the structure of the earth and plate tectonics. structure of the earth the earth is made up of 3...
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The Structure of the Earth and Plate Tectonics
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Structure of the Earth
• The Earth is made up of 3 main layers:– Core– Mantle– Crust
Inner core
Outer core
Mantle
Crust
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The Crust• This is where we live!
• The Earth’s crust is made of:
Continental Crust
- thick (10-70km)- buoyant (less dense than oceanic crust) - mostly old
Oceanic Crust
- thin (~7 km)- dense (sinks under continental crust)- young
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How do we know what the Earth is made of?
• Geophysical surveys: seismic, gravity, magnetics, electrical, geodesy– Acquisition: land, air, sea and satellite
– Geological surveys: fieldwork, boreholes, mines
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What is Plate Tectonics?
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• If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle.
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Plate Tectonics• The Earth’s crust is divided into 12 major
plates which are moved in various directions.• This plate motion causes them to collide, pull
apart, or scrape against each other.• Each type of interaction causes a
characteristic set of Earth structures or “tectonic” features.
• The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.
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World Plates
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What are tectonic plates made of?
• Plates are made of rigid lithosphere.
The lithosphere is made up of the crust and the upper part of the mantle.
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What lies beneath the tectonic plates?
• Below the lithosphere (which makes up the tectonic plates) is the asthenosphere.
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Plate Movement• “Plates” of lithosphere are moved around by
the underlying hot mantle convection cells
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Practical Exercise 1
Supercontinents!
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What happens at tectonic plate boundaries?
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• Divergent
• Convergent
• Transform
Three types of plate boundary
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• Spreading ridges– As plates move apart new material is erupted to
fill the gap
Divergent Boundaries
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Age of Oceanic Crust
Courtesy of www.ngdc.noaa.gov
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• Iceland has a divergent plate boundary running through its middle
Iceland: An example of continental rifting
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• There are three styles of convergent plate boundaries– Continent-continent collision– Continent-oceanic crust collision– Ocean-ocean collision
Convergent Boundaries
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• Forms mountains, e.g. European Alps, Himalayas
Continent-Continent Collision
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Himalayas
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• Called SUBDUCTION
Continent-Oceanic Crust Collision
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• Oceanic lithosphere subducts underneath the continental lithosphere
• Oceanic lithosphere heats and dehydrates as it subsides
• The melt rises forming volcanism
• E.g. The Andes
Subduction
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• When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone.
• The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench.
• The worlds deepest parts of the ocean are found along trenches. – E.g. The Mariana Trench is 11 km deep!
Ocean-Ocean Plate Collision
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• Where plates slide past each other
Transform Boundaries
Above: View of the San Andreas transform fault
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Practical Exercise 2
Where will the UK be in:1,000 years?
1,000,000 years?
1,000,000,000 years?
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…what’s the connection?
Volcanoes and Plate Tectonics…
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•Composite Cone
•Cinder Cone
•Shield
Three Types of VolcanoesEach are different because of the way they erupt
or the types of materials they erupt
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Composite Cone*Most explosive eruptions
*built of lava, cinders, and ash.
*The size increases after an eruption.
*Also called strato volcano.
*Serves as a transportation system for magma to rise to the surface from deep
within Earth’s crust.
*Can be so powerful that part of the volcano can be blown away, reshaping the mountain
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Cinder Cone*Formed by lava fragments called cinders
*Has only one vent in which magma can flow
*Lava fragments burst into the air and then fall into the vent of the volcano.
*Have steep sides
*Not as large as composite or shield volcanoes.
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Shield *Look like shields with their gentle sloping
sides
*Slopes are caused by eruptions
Eruptions usually have fluid lava which flows from it.
*Lava flows not only from the top but also from the cracks in the ground.
*Slow to erupt so usually animals and people have enough time to escape.
*Some of the largest volcanoes in the world
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Volcanism is mostly focused at plate margins
Pacific Ring of Fire
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Pacific Ring of Fire
Hotspot volcanoes
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• Hot mantle plumes breaching the surface in the middle of a tectonic plate
What are Hotspot Volcanoes?
Photo: Tom Pfeiffer / www.volcanodiscovery.com
The Hawaiian island chain are examples of hotspot volcanoes.
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The tectonic plate moves over a fixed hotspot forming a chain of volcanoes.
The volcanoes get younger from one end to the other.
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…what’s the connection?
Earthquakes and Plate Tectonics…
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• As with volcanoes, earthquakes are not randomly distributed over the globe
• At the boundaries between plates, friction causes them to stick together. When built up energy causes them to break, earthquakes occur.
Figure showing the distribution of earthquakes around the globe
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Where do earthquakes form?
Figure showing the tectonic setting of earthquakes
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Plate Tectonics Summary• The Earth is made up of 3 main layers (core,
mantle, crust)• On the surface of the Earth are tectonic
plates that slowly move around the globe• Plates are made of crust and upper mantle
(lithosphere)• There are 2 types of plate• There are 3 types of plate boundaries• Volcanoes and Earthquakes are closely
linked to the margins of the tectonic plates