Chapter 4 -Volcanism & Extrusive RocksQuiz #1 GEOL1113H - Chapter 3 Tuesday, September 11, 2007PowerPoint PresentationSlide 4Slide 5Slide 6Slide 7Pressure Effects on Volatile-rich SystemsVolatile Control on Eruption StyleSlide 10Slide 11Slide 12obsidianandesite (porphyritic)Slide 15Slide 16pumice (frothy)volcanic bombs: rapidly cooled magma thrown from venttuff: rock composed of fine-grained pyroclastic materialSlide 20Slide 21Slide 22Gary Rosenquist Photo Sequence - Mt. St. Helen’s, May 18, 1980 (occurred in three minutes)Mt. St. Helen’s eruption column - May 18, 1980Slide 25Mt. St. Helen’s May 18, 1980 devastationvolcano after May 18, 1980 with lava dome inside craterwhat happened at Mt. St. Helens?Slide 29Slide 30Crater lake - Wizard Island - 5 kBP Eruption Mt. Mazamacaldera formation from eruption of ancient Mt. MazamaSlide 33Slide 34Cascade EruptionsSlide 36Slide 37VEI ReduxSlide 39Slide 40Slide 41devastation of St. Pierre, Martinique by pyroclastic flowsPlymouth, Montserrat - Oct. 1997Deadliest Eruptions Since 1500 ADEruption Frequency vs. VEIChapter 4 -Volcanism & Extrusive RocksPhoto Credit: S. YoungQuiz #1 GEOL1113H - Chapter 3 Tuesday, September 11, 20071. Mafic magma is generated at divergent boundaries because ofa) water under pressureb) magmatic underplatingc) melting in the lithosphered) decompression melting of upwelling asthenosphere2. The major difference between intrusive and extrusive igneous rocks isa) chemical compositionb) the type of minerals found in the rockc) where the rocks solidify (i.e. cool and crystallize)d) all of the abovevolcanism• process that results in expulsion of molten rock on surfaceexamples:in any given year about 50 eruptions occur--about 600 volcanoes have erupted 200 times in past 2,000 years--lava and hot particles (pyroclasts) erupt and build volcanoesQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.KilimanjaroQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Mt. FujiQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Mount VesuviusQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Kilaueavolcanism: benefitsatmosphere -- created from gases released by magmashydrosphere -- produced from condensation of water vapor released by volcanismbiosphere -- has positive and negative effects• lava flows and ash weather to produce fertile soils• violent eruptions can destroy nearly all life in their paths• large amounts of ash and volcanic gases in atmosphere can trigger rapid climate changes and lead to mass extinctionsother benefits --• added real estate• geothermal energy• spectacular sceneryliving with volcanoes:QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.mythology: Pele (Hawaii) exiled from Tahiti by her father because of her temper QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.geothermal energy: Iceland source of inexpensive and clean energy QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.volcanic catastrophes: Pompeii, Tambora, Martinique, Nyos QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Pompeii: 79 AD; VesuviusQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Tambora: 1815; 90,000 killed;larger than Krakatoa;year with no summerQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Martinique: 1902; PeleQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Lake Nyos: 1986; CO2 gasreleased;hugged groundnot all volcanoes are the same!contrast Mt. St. Helens with HawaiiWhy?violence of eruptions controlled by:• dissolved gases in the magma --water vapor, carbon dioxide, sulfur dioxide, etc. andease/difficulty by which they escape• viscosity of the magma (fluid’s resistance to flow) -- silica content: higher silica has higher viscosity -- temperature: cooler lavas have higher viscosities -- dissolved gases: more dissolved gases yield lower viscositiesQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Pressure Effects on Volatile-rich SystemsFrom: Best, 2003From: Sparks, 1978Volatile Control on Eruption Styleinvestigation of volcanismrocks, gases, and events observed at modern eruptions are compared to similar ancient lavas to infer past activity composition of rocks (silica content)rhyolite: high silica; light colorQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.basalt: low silica; dark colorandesite: intermediate silica; intermediate colorextrusive texturesglassy: without mineral crystalsobsidianfine-grained (aphanitic): crystals < 1 mmporphyritic: large crystals in a matrix of small crystalsandesiteQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.basaltextrusive texturesvesicular: frothy (trapped gas bubbles)fragmental: particles blasted apart by eruptiondust and ash ( < 2 mm)cinders ( 2 - 64 mm)blocks and bombs ( > 64 mm)pyroclasts -- hot particlesQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.pumiceQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.cinder coneobsidianandesite (porphyritic)andesite under microscope: note small/big crystalsvesicles representgas bubblesvesicular basaltpumice (frothy)volcanic bombs: rapidly cooled magma thrown from venttuff: rock composed of fine-grained pyroclastic materialQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.tuffvolcanic landformsvent: opening through which lava eruptscrater: depression over the vent at the summit of the volcanocaldera: depression much larger than original crater ( > 1 km)QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.last major eruption was Mount Saint Helensin 1980(andesitic)renewed dome growthin october 2004volcanic chain inPacific Northwestfrom northern Californiato British ColumbiaCascade volcanoesGary Rosenquist Photo Sequence - Mt. St. Helen’s, May 18, 1980(occurred in three minutes)Mt. St. Helen’s eruption column -