1. VOLCANOES
OUR CHANGING EARTH

3. VOLCANOES VOLCANOES FORM WHEN MAGMA ERUPTS ONTO THE SURFACE
THIS OCCURS ALONG PLATE BOUNDARIES
MAGMA IN A CHAMBER CAN SIT THERE FOR MONTHS OR YEARS!

4. VESUVIUS

5. VESUVIUS COMPOSITE VOLCANO FORMS AT BOUNDARY OF CONVERGING PLATES
SIT QUIET FOR VERY LONG TIME, THEN EXPLODE VIOLENTLY

6. Composite Volcanoes

7. Composite Volcanoes

8. MEXICO

9. CINDERCONE VOLCANO ERUPTS SUDDENLY
SPREAD OVER GREAT DISTANCE AND RISES UPWARD

10. Cinder Cone Volcano

11. Cinder Cone Volcano Paricutin in Mexico

12. HAWAII

13. SHIELD VOLCANOES HAWAIIN VOLCANOES FORM OVER HOT SPOTS IN THE MANTLE.
LOTS OF LAVA FLOWS. LOW IN SILICA AND FORMS A SHIELD.

14. Shield volcanoes

15. Shield volcanoes - Hawaii

16. Magma
Type
Chemical
Composition
Temperature
(degrees C)
Viscosity
Gas Content
Basaltic
45-55% SiO2;
High in Fe, Mg, Ca; Low in K, Na.
Low
Andesitic
55-65% SiO2;
Intermediate Fe, Mg, Ca, Na, K
Intermediate
Rhyolitic
65-75% SiO2;
Low in Fe, Mg, Ca; High in K, Na
High

17. Active, Dormant, Extinct
ACTIVE – ERUPTING RIGHT NOW
DORMANT – SLEEPING, COULD ERUPT BUT NOT
EXTINCT – HAS NOT ERUPTED FOR THOUSANDS OF YEARS AND PROBABLY WILL NEVER DO SO AGAIN