1. Volcanoes

2. Target #16- I can summarize the conditions needed for magma to form
Despite the high temperature in the mantle, most of the layer remains solid due to extreme pressure
Magma: liquid rock produced under Earth’s surface

3. Melting Point: the temperature at which a substance will change from a solid to a liquid
Magma can form in three ways
Temperature rises above the melting point of rock
Pressure decreases lowering the melting point of rock
Addition of fluids, like water, can decrease the melting point
Target 16- cont.

4. Target 17- I can define volcanism Target #18- I can differentiate between magma and lava
Volcanism: any activity that includes the movement of magma and gases toward or onto Earth’s surface
Magma rises because it is less dense than the surrounding rock
magma that flows onto Earth’s surface is called lava
Flows from an opening, or vent

5. Target #19- I can differentiate between mafic and felsic magma
When magma erupts from a volcano and then cools & hardens, it forms an igneous rock
Mafic: magma that is rich in magnesium and iron
Dark in color
Makes up oceanic and continental crust
Felsic: magma that is rich in feldspar and silica
Light in color
Makes up continental crust only

6. Target #20- I can describe viscosity
Viscosity: resistance to flow
Affects the force with which a particular volcano will erupt
Target #20- I can describe viscosity

7. Target #21- I can describe quiet eruptions
Form from mafic magma
Low viscosity
Occur with oceanic volcanoes
Magma “oozes” out of the vent

8. When mafic lava cools rapidly, a crust forms on the surface of the flow
If the lava continues to flow after the crust forms, the crust wrinkles
Pahoehoe: a volcanic rock that forms from hot fluid lava
As it cools it forms a smooth, ropy texture
Means “ropy” in Hawaiian
Target #22- I can describe the lava rocks produced from quiet eruptions

9. Target #22- cont.
If the crust deforms rapidly, or grows too thick to form wrinkles, the surface breaks into jagged chucks
Aa: a jagged volcanic rock that forms from lava that
has the same composition as pahoehoe
Blocky Lava: a volcanic lava that has a high silica content, and is highly viscous

10. Target #23- I can describe explosive eruptions
The felsic lavas of continental volcanoes tend to be cooler and stickier than the fluid lavas produced by oceanic volcanoes
Pyroclastic material: fragments of rock that form during a volcanic eruption

11. Bellwork
What are the differences between an explosive eruption and a quiet eruption?

12. Types of Volcanoes

13. Target #24- I can identify where volcanoes are located
Volcanoes are usually located at the edge of plate boundaries
Ex: A major zone of active volcanoes encircles the Pacific Ocean
Known as the Pacific Ring of fire
Subduction zones
Continental-oceanic convergent boundaries
Oceanic-Oceanic convergent boundaries
Target #24- I can identify where volcanoes are located

14. Target #24 cont.
The largest amount of magma is found at divergent boundaries along mid-ocean ridges
The magma erupts to form underwater volcanoes
These volcanoes produce pillow lava

15. Target #25- I can differentiate between shield, cinder, and composite volcanoes
Shield Volcanoes: volcanic cones that are broad at the base and have gently sloping sides
Covers a wide area
Generally forms from quiet eruptions
Layers of hot, mafic lava flow out around the vent, harden, and slowly build up to form the cone
Ex: Hawaiian Islands

16. Target #25- cont. Cinder Cones: a volcano that has a very steep slope
Not usually tall- max height is not more than a few hundred meters
Form from explosive eruptions and are made of pyroclastic material

17. Composite Volcanoes: made of alternating layers of hardened lava and pyroclastic material
Quiet eruptions deposits lava and an explosive eruption follows depositing ash
Also known as stratovolcanoes
Develop to form large volcanic mountains
Target #25- cont.

18. Target #26- I can describe a caldera
Caldera: a large, circular depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink
Calderas may fill with water to form lakes
Ex: Mount Mazama in Oregon (known as Crater Lake)
Target #26- I can describe a caldera

19. Target #27- I can describe how a hot spot forms an island chain
Hot Spot: an area of volcanic activity within the interior of a tectonic plate
Magma rises from the mantle in the middle of a plate, and not at a plate boundary
The rising magma creates a volcano, producing an island
As the plate shifts over the magma, a new volcano and new island is formed
Continues creating a chain of islands
Ex: Hawaiian Islands
Target #27- I can describe how a hot spot forms an island chain