Plate TectonicsChapter 9.2 – 9.3

Plate Tectonics• Proposed in 1965 by Tuzo Wilson = combination of

Wegener & Hess’s ideas.

• Convection Currents move the lithospheric plates causing geologic activity – (mountain building, volcanic eruptions and earthquakes)

Convection Currents

Upper Mantle - COOLER

Lower Mantle - HOTTER

The magma in the lower mantle is warmer. It expands, becomes less dense and rises.When it reaches the upper mantle it cools, contracts, becoming more dense and sinks.This constant rise and fall of magma causes the convection currents that drive plate tectonics.The crust plates ride along on top of these convection currents.

Earth Layers1. Lithosphere: the

ridged crust and upper part of the mantle.- Cool, hard and solid- Breaks very easily

2. Asthenosphere: the lower mantle– Hot and plastic-like– Flows easily

• The lithosphere is broken up into 7 large plates and 20 smaller plates

• The plates have boundaries

• As they move they affect one another.

Convergent Boundary Divergent Boundary

Transform Boundary

Plate Tectonics Reference Table

You need to know how to read this table!!

Pacific Plate – Where the Action is!

RING OF FIRE!!

HawaiiHawaii is a chain of islands made from an underwater volcano.

Yet Hawaii is NOT on a plate boundary.

How was Hawaii created?

Hawaiian Hot Spot• Hawaii is in the middle

of the Pacific Plate

• Not on a boundary.

Magma Rises under Hawaii

•Hot spot is located in the mantle and does not move

•The Pacific Plate moves NW over the hot spot forming a line of volcanoes.

Plate Boundaries!!

Divergent Convergent

Transform

Divergent Boundary • When Plates Divide or Separate

Step 1 – Rift Valley• Magma pushes up cracks in the crust

• Convection causes the separated plates to move and form a rift valley.

Step 2 – Add Water• The valley widens and begins to be filled with

water. (Red Sea)

Step 3 – Ocean Formed

• Eventually an ocean forms – At the rate of 6

cm per year

Ex. Mid Atlantic Ridge

Divergent Boundaries Map

Transform Boundary• Two Plates slide past

each other

• Also called strike-slip boundary

• Example: San Andreas Fault in California

San Andreas Fault• The Pacific Plate

moves North

• The North American Plate moves South

San Andreas Fault• Causes stress that

leads to Earthquakes in California

Convergent Boundaries• 2 Plates colliding into

each other.

• Example: Himalayan Mountains formed when India collided with Asia

• We will Continue these notes tomorrow!!! There is a lot to know about Convergent Boundaries!