26 September 2007 mar110_L10_PT_volcanoes_26sep07.doc 1 1MAR110 LECTURE #10 Plate Tectonics Volcanoes Figure 10.2 Mid Ocean Ridge Magma As new crust is formed along the ridge axis the older crust is pushed to either side forming bands of rock parallel to the ridge. The upward moving magma in the rift zone forces its way through the oceanic crust, forming underwater volcanoes where the magma breaks through as pillow lava. (?) Figure 10.1 Ocean Basin Volcanism Mid-ocean ridge volcanism produces ocean crust and occasional volcanic islands which when underwater are called seamounts. Isolated “hotspots” produce mid-ocean island chains. In a subduction zone, volcanoes are formed by the rising of melted lithosphere magma. (ItO)26 September 2007 mar110_L10_PT_volcanoes_26sep07.doc 2 2 GuyotGuyotor Flator Flat--topped Seamounttopped SeamountFigure 10.4 Volcanic Island Chain Formation Isolated stationary mantle hotspots can produce chains of volcanic islands and seamounts in the mid-ocean - like the Hawaiian island chain (right). (ItO, LEiO) Figure 10.3 Underwater Volcanoes - Seamounts Underwater volcanoes can be formed in the region of mid-ocean ridges when mantle magma chambers remain connected. Once the volcano is carried away and disconnected it becomes “extinct" and is called a seamount. (NG)26 September 2007 mar110_L10_PT_volcanoes_26sep07.doc 3 3 Figure 10.6 Hawaiian Volcanism The Big Island of Hawaii is the only currently active volcanic island in the Hawaiian chain. There are three active cones on the island: Mauna Loa, Kilauea, and Hualalai. Three views of lava flows from Kilauea. (ItO, NG??) Figure 10.5 Hot Spot Island Formation Isolated stationary mantle hotspots can produce chains of volcanic islands and seamounts in the mid-ocean - like the Hawaiian island chain (right). (ItO, LEiO)26 September 2007 mar110_L10_PT_volcanoes_26sep07.doc 4 4 Figure 10.8 Juan de Fuca Plate Subduction The plate subduction in the northeast Pacific (offshore of Washington and Oregon) generates a chain of volcanic mountains known as the Cascades. ashore , (NG) Figure 10.7 Subduction Zone Volcanism A map of the major tectonic plates showing the types of boundaries and where they may be found. Red lines indicate areas with significant subduction zone volcanic activity near or on land. (LEiO)26 September 2007 mar110_L10_PT_volcanoes_26sep07.doc 5 5 Figure 10.9 Subduction Zone Volcanism Northeast Pacific Deep magma chambers - formed by the friction between the subducting Juan de Fuca plate and the North American plate – and feed the active volcanoes and spawn earthquakes in the Cascade Range. An active erupting volcano produces volcanic “bombs” (small to large pieces of solidified magma) and at times huge amounts of smoke (fine particles) and somewhat larger ash which tends to settle back to earth in the region. Besides slower lava flows, this kind of volcanic action can also produce superheated, high-speed pyroclastic flows that in turn can trigger landslides and mudflows. On occasion when the magma conduits are blocked major explosions can occur like mt St Helens in the ‘80s.(NG) Figure 10.10 Subduction Zone Volcanism - Mt St Helens26 September 2007 mar110_L10_PT_volcanoes_26sep07.doc 6 6 Figure 10.12Subduction Zone Volcanism The friction created when one plates subducts underneath another , causes the crustal and lithospheric rocks to melt (i.e. become magma) creating greater pressure that forces the less dense magma upward through the denser rock above to form volcanoes at the surface(ItO?) Figure 10.11 Mt St. Helens Explosion Impact26 September 2007 mar110_L10_PT_volcanoes_26sep07.doc 7 7 Figure 10.13 Mt Etna Volcanism in the Med The pressure in the chamber deep in the earth forces the magma upward to form an active, growing Mt Etna at the surface in sicily, Italy. (ItO?)26 September 2007 mar110_L10_PT_volcanoes_26sep07.doc 8 8 Figure 10.15 An active Mt Vesuvius Buries Pompeii -79 AD . (ItO?) Figure 10.14 Mt Vesuvius (1663) in coastal Italy. (ItO?)26 September 2007 mar110_L10_PT_volcanoes_26sep07.doc 9 9 Figure 10.16 Mummified Remains of Pompeiian Victims. (NG) Figure 10.17 A Slumbering Mt Vesuvius hovers high over Pompeii Ruins . (ItO?)26 September 2007 mar110_L10_PT_volcanoes_26sep07.doc 10 10 Figure 10.18 Krakatoa 1883 . (NH) Figure 10.18 Santorini .