Plate Tectonics

Plate TectonicsPlate TectonicsEvolution of the Earth

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InteriorInterior

Crust

Upper MantleLower Mantle

Outer CoreInner Core

InteriorInterior

2851 km

2259 km1220 km

What’s in the Earth’s Layers:Crust: is made up of Silicates which are cooler-rigid rock

Mantle: -made up softer weaker rock that can flow slowly.

Core:-Outer core: liquid metal and very hot!-Inner core: solid metal and very high pressure!

VolcanoesVolcanoes• Volcanoes are the result of hot spots within the

crust or mantle of the earth.• The hot, liquid rock will break through weak spots

in the surface and form volcanoes or flood basalts. These are called Effusive/Quiet Volcanoes

• Many volcanoes do not release lava, instead they spit ash. These are called Explosive Volcanoes

• The type of volcano is determined by the materials in it. Go to: http://www.nationalgeographic.com/forcesofnature/interactive/index.html

http://www.nationalgeographic.com/forcesofnature/interactive/index.html

Volcanoes

Dissolved Gases

Silica Content

Type of Volcano Looks like…. Effusive or Explosive

High High

High Low

Low High

Low Low

Fill in the following table to determine how quiet and explosive volcanoes differ:

VolcanoesVolcanoes

Quiet lava flows

VolcanoesVolcanoes

Mt. St. Helen before the explosive eruption

VolcanoesVolcanoes

VolcanoesVolcanoesTime lapse of the eruption

VolcanoesVolcanoes

Mt. St. Helen after the eruption

VolcanoesVolcanoes

Mt. St. Helens begins the rebuilding process

Flood basalts: When volcanic eruptions coats a thick layer of cooled magma over the surface of the earth.

Flood basalts: When volcanic eruptions coats a thick layer of cooled magma over the surface of the earth.

This is IGNEOUS ROCK.Igneous Rock is a type of rock that is made in the mantle

VolcanoesVolcanoes

Where does the energy to make a Volcano come from?

Where does the energy to make a Volcano come from?

The earth’s core is extremely HOT!

Magma in the mantle is always moving in the earth because of

the Earth’s Core, which causes Convection:

Hot materials rise and cool materials

sink.

• This causes the plates to move with the magma of the mantle to: 1) move apart

(Divergent Boundaries) or• 2) move together (Convergent Boundaries)

and even • 3) past one another (Transform Boundaries.)

Because Plates move they cause the magma to be released through cracks in the earth’s crust creating volcanoes.

Volcano locations:Why at these locations?

Volcano locations:Why at these locations?

The answer is Tectonic PlatesThe answer is Tectonic Plates

The reason volcanoes occur at specific locations:

1. Plate Tectonics Move at a Convergent Zone: (together)

• Convergent Zones: Volcanoes


2. At Divergent Zones: (a part)

Tectonic PlatesTectonic Plates


Another source of evidence is based on seafloor ages which get younger as we approach sea floor ridges

Pangea• What is Pangaea? • Pangaea was a super continent at one time.• Scientists use the similarity of rock types and fossil types that date to the

same age to support their theory that the continents were connected to form a super continent.

• The map below give just one example of areas on different continents that show the same fossils and rock types.

PangeaPangea

PangeaPangea

PangeaPangea

The break up of Pangea


3. Magma moves to the surface of the earth near a weak spot and can activate a magma chamber

• http://sio.ucsd.edu/volcano/about/magma.html4. This can happen over a HOTSPOT. The Hawaiian Islandshave formed because a platemoved over a hotspot.

http://sio.ucsd.edu/volcano/about/magma.html

Mid-Plate HotspotsMid-Plate Hotspots

What types of energy are taking place to have a volcano?

• Mechanical Energy: – Magma moves from the interior earth up to a weak

portion in the earth’s crust.– Magma also moves out from the volcano. – Ash and rock can also move out from a volcano like in a

pyroclastic flow.• Heat Energy

– The earth’s core has large amounts of heat that escape at the earth’s surface through a volcano

Draw how a volcano works by using words to describe the process such as: magma, crust, mantle, mechanical energy, heat energy

EarthquakesEarthquakes• Earthquakes are a result of motion within the

earth.• This only occurs where the earth is solid and

therefore can only occur within about 100 miles of the surface

• Earthquakes provide the best evidence regarding the interior structure of the Earth.

EarthquakesEarthquakes



EarthquakesEarthquakesA. Where the earthquake occurs

B. Directly above the earthquake C. Where the land masses move past one another D. Where the land will either drop down, jet up or change along the fault. E. Waves that move outward causing the shaking movement of the earth.

