lecture 3 09 09 2014 Other linear features on ocean floor indicate plate tectonics Hawaiian hot spot each of the islands were formed by a hot spot age of each volcano indicates time it was situated over mantle plume Kauai is the oldest of the large islands in the Hawaiian chain 09 09 2014 subduction zones plates move together destroy oceanic crust spreading center plates move apart create oceanic crust Ocean Continent Subduction Ocean crust Continental crust o Ocean plate dives down under cont crust Form trench wherever you have a subduction zone you will always have a trench Trenches are anywhere from 6 10km deep o As ocean crust keeps diving down into mantle it heats up At about 150km deep it starts to melt turn to magmas Magmas burn way up through continental crust to surface and eventually form volcano o Rock that comes out of continental style volcanoes are called Andesite remember b c Andes mountains are best example of ocean continent subduction o New ocean crust made of basalt o New continental crust made of granite Andesite more particular kind of granite that comes out of ground Ocean Ocean Subduction Zone Destroys old oceanic crust Makes new ocean crust Ocean lithosphere subducts under other ocean lithosphere o When two oceanic plates collide the older one which is always more dense will always subduct under the newer younger oceanic lithosphere When it hits 150km down just like ocean cont the overlying subduction crust melts except the melt material is basalt o Since it is burning through other oceanic crust what emerges is basalt o End up with volcanic island arc basically chain of volcanic islands all made of basalt Challenger Deep Marianas Trench 10971m deep almost 7 miles Most of the worlds trenches surround the pacific known as Ring of Fire Most people think of ring of fire as ring of volcanoes surrounding the pacific which is true but only reason there are volcanoes is because of all of the subduction which causes trenches 09 09 2014 4 setting of where you find volcanoes There is 1500 active volcanoes 20 erupting currently Active means they could erupt Most are not shown on ocean floor 4 Settings for Volcanoes 1 subduction zones like the Andes or the Cascades 2 spreading centers 3 hot spots like hot spots of Hawaii 4 continents pulling apart like the rift valley in East Africa Shield Volcano oceanic crust o not steep sides o basalt liquidy very hot o continuous eruptions o not explosive o not hazardous main reason why people can live in Hawaii o lava flows Strato Volcano Continental crust o Steep sides o Andesite sticky o Rare eruptions o Explosive o Hazardous b c lots of pressure builds up o Lava flows ash cinters o Pyroclastic flows big killers of strato volcanoes landslides full of gas ash rock move down volcano at 50 100mph 500 1000 degrees 09 09 2014 Shield volcanoes Settings o on ocean crust o ocean ocean subduction zones o spreading centers o hot spots Hot spots Hawaii Basically made of basalt It is a big shield volcano Mauna Kea 13 796 ft above sea level Iceland shield volcano On spreading center Santa Cruz volcano In Galapagos Sierra Grande New mexico Olympus Mons On Mars Height 20km Pinacate volcano In Sonora Shield volcano action Magma burns way up through the top Comes out of Summit Caldera 09 09 2014 Questions to keep out for in video of volcanoes below sea surface 80 importance of Kilauea most active volcano on earth it is the most benign At 2000 degrees F its fluid lava can flow for miles temperature of lava 700 degrees F underwater over 2000 desgrees F Kilauea key to forecasting eruptions each volcano is unique has own pulse own life cycle o but the one rule of forecasting applies to all the key to the future is the past nature of magma 09 09 2014 Strato volcanoes Settings o On continental crust o Ocean continent subduction zones Like andes cascades o Continental Rifts East African rift o Hot spots Like Yellowstone Steep sides Rock that emerges is Andesite Lava is medium hot makes it sticky B c lava is sticky the eruptions are explosive They are very hazardous Lava flows ash cinders pyroclastics flows ash gas rock are what erupt from the strato volcanoes Continental rifting Mt St Helens Was 9 677 ft tall Is now 8 365 ft tall Eruption May 18 1980 Typical strato volcano How do we predict the next eruption Most active Least active Eruption during your life Look at the history of the volcanoes volcanic activity How often it erupts when the last time it erupted was Sunset Crater In AZ 800 years ago 09 09 2014 Questions to keep in mind from movie What else comes from volcanoes besides magma Pyroclastic flow made up of and Rock gas ash It consumes nearly everything as it goes down mountain Nature of magma How many potentially active volcanoes How many peoples lives at risk from volcanoes A volcano does not need to explode to be dangerous 09 09 2014 Third type of volcanoes Caldera Crater Lake Oregon o Yellowstone o Caldera eruptions are very rare Think last eruption was 75 000 yrs ago How much magma erupts o Look at pic 09 09 2014 Things to remember Hot spot stays still plate moves over top of rising plume of magma Hawaii Ocean continent subduction Ocean ocean subduction Lots of subduction zones around pacific Ring of Fire 4 settings for volcanoes hot spots mid ocean ridges subduction zones continental rifts 3 types of volcanoes shield strato caldera 1500 active around the world 20 erupting 09 09 2014 09 09 2014 09 09 2014 09 09 2014 09 09 2014