Plate Tectonics Plate Boundaries Causes of Plate Tectonics

 The Earth’s crust and rigid upper mantle are broken into sections called plates  Plates move around on top of the asthenosphere like ships

 The crust and rigid part of the upper mantle = lithosphere  100 km thick  Less dense than the material below it so it “floats”

 The plastic-like layer below the lithosphere = asthenosphere  The plates of the lithosphere float on the asthenosphere

 Ocean plates - plates below the oceans – denser basalt  Continental plates - plates below the continents

 What is the theory of plate tectonics?  What is the lithosphere?  What is the asthenosphere?  What is the connection between the two?  What are the two types of plates?

 Boundary between two plates that are moving apart or rifting    RIFTING causes SEAFLOOR SPREADING

 Mid-ocean ridges  Rift valleys  Fissure volcanoes

Lava Fountains, Krafla Volcano Thingvellir Fissure Zone, Iceland

Erte Ale Summit Crater, Ethiopia Oldoinyo Lengai, East African Rift ZoneOldoinyo Lengai, East African Rift Zone [

 Map of East Africa showing some of the historically active volcanoes(red triangles) and the Afar Triangle (shaded, center) - - a so-called triple junction (or triple point ), where three plates are pulling away from one another: the Arabian Plate, and the two parts of the African Plate (the Nubian and the Somalian) splitting along the East African Rift Zone. USGS website

 This image shows several fault scarps that are progressively farther away. Essentially we are looking at the edges of several horst (risen) blocks from within a graben (valley) that contains Lake Baringo.

 Boundaries between two plates that are colliding    There are 3 types…

 Ocean plate colliding with a less dense continental plate  Subduction Zone: where the more dense plate slides under the less dense plate  VOLCANOES occur at subduction zones; trenches

Subduction Zone Subduction – Process by which the ocean floor sinks beneath a deep- ocean trench and back into the mantle; allows part of the ocean floor to sink back into the mantle

Subduction Zone Deep-Ocean Trench – Occurs at subduction zones. Deep underwater canyons form where oceanic crust bends downward

Subduction Zone

 Ocean plate colliding with another ocean plate  The more dense plate slides under the less dense plate creating a subduction zone called a TRENCH

Map of Alaska

 A continental plate colliding with another continental plate  Have Collision Zones:  a place where folded and thrust faulted mountains form.

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 Boundary between two plates that are sliding past each other  EARTHQUAKES along faults

 What are the three types of boundaries?  What direction do plates go for each?  Which boundary has a subduction zone…what occurs at a subduction zone?

 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.

 Slab pull - Cold, sinking lithosphere at the edges of a tectonic plate pulls the rest of the plate across earth’s surface.  Ridge push – Gravity pulls newly formed lithosphere downward and away from the mid-ocean ridge. The rest of the plate moves because of this force.

 click here for interactive map click here for interactive map  BBC video click here BBC video click here  Japan’s Tsunami  click here click here

 What causes plates to move?  How is a convection current formed?  Explain slab pull  Explain ridge push