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How Do Earths Plates Move? Chapter 1, Section 2, pD14-19.

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Presentation on theme: "How Do Earths Plates Move? Chapter 1, Section 2, pD14-19."— Presentation transcript:

1 How Do Earths Plates Move? Chapter 1, Section 2, pD14-19

2 The Movement of Earths Plates Lithospheric plates float on asthenosphere – Interact with other plates as they move Divergent boundary: plates move away from each other Convergent boundary: plates collide Transform-fault boundary: plates grind past each other – Plate movements have produced most of the worlds: Volcanoes Earthquakes High mountain ranges Deep-ocean trenches – Can occur along plate boundaries or old plate boundaries

3 Divergent Boundary Hypothesis: divergent boundaries caused by: – Magma pushed upwards under a plate – Magma melts, stretches, and cracks the plate – Magma oozes into the gap – Magma cools forming new crust If pressure is great enough – magma erupts as volcano

4 Divergent Boundary Most divergent boundaries: – Mid-ocean ridge: chain of mountains that run through all the worlds oceans Rift: a deep valley – Forms where plates move apart Sea-floor spreading: process where magma is slowly pushed up through cracks in a rift and cools to form new sea floor – Rocks on each side of the rift are slowly pushed away – Atlantic Ocean formed this way over last 165 million years

5 Divergent Boundary Some divergent boundaries occur within continents – East African Rift (Great Rift Valley) Small plates moving away from African plate One day east Africa will split from the rest of Africa Started millions of years ago – Crust stretched thin by spreading plates – Two cracks opened up in crust – Floor of the rift valley dropped hundreds of feet – Cliffs and volcanoes on both sides of the valley today

6 Convergent Boundary Old crust melts at convergent boundaries where plates collide – Balance the new crust being formed at divergent boundaries – Earths size is not changing

7 Convergent Boundaries Two oceanic plates collide – One plate is pushed under the other (subduction) Subducting plate melts in asthenosphere Volcanic islands form above the melting plate Collision causes deep-ocean trench to form – Deepest trench on Earth – Mariana trench

8 Convergent Boundaries Two continental plates collide – Plates crumple and fold forming mountains Produced some of worlds highest mountain ranges – Himalayas » India crashing into Asia » Himalayan peaks are still rising 5 cm a year

9 Convergent Boundaries Oceanic plate collides with continental plate – Oceanic plate subducts under continental plate Oceanic plate more dense Oceanic plate melts in asthenosphere – Mountains and volcanoes form along boundary Andes mountains

10 Convergent Boundaries Destruction of plates causes a lot of activity along convergent boundaries – 80% worlds volcanoes – 90% worlds earthquakes Mt. St. Helens volcano in Washington state – Sometimes violent activity continues at old convergent boundaries

11 Transform Fault Boundaries Two plates move past each other in opposite directions at transform boundary – Most occur in oceanic crust – A few are within continents San Andres fault – Pacific plate moving past North American plate – Part of California may be an island if movement continues for millions of years

12 Transform Boundaries Earthquakes are common along transform fault boundary – San Andres fault has many earthquakes Volcanoes & mountains usually dont form here

13 Earths Surface Changes Over Time Earths plates move – Carry continents and oceans with them Continents and oceans were in different places in past They will continue to move to other places in the future – Rocks, volcanoes, and earthquake patterns Help form hypothesis of how Earths surface changed over past 500 million years

14 Earths Surface Changes Over Time Ancient continents separated & then collided again in different locations – North American & African plates collided 225 mya Formed supercontinent Pangaea Collision formed southern Appalachian mountains – Might have been taller than Himalayas

15 Earths Surface Changes Over Time Movement of continents cause oceans to disappear and new oceans to open – South American & African plates split apart Formed South Atlantic ocean 135 mya

16 Summary Earths plates interact in different ways: – Plates move away at divergent boundaries – Plates collide at convergent boundaries – Plates grind past others at transform boundaries The movement of plates cause Earths continents to: – Move apart – Move together – Slide past one another

17 HomeworK Read Section 2, pD14-19 Answer ?s on Google form or WS

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