GEO 101-007 Chapter 5 Lecture Notes
GEO 101-007 Chapter 5 Lecture Notes GEO 101-007
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This 6 page Class Notes was uploaded by Jennifer Gintovt on Wednesday September 16, 2015. The Class Notes belongs to GEO 101-007 at University of Alabama - Tuscaloosa taught by Dr. William Lambert in Summer 2015. Since its upload, it has received 36 views. For similar materials see The Dynamic Earth in Geology at University of Alabama - Tuscaloosa.
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Date Created: 09/16/15
GEO 101007 91615 Chapter 5 The Wrath of Vulcan Volcanic Eruptions The year without a summer 1816 Iune 67th 1816 6 inches of snow in NY state Crop failure and significant food shortages Price of food increased sharply 1815 Eruption of Mount Tambora Indonesia 4000 feet of mountain was removed by eruption gt71000 fatalities Rock and ash ew into the atmosphere Toxic gases also were added to the atmosphere Additions to the atmosphere is thought to have lowered global temperatures Volcanic Eruptions affect us all Hazards associated with volcanic eruptions Ash cloud so dense that solar radiation is re ected back to space resulting in short term global cooling or Water vapor and C02 create greenhouse effect resulting in warming Water vapor and other gases SOZ HCl HF produce acid rains that kill crops and livestock 2011 eruption of Grimsvotn Iceland 0 900 ights canceled over a 3day span British airways ight 9 1982 o Flew into an ash cloud by mistake o All 4 engines failed 0 Had to glide out of ash cloud and restart enough engines to y to safety Mt Vesuvius Pompeii Italy City buried under 1320 feet of volcanic ash after Mt Vesuvius eruptio9n in 79 AD Another eruption is not a matter of quotifquot but rather a matter of when Surrounding population approximately 3 million Origin of the term Volcano Vulcano Italy 0 Vulcan God of Fire Simply put Volcanic eruptions transfer material from inside the Earth to the planet s surface GEO 101007 91615 The products of volcanic eruptions Lava ows sheets or mounts of lava that ow onto the ground surface or sea oor in molten form and then solidify Review Viscosity resistance to ow 0 Melts with a high viscosity do not ow easily Review Factors affecting viscosity temperature volatile content silica content Hot lava with a high concentration of volatiles and low concentration of silica ows easily Three types of lava ows based on silica content 1 Basaltic mafic chemistry low silica content 2 Andesitic intermediate chemistry medium silica content 3 Rhyolitic felsic chemistry high silica content Basaltic Lava Flow Basaltic mafic lava ows have very low viscosity when first emerging from the ground due to high heat and low silica content Typically ow less than 10km 6 miles from the source but up to 500 km 310 miles in rare cases Very surface of lava begins to solidify relatively quickly Basaltic Lava Flow Features Lava tube the empty space left when a lava tunnel drains this happens when the surface of a lava ow solidifies while the inner part of the ow continues to stream downhill Pahoehoe Hawaiian term a lava ow with a surface of smooth glassy ropelike ridges Hawaiian term a lava ow with a rubbly surface Columnar jointing a type of fracturing that yields roughly hexagonal columns of basalt when a dike sill or lava ow cools Pillow basalts glassencrusted basalt blobs that form when magma extrudes on the sea oor and cools very quickly pressure plays role Andesitic Lava Flow Andesitic intermediate lava ows have higher viscosity due to higher silica content vs basaltic lava ow Typically ow less than 10 km 6 miles from the source Flows slowly so surface has time to cool angular blocks develop Rhyolitic Lava Flow Rhyolitic felsic lava ows have highest viscosity due to highest silica content also tend to be coolest GEO 101007 91615 Typically ow less than 12 km 0612 miles from the source May form a lava quotdomequot Very blocky Dionisio Pulido Farmer who experienced an earthquake that quickly formed into a volcano on his farm Paricutin Volcano 1943 Mexico Volcaniclastic deposits fragmental igneous materialquot Pyroclastic debris from basaltic eruptions weak eruptions Lapill39 Latin for little stones Pea to plumsized fragments of glassy lava and scoria aka cinders Bombs Apple or largersized fragments Solidify while still in the air May become streamlined during ight Pyroclastic debris from andesiticrhyolitic eruptions explosive eruptions Ash tiny shards of glass from lava sprayed high into the air Two types of lapilli may also be produced Volcanic Ash Some ash reaches high altitude and falls back to earth like snow However gravity quickly returns some ash to the ground as a pyroclastic ow or glowing avalanche French nu e ardente St Pierre Caribbean Islands Population of 28000 Two survivors 1902 pyroclastic ow 450 C 842 F 300 km per hour 186 miles per hour GEO 101007 91615 A Few more terms Tephra unconsolidated loose deposits of pyroclastic grains regardless of size Tuff Ash or ash mixed with lapilla that has been buried and transformed into solid rock Lahar Mobile mixtures of ash coarser debris and water i few more terms 7 Crater vs Fissure Eruption At a crater eruption lava spouts from a chimneyshaped conduit At a fissure eruption lava erupts as a curtain along a crack Volcanic Caldera Formation As an eruption begins the magma chamber in ates with magma During an eruption the magma chamber drains and the central portion of the volcano collapses downward The collapsed area becomes a caldera Later a new volcano may begin to grow within the caldera Three types of Volcanoes 1 Shield volcanoes 2 Cinder volcanoes 3 Stratovolcanoes aka composite Shield Volcano Not explosive basaltic mafic lava relatively safe Cinder Cone Volcano sputters tephra out basaltic lava but more gas content relatively safe GEO 101007 91615 Stratovolcanoes or composite Classic Volcano Shape Very explosive rhyolitic felsic lava dangerous Effusive Eruptions Mainly basaltic lavas low viscosity shield volcanoes Explosive eruptions Mainly rhyolitic lavas high viscosity stratovolcanoes Mt St Helens 1980 eruption Washington state 57 causalities Damage cost 27 billion Volcanic activity is NOT random Stratovolcanoes occur at convergent plate boundaries Shield volcanoes above hot spots Cinder cones develop at continental rifts each volcano type can occur in other settings Active dormant and extinct volcanoes Active volcanoes that are erupting have erupted recently or are likely to erupt soon Dormant volcanoes that have not erupted for hundreds or thousands of years but have the potential to erupt again Extinct volcanoes that were active in the past but have shut of entirely and will never erupt again 0 Example Devils Tower Wyoming Predicting eruptions 1 Earthquake activity 2 Changes in heat ow 3 Changes in shape 4 Increases in gas emission and steam Earthquake activity As large volumes of magma moves up from below rock moves and cracks releasing energy that can be detected as small earthquakes An increase in earthquake activity might suggest a future eruption Changes in heat ow As large volumes of magma moves up from below more heat is brought near the surface Melting snow on volcano summit might suggest a future eruption GEO 101007 91615 Changes in shape As large volumes of magma moves up from below the volcano will actually bulge Measurable bulging of volcano might suggest a future eruption Increase gas steam As large volumes of magma moves up from below more gases and steam will vent from the volcano These gas increases might suggest a future eruption Volcanic eruptions remain largely unpredictable Despite all our advances in technology we are not able to give proper warning of upcoming volcanic eruptions Millions of people risk their lives every day due to their proximity to active volcanismincluding this guy