Plate TectonicsPlate Tectonics

Objectives Objectives

• Describe and draw the internal Describe and draw the internal workings of the earthworkings of the earth

• Explain the structure of the earth’s Explain the structure of the earth’s crustcrust

• Describe and explain the tectonic cycleDescribe and explain the tectonic cycle

• Explain the theory of plate tectonicsExplain the theory of plate tectonics

• Understand the formation of landforms Understand the formation of landforms (features) associated with plate (features) associated with plate margins. margins.

The Earth KeywordsThe Earth Keywords• Crust

• Mantle

• Lithosphere

• Asthenosphere

• Outer core

• Inner core

KEYWORDS STRUCTURE OF KEYWORDS STRUCTURE OF THE EARTH THE EARTH

• CrustCrust – outer part of the earth. Very thin – outer part of the earth. Very thin

• MantleMantle – middle part of the earth semi – middle part of the earth semi molten rock. Moves plates by molten rock. Moves plates by convection currents.convection currents.

• LithosphereLithosphere- marks change from crust - marks change from crust to mantle (very thin)to mantle (very thin)

• AsthenosphereAsthenosphere – piece of the mantle – piece of the mantle nearest the crust. nearest the crust.

• Outer core Outer core – iron and nickel (liquid)– iron and nickel (liquid)

• Inner core Inner core – iron and nickel (solid)– iron and nickel (solid)

Structure of the EarthStructure of the Earth

Internal Structure of EarthInternal Structure of Earth

• Crust – solid rock, aka lithosphere, 3-10km Crust – solid rock, aka lithosphere, 3-10km thick under ocean, 70km thick under thick under ocean, 70km thick under continentscontinents

• Mantle – semi-molten rock (magma), aka Mantle – semi-molten rock (magma), aka asthenosphere, convection currents cause asthenosphere, convection currents cause plate movementsplate movements

• Outer core – molten rock mainly consisting of Outer core – molten rock mainly consisting of ironiron

• Inner core – up to 5000Inner core – up to 5000°C, solid nickel & ironl. °C, solid nickel & ironl.

The Earth’ s CrustThe Earth’ s Crust

• What do you know about the earth’s What do you know about the earth’s crust from Junior Cert??crust from Junior Cert??

The Earth’s Crust KeywordsThe Earth’s Crust Keywords

• Oceanic Crust Oceanic Crust

• Continental CrustContinental Crust

• Plates Plates – When the crust is broken up – When the crust is broken up and splits into large pieces of rock. and splits into large pieces of rock.

• Plate Tectonics Plate Tectonics – The study of plates, – The study of plates, their movements and the landforms their movements and the landforms that are created. that are created.

• Tectonic cycle Tectonic cycle – when plates collide – when plates collide and separate. and separate.

Plate tectonics keywords Plate tectonics keywords • WegnerWegner

• PangaeaPangaea – name given to the earth. – name given to the earth. One large area of land. One large area of land.

• Continental Drift Continental Drift – the moving of – the moving of plates, land and oceans. plates, land and oceans.

• Sea Floor Spreading Sea Floor Spreading – new crust – new crust being created.being created.

• HessHess

Theory of Plate Tectonics – Theory of Plate Tectonics – Continental DriftContinental Drift

• Alfred Wegener (1912) – single land Alfred Wegener (1912) – single land mass called Pangaea, broke to form mass called Pangaea, broke to form todays continentstodays continents

• Theory backed by similar rocks & Theory backed by similar rocks & fossils found in Brazil and west Africafossils found in Brazil and west Africa

• However, Wegener could not explain However, Wegener could not explain how the continents moved aparthow the continents moved apart

Theory of Plate Tectonics – Sea Theory of Plate Tectonics – Sea Floor SpreadingFloor Spreading

• Harry Hess (1960s) studied the age Harry Hess (1960s) studied the age of rocks in the Atlantic Oceanof rocks in the Atlantic Ocean

• The newest rocks were found nearest The newest rocks were found nearest the Mid-Atlantic Ridge, while the the Mid-Atlantic Ridge, while the oldest were found closer to the US oldest were found closer to the US coastcoast

• Theory states that the sea floor is Theory states that the sea floor is constantly expanding as new magma constantly expanding as new magma forces its way up between the platesforces its way up between the plates

Tectonic CycleTectonic Cycle

• Crustal plates move due to convection currents in Crustal plates move due to convection currents in the mantlethe mantle

• These currents are powered by the Earth’s core, These currents are powered by the Earth’s core, causing magma to heat, rise, cool and sink in a causing magma to heat, rise, cool and sink in a circular motioncircular motion

• This movement pulls the plates apart This movement pulls the plates apart (diverging/separating) or together (diverging/separating) or together (converging/colliding)(converging/colliding)

