1. Global Volcanoes http://earthref.org/SCC Scripps Classroom Connection

2. Where do volcanoes occur? Volcanoes occur at: 1. Hotspots 2. Plate Boundaries -Convergent (subduction zones) -Divergent Scripps Classroom Connection http://earthref.org/SCC

3. What are hotspots? Hotspots  Spot on Earth with volcanism  Can occur in the middle of tectonic plates  Hotspots don’t move  Tectonic plates move over hotspots  Makes a chain of volcanoes, like Hawaii Scripps Classroom Connection http://earthref.org/SCC Hawaii

4. Hotspot volcanoes Ocean Hotspots  Shield volcanoes, Hawaiiian Islands  Fast moving, basaltic lava  Effusive  Stratovolcanoes, Canary Islands  Alternating lava and ash  Explosive Continental hotspots  Explosive  Yellowstone Caldera, Wyoming Scripps Classroom Connection http://earthref.org/SCC

5. Subduction Zones Subduction Zone Volcanoes  Most major volcanoes found near subduction zones  Stratovolcanoes  Most dangerous Two different types: 1. Ocean-Ocean 2. Ocean-Continent Scripps Classroom Connection http://earthref.org/SCC

6. Ocean-Ocean Subduction Volcanoes Ocean-Ocean  Island Volcanic Arcs  Japan  Aleutian Islands, Alaska Scripps Classroom Connection http://earthref.org/SCC

7. Ocean-Continent Subduction Volcanoes Ocean-Continent  Continental Volcanic Arcs  Andes Mountains, South America  Cascades, N.W. United States Scripps Classroom Connection http://earthref.org/SCC

8. Spreading Centers Tectonic Spreading Centers ● Under the ocean  Mid-ocean ridges ● On Land  Continental rifts ● Almost continuous volcanism ● Create new oceanic crust Scripps Classroom Connection http://earthref.org/SCC

9. Mid-Ocean Ridge Volcanoes  Volcanoes form on fissures parallel to the ridge axis  Hundreds of volcanoes along each ridge, near- continuous volcanism  Erupt basalt  Create new oceanic crust Scripps Classroom Connection http://earthref.org/SCC

10. ● Most volcanoes occur at plate boundaries: 1. Subduction zones 2. Mid-ocean ridges ● Some volcanoes occur at hotspots: 1. Ocean floor 2. Continental Scripps Classroom Connection http://earthref.org/SCC Global Volcano Conclusions