Plate Tectonics The lithosphere (crust and upper part of mantle) is broken into 15 pieces called tectonic plates! The places where the tectonic plates meet each other are called plate boundaries!
CRUST!!!!! CONTINENTAL CRUST OCEANIC CRUST Underlies oceans Thinner than continental crust Denser • Underlies the land • Thicker than oceanic crust • Less dense
Why do Plates Move? Scientists now know that the plates move because of Convection Currents in the mantle which push the plates.
Well how exactly do convection currents work in the mantle?? Basically the asthenosphere (which is the layer below the lithosphere) has plasticity. Plasticity is the ability for the weak solid to flow like a liquid.
All this plate movement creates three types of plate boundaries. Divergent Boundaries 2. Convergent Boundaries 3. Transform Boundaries
Divergent Boundary • Also called a spreading boundary because the plates are moving apart • When the plates separate, magma is forced up through the crack, which creates new land as it cools. MAGMA RISING NEW LAND FORMED PLATES MOVING APART
Divergent Boundaries • Since divergent boundaries create new land, they are called constructive boundaries. Volcanoes are formed along divergent boundaries!
Sea Floor Spreading • Two oceanic plates are separating • In the ocean, magma rises from below, cools, and creates new sea floor. • Ocean floor is continuously being added and also being moved. It is like a conveyor belt.
Sea Floor Spreading YOUNGEST CRUST OLDEST CRUST
Mid-Oceanic Ridges Underwater mountains formed along divergent boundaries when magma cools
Rift Valley • Two continental plates separating • Great Rift Valley on the continent of Africa. The Arabian Plate is pulling away from the AfricanPlate
Divergent Boundaries are associated with…….. • Volcanoes • Sea floor spreading • Mid-oceanic ridges • Rift valleys
Convergent Boundaries • Also called a colliding boundary because the plates are moving towards each other. • Also called destructive boundary because land is destroyed here • Three types of convergent boundaries • Oceanic-oceanic • Oceanic-continental • Continental-continental
Oceanic- Oceanic Convergent One of the plates will be forced underneath the other plate, creating trenches and volcanos.
Oceanic- Continental Convergence The denser oceanic crust will be subducted underneath the lighter continental crust, creating a trench and volcanoes.
Subduction • Occurs when one plate that is denser meets a lighter plate. • The denser plate is forced underneath and destroyed in the asthenosphere • Creates trenches and volcanoes
Oceanic- Oceanic BoundariesandOceanic- Continental Boundariesare associated with… Subduction Volcanoes Earthquakes Trenches
TRENCH VOLCANOES SUBDUCTION
Continental- Continental Two continental plates meet, begin to buckle and build mountain ranges
Transform Boundaries The plates slide past each other in opposite direction and are called fractures. Transform Boundaries are associated with earthquakes and volcanoes. Crust is neither lost nor destroyed.
San Andreas Fault Two major Earthquakes during the last century: • 1906 Earthquake destroyed the city. • 1989 Loma Prieta Earthquake was captured on television because the World Series baseball game was about to start.