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Plate Tectonics David S kidmore T urner 11/14/12 1 st period. Wegener's Theory .

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wegener s theory
Wegener's Theory
  • A German scientist named Alfred Wegener proposed a hypothesis called the continental drift. Alfred Wegener hypothesized that the continents once were all together in one mass, this was called the super continent. Over millions of years his hypothesis became a reality the super continent began breaking away into smaller continents over a peroid of 200 million years and to this present day they remain where they drifted many years ago.
  • Alfred's Wegener's hypothesis was correct, he reasoned that if the continents had once been joined fossils, plants and animals would be found in the areas where the continents were once connected.
  • Geologic evidence supported Wegener's hypothesis of continental drift due to the ages and types of rocks in coastal regions separated areas now, but once combined which now are western Africa and eastern south America.
  • Climate changes also had a reason to support his hypothesis because where the continents use to be it had glaciers now in Southern African and South America its way to warm for glaciers


  • Despite Alfred's evidence of all things that supported his hypothesis . Alfred's ideas were strongly opposed by other scientists. They rejected the mechanism by which Wegener proposed about the supercontinent moving. Before he could find any more geologic evidence to support his hypothesis Alfred Wegener died in 1930.
pangaea and panthalassa
Pangaea and Panthalassa
  • The supercontinent Pangaea formed about 300 million years ago during the Paleozoic era. About 200 million years ago Pangaea began to break away into 2 continents a large rift split the continent from east to west. As this rift went on that’s how north Atlantic ocean was formed another rift was made and split which formed the south Atlantic ocean. With the continents in there present position as they started to collide it welded new crust onto the continents this formed mountain ranges such as the rocky mountains and the indies. This caused new oceans to open but also to close some to scientist predict that in 250 million years the continents will collide back together and become one.
  • When all the continents were the supercontinent long ago there was one single large ocean called pathalassa that covered earths surface but as the continents moved into there current positions new oceans formed and pathalassa didn’t exist anymore.
  • Accretion is where terranes become part of a continent, terranes forms mountains, while some will just add surface area to a continent
  • One way a continent can change is by breaking apart from each other this process is called rifting. As a result of rifiting happening new smaller continents may form through this process.
  • Scientists believe that as heat from the mantle builds up beneath the continent the lithosphere becomes thinner and begins to weaken and eventually a rift will form in that zone and they will begin to break apart.
plate movements
Plate Movements
  • Geologic evidence shows that there is a lot of climate change in many continents that have had continental drift over the past 200 million years ago. An example of this would be Sahara in Africa, today it is one of the hottest places on earth,but when the continents were together it was covered by a thick ice sheet but over time as the continents seperatedtempertures changed and the ice melted.
  • Lithosphere is the solid outer layer of earth that consists of The crust and the rigid upper part of the mantle.
  • Plate tectonics is the theory that explains how large pieces of the lithosphere form the thin outer shell on earth the plates move and change shape over time.
  • Asthenosphere is the solid plastic layer of the mantle beneath the lithosphere it is made of mantle rock that flows very slowly, which allows tectonic plates to move on top of it .
how plates move
How Plates Move
  • Tectonic plates can move from earthquakes this happens because two or more plates will meet in the same area and will have sudden movements, volcanoes can make plates more due to magma that erupts on earth surface. Near the pacific ocean they have a lot of earthquakes zones and active volcanoes , that’s how we know its surrounded by plate boundaries
three types of plate b oundaries
Three types of Plate Boundaries
  • The 3 types of plates boundaries are divergent convergent and transform bounders.
  • A divergent boundary-is a boundary that is between tectonic plates that are moving away from each other most divergent boundaries are located on the ocean floor.
  • A convergent boundary-is a boundary that forms were 2 plates collide. There are 3 types of convergent boundaries that can happen in a process.
  • Transform boundaries-are boundaries between tectonic plates that are sliding past each other horizontally.
  • Isostatsy- its when two forces are balanced in the lithosphere and asthenosphere, this occurs when parts of earth crust changes.
isostatic adjustments
Isostatic Adjustments
  • Isostatic adjustments is where movements of the lithosphere to reach isostatsy as the isostatic adjustments occur in areas of the crust are bent up and down this bending causes rock in that area deform.
s tress
  • Stress-is the amount of force per unit area that acts on a rock, as the earths lithosphere moves the rock in the crust it squeezed stressed and twisted , these actions exert force on the rock, there are three types of stresses one is compression , tension and the last one is shear stress.
divergent boundary
Divergent Boundary

