Download presentation
Presentation is loading. Please wait.
1
How Do Earth’s Plates Move?
Chapter 1, Section 2, pD14-19
2
The Movement of Earth’s 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 world’s: 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 world’s 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 Earth’s 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 world’s 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% world’s volcanoes 90% world’s 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 don’t form here
13
Earth’s Surface Changes Over Time
Earth’s 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 Earth’s surface changed over past 500 million years
14
Earth’s 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
Earth’s 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 Earth’s 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 Earth’s continents to: Move apart Move together Slide past one another
17
HomeworK Read Section 2, pD14-19 Answer ?s on Google form or WS
Similar presentations
