Earthquakes & Plate Tectonics

Pangaea An ancient supercontinent that scientists believe existed from about 200 to 300 million years ago.

How is this possible?!?!? Geological Changes—3:25

Continental Drift Alfred Wegener was the 1st scientist to come up with the idea of “continental drift” His idea was that the continents slowly moved away from each other. This supercontinent was called Pangaea.

Continental Drift Evidence Minerals, fossils, and mountains, on now different continents, match if the continents were together The Mystery of Brachiosaurus (~3 min)

Plate Tectonics Theory The lithosphere is divided into a number of large and small plates and the plates are floating on the mantle.

Lithosphere = the Earth’s crust plus the upper portion of the mantle layer

Plate Boundaries

Plate Boundaries Divergent boundary: Plates are moving away from each other Mid-ocean ridges are created and new ocean floor plates are created called Seafloor Spreading

Seafloor Spreading Theory: Ocean floors are moving like broad conveyor belts Forms new crust through the upwelling of magma

Plate Boundaries Divergent boundary:

Convergent Boundary: plates are moving toward each other and are colliding (3 types)

Convergent Boundaries Create: Subduction zone-Places where plates are moving toward each other and one plate melts under the other and the magma moves upward to form volcanoes.

1. When Ocean Plates collide with Continental Plates Create subduction zones, Trenches Create near coast volcanoes Example: Cascade Mountains

2. When Ocean plates collide with other Ocean plates Island arcs are created (a pattern of volcanic islands created from a subduction zone that is located off the coast) Example: Japan and Philippines

3. When a Continental plate collides with another Continental plate Mountain ranges are created (example: Himalayan Mountains)

What About Hawaii? Do you see any plate boundaries there? Hawaii

What About Hawaii? Hawaiian Volcanoes form from HOT SPOTS Hot spots are places where the mantle is unusually hotter than other parts of the mantle or an unusually weak (thin) part of the crust…(we’re not sure why)

Hot Spots Magma that may originate in the mantle or outer core will move upward, breaking the surface and forming a volcano, they are independent of plate boundaries and a chain of volcanoes may form as the plate moves across a hot spot.

Hot Spots (Examples: Hawaiian Islands and Yellowstone National Park)

Transform Fault Boundary Plates are neither moving toward nor away from each other, they are moving past one another.

Transform Fault Boundary The plates may move in opposite directions or in the same directions but at different rates and frequent earthquakes are created (example: San Andreas Fault)

San Andreas Fault

Why is Earth not getting bigger or smaller? NOTE: Plates are destroyed as fast as they are created (2 ways) Plates may be subducted and melted or may push be pushed upward to form mountains

Convection Currents Convection currents occur within the mantle The up-welling leg of the current creates a divergent boundary which produces midocean ridges

Convection Currents

Seafloor Spreading The down-welling leg of the current creates one type of convergent boundary that results in trenches and a subduction zone