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Volcanoes Volcanoes Mountains built up by molten rock that has risen to the earth’s surface through a vent. Volcanologist – a volcano geologist Volcano Terms Molten rock inside the earth – Magma The source of magma at the bottom of the vent – Magma chamber Connects the magma chamber with the earth’s surface – Vent Magma that reaches the earth’s surface – Lava Layered structure of lava, ash, or both that was built up by successive eruptions – Volcanic cone Secondary cone that forms on the side of the main cone or is completely separate from it – Parasitic cone Depression at the top of the cone – Crater Enlarged depression caused by an explosion or the collapse of a volcanic cone; often filled with water – Caldera Volcanic Emissions Gaseous Emissions Dissolved gases separate from the magma because of reduce pressure as the magma approaches the surface Glowing avalanche – mixture of hot solid particles suspended in water vapor and other gases – At night it glows a dull red – So heavy that it flows quickly down a volcano’s slope instead of rising into the air – Also called a pyroclastic flow – Can move at up to 93 mph and contain gases from 100-800*C – Suffocates or incinerates everything in its path Superheated water vapor – Lahar – a mud-flow of volcanic ash mixed with water At Nevado del Ruiz in Colombia over 23,000 people died when a lahar, started by a relatively minor eruption of the volcano, swept down the river valleys on the side of the edifice and destroyed Armero and Chinchina. The footage of rescue efforts after the lahar were devastating and heartbreaking. Sadly, this disaster was mostly preventable as the citizens of these towns could have had at least an hour's warning to walk to higher ground, but the Colombian government did not have an effective plan in place. I clearly remember driving through the area hit by the lahar a few years after it occurred. The whole area paved by the mud, rock hard by the time I saw it a few years later. However, if any good came from this event, it was that it opened many people's eyes around the world to the dangers posed by volcanoes and the relatively simple solutions to preventing tragedies like this. Fumaroles – a vent in the ground where steam and gases from volcanic activity escape – Carbon dioxide escaping from fumaroles can be dangerous Liquid Emissons Thin, runny magma is more likely than thick magma to remain fluid enough to flow as lava. Lava causes fewer deaths than other types of volcanic emissions because of its slow rate of flow. Pahoehoe lava flow – Fast flowing lava – Has a shiny surface and an appearance similar to twisted rope when hardened ‘A’a lava flow – Slow flowing lava that has a rough broken surface with sharp edges when hardened Pillow lava flow – Forms under water Solid Emissions Solidified lava; also called pyroclastic materials – Ash – tiny, angular, glassy fragments – Tephra – an accumulation of loose ash – Cinders – pieces of solidified magma a little larger than ash – Bombs – masses of lava that solidify while flying through the air Classifying Volcanoes There are three major ways to classify volcanoes. – Structure – Activity – Explosivity Structure Shield Volcano Cinder Cone Volcano Composite Volcano Shield Volcano Emits mostly lava in quiet eruptions Dome shaped with relatively flat slopes Broadest type of volcano Examples of Shield Volcanoes Hawaiian Islands Mauna Loa – the world’s largest active volcano Mauna Kea - greatest actual height of any mountain on earth Surtsey – formed a new island in 1963 – Now supports plant life and animals Olympus Mons on Mars – Largest volcano in the solar system Island of Hawaii Surtsey Olympus Mons on Mars Olympus Mons, Mars Maxwell Montes, Venus Mt. Everest, Earth Cinder Cone Volcano Emits mostly cinders, ashes, and bombs Relatively steep slopes Results from a single, short eruptive period – Typically small Paricutin in Mexico Paricutin Composite Cone Volcano Emits lava and solid debris in alternately quiet and explosive eruptions Size is between shield and cinder cone Typical “volcano shape” Most volcanoes are composite volcanoes. – Fuji in Japan – Mt. Rainer and Mt. St. Helens in Washington – Mt. Vesuvius in Italy Mt. Fuji Mt. Rainier Classified by Historical Activity When classifying a volcano by activity, scientists must consider – Time since last eruption – Associated earthquake activity – Nearby hot springs – Changes of elevation within the volcano’s crater or caldera Active Volcano Has erupted within historical times or shows signs that it could erupt at any time – Mauna Loa in Hawaii – Vesuvius in Italy – Mt. St. Helens in Washington Continuous Volcano Mt. Stromboli, Italy The eruptions of Stromboli are seen best at night, when chunks of lava blasted out of the volcano trace bright red arcs in the sky. In fact, it's such an iconic type of eruption that geologists have named an entire class of eruptions after Mount Stromboli. Whenever you get a volcano blasting out blobs of hot lava, gas, and rocks in arcs from its volcanic vent, that's a strombolian eruption. Dormant Volcano Has not erupted in historical times but could erupt based on seismic indications of tectonic activity beneath the volcano – Mt. Rainier in Washington – Mauna Kea in Hawaii Some of the largest and most expensive telescopes are built on the summit. Extinct Volcano No historical record of eruptions No significant seismic activity Evidence of long periods of inactivity based on erosion patterns – Almost any supposedly extinct volcano has the potential to erupt again. – A volcano cannot be classified as truly extinct until the magma chamber has been exposed by erosion. Classified by Explosivity Volcanic Explosivity Index (VEI) – A scale of 1 – 8 which estimates the explosive power of a volcanic eruption Mt. Tambora in Indonesia (1815) – Category 7 – Most powerful eruption in recorded history The Yellowstone Caldera in Yellowstone National Park was believed to be formed by a category 8 eruption. Mt. Tambora Category 7 Eruption Classified by Location Most active volcanoes are located in two volcano belts Circum Pacific Belt Ring of Fire Alpine – Himalayan Belt Heated Groundwater How is Groundwater Heated? Geothermal gradient – the rate of temperature change with depth – The earth’s temperature rises between 15 50* C per kilometer of depth in the crust. Core temperature is approximately 5000* C Surface temperature is about 30* C Magma Intrusions Hydrothermal Processes Hot Springs – an area where heated water rises to the surface in a liquid state. – The heated groundwater dissolves minerals in the rocks that it flows through. – The hot water cools when it reaches the surface and the minerals precipitate. Mud pots – hot springs that come to the surface in volcanic ash and cinder fields Mammoth Hot Springs Yellowstone Park Warm Springs, Georgia Geysers Thermal springs that eject water from the ground at intervals For a geyser to occur there must be – Heat, water, and a plumbing system – Scientists think geysers are heated with magma Geyserite – a whitish deposit consisting of silica dissolved from the igneous rock through which the hot water has passed Geothermal Energy The internal energy of the earth – Especially evident in areas where hot springs, fumaroles, and geysers exist Uses for Geothermal Energy Resorts use hot spring for bathing and swimming Heating homes and businesses Generating electricity More than 85% of the homes in Iceland are heated by geothermal steam The US is the largest producer of geothermally generated electricity. – Enough to continually supply 130,000 homes Difficulties in Developing Geothermal Energy Deciding where to explore – Not many areas have heat close enough to the surface to be accessible. Obtaining funding to drill exploratory wells – The financial risk discourages investors.