• New crust is created where plates separateNew crust is created where plates separate• When plates collide, the front of the heavier plate When plates collide, the front of the heavier plate

gets dragged underneath the lighter plate due to gets dragged underneath the lighter plate due to gravity – this is known as SUBDUCTIONgravity – this is known as SUBDUCTION

Video Clips

•http://www.youtube.com/watch?v=QDqskltCixA&sns=em

•http://www.youtube.com/watch?v=QDqskltCixA&sns=em

•Continental Drifthttp://www.youtube.com/watch?v=GYVS_Yh6dTk&feature=fvwrel

PLATE BOUNDARIES PLATE BOUNDARIES KEYWORDS KEYWORDS

•Destructive Plate Boundary (Convergent)

•Constructive Plate Boundary (Divergent)

•Conservative (transverse or transform) plate boundary

Plate BoundariesThere are three types of plate

boundaries. 1. Destructive/convergent (land

destroyed)2. Constructive/divergent (land

created)3. Conservative/transform (land is not

destroyed or created)

1. Destructive Plate BoundariesPlates move together and collide

destroyingthe crust. This happens in 3 situations. 1. Between oceanic and continental

plates2. Between two oceanic plates3. Between two continental plates

Oceanic – Continental Plate Collision= Subduction zones

• Subduction occurs

• The melted crust turns to magma and moves up through the continental crust to create some of the most explosive volcanoes in the world e.g Mount St. Helen in the USA

• Where the two colliding plates meet a deep trench is created. (trenches mark all subduction zones).

• The Pacific Ring of Fire is so named because many active volcanoes are created at subduction zones mark the edge of the Pacific plate. Eg. Mount Fuji.

Oceanic – oceanic plate collision = trenches and island

arcs• When two oceanic plates collide one is usually subducted beneath the other. When one plate goes beneath the other deep trenches form. These are the deepest part of the ocean.

• Marked by curved zones of volcanic islands known as island arcs. These volcanoes form when the subducted plate descends and melts, creating rising bubbles of magma that break through the crust above.

• These active volcanoes have built up on the sea floor over millions of years until they appear above the surface of the water. E.g Japanese islands.

Continental – ContinentalFold Mountain

• When 2 continental plates collide fold mountains are created.

• Himalayas and the Alps.

• Fold mountians are often composed of sedimentary rocks such as limstone that formed beneath the sea.

• When two continental plates collide subduction does not occur . Colliding continental plates tend to move upwards or sideways, this can sometimes cause devasting earthquakes e.g Pakistan 2005.

Activity

•Draw a diagram of a destructive plate boundary

2. Constructive (divergent) plate boundaries = mid ocean ridges• These occur where plates are pulled apart by the convection currents below.

• As the crust splits, a rift valley is formed allowing magma to rise and fill the gap creating new crust. Shallow earthquakes and volcanoes also occur e.g. Iceland 2010.

• As magma becomes solid it forces the plates apart even further allowing more magma to rise.

• Over millions of years the ocean floors have been created this way. (Sea floor spreading)

• Eg. Mid Atlantic Ridge. The crust is moving about 5cm per year. 25km per million years.

• E.g. Sea floor spreading in Iceland. Iceland formed where the mid atlantic ridge appears above the sea. Iceland is getting wider due to the process of sea floor spreading. It has over 200 active and dormant volcanoes.

Activity

•Draw the diagram of a constructive plate boundary

3. Conservative (transform or transverse) = fault lines

• Where two plates slide past each other.

• These boundaries are marked by fault lines. They are thousands of kilometers long and up to 8km deep. E.g San Andreas Fault in California. (1,300km long).

• At this fault the Pacific plate and the North American fault are both moving in a north west direction.

• The Pacific plate is moving at a faster pace (5cm per year) this is

not smooth and the plate may stick .

• This leads to a build up of pressure between the two plates until they suddenly go past each other causing an earthquake.

• In the 1906 San Francisco earthquake the Pacific plate moved over 6m in one minute.

• The Haiti 2010 earthquake occurred on a transform boundary between the Caribbean and North American plate.

Activity

•Draw the diagram of a conservative boundary.

Tectonic Activity in the middle of plates = hotspots

• Volcanoes can be found thousands of miles from the edges of plates.

• Occur where high temps in the mantle produce a rising fountain (plume) of a molten rock known as a hotspot.

• Hotspots are extremely hot areas deep in the upper mantle (asthenosphere). The magma rises up and pushes through the plate above. This creates a volcanoe. E.g Hawaiian Islands

The Hawaiian Islands •A chain of volcanic islands in the middle of

the Pacific plate located over 3,200km from the nearest plate boundary.

•As the pacific plate moves over the hotspot volcanoes grow, become dormant and eventually become extinct.

•Hawaiian hotspot is about 500 – 600km wide and approx 86million years old.

Summary Video

•http://www.youtube.com/watch?v=KCSJNBMOjJs&sns=em

55 mins long.