1. Volcanoes and You

3. 1. What is a volcano?
A volcano is a mountain that forms when layers of lava and volcanic ash erupt and build up around a vent.

4. Active v. Dormant Volcanoes
Most of Earth’s volcanoes are dormant, meaning not active.
There are over 600 active volcanoes currently on Earth. Active means erupted in the last 1,000 years.

5. Where is the nearest volcano to Tucson located?

6. Is it A-Mountain?
A-Mountain is composed of igneous extrusive rocks, but is not itself a volcano

7. What about Picacho Peak?
Picacho Peak, which you pass when going to Phoenix, is made up of igneous rocks. Like A-Mountain, it looks like a volcano, but it is not one.

8. Nearest local volcano to us
Nearest local volcano to us... Sunset crater, near Flagstaff, which last erupted in 1065.

9. 2. Features of a volcano
Magma – melted rock/molten material below Earth’s surface.
Vent – Opening in Earth’s surface where magma can flow out.
Lava – Magma that has flowed out of the Earth’s surface.
Crater – Opening at the top of a volcano
Ash and Gas – Explode out of the crater.

10. Features of a volcano
Magma

11. 3. Where do volcanoes occur? Volcanoes can occur at 3 places
Divergent boundaries – an area where Earth’s tectonic plates are moving away from each other.
Diagram:
Example: volcanoes in Iceland

12. Divergent volcanoes in Iceland

13. Where do volcanoes occur?
Convergent boundaries – an area where Earth’s tectonic plates collide into each other. Volcanoes form when one plate subducts, or slides under the other plate.
Diagram:
Example: Andes Mountains in South America, Cascade Mountains in NW USA

14. Convergent volcanoes

15. Mt. St. Helens...before and after 1980 erruption

16. Where do volcanoes occur?
Hot spots – parts of Earth’s mantle that are hotter than surrounding material, forming melted rock which rises to the surface as magma.
Diagram:
Example: Hawaiian
Islands

17. Hawaiian volcanoes
Pu’u O’o crater (left) and Kilauea crater (right) both located in Hawaii Volcanoes National Park. Kilauea is considered the most active volcano on Earth, as it’s been continually erupting since 1983.
for live web cam of Pu’u O’o crater

18. Hot spot is making the Hawaiian Islands
As the Pacific plate moves over the (stationary) hot spot, more islands form. Newest island is Loihi, which is still several miles below the surface of the ocean.

19. More Hawaiian photos. Lava under this hot spot is basaltic – not explosive and slow. One can easily walk away from advancing lava.

20. 4. 2 types of volcanic eruptions
Magma that contains trapped gases causes eruptions to be explosive. Think of shaking a can of soda and then opening it.
Explosive eruptions have a lot of silica in the magma, for example melted granitic rocks. Mt. St. Helens is a good example of an explosive volcano.
Magma with little silica is effusive and flows quietly from the volcano. Quiet eruptions have basaltic magma. Good examples of quiet eruptions are Hawaii and Iceland.

21. 5. 3 types of volcanoes, based on material and eruption style
Shield volcanoes - are broad, gently sloping volcanoes built from fluid basaltic lavas.
Mauna Loa – the world’s largest shield volcano

22. 3 types of volcanoes
Composite OR stratovolcanoes - composed of both lava flows and pyroclastic material. They tend to have steep sides, and can have explosive eruptions.
Mt. Shasta (California) is a composite volcano.

23. 3 types of volcanoes
Cinder cone- forms when material is ejected high into the air and falls back to Earth as a pile around the vent. Usually small, with lots of water and gas in the magma.
Mt. Shasta (California) is a composite volcano.

24. Compare sizes of volcanoes

25. Mt. Saint Helens eruption - 8:27 am

26. 8:32 am

27. 8:33 am

28. New lava dome in Mt. St. Helens

29. Fuego Volcano in Guatemala

30. Colima volcano in Mexico

31. Mt. Wrangell in Alaska

32. Mauna Kea and Mauna Loa

33. Mount Pinatubo in the Philippines

34. Mt. Fuji in Japan

35. Mt. Krakatoa, Sumatra

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