1. Volcanoes
Erupting with fun!

2. Magma vs. Lava
Magma is liquid rock produced under the Earth’s surface but Magma becomes Lava as soon as it leaves the Earth and flows outside.
Lava
Magma

3. Magma
Magma can form under three conditions: 1. If rock temperature rises above its melting point then it will melt into magma 2. Rock can melt when too much pressure is removed from rock that is above its melting point 3. The addition of fluids, such as water, may lower the melting point of some rock and cause it to melt

4. Volcanism
Volcanism is any activity that includes the movement of magma onto Earth’s surface
A volcano is a vent or fissure in Earth’s surface through which magma and gases are expelled

5. Location and Formation Of Volcanoes
Most volcanoes occur in convergent and divergent boundaries of tectonic plates A major zone of active volcanoes is located in the “Pacific Ring of Fire” which is also a major earthquake zone

6. Locations of Volcanoes
Some tectonic boundaries include:
Subduction Zones
Mid-Ocean Ridges
Hot Spots

7. A subduction zone is where one tectonic plate moves under another
Subduction Zones
A subduction zone is where one tectonic plate moves under another

8. Mid-Ocean Ridges
A long, undersea mountain chain that has a steep, narrow valley at its center.
Forms as magma rises from the asthenosphere
Creates new ocean floor as tectonic plates move apart (sea floor spreading)

9. Hot Spots
Areas of volcanism within the interiors of lithospheric plates
The Hawaiian Islands were created by a hot spot
See HOT demo!

10. Types of Volcanic Eruptions
Quiet volcanoes have mafic magma which is rich in magnesium and iron. Mafic magma is dark in color with runny lava
Explosive volcanoes have felsic magma which is rich in light-colored silicate materials and is thick and sticky.
Compare water boiling (quiet volcano) to thick spaghetti sauce boiling (explosive volcano)

11. Pyroclastic Materials
“Pyro” means fire
Pyroclastic materials include fragments of rock that form during volcanic eruptions

12. Types of Pyroclastic Materials (from smallest to largest
Volcanic dust
Volcanic ash
Lapilli—means little stones…they normally fall near the vent
Volcanic bombs—clots of lava that are thrown out of the volcano & become round or spindle shaped as they go through the air
Volcanic blocks—solid rock that is blasted through the vent…some are as big as a house!!

13. Read “What Volcanoes Can Produce”

14. Types of Volcanoes Shield volcanoes Cinder Cones
Composite Volcanoes (Stratovolcanoes)
Calderas

15. Shield Volcanoes Wide base Gently sloping sides
Forms from quiet eruptions

16. Cinder Cone Volcanoes Steep slopes
Form from explosive eruptions and are made of pyroclastic materials

17. Composite Volcanoes (Stratovolcanoes)
Made with alternating layers of hardened lava flows and pyroclastic materials
This type of volcano alternates quiet and explosive eruptions

18. Calderas
This type of volcano is created when the magma chamber below a volcano empties and the cone collapses
The collapse leaves a large basin-shaped depression (crater)
Some calderas eventually fill with water to become lakes

19. Read “What Are Volcanoes?” and answer questions