Sea-floor Spreading

  • As divergent boundaries magma, from the astherosphere rises to the surface as the plates move apart. A mid-ocean ridge is the rock that will sit higher than the sea floor because it will be less dense. The Red Sea is an example of this.

An example of this would be the red sea which occupies a big rift valley formed by the separation of the African and Arabian plates

  • Magnetic reversals

Geologic evidence says that the earth’s magnetic field was not always pointing north. There are rocks that are normal polarity and reversed polarity. The rocks that the point north and in the same time period are normal polarity. The rocks that point south and fall into specific time periods are reversed polarity. When scientists put the periods of normal and reverse polarity in chronological order, it made a pattern. This pattern is called the geomagnetic reversal time scale.

magnetic symmetry
Magnetic Symmetry
  • Magnetic symmetry-is a magnetic patterns on the ocean floor. Scientists geomagnetic reversal time scale to help them unravel the mystery of these magnetic patterns.
  • They found rocks on the ocean floor that were symmetrical the rocks in the center were the youngest , and the oldest were on the ridges. The fact is new rocks form at the center then as they grow older the move away to the ridges.
normal fault
Normal Fault
  • Normal fault-is a fault in which the hanging wall moves downward relative to the footwall, normal faults are commonly form at divergent boundaries, where the crust is being pulled apart by tension . Normal faults go up down and side to side.

An example of normal fault is the great rift valley of east Africa which was formed by large-scale normal faulting.

convergent boundaries
Convergent boundaries
  • Continental + Oceanic crust-the oceanic lithosphere is dense so it will sink under the continental lithosphere. As oceanic plate sub ducts, it will heat up and release fluids in the mantle above it all. These fluids cause a material to melt which will form magma.
landforms produced
Landforms Produced
  • An example of this landform is volcanic mountains.
  • Despite the high temperature in the mantle, most of this zone remains solid because of the large amount of pressure from the surrounding rock. Sometimes however solid mantle and crust melt to from magma or liquid rock that forms under earths surface.
3 conditions
3 Conditions
  • Magma can form under three conditions . First if the temperature of rocks above the melting point of the minerals the rock is composed of the rock will melt, second if enough pressure is removed from the rock the melting point will decrease and the rock will melt. Third the addition of fluids such as water may decrease the melting point of some minerals in the rock and cause the rock to melt.
  • When magma erupts onto earths surface the magma is called lava. As lava flows from an opening or vent the material may build up as a cone of material that may eventually form a mountain.
v olcano
  • The vent in earths surface through which magma and gases are expelled is called a volcano.
  • Volcanos occur near both convergent and divergent boundaries of tectonic plates.
common locations
Common Locations
  • The Pacific Ring of Fire (or just The Ring of Fire) is an area where a large number of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a 40,000 km (25,000 mi) horseshoe shape, it is associated with a nearly continuous series of oceanic trenches volcanic arc, and volcanic belts and/or plate movements. The Ring of Fire has 452 volcanoes and is home to over 75% of the world's active and dormant volcanoes.It is sometimes called the circum Pacific belt or the circum Pacific seismic belt.
  • Eruption of Mount St. Helens on July 22, 1980.
  • About 90%of the world's earthquakes and 81% of the world's largest earthquakes occur along the Ring of Fire. The next most seismic region (5–6% of earthquakes and 17% of the world's largest earthquakes) is the Alpidebelt, which extends from Java to Sumatra through the Himalayas the Mediterranean and out into the Atlantic. The Mid-Atlantic Ridge is the third most prominent earthquake belt.
active volcanoes
Active Volcanoes

If you were to plot the locations of the volcanoes that have erupted in the past 50 years, you would see that the locations form a pattern across earths surface. Like earthquakes most active volcanoes occur in zones near both convergent and divergent boundaries.

