The Structure of the Earth and Plate Tectonics

Structure of the Earth

• The Earth is made up of 3 main layers:– Core– Mantle– Crust

Inner core

Outer core

Mantle

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?

• Divergent

• Convergent

• Transform

Three types of plate boundary

• Spreading ridges– As plates move apart new material is erupted to

fill the gap

Divergent Boundaries

Age of Oceanic Crust

Courtesy of www.ngdc.noaa.gov

• Iceland has a constructive plate boundary running through its middle

Iceland: An example of continental rifting

Collision Boundaries

• Forms mountains, e.g. European Alps, Himalayas

Continent-Continent Collision

Himalayas

• It’s called SUBDUCTION

Destructive Boundaries

• 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

• Where plates slide past each other

Conservative Boundaries

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?

…what’s the connection?

Volcanoes and Plate Tectonics…

Volcanism is mostly focused at plate margins

Pacific Ring of Fire

- Subduction - pulling apart - Hotspots

Volcanoes are formed by:

Pacific Ring of Fire

Hotspot volcanoes

• 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.

The tectonic plate moves over a fixed hotspot forming a chain of volcanoes.

The volcanoes get younger from one end to the other.

…what’s the connection?

Earthquakes and Plate Tectonics…

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

• 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

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)