10/29/13. Plate Boundaries. 3 types of plate boundaries: Divergent (divide) Convergent (collide) Transform (slide past)

Transcription

1 Plate Boundaries 3 types of plate boundaries: Divergent (divide) Convergent (collide) Transform (slide past) 1

2 Remember the plates are in motion. When plates move, they can either: A) converge (collide) B) pull apart (divide) C) slide along past one another Either way, changes will occur along the boundaries of the plates. #1) Divergent Boundaries Are boundaries between two plates that are moving apart (dividing) or rifting RIFTING causes SEAFLOOR SPREADING 2

3 Divergent Boundaries.. Most occur at the mid-ocean ridges Divergent boundaries that occur on land are called rift valleys (ex: Great Rift valley in Africa) What is a rift valley? How are rift valleys formed? A rift valley is a deep valley that forms along a divergent boundary on land Rift valleys form as two slabs of Earth s crust slide apart 3

4 What could eventually happen at the Great Rift Valley in Africa? The rift may someday split the eastern part of Africa away from the rest of the continent Divergent boundaries also cause volcanic fissures!!! This is a vent through which lava erupts, but there is usually no explosive activity. Volcanic fissures 4

5 #2) Convergent Boundaries Boundaries between two plates that are colliding There are 3 types Convergent Boundaries A plate boundary where two plates move toward each other Collisions can occur between: oceanic crust and oceanic crust oceanic crust and continental crust continental crust and continental crust 5

6 When two plates collide, the of the plates determines which one comes out on the top. density Ocean plate colliding with a less dense continental plate And meet at a Subduction Zone: (where the more dense plate slides under the less dense plate) VOLCANOES occur at subduction zones Type 1 6

7 How do these volcanoes form? High temperature from the magma causes the rocks to melt along the subduction slab as it goes under the other plate. Magma seeps up along the plate boundary forming volcanoes. Ex: St. Andes mtns along the Nazca plate and S. American plate boundary: When one oceanic plate collides with another oceanic plate, the more dense plate slides under the less dense plate creating a subduction zone called a TRENCH Type 2 7

8 A continental plate colliding with another continental plate Have Collision Zones: a place where mountains will form Type 3 Continental/Continental cont d Because the plates are less dense than the material in the asthensosphere, the two plates collide and crumble up forming mountain ranges. There is little or no subduction here, so volcanoes do not form. 8

9 Result of the Eurasian and the Indian-Australian Plates Colliding The Himalayas Where are the Himalayas? 9

10 Quick Check #1: What occurs when plates carrying oceanic crust collide? The more dense plate dives back into the mantle (subduction) The collision between oceanic plates causes deep-ocean trenches #2 What occurs when plates carrying oceanic and continental crust collide? The more dense oceanic crust sinks and plunges (subducts) beneath the less dense continental crust The collision between oceanic plates and continental plates can cause a volcanic eruption 10

11 #3 What occurs when plates carrying continental crust collide? Plates crash head-on causing mighty mountain ranges. #3) Transform Fault Boundaries Boundary between two plates that are sliding past each other Crust is neither created nor destroyed 11

12 What is a Fault? Is a break in the Earth s crust where slabs of rock slip past each other Ex: San Andreas Fault where many Earthquakes occur: What Earth-changing event occurs on a transform boundary? Earthquakes frequently occur at transform boundaries 12

13 Video Review of plate tectonics and boundaries.. Watch lesson one of the video review from the link below. Be prepared to answer questions after the video!!! Video clip : Lesson 1 "Plate Tectonics" Review Questions... What are the three types of boundaries? What direction do the plates go for each type? Which boundary has a subduction zone what occurs at a subduction zone? 13

14 So What Causes Plate Tectonics? (The continent s slow dance) Convection Currents Hot magma in the Earth moves toward the surface, cools, then sinks again. Creates convection currents beneath the plates that cause the plates to move. 14

15 What causes plates to move? Because there is an unequal distribution of heat, hot plastic-like rock is forced to the top of the surface where it will cool, thicken (denser), and sink. It s the transfer of heat inside the Earth that provides the energy to move the plates and causes many of our surface features to form. Plates move at a rate of between and centimeters per year. one ten 15

16 The North American and Eurasian plates float away from each other at a rate of fingernail growth. This is a rate of per year. 2.5 centimeters Figure 29: Posing Questions What questions would you need to answer in order to predict where the continents will be in 50 million years? You would need answers to how fast and in what direction each plate is moving 16

17 Review Questions... What causes plates to move? How is a convection current formed? How do we know the plates are really moving? 1) We can feel it in the form of seismic waves from earthquakes!! 2) We can see it as volcanoes erupt! 3) We can see it from how our land changes from the volcanoes and earthquakes!!! 17

18 Bellwork 10/31/13 Retake this pre-test and see how much you have learned!! If you change an answer, rewrite it BESIDE your original answer. Practice Unscramble the following words: - gneivdret - boundary where two plates pull apart - areinmls - a non-living, inorganic solid - sarfmrotn - where plates slide past each other; earthquakes occur - utalf - a break in the Earth s crust 18