8.4 Plates converge or scrape past each other

Learning Goals Students will: -describe what happens when two continental plates converge. -identify what happens when an oceanic plate converges with another plate. -identify what happens when one plate scrapes past another.

3-Minute Warm-Up Write all the statements. If they are not true, correct them. 1.At a divergent boundary, tectonic plates collide. 2.Rift valleys form at divergent boundaries in the ocean and on land. 3.Divergent boundaries in the ocean are also called spreading centers.

3-Minute Warm-Up Decide if these statements are true. If not, correct them. 1.At a divergent boundary, tectonic plates collide. False-At a divergent boundary, tectonic plates move apart. 2.Rift valleys form at divergent boundaries in the ocean and on land. true 3.Divergent boundaries in the ocean are also called spreading centers. true

Tectonic plates push together at convergent boundaries At convergent boundaries crust is either folded or destroyed subduction—the process by which an oceanic tectonic plate sinks under another plate into Earth’s mantle 3 types of convergent boundaries: –Continental-continental collision –Oceanic-oceanic subduction –Oceanic-continental subduction

Continental-continental collision (land and land) continental-continental collision—occurs where two plates carrying continental crust push together Because both crusts are the same density, neither plate can sink beneath the other Their edges crumple and fold Sometimes the folds can be pushed up and form mountains M1GTect/dContCollisionMovies/IndiaAsia Collision.mov

Oceanic-oceanic subduction (ocean and ocean) oceanic-oceanic subduction—occurs where one plate with oceanic crust sinks under another plate with oceanic crust When oceanic crusts meet, the older crust sinks because it is colder and denser than the younger crust The older crust sinks into the asthenosphere Two landforms that occur: –Deep-ocean trenches—deep canyons that form in the ocean floor as a plate sinks –Island arcs—chains of volcanic islands that form on the top plate, parallel to the deep-ocean trench (ex: Japan and Philippine Islands)

Oceanic-continental subduction (ocean and land) oceanic-continental subduction—occurs when oceanic crust sinks under continental crust Oceanic crust sinks because it is denser Two landforms occur: –Deep-ocean trenches-deep canyons. As the oceanic crust moves, it often causes underwater earthquakes –Coastal mountains—they form parallel to the coast and sometimes these mountains are volcanoes

nloads/M1GTect/cSubductionMo vie/Subduction.mov

Tectonic plates scrape past each other at transform boundaries Tectonic plates scrape past each other at transform boundaries At a transform boundary, crust is neither formed or destroyed. They move past each other in opposite directions. In California, where we live, there is part of a transform boundary called the San Andreas fault

The theory of plate tectonics helps geologists today By studying the rocks, geologists can uncover the history of any region This helps scientists predict what will happen along plate boundaries –Earthquakes along transform boundaries –Volcanic activity near subduction areas

Questions Draw and label the 3 types of convergent boundaries. (6 pts.) What are deep-ocean trenches? (1 pt.) What are island arcs? (1 pt.) Explain how coastal mountains are formed (2 pts.) What makes the San Andreas Fault a transform boundary? (1 pt.) Why is the theory of plate tectonics so important to geologists? (1 pt.)