Geography 12Plate Tectonics

Ms. Inden

Take a look at this picture of the Ring of Fire! The area that we are discussing is the darker peachy-pink area that surrounds the Pacific Ocean.

The Ring of Fire is where

a lot of volcanoes

and earthquakes occur. WHY

HERE??

The Structure of the Earth

The earth’s crust

• The outer crust of the Earth is a thin layer, like the shell of an egg.

• Continental crust is called SIAL

• Under it, and also the ocean floor is called SIMA

Sima – See many

fish

Sial – See alpine

meadows

Plate Tectonics

• The crust is broken into pieces, or plates

• At the edges of these plates, you will find most of the world’s volcanoes and earthquakes

• The reason is that these plates are MOVING! (more on that in a few slides)

You are here!

Pacific Ocean

Atlantic Ocean

Edges of the plates are in yellow, Earthquakes of the

last 100 years are in red

This is a map of the

Earth – Can you see it?

Africa

Remember that the earth is made up of

broken plates of crust?

The area surrounding the Pacific Ocean is known as the Ring of Fire, because of the volcanoes that occur

around its edges – mainly because of the type of plate boundary – subduction – we’ll learn more about

that.

Ring of Fire

Here it is again, without the plates

Volcanoes also happen over hotspots – not just where plates come together .

These places are called hot spots – like Hawaii and the Galapagos Islands.

RED DOTS ARE HOT SPOTS

Here are the Earth’s Plates on a map of the world

What plates are next to the British Columbia and the rest of North America (i.e., next to California and the San Andreas Fault?)

Remember that these plates are moving? How?

• Idea: Convection Currents:

Cooled material sinks back down, heats and rises again.

Because the plates move, they create mountains,

trenches, volcanoes, earthquakes

So, these currents of rising and then sinking molten rock (moving very slowly) acts like conveyor belts that move the

plates around – this is the theory of plate tectonics

Here, one plate dives under the other, which creates fold mountains and volcanoes like Mt. St. Helen’s, Mt. Baker, Mt. Bachelor – a row, or arc of volcanoes.

Here, plates slide past each other, creating the San Andreas Fault.

Here are pictures showing the North American land forms we just looked at:

San Andreas Transform Fault

Mt. Bachelor

Mt. St. Helen’s

Mt. Hood

These faults, occurring at plate boundaries, or cracks in

the earth, come in three different types:

• Diverge means to pull apart• Converge – means to come together• Transform faults slide past each other

3 types of faults

• Diverge means

• Converge means

• Transform –

When plates pull apart this creates a ridge – because magma wells up• One major diverging

plate is the mid-Atlantic Ridge

• Mid means middle, and the Atlantic is the ocean, right?

• So, this mountain ridge is in the middle of the Atlantic

Mid-Atlantic Ridge –another look

Can you see the plates that create the Mid-Atlantic Ridge?

Transform Faults – plates or faults sliding past each other

• The big one is the San Andreas Fault in California

Two types of land forms occur when plates converge: 1. Subduction

Zone• Remember that converge means to come

together

• Called subduction:– where an ocean plate dives under a continental plate

• Creates a trench – like along the Andes Mountains, and helps build the mountains

• See how it creates volcanoes there – like Mt. St. Helens, Mt. Bachelor, Mt. Baker, Mt. Hood

Two types of land forms occur when plates converge: 2. Fold

Mountains• Remember that converge means to

come together

• Sometimes this creates mountains – like the Rockies, and the Himalayas

This is how BC was formed and we live on a high plateau ourselves

Here is another look at the 3 types

Terms for Volcanoes

• Molten or melted rock that is below the surface is called magma

• Molten or melted rock at the earth’s surface is called lava

• Volcanic ash also comes out of the volcano

When Mt. St. Helens erupted in 1980, ash and light rock was

blown north and west as far as the Manitoba/Ontario border

What is an earthquake?

• Earthquakes happen when the earth (rock masses) moves suddenly along a crack or fault in the earth’s crust

• Faults - cracks or breaks in the earth’s surface

• The movements of the earth can be up and down, and side to side

• Take a look for the fault – the broken line of earth

• An earthquake occurs at the focus, underground

• The epicenter of the earthquake is right above it at the surface