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The Structure of the Earth and
Plate Tectonics
Structure of the Earth
Mantle
• The Earth is
made up of 3
main layers:
Outer core
Inner core
– Core
– Mantle
– Crust
Crust
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
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
What is Plate Tectonics?
• 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.
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.
World Plates
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.
What lies beneath the tectonic plates?
• Below the
lithosphere
(which makes
up the tectonic
plates) is the
asthenosphere.
Plate Movement
• “Plates” of lithosphere are moved around by
the underlying hot mantle convection cells
Practical Exercise 1
Supercontinents!
What happens at tectonic
plate boundaries?
Three types of plate boundary
• Divergent
• Convergent
• Transform
Divergent Boundaries
• Spreading ridges
– As plates move apart new material is erupted to
fill the gap
Age of Oceanic Crust
Courtesy of www.ngdc.noaa.gov
Iceland: An example of continental rifting
• Iceland has a constructive
plate boundary running
through its middle
Collision Boundaries
Continent-Continent Collision
• Forms mountains, e.g. European Alps, Himalayas
Himalayas
Destructive Boundaries
• It’s called SUBDUCTION
Subduction
• Oceanic lithosphere
subducts underneath the
continental lithosphere
• Oceanic lithosphere heats
and dehydrates as it
subsides
• The melt rises forming
volcanism
• E.g. The Andes
Conservative Boundaries
• Where plates slide past each other
Above: View of the San Andreas
transform fault
Practical Exercise 2
Where will the UK be in:
1,000 years?
1,000,000 years?
1,000,000,000 years?
Volcanoes and Plate
Tectonics…
…what’s the connection?
Pacific Ring of Fire
Volcanism is
mostly
focused at
plate
margins
Volcanoes are formed by:
- Subduction - pulling apart - Hotspots
Pacific Ring of Fire
Hotspot
volcanoes
What are Hotspot Volcanoes?
• Hot mantle plumes breaching the
surface in the middle of a tectonic plate
The Hawaiian island chain are
examples of hotspot volcanoes.
Photo: Tom Pfeiffer / www.volcanodiscovery.com
The tectonic plate moves over a fixed hotspot
forming a chain of volcanoes.
The volcanoes get younger from one end to the other.
Earthquakes and Plate
Tectonics…
…what’s the connection?
Size
DATE-TIME
y/m/d h:m:s
LAT
deg
LON
deg
DEPTH
km
1
2.8
2011/10/02 17:48:59
19.415N
-156.343W
2
5.2
2011/10/02 16:49:04
37.392N
141.441E
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
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
11
5.0
2011/10/02 09:19:25
8.385N
126.723E
12
4.7
2011/10/02 06:37:40
-33.034S
-178.751W
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
Region
12.4 HAWAII REGION, HAWAII
18.5 EAST COAST OF HONSHU, JAPAN
133.0 PUERTO RICO REGION
0.2 CENTRAL CALIFORNIA
46.9 MINDANAO, PHILIPPINES
35.0 SOUTH OF THE KERMADEC ISLANDS
10.0 SOUTHERN MID-ATLANTIC RIDGE
• As with volcanoes, earthquakes are not
randomly distributed over the globe
Figure showing
the distribution of
earthquakes
around the globe
• At the boundaries between plates, friction
causes them to stick together. When built up
energy causes them to break, earthquakes
occur.
Where do earthquakes form?
Figure showing the tectonic setting of earthquakes
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
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
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)