pyroclastic material
Pyroclastic Material
  • Consists of fragments of rock that form during a volcanic eruption. When a volcano erupts the dissolved gases within the lava escape and send molten and solid particles shooting into the air. So felsic lava tends to explode and throw pyroclastic material into the air.
  • Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress. In everyday terms (and for fluids only), viscosity is "thickness" or "internal friction". Thus, water is thin having a lower viscosity, while honey is "thick", having a higher viscosity. Put simply, the less viscous the fluid is, the greater its ease of movement fluidity. Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. For example, high-viscosity magma will create a tall, steep stratovolcano, because it cannot flow far before it cools, while low-viscosity mafic lava will create a wide, shallow-sloped shield volcano.
  • With the exception of superfluids, all real fluids have some resistance to stress and therefore are viscous. A fluid which has no resistance to shear stress is known as an ideal fluid or inviscid fluid. In common usage, a liquid with the viscosity less than water is known as a mobile liquid, while a substance with a viscosity substantially greater than water is simply called a viscous liquid.
how magma contents produce explosive eruptions
How magma contents produce explosive eruptions.
  • Unlike the fluid lava produces by oceanic volcanoes , the felsic lavas of continental volcanoes such as mount St. Helens tend to be cooler and stickier. Felsic lavas also contain large amounts of trapped gases such as water vapor and carbon dioxide.
types of volcanoes
Types of Volcanoes
  • The first type of volcanoes is shield volcanoes , there volcanic cones that are broad at the base and have gently sloping sides. A shield volcano covers a wide area and generally forms from quiet eruptions. Layers of hot lava flow out around the vent.
  • The seconded type is a cinder cone, a type of volcano that has very steep slopes. The slop angles od the cinder cone can be close to 40 degree and the slopes are rarely more then a few hundred meters high.
  • The third is a composite volcano , composite volcano are made of alternating layers of hardened lava flows and pyroclastic material. During a quiet eruption lava flows cover the sides of the cone. Then when an explosive eruption occurs large amounts of pyroclastic material are deposited around the vent.

Composite Shield

  • Cinder caldera

When a magma chamber below a volcano empties, the volcanic cone may collapse and leave a large , basin-shaped depression. It erupts that discharge large amounts of magma can also cause a caldera to form . Krakatau a volcanic island in indonesia .

oceanic o ceanic crust
Oceanic + Oceanic Crust
  • This collision happens by one plate that sub ducts under the other plate. When this happens a deep-ocean trench is formed fluids are released from the sub ducted plate which causes mantle rock to melt. Which will form magma, Then the magma will rise to the top and form an island arc. An island arc is also a chain of volcanic islands.
related landforms
Related Landforms
  • An example of landforms is japan.
collision zones
Collision Zones
  • Continental + Continental Crust-in this collision the continental lithosphere collide , but neither of them sub duct because of the plates are not dense enough to sub duct under the other plates
landforms produced1
Landforms Produced
  • The himalayas are an example.
compression and uplift
Compression and Uplift
  • When colliding the edges crumple and thicken which will cause up lifts that form large mountain ranges.
transform boundary
Transform Boundary
  • Reverse faults-a reverse fault if formed when compression causes the hanging wall to move upward relative to the footwall. A thrust fault is a special type of reserve fault. This fault plane is at a low angle of nearly horizontal, because of the low angle, the rock on the hanging wall is pushed up and over the rock of the footwall. You will find reverse faults in the Rockies and the Alps.
strike slip faults
Strike-slip Faults
  • strike-slip fault happens when a fault plane slides horizontal. This happens form chear stress sometimes they can be vertical. This types of faults commonly happen at transform boundaries. This is where tectonic plates grind as they move in opposite directions. These motions plates edges. Strike-slip faults occur as groups of smaller faults.
  • The stress that stretches and pulls a body apart would be called tension. The rocks become thinner when they are pulled apart by tension. When tectonic plates pull apart it is tension.
shear stress
Shear Stress
  • Shear stress distorts the body. This is caused by the body being pulled in opposite directions. When rocks are sheared they bend and break apart or twist when sliding past each other.
related landforms1
Related Landforms
  • An example of reverse fault is the Rocky's and alps.
  • Elastic rebound- scientists believe that elastic rebound is a result of earthquakes. It is a sudden return of elastically deformed rock it its undeformed shape. The rocks on each side of a fault rock move very slowly. If the fault is locked , stress in the rocks increase. When the rocks are stressed past the point at which they can maintain their integrity, they fracture. The rocks then separate at their weakest point and rebound.
  • Many scientists study earthquakes because earthquakes are the best tool earth scientists have for investigating earths internal structure and dynamics. These scientists have developed special sensing equipment to record locate and measure earthquakes. Seismology is the study of earthquakes and seismic waves.
  • Seismograph is vibrations in the ground that can be detected and recorded by using and instrument.
    • A modern 3 component seismograph consists of 3 sensing devices. One device records horizontal motion one from eat to west motion and the other for north to south motion. Seismographs record motion into electronic signals.
  • The location within earths along a fault at which the first motion of an earthquake occurs is called the focus.
  • Although the focus depths of earthquakes vary about 90% of continental earthquakes have a shallow focus. Earthquakes that have foci take place within 70km of earths surface earthquakes that have an immediate foci occur at depths between 70km to 300km
  • The point of the earths surface directly above an earthquakes starting point or focus.
seismic waves
Seismic Waves

