Forces Below Earth’s Surface• Earth has 3 Layers: Crust, Mantle, Core

• Crust = 30 miles thick, landmasses and ocean floor

• Mantle 1,800 miles thick; magma (molten/melted rocks

• Outer Core 1,400 miles thick—mostly liquid iron and nickel

• Inner Core 700 miles thick 12,000*F – hotter than the surface of the sun. Solid b/c of pressure.

The Crust• This is where we live!

• The Earth’s crust is made of:

Continental Crust

- thick (10-70km)- buoyant (less dense than oceanic crust) - mostly old

Oceanic Crust

- thin (~7 km)- dense (sinks under continental crust)- young

How do we know what the Earth is made of?

• Geophysical surveys: seismic, gravity, magnetics, electrical, geodesy– Acquisition: land, air, sea and satellite

– Geological surveys: fieldwork, boreholes, mines

What is Plate Tectonics?

• If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle.

That’s because they did! Continents were once united in a single supercontinent (Pangea) & have been moving for 200 million years

continental driftContinental Drift TrailerPangaea

• Plate Tectonics-theory that Earth’s surface (crust) is divided into slow-moving plates, or pieces.

Plate Tectonics: • The Earth’s crust is divided into 7-8 major plates (plus

smaller ones) which are moved in various directions.• This plate motion causes them to collide, pull apart, or

scrape against each other.• This caused the continents to split apart and causes the

formation of mountains, volcanoes, and several types of natural disasters.

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1. North American Plate •Where we live!

2. Eurasian Plate•All of Europe and part of Asia.

3. African Plate

4. South American Plate

5. Indo-Australian Plate• Includes India and Australia.

6. Pacific Plate •The only plate that is all ocean.

7. Antarctic Plate

1. Which plate are we on?2. What plates border the Eurasian plate?3. What plate is south of the African plate?

What happens at tectonic plate boundaries?

• Divergent

• Convergent

• Transform

Three types of plate boundary

Divergent Plates• When plates separate, gaps form & magma rises

up– Lava-magma that reaches Earth’s surface– This can expand the size of ocean floor!!

Divergent Plates• Divergent plates can also result in the formation

of islands—like Iceland! •As the North American and Eurasian plates were pulled apart volcanic activity occurred along the cracks.

•With many eruptions over time the island grew out of the sea!

• There are three styles of convergent plate boundaries– Continent-continent collision– Continent-oceanic crust collision– Ocean-ocean collision

Convergent Boundaries

• Forms mountains, e.g. European Alps, Himalayas

Continent-Continent Collision

Himalayas

• Called SUBDUCTION, also creates mountains (along coasts)

Continent-Oceanic Crust Collision

• When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone.

• The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench.

• The worlds deepest parts of the ocean are found along trenches. – E.g. The Mariana Trench is 11 km deep!

Ocean-Ocean Plate Collision

– Where plates slide past each other, causing

– Earthquakes-sudden, violent movements of Earth’s crust

– Tsunamis –giant, super destructive ocean waves caused by earthquakes in the ocean

Transform Boundaries

…what’s the connection?

Volcanoes and Plate Tectonics…

- Subduction - Rifting - HotspotsVolcanoes are formed by:

• Hot mantle plumes breaching the surface in the middle of a tectonic plate

What are Hotspot Volcanoes?

Photo: Tom Pfeiffer / www.volcanodiscovery.com

The Hawaiian island chain are examples of hotspot volcanoes.

Ring of Fire • Ring of Fire = circle of

volcanoes, earthquakes, and tsunamis along the rim (outer edge) of Pacific Ocean.

• Caused by the Pacific Plate (ocean plate) sliding against continental plates in Asia, Australia, South America, and North America

Volcanism is mostly focused at plate margins

Pacific Ring of Fire

The Ring of Fire: • 75% of Earth’s volcanos.• 80% of Earth’s tsunamis. • 90% of Earth’s earthquakes.

Krakatoa • Volcanic island in

Indonesia. • 1883 eruption lead to

huge tsunamis and destroyed over 2/3 of the island.

• The explosion is the loudest sound ever heard people over 3,000 miles away heard it.

Plot Latitude & Longitude Coordinates to find Disasters on the Ring of Fire!

Earthquake at 40*N, 120*W

Volcano at 0*, 160*E