The Structure of the Earth and Plate Tectonics
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Transcript of The Structure of the Earth and Plate Tectonics
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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 what we live on!• The crust has 2 types:
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 constructive plate boundary running through its middle
Iceland: An example of continental rifting
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Collision Boundaries
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• Forms mountains, e.g. European Alps, Himalayas
Continent-Continent Collision
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Himalayas
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• It’s called SUBDUCTION
Destructive Boundaries
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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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• Where plates slide past each other
Conservative 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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Volcanism is mostly focused at plate margins
Pacific Ring of Fire
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- Subduction - pulling apart - Hotspots
Volcanoes are formed by:
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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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Size DATE-TIMEy/m/d h:m:s LATdeg LONdeg DEPTHkm Region
1 2.8 2011/10/02 17:48:59 19.415N -156.343W 12.4 HAWAII REGION, HAWAII
2 5.2 2011/10/02 16:49:04 37.392N 141.441E 18.5 EAST COAST OF HONSHU, JAPAN
3 3.7 2011/10/02 16:13:03 61.610N -151.936W 92.9 SOUTHERN ALASKA
4 3.2 2011/10/02 16:12:29 62.148N -151.256W 82.5 CENTRAL ALASKA
5 5.3 2011/10/02 14:57:00 1.356N 126.220E 40.1 MOLUCCA SEA
6 4.8 2011/10/02 14:39:13 1.458N 126.314E 46.9 MOLUCCA SEA
7 3.6 2011/10/02 13:39:45 18.951N -65.722W 133.0 PUERTO RICO REGION
8 5.1 2011/10/02 13:30:13 38.447N 144.445E 24.3 EAST COAST OF HONSHU, JAPAN
9 4.7 2011/10/02 11:43:00 56.023N 162.499E 43.7 EAST OF KAMCHATKA, RUSSIA
10 2.5 2011/10/02 11:06:09 37.641N -119.416W 0.2 CENTRAL CALIFORNIA
11 5.0 2011/10/02 09:19:25 8.385N 126.723E 46.9 MINDANAO, PHILIPPINES
12 4.7 2011/10/02 06:37:40 -33.034S -178.751W 35.0 SOUTH OF THE KERMADEC ISLANDS
13 2.8 2011/10/02 04:03:05 18.850N -67.343W 14.5 PUERTO RICO REGION
14 3.6 2011/10/02 03:53:38 51.710N -171.584W 33.2 FOX ISLANDS, ALASKA
15 4.5 2011/10/02 03:36:04 51.495N -179.369W 59.6 ANDREANOF ISLANDS, ALASKA
16 3.2 2011/10/02 01:23:51 19.452N -65.814W 30.7 PUERTO RICO REGION
17 3.5 2011/10/02 01:05:15 18.277N -68.019W 105.0 DOMINICAN REPUBLIC
18 4.8 2011/10/02 00:25:20 -38.959S -17.409W 10.0 SOUTHERN MID-ATLANTIC RIDGE
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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 4 types of plate boundaries• Volcanoes and Earthquakes are closely
linked to the margins of the tectonic plates
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Monday 10th October
• Glossary to finish
• Homework due in today (some did it during lesson)
• Look at the assessment (going to do it P2 Tuesday)
• Compare the way rich and poor countries react toEQs
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Extra Glossary words
• Shield volcano – is a volcano made of BASIC lava (like the ones in Hawaii) the sides gently slope as the lava is runny like custard
• Composite – a volcano made of alternate layers of lava and ash – looks like a triangle (classic volcano shape)