Aim: How do the plates of the Earth move? Do Now: - What things occur on the surface or just below the surface of our planet that might indicate the crust is moving?
I. Types of Plate Boundaries 1. Divergent boundaries form where two plates move apart.
• Rift valleys are found between the divergent plates. • Oceanic ridges are found on either side of the rift valley.
• Seafloor spreading produces new oceanic crust at divergent plate boundaries
2. Convergent boundaries form where two plates move together. Which type of crust sinks under the other and why? Oceanic crust sinks since it is more dense.
trenches mark the area where subduction zones occur. Subduction zones occur when one plate is forced down into the mantle beneath a second plate, where it melts into magma. trenches mark the area where subduction zones occur. Subduction zone
A. Oceanic Crust vs. Continental Crust Oceanic crust sinks below the continental crust. • Continental volcanic arcs form from the rising magma. (example: Andes Mountains)
B. Oceanic Crust – Oceanic Crust One of the two plates sinks under the other. • Volcanic island arcs form as volcanoes under-sea grow and reach the surface (example: Aleutian Islands)
B. Continental Crust – Continental Crust • The two continents collide and are forced upward. • Mountain ranges form from the uplift of these continents (example: Himalayan Mountains)
3. Transform fault boundaries form where two plates grind/slide past each other. They move parallel
Faults and fractures - cuts and cracks. - commonly found near ocean ridges.
San Andreas fault in California is an example of a transform boundary
II. Causes of Plate Motion Convection currents within the mantle are the driving force of plate movements.
Convective flow is the motion of matter resulting from changes in temperature.
Ridge Push Slab Pull Convection currents push the plates along the mantle. Convection currents pull the plates into the mantle
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