1. Volcanoes

2. Where do we find volcanoes?
Most of the 550 active volcanoes are found along the edges of the Earth's plates.
More than half of them encircle the Pacific Ocean in the so-called Ring of Fire.

3. Parts of a volcano

4. What is a VOLCANO?
An opening in the earth’s crust through which molten lava, ash and gases erupt that originate in the mantle.
MAGMA is an underground pool of molten rock. When it comes to the surface of the Earth, it is called LAVA.

5. CRATER – roughly circular top of vent
VENT – opening where magma flows out

6. Volcano Terms
SILL – horizontal layer of magma that flows between the layers
DIKE – vertical layer of magma that cuts through the layers

7. Shiprock, New Mexico—vent and dike of old volcano
Devil’s Tower, Wyoming—old volcanic vent

8. Volcanic—dust, ash, cinders, and bombs
Volcanic Dust—less than .25 mm
Volcanic Ash—size of rice grains
Volcanic—dust, ash, cinders, and bombs
Cinders—size of golf balls
Volcanic Bombs—few centimeters to meters

9. Lahar vs. Pyroclastic Flow
Lahar—mudflow with rocks, other debris, and water

10. Pyroclastic Flow— fast moving current of extremely hot gas

11. Shield Volcano Broad volcano with gently sloping sides
Gentle eruptions of lava
Example: Mauna Loa, Hawaii
Olympus Mons (Mars) – Largest in Solar System

12. Galapagos Islands
Ecuador
Mauna Loa
Hawaii
Rangitoto
Island
New Zealand

13. Cinder Cone Volcano Very steep sides. Violent eruptions.
Usually not taller than 1000’.
Most abundant
Example: Paricutin, Mexico

14. 1943--cinder cone erupted on a farm near Paricutin
1943--cinder cone erupted on a farm near Paricutin. It built up a cone to 1,200 feet covering 100 square miles over the course of nine years.
Paricutin, Mexico
SP Crater, Flagstaff, Arizona
Cerra Negro, Nicaragua

15. Composite Volcano (Stratovolcano)
Steep sides, symmetrical cones
Built up through eruptions of lava flows, volcani ash, cinders, and bombs
Examples: Mt. Hood, Mt. Rainier, Mt. St. Helens

16. Mount Fuji, Japan
Mount Hood, Oregon
Mount Rainier, Washington
Mount Shasta, California

17. Mt. St Helens BEFORE 1980

18. Mt. St. Helens AFTER 1980