Waves fall under two categories:

1) P-Waves: occurs when fault moves past each other horizontally, cause a compressed wave.

2) S-Waves: occurs when faults move vertically, causes a wavy wave.

* Both display Mechanical Energy!

Both Body Waves and

Surface Waves will differ in both S & P

Waves:

http://www.answers.com/topic/pswaves-jpg-1

Seismograph: Measures movement in the earth.

Seismograph: Measures movement in the earth.

Finding an Earthquake’s EpicenterFinding an Earthquake’s Epicenter

Earthquakes occur often!

http://www.seis.utah.edu/../req2webdir/recenteqs/index_map.map

http://www.seis.utah.edu/../req2webdir/recenteqs/index_map.map

Earthquakes occur at plate boundaries more frequentlyEarthquakes occur at plate boundaries more frequently

Location of worldwide earthquakes


Earthquakes by depth.Notice that the deep earthquakes occur only at subduction zones.

• The bigger the magnitude of the earthquake, the more mechanical energy there is.

• Go to: http://www.nationalgeographic.com/forcesofnature/interactive/index.html

• Fill out the following table:

Bed rock Low Description of Damage

High

Fault Low

High

Land fill Low

High

http://www.nationalgeographic.com/forcesofnature/interactive/index.html

Different Forms of Energy In the Earth

• Mechanical Energy: Energy due to motion• Heat energy: energy due to heat• Potential energy: energy that is built up but

not yet released• Kinetic Energy: energy that is occurring (in

motion)



Today plate boundaries are determined by examining the location of volcanoes and earthquakes.

Volcanoes result from the friction (heat) of the platesmotion.

Earthquakes occur where plate rub against one another

Plate BoundariesPlate Boundaries• Convergent – plates move toward one

another

• Divergent – plates move away from each other

• Transform – plate moves sideways from each other

Faults occur at these Plate boundaries, where land masses move. These faults when moved release energy in the form of an earthquake.

There are 3 different faults:

1. Normal Fault: as stress is pulled away on the plates, one land mass slips down. (Divergent Plate boundary)

2. Reverse Fault: as two plates come together one land mass jets up above the other making a hanging wall. (Convergent Plate Boundary)

3. Transverse Fault: occurs as two plates slide past one another. (Transform plate boundary)

Tectonic PlatesTectonic PlatesVolcanoes





Another source of evidence is based on seafloor ages which get younger as we approach sea floor ridges


Our final piece of evidence is the magnetic record of the ocean floor.

This shows the pattern of reversal and we find a near perfect mirror image on opposing sides of the ridge




Composition vs. MotionComposition vs. Motion

We can look at the interior of the Earth based on the composition of the rocks or based on the movement

Based on CompositionBased on Composition

• Crust – solid, relatively low density silicate rock• Mantle – Semi fluid, denser, mafic (iron and magnesium

bearing) rocks• Core – Liquid then solid iron and nickel with traces of

heavier elements

Plate TypesPlate Types• Oceanic plates: basalt

– Dark (black) and dense rock type composed of silicates, iron and magnesium

• Continental plates – granite and andesite– Light colored (pink, white and

gray) and low density rock type composed almost entirely of silicates.

Plate BoundariesPlate Boundaries

Plate BoundariesPlate Boundaries

Convergent PlatesConvergent Plates



Convergent PlatesConvergent PlatesThe only subduction zone in the AtlanticThe only subduction zone in the Atlantic


Black arrows show subduction zones and the direction of plate movement


Looking at the depthof earthquakes showsthat angle that the plate is being subducted

Divergent PlatesDivergent Plates




Transform PlatesTransform Plates



Transform PlatesTransform Plates

San Andreas Fault



Why do the Plates Move?Why do the Plates Move?

Why do the Plates Move?Why do the Plates Move?• No single idea explains everything but we can

identify several forces that contribute to the movement of the plates.– Slab pull

• The sinking of the cooled dense oceanic plates pulls on the rest of the plate

– Ridge rises• The material deposited on the top of the ridge slides downs from

the rise pushing on the plate– Convection

• Movement within the mantle could be part of the driving force behind the motion of the plates.

The Big PictureThe Big Picture

Pangea• What is Pangaea? • Pangaea was a super continent at one time.• Scientists use the similarity of rock types and fossil types that date to the

same age to support their theory that the continents were connected to form a super continent.

• The map below give just one example of areas on different continents that show the same fossils and rock types.

PangeaPangea

PangeaPangea

PangeaPangea

The break up of Pangea

Where are we going?Where are we going?

We appear to be headed for another super continent as North America,

South America, Asia and Australia converge in the ever shrinking Pacific Ocean

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Plate Tectonics