As rocks along a fault slip into new positions, the rocks release energy in the form of vibrations.

These waves travel outward in all directions from the focus through the surrounding rock

body waves
Body Waves
  • Body waves can be put into two main categories S waves and P waves also called as primary waves or compression waves
p waves
P Waves
  • P waves cause particles of rock to move in a back and forth direction that is parallel to the direction in which the waves are traveling. P waves can move through solids liquids and gases.
s waves
S Waves
  • S waves are called secondary waves or shear waves are the second fastest seismic waves and arrive at detection sites after p waves. S waves cause particles of rock to move in a side to side direction that is perpendicular to the direction in which the waves are traveling .
surface waves
Surface Waves
  • Surface waves form from motion along a shallow fault or from the conversation of energy when P waving and S waves reach earths surface . Although surface waves are the slowest moving waves they may cause the greatest damage during an earthquake.
how seismic waves led to determination of earths interior
How seismic waves led to determination of earths interior
  • Seismic waves are useful to scientists in exploring earths interior. The compostion material through the P waves and S waves travel affects the speed and direction of the waves. P waves travel fastest through materials that are very rigid and are not easily compressed.
earthquakes not resulting from movement along plate boundaries
Earthquakes not resulting from movement along plate boundaries
  • Not all earthquakes result from movement along plate boundaries. The most widely felt series of earthquakes in the history of the united states did not occur near an active plate boundary. Instead these earth quakes occurred in the middle of the continent near New Madrid , Missouri, in 1811 and 1812. The vibrations from the earthquakes that rocked New Madrid were so strong that they caused damage as far away as South Carolina.

The measure of the strength of an earthquake is called magnitude. Magnitude is determined by measuring the amount of ground motion caused by an earthquake. Seismologists express magnitude by using a magnitude scale.

  • Before the development of magnitude scales the size of an earthquake was determined based on the earthquakes effects. A measure of the effects of an earthquake is the earthquakes intensity.
mercalli scale
Mercalli Scale
  • It expresses intensity in roman numerals from 1 to 12 and provides a description of the effect of each earthquake intensity.
  • An earthquake whose epicenter is on the ocean floor may cause a giant ocean wave .
  • Tsunami cause serious destruction if it crashes into land. A tsunami may begin to form when a sudden drop or rise in the ocean floor occurs because of faulting associated with undersea earthquakes.
hot spots
Hot Spots
  • An example of hot spots are Hawaiian Islands. Hot spots are volcanically active areas that lie far from tectonic plate boundaries.
dome mountains
Dome Mountains
  • An example of a dome mountain is the black hills of south Dakota and the Adirondack mountains of New York. Dome mountains form when tectonic forces gently uplift rock layers.