1. Volcanic Activity

2. Magma Reaching the Surface Materials of asthenosphere under great pressure Materials of asthenosphere under great pressure Magma less dense than surrounding rock Magma less dense than surrounding rock Magma rises until it reaches the surface or becomes trapped by rock layers Magma rises until it reaches the surface or becomes trapped by rock layers

4. A Volcano Erupts Dissolved gases in magma are under tremendous pressure Dissolved gases in magma are under tremendous pressure As magma rises pressure decreases As magma rises pressure decreases Gases dissolved in magma rush out, carrying magma when an opening develops in weak rock on the surface Gases dissolved in magma rush out, carrying magma when an opening develops in weak rock on the surface

6. Inside a Volcano

7. Characteristics of Magma Force of volcanic eruption impacted by: Force of volcanic eruption impacted by: –Gas dissolved in magma –Thickness of magma –Temperature –Silica content

8. Characteristics of Magma Some magma thick- flows slowly Some magma thick- flows slowly Some more fluid- flows easily Some more fluid- flows easily Viscosity describes a liquids resistance to flow- higher viscosity, greater resistance Viscosity describes a liquids resistance to flow- higher viscosity, greater resistance http://www.seed.slb.com/en/scictr/lab/vis co_exp/index.htm http://www.seed.slb.com/en/scictr/lab/vis co_exp/index.htm http://www.seed.slb.com/en/scictr/lab/vis co_exp/index.htm http://www.seed.slb.com/en/scictr/lab/vis co_exp/index.htm

9. Characteristics of Magma Temperature impacts thickness- hotter, more fluid Temperature impacts thickness- hotter, more fluid More silica- thicker magma More silica- thicker magma –High silica- light lava, too sticky, doesn’t flow far, forms rhyolite, pumice, & obsidian –Low silica- flows easily, dark colored, forms basalt

10. Types of Eruptions Quiet Eruptions Quiet Eruptions –Quiet eruption if magma flows easily –Gases bubble out gently –Lava oozes quietly from vent –Ex. Hawaii, Iceland –Forms from basaltic material, low in silica –Type of crust?!?

12. Types of Volcanic Eruptions Explosive eruptions Explosive eruptions –Thick & sticky magma- explosive eruption –Dissolved gases can’t escape, pressure builds up, it explodes –Magma pushed out of volcano w/incredible force –Pyroclastic flow hurls ash, cinders, bombs –Forms from granitic material, high in silica –Crust type?!?

14. Stages of a Volcano Active- erupting or shows signs of erupting in near future Active- erupting or shows signs of erupting in near future Dormant- sleeping, expected to awaken in future & become active Dormant- sleeping, expected to awaken in future & become active Extinct- unlikely to erupt again Extinct- unlikely to erupt again

15. Other Volcanic Activity Hot spring Hot spring Geyser Geyser Geothermal energy Geothermal energy