1. Volcanism CGF3M – Cooper/2013

2. What is a Volcano? word Volcano comes from island of Vulcano off the coast of Sicily.word Volcano comes from island of Vulcano off the coast of Sicily. volcanoes are built by the accumulations of their own eruptive products - lava, gas, ash flows and tephra (airborne ash and dust).volcanoes are built by the accumulations of their own eruptive products - lava, gas, ash flows and tephra (airborne ash and dust). Is a conical hill built around a vent that connects with reservoirs of molten rock below the surface of the earth.Is a conical hill built around a vent that connects with reservoirs of molten rock below the surface of the earth. Driven by buoyancy and gas pressure, the molten rock (called Magma), which is lighter than the surrounding solid rock, forces its way upwardDriven by buoyancy and gas pressure, the molten rock (called Magma), which is lighter than the surrounding solid rock, forces its way upward

3. As the rising magma nears the Earth’s surface, pressure decreases - causes the gases in the magma to expand.As the rising magma nears the Earth’s surface, pressure decreases - causes the gases in the magma to expand. Lava – magma on surfaceLava – magma on surface Eruptions can be violent or non – violentEruptions can be violent or non – violent Larger fragments fall around the vent, and mountain takes its shape.Larger fragments fall around the vent, and mountain takes its shape.

5. Types of Volcanoes Stratovolcanoes (also called composite volcanoes) Built from alternating layers of lava and cinders Tall, steep-sided cone with a bowl-shaped depression (crater/vent) at the top. Produce violent eruptions Eg. Mount St. Helens Calderas Most violent eruptions – can destroy the entire center portion of a volcano. Large quantities of ash and dust are emitted and fill the atmosphere. Ground subsides/collapses into emptied magma chamber. Forms huge depression called a Caldera Eg. Krakatoa in Indonesia, Yellowstone in Wyoming/Montana

6. Types of Volcanoes Shield Volcanoes build up of successive lava flows Broadly rounded domes with gentle slopes. Some of the largest volcanoes in the world. Some of the largest volcanoes in the world.Non-explosive. Eg. Hawaiian Island volcanoes Cinder Cones Simplest type of volcano. Built from blobs of lava, ejected from a single vent. Gas-charged lava is blown violently into the air. This lava breaks into smaller fragments that solidify and fall as cinders around the vent.

7. Types of Volcanoes Hotspots A plume of upwelling magma deep in the mantle that melts through the lithosphere and reaches the sea floor. Eg. Hawaiian Islands, Iceland Hotsprings and Geysers Hot rock material near the Earth’s surface and heats ground water. When it reaches the surface, produces hot springs. Some areas produce jet-like emissions of steam and hot water (geysers).

8. Shield Volcano

9. A Cinder Volcano

10. Composite Volcanoes

11. A Crater Lake formed in a Caldera

12. Products of volcanic eruption http://www.geology.sdsu.edu/how _volcanoes_work/Thumblinks/pro ducts_page.html

13. Explosivity Many eruptions are relatively quiet - characterized by calm, nonviolent extrusion of lava flows on the earth's surface. If the material is fluid in nature - called Pyroclastic Flow (typical hot lava that flows down a volcano). Other eruptions are highly explosive and are characterized by the violent ejection of fragmented volcanic debris (tephra) linked to the composition of the magma underlying the volcano

14. The controlling factors on explosivity are viscosity, temperature, and the amount of dissolved gases in the magma. Nonexplosive eruption Eruption of the Pu'u O'o volcano on the east zone of the larger Kilauea volcano, Hawaii. http://www.geology.sdsu.edu/how_volcanoes_ work/Thumblinks/Puuoo84_page.html

15. http://www.geology.sdsu.edu/how_volcanoes_wo rk/Thumblinks/msh5_page.html Explosive Eruption: Eruption of a voluminous plume of tephra is typical of explosive eruptions, as demonstrated in the 1980 eruption of Mt. St. Helens. These eruptive tephra plumes can travel tens of kilometers into the stratosphere.

16. Gas How does the amount of dissolved gases affect the explosivity of volcanoes? dissolved gases in the magma provides the force for explosive eruptions. magma rises toward the surface, dissolved gases in the liquid rock begin to come out of the mixture, and bubbles begin to form in the magma more the gas the more explosive the volcano

17. Viscosity How does viscosity affect explosivity? the ability of a substance to resist flow (inverse of fluidity). Magma may contain a material that is crystal in structure called silca magma with a higher silica concentration has a higher viscosity

18. Temperature higher the temperature, the more fluid a substance becomes, thus lowering its viscosity. lava in this case is thin and runny and gases escape easily.

19. Measuring Eruptions Every year approx. 60 volcanoes erupt (most activity weak. eruption magnitude scale - called the Volcanic Explosivity Index or VEI based on a number of things that can be observed during an eruption

20. VEIDescriptionPlume HeightVolumeClassificationHow oftenExample 0non-explosive< 100 m1000s m3HawaiiandailyKilauea 1gentle100-1000 m10,000s m3Haw/StromboliandailyStromboli 2explosive1-5 km1,000,000s m3Strom/VulcanianweeklyGaleras, 1992 3severe3-15 km10,000,000s m3VulcanianyearlyRuiz, 1985 4cataclysmic10-25 km100,000,000s m3Vulc/Plinian10's of yearsGalunggung, 1982 5paroxysmal>25 km1 km3Plinian100's of yearsSt. Helens, 1981 6colossal>25 km10s km3Plin/Ultra-Plinian100's of yearsKrakatau, 1883 7super-colossal>25 km100s km3Ultra-Plinian1000's of yearsTambora, 1815 8mega-colossal>25 km1,000s km3Ultra-Plinian10,000's of yearsYellowstone, 2 Ma Volcanic Eruption Index

22. White Island, New Zealand

24. Pu’u in Hawaii

25. Environmental Hazards Devastates plant and animal life, and human habitation. From clouds of gases, from lava flows, from ash and cinder, from associated earthquakes, from waves generated by underwater volcanoes, etc. Importance of volcanoes: Tourism – beautiful New land/fertile soil for growing crops Geo-thermal activity provides energy to us. Minerals/materials for us to use

26. Volcanoes can in one of the following three states: Active, extinct or dormant THE END!