Geo sci final - Introduction to Volcanoes What is a volcano...

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Building a Volcano Melting at the Mantle Pre-Eruption Inflation Change in tilt, distance Number of Earthquakes olcano inflates prior to eruption Volcano in repose Introduction to Volcanoes What is a volcano? - A place on the earth’s surface where molten rock and gases are erupted. - A hill or mountain built up by the eruption of molten rock Stratavolcano – “Ideal Volcano” - Cones are built up of layers of lava and volcanic ash. - Examples: o Mount Hood, Cascades o Mount Shasta, Cascades Cinder Cones - Simplest type of volcano - Built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone. - Examples: o Haleakala, HI o Surtsey, Iceland o Paricutin, Mexico Shield Volcanoes - Formed mostly from the solidification of lava flows of basalt - Lava flows are low viscosity – fluid travels great distances - Examples: o Mauna Loa, HI World’s largest volcano 13,690 ft about sea level 33,000 ft from ocean floor o Mauna Kea, HI o Kilauea, HI o Newberry, Oregon - Composed of vicious lavas and ash, shield volcanoes are made of fluid basalt lava flows - Lava flows give volcanoes a shield like shape 1
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- Olympus Mons o Giant shield volcano on Mars o Believed to be the largest volcano in the solar system Holes and Craters - Mars and explosion craters are produced when hot magma reacts violently with shallow water or water soaked ground - Example: o Zuni Maar, New Mexico o Vitti, Iceland o Crater Lake, Oregon Different kind of hole in the ground What is now left of a large stratavolcano that blew itself to bits 6,845 years ago o Long Valley Caldera, CA Some volcanic holes in the ground are too big to be appreciated Formed by a collapse bout 760,000 years ago following a gigantic explosion Last eruption was 600 yrs ago Fissures - Lava erupting from cracks can produce huge thick piles of lava o Eastern Iceland o Krafla, Iceland o Snake River Plain, Idaho Where do volcanoes occur? - Plate Margins o Spreading Margins Mid-Ocean Ridges – Iceland Rifting Continents – E. African Rift o Converging Margins Island Arcs – Aleutians, Japan Continental Margins – Cascades, Andes - Plate Interiors o Oceanic Plates - Hawaii o Continental Plates – Yellowstone Volcanic Activity - Total number of recognizable volcanoes: 10,000 - Active – Volcanoes known to have erupted during historical times - 529 - Dormant – Volcanoes that have no erupted during historical times, but will probably erupt again – 1,340 - Extinct – Volcanoes that are unlikely to erupt again - 500 currently active volcanoes - 5-10 volcanoes erupt per month (50/yr) - 262,000 people have been killed by volcanoes since 1600 A.D.
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