  “Pressure” waves Fastest seismic wave. › Avg. speed in crust = 6.1 km/s Particles of rock move in a back-and-forth direction.
  • 20.  Body waves traveling through only solids are called S waves.  “Secondary” Waves  “Shear” Waves Second fastest seismic wave. › Avg. speed in crust = 4.1 km/s Particles of rock move in a side-to-side direction.
  • 21.  Rayleigh waves are surface waves causing the ground to move with an elliptical, rolling motion. Love waves are surface waves causing the ground to move with a side to side motion perpendicular to the direction of the traveling wave.
  • 22.  Vibrations in the ground can be detected and recorded using an instrument known as a seismograph. › First seismograph by Chinese astronomer, Chan Heng.  Each of the 8 dragons had bronze ball in its mouth  fell with tremor. A tracing of an earthquake motion recorded by a seismograph is called a seismogram. A person who studies earthquakes is a seismologist and the study of earthquakes is called seismology.
  • 23.  To determine the distance to an epicenter, scientists analyze the arrival times of the P waves and the S waves. › The longer the lag time between the arrival of the waves, the farther away the earthquake occurred. Scientists use computers to calculate how far an earthquake is from a given seismograph station. What is the lag time for the earthquake recorded on the seismogram to the left?
  • 24.  A measure of the strength of an earthquake is called magnitude. › Determined by measuring the amount of ground motion caused by an earthquake. The Richter Scale was used throughout the 20th century to study magnitude. › It is a logarithmic scale, meaning the numbers on the scale measure factors of 10.  Therefore, an earthquake measuring a 4.0 on the Richter Scale is 10 times larger than one measuring at a 3.0.
  • 25.  Scientists now prefer to measure the magnitude of earthquakes with the Moment Magnitude Scale. › It is a measurement of earthquake strength based on the following:  Size of the area of the fault.  Average distance the fault blocks move.  Rigidity of the rocks in the fault zone. Although this scale gives similar values as the Richter Scale, this one is more accurate.
  • 26.  Before the development of the magnitude scales, the size of an earthquake was determined based on the earthquake’s effects on the area. A measure of the effects of an earthquake is called the intensity. The Modified Mercalli Scale expressed intensity in Roman Numerals I to XII (highest- total destruction).
  • 27.  Any activity including the movement of magma onto Earth’s surface is called volcanism. › Molten rock beneath Earth’s surface is called magma. › Once it erupts onto the surface, it is termed lava. The vent in Earth’s surface through which magma and gases are expelled is called a volcano. › Most active volcanoes occur in zones near both convergent and divergent plate boundaries.
  • 28.  Many volcanoes are located along subduction zones, where one tectonic plate moves under the other. › As the subducting plate gets deeper into the asthenosphere, the rock melts and forms magma. › The magma rises through the lithosphere (less dense) and erupts on Earth’s surface.
  • 29.  Not all volcanoes develop along plate boundaries. › Areas of volcanism within the interiors of the lithosphere are called hot spots.  Most form where columns of solid, hot material from the deep mantle, called mantle plumes, rise and reach the lithosphere.  The plume will spread out and magma will break through the Earth’s crust resulting in the formation of a hot spot volcano (HI Island formation).
  • 30.  Mafic (dark-colored; rich in Fe and Mg) magmas are common with non-explosive volcanic eruptions since gases can easily escape  generally quiet. Most common type of eruption. Produce relatively calm flows of lava, but can produce huge amounts of it.
  • 31.  Felsic (light-colored; high Si content) magmas are common with explosive eruptions since large amounts of gases are trapped inside. › Effects can be incredibly destructive. During explosive eruptions, clouds of hot debris, ash, and gas shoot rapidly out from a volcanic vent. › Fragments of rock forming during a volcanic eruption is called pyroclastic material.
  • 32.  The viscosity of magma, or its resistance to flow, affects the force with which a particular volcano will erupt. › A glass of milk has LOW viscosity, flowing more quickly.  Common with mafic magmas. › A milkshake has HIGH viscosity, flowing slowly.  Common with felsic magmas. Four main types of lava:  Pahoehoe  Aa  Blocky Lava  Pillow Lava
  • 33.  Lava flowing similar to wax dripping from a candle (LOW viscosity). As it cools, it forms a smooth, rope-like texture.
  • 34.  Lava flowing quickly (LOW viscosity), forming a brittle crust. The crust is torn into jagged pieces as molten lava continues to flow underneath.
  • 35.  Higher Si content than Aa; cooler, stiff lava usually oozing and flowing slowly (HIGH viscosity) from a volcano after an explosion. Cooled lava eventually breaks into blocks.
  • 36.  Forms when lava erupts underwater. This lava flows quickly (LOW viscosity) and has rounded lumps resembling pillows.
  • 37.  Magma rises to the surface, like an air bubble in a honey jar. › This happens because the magma is less dense than surrounding rock. Three main types of volcanoes: › Shield Volcanoes › Cinder Cone Volcanoes › Composite Volcanoes
  • 38.  When the magma chamber below a volcano empties, the volcanic cone may collapse and leave a large, basin- shaped depression called a caldera. Calderas may later fill with water to form lakes. › Common example: Crater Lake, OR