1. VOLCANOES

2. VOLCANOES
Up until now, we have discussed the earth and its construction.
We have discussed the crust and plates and plate tectonics.
In a way, our discussion of volcanoes will extend that old knowledge.

3. VOLCANOES
A volcano is a weak spot in the crust where magma leaks to the surface.
When magma escapes to the surface, it’s called lava.

4. VOLCANOES There are about 600 active volcanoes on land today.
We know there are many more beneath the sea, but because there are parts of the ocean floor which are inaccessible, it is difficult to map or even count them.

5. VOLCANOES Volcanoes often occur in belts.
One of the most well known volcanic belts is the Ring of Fire around the rim of the Pacific Ocean.

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7. VOLCANOES
You may have noticed that he volcanic belts occur near the boundaries of the earth’s plates.
This is because when diverging or converging occurs cracks form in the crust which make it easy for volcanoes to occur.

8. VOLCANOES
Underwater volcanoes spew magma constantly and slowly form ridges or underwater mountains.
This happens at diverging plates.
There may be a time in the future where our map looks nothing like it does today!

9. VOLCANOES When oceanic plates converge, volcanos can be created.
The plate that subducts gradually melts as it gets closer to the warm material of the mantle.
Since magma is less dense than the rock above it, it rises to the surface.
Hence, a volcano is formed.

10. VOLCANOES
Since volcanos often occur in bands, islands that spring from the ocean often do so, likewise, in bands.
These are called island arcs.
These arcs echo the shape of the ocean trench.

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This can occur when an oceanic plate subducts beneath a continental plate.
This produced the Andes Volcanoes in South America and the Pacific Northwest Volcanoes in the United States!

13. VOLCANOES Not all volcanoes form along a ridge.
Some volcanoes form at what we call hot spots.

14. VOLCANOES
This happens when material from deep within the mantle rises, then melts forming magma.
When this magma breaks through the crust, we call it an eruption and another volcano is formed.

15. VOLCANOES Hot spots can form near a fault or in the center of a plate.
There is one very famous hot spot under Yellowstone National Park.
What did that form?

16. VOLCANOES
Volcanic eruptions have been explained in many ways over the years.
In Hawaii, there are many myths about the goddess of volcanoes, Pele.
When she is angry, volcanoes erupt.
Pele’s Hair is formed when lava sprays from the ground and hardens in thin strands.

17. VOLCANOES
Deep beneath the surface under volcanoes there is always a pocket of magma.
This pocket is called a magma chamber.
The magma moves upward through a pipe or a long tube that runs from the chamber to the surface.

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Molten rock and gas can leave a volcano through what’s called a vent.
Often there is a central vent on top of a volcano, but it may have several more secondary vents along the sides.

19. VOLCANOES
The area covered by lava as it pours from a vent is called a lava flow.
Oftentimes the central vent will have a bowl-shaped crater around it.
This is called a crater.

20. VOLCANOES You guys know that trick I do with the pop bottle?
That happens because under pressure, the carbon dioxide in pop is very compacted.
When you open the pop and release the pressure, the carbon dioxide can expand.
This is also why pop bubbles when you open it.

21. VOLCANOES This is what happens in a volcanic eruption as well.
Magma is under enormous pressure and when that pressure is released, the gasses in it expand and an eruption occurs.

22. VOLCANOES
That pressure builds until the magma flows or explodes out of the vent.
Once all the magma has escaped, the remaining gasses escape.

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In a geologist’s eyes there are two types of eruptions…quiet or explosive.
Quiet eruptions occur if the magma is low in silica.
This magma has low viscosity and flows easily.
Because of this gasses bubble out gently.

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As you could imagine, when the magma is high in silica, oftentimes eruptions are explosive.
Because of its high viscosity the magma often plugs the pipe.
And the pressure builds…and builds until and explosion happens.

25. VOLCANOES Explosive eruptions can actually break lava.
When it cools it can be as small as dust or as large as gravel on a playground.
When there is an explosive eruption, the mixture of hot gasses, ash, and cinders is called pyroclastic flow.

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While they are very different, both types of eruptions cause significant damage.
Quiet eruptions spew lava constantly setting fire to and burying a large are around the volcano.

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An explosive eruption causes clouds of deadly gasses, ash and cinders.
The ash alone can bury entire towns.

28. VOLCANOES
A volcano’s activity can last from a decade to ten million years.
Geologist work tirelessly to determine whether or when a volcano will erupt again.

29. VOLCANOES A volcano has three stages of activity. The first is active.
These are volcanoes that is erupting or shows signs of erupting in the near future.

30. VOLCANOES The second type is dormant.
These volcanoes are ones that scientist expect to awaken in near future.

31. VOLCANOES The final type is extinct.
This is one that is unlikely to ever erupt again.

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Geologists use what’s called a tiltmeter to detect slight changes in elevation near a volcano.
This can let geologists know when or if a volcano will erupt again.

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As destructive as volcanoes can be, they can create some of the world’s most spectacular and awe-inspiring landforms.
Mount Fuji in Japan is one of the most beautiful and perfectly formed mountains in the world.

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Volcanic eruptions can create landforms made of lava, ash and other materials.
These landforms include…
Shield volcanoes
Cinder cone volcanoes
Composite volcanoes
Lava plateaus

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Shield Volcanoes are formed when lava spews slowly and over time creates layers of solidified magma that create a gently sloping mountain.
The Hawaiian Islands are an example of shield volcanoes.

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Cinder Cone Volcanoes are when the debris from volcanoes gathers and forms a pile through which magma is still released.

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Composite Volcanoes are when layers of solidified lava alternate with layers of ash.

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Lava Plateaus are when exceptionally viscous lava spreads far before solidifying.
This creates a wide area of hardened magma that more resembles a plateau than a mountain.

39. VOLCANOES Sometimes, volcanic mountains collapse.
When this happens the resulting crater is called a caldera.
It happens when the magma chamber is emptied and the hill falls in on itself.
The crater fills with water very often.

40. VOLCANOES
Even with all the danger, people choose to live near volcanoes.
The reason for this is because they choose to take advantage of the incredibly fertile soil.
Volcanic ash is rich in potassium, phosphorus and many other substances excellent for farming.

41. VOLCANOES Many more landforms can be formed by magma as well.
The include…
Volcanic Necks
Dikes
Sills
Batholiths
Dome Mountains

42. VOLCANOES
A Volcanic Neck is when the water wears away the rock around a pipe where magma has hardened inside.

43. VOLCANOES
Dikes and Sills are basically rock ridges formed from magma leaking from a long crack in the crust.
Dikes form vertically.
Sills form horizontally.

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A batholith is formed when a large body of magma cools within the crust.

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Dome Mountains form when a batholith is pushed toward the surface by tectonic forces.

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Hot springs and geysers are two other creations of volcanoes.
Hot Springs are when groundwater is heated and slowly rises to the surface, collecting in a pool.
Geysers are more violent, and shoot from the surface due to built up pressure.

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Some people use the pressure built up from the volcanic areas to produce power.
This is called geothermic energy and it can be used to produce heat and electricity.