DA EOSC 114 Learning Goals Volcanoes

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Department
Earth and Ocean Sciences
Course
EOSC 114
Professor
Leah May Ver
Semester
Fall

Description
Ch.3 Learning Goals 1. Explain what magma - Magma is formed by melting pre-existing rock in earth’s interior density and magma - Melted rock is less dense than solid rock so it will rise towards viscosity are the surface - For magma to rise through the crust, it must be: (1) less dense than the crust (2) runny enough to flow (low viscosity) (3) hot enough to stay liquid - Lava is the solid rock formed when magma erupts and cools - Viscosity is the resistance to flow - More Silica magma=higher viscosity 2. Explain why some - Low viscosity + low gas content= lava magmas erupt explosively - High viscosity + high gas content= pyroclastic material (as pyroclastic material) - Felsic magma form a lower temperature, high gas content have and some magmas erupt high viscosity and tend to erupt explosively; forms lighter colored effusively (as lava) felsic rocks called rhyolites - Mafic magmas form a high temperature, low viscosity and gas content and tend to erupt effusively (non-explosively); forms mafic dark colored rocks called basalts 3. Explain the differences Pahoehoe- ropy-textured, smooth and moves much more quickly between pahoehoe and a’a than a’a lava lavas A’a- rubble-y flow top consisting of broken fragments of lava and is chunky and viscous - Pahoehoe can change to a’a 4. Describe the different There are 6 different types of volcanic eruptions: types of volcanic eruptions 1. Hawaiian- contain low viscosity basaltic magma and are and how they are related non-explosive to magma properties 2. Strombolian- mildly explosive and usually contain basaltic or andesitic magma and lava bombs, which are chunks of magma that solidify midair 3. Vulcanian- contains viscous, andesitic or rhyolitic magma and are very explosive 4. Pelean- have an avalanche of ash and are violently explosive 5. Plinian- sustained column of ash and are characterized by pyroclastic flows and andesitic/rhyolite ash. They are violently explosive 6. Phreatomagmatic- caused by magma coming into contact with water, causing it to become even more explosive. This can occur with any type of magma - Some cases, magma erupts and cools so quickly that crystallization does not occur=solidifies into glass = volcanic glass (obsidianmassive, pumicecontain bubbles/vesicles) 5. Describe the Mafic Volcanic Landform: very fluid (low viscosity) and can morphology, dominant travel long distances from a vent (30 km/hr) rock type and typical 1. Shield volcano: tens of kilometer high and over 100 km eruption style of the across; repeated eruption of basaltic lava flows form most different types of of a shield volcano; have small eruptive centers called volcanoes cinder cones that are present on flanks 2. Cinder cones: are the smallest types of volcano and can occur on the sides of shield volcanoes. They are mafic and mildly explosive, created from pyroclastic material. They usually erupt only once and never again. Intermediate to felsic magma: erupts explosively, producing ash columns that penetrate to higher than 40 km into atmosphere; ash travels around the world due to upper level winds and falls when wind dies to form layers that blanket landscape (Mt. St. Helens) 1. Composite volcano/ stratovolcano: composed of alternating layers of lava flows and pyroclastic layers, along with volcanic domes and tabular intrusions known as dykes and sills; tall, conical, and have steep slopes. They can erupt many times and are frequently explosive, and can stay active for ~100k years. - Lava dome: pile of viscous lava that forms over a vent; mushroom-like shape and does not travel far from vent; may stand alone or be erupted in the center or on the flank of existing volcano; Felsic Volcanic Landform Felsic Volcanic Landform- Calderas: very large depressions in earth’s crust caused by voluminous eruption of explosive felsic pyroclastic material; 10s to over 100 km across and kilometers deep; not to be confused with a crater (depression on top of a volcanic vent and typically only 10s to 100s of meters across) - Most explosive volcanoes but erupt infrequently Most hazardous volcanoes are composite volcanoes and calderas 6. Explain what lava flows, Mafic Lava Flows: low viscosity that erupt at 1200-1400 C, NOT fire fountains, lava bombs, explosive; divided into pahoehoe and a’a lava flows and volcanic ash are and how they form Fire Fountains: small explosive eruptions created by basaltic lava that contain lots of gas causing fire to shoot up from the volcano. The magma can fall back on to the ground and turn into lava. Ash particles: smallest pyroclasts (high-silica) that form from fragmentation of a frothy magma when the pressure within the gas bubbles exceeds the strength of the viscous magma Bombs & Blocks: largest pyroclasts; explosively ejected during eruption which then cool in midair to form balistic rocks 7. Describe the particular Mafic Lava Flows: people are able to run out of the way so main hazards associated with hazard is infrastructure damage lava flows, fire fountaining, lava bombs, Fire fountain: generally not dangerous but can turn into lava and ash fall flows Lava bombs: are dangerous if they fall and hit people Ash particles: ash columns form and is picked up by global winds, ash injected into stratosphere can contribute to a lower amount of solar radiation reaching Earth’s surface, and therefore to global cooling; can choke vehicle and airplane engines, aggravate respiratory ailments, bury homes and other structures and/or cause their collapse, and cover valuable agricultural land= decreasing food supply leading to famine 8 . Explain what Pyroclastic flows: avalanches of hot gas and pyroclastic pyroclastic flows, lahars, fragments; consists of ash, lapilli, crystals, and lithic fragments; volcanic domes, sector confined to low areas in the topography; travels up to 300-400 collapses, lateral blasts, km/hr and is generally in the 500-700 C range made by (1) and toxic gases are and collapse of dome (2) over spilling crater rim (3) direct blast (4) how they form eruption column collapses Lahars: volcanic mud or debris flows are extremely destructive mixtures of water, ash, rock fragments of all sizes, and debris that travel swiftly down slope form a volcano up to 50 km/hr; may occur after volcanic activity has ceased or when hot associated with pyroclastic eruptions Toxic gasses: released by a volcano during or between active eruptions; water, carbon dioxide are the most common components Volcanic landslide (sector collapse): down slope failure of a portion of a volcanic edifice caused by a mixture of water and clay turning in to mudflows or debris flows= debris avalanche. An eruption, called a lateral blast can then result due to the lowered pressure on the magma 9. Describe the particular Pyroclastic flows: most lethal of eruptive products; all life and hazards associated with structures in its path are des
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