Lecture 9 - Exploding Earth

Lecture 9 - Exploding Earth - • 

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Unformatted text preview: •  !"#$%&'(")&*"+,-.)&"/&,01&2$0/#%3!!"#!$%!&'!('&)*+!,'%%$-(*!#'! %.$#/0!#0*!123!'4!3'5+!6*(1!#+$,7!8'5!9:;<!2=*&1!#0*!6*(1! #+$,!'&!#0*!123!3'5!02>*!%$)&*1!5,!4'+7! •  !"#$%4(")& –  (*2>*%!2#!?!,@!'&!#0*!AB#0C!D2@!'&!#0*!?%#! –  -5%*%!.$((!-*!$&!4+'&#!'4!E2@$(#'&!E2((! –  .*2+!%5$#2-(*!/('#0$&)F4''#.*2+! •  567&8#$)&9:2#&80;(/!2+*!2>2$(2-(*!*>*+3!9'&C!G*1C!H+$! 4+'@!??IABJ?KIAB!$&!L;M!K?D! •  <;"=&>!2>2$(2-(*!4+'@!H+$123C!;*,#7AB#0!2#!DIAB2@!5&N(! <[email protected]!!8'5!.$((!02>*!?!2=*@,#!'&(3C! .$#0!RSBB@$&!#'!/'@,(*#*!#0*!2=*@,#7!!;TUV!2((!+*%,'&%*%! 2&1!#'!,+*%%!#0*!;:M9"<!-5='&!.0*&!6&$%0*1W! Exploding Earth: volcanoes 1. Introduction 2. Terminology 3. Location of Volcanic Activity 4. Types of Lava 5. Types of Volcanoes 6. Volcanic Hazards 7.  Volcanic Rocks http://volcanoes.usgs.gov/ •  !! April 2010 750 tonnes •  Eruption ofer second of ash !! p •  T%0!,(5@*!1$%+5,#*1! X$)0#%!#'F4+'@!V5+',*! 4'+!%*>*+2(!.**Y%! Mt. St. Helens http://vulcan.wr.usgs.gov Erupted in 1980: recent activity 2004-2006 (but on-going) •  Ongoing earthquake activity below •  Movement of magmaolcano the v Sept 2004 Sept 2005 lots of small earthquakes near the surface growth of lava dome - 2005 Why is it important to understand how volcanoes work? –  To understand/predict volcanic hazards # killed Laki (1783), Iceland >10000 Mt Pelee ( 1902), Martinique >30000 Mt St. Helens ( ) 1980 1985 Nevado del Ruis ( ), Columbia 1997 Montserrat ( ), Martinique 62 >20000 19 - To understand the nature of earth's interior - Resource exploration (rare gems are related to volcanic activity) - Geothermal NRG - New Zealand, Iceland, Canada (BC) produces it •  MAGMA: Molten Rock •  LAVA: magma that reaches the earth's surface •  Pyroclastic degree: lava and rock fragments ejected during a volcanic eruption volcanic bomb (ball of l ava) Lapilli - small ball of lava (smaller than a dime) Ancient Volcanic Ash layers - can cause health issues b/c ash is so small you cant tell what it is •  •  VENTS - opening through which eruption takes place VOLCANO - hill or mountain produced by volcanism •  Crater - •  depression over vent CALDERA - depression; > 1 km wide Where do we find volcanoes? •  D IVERGENT PLATE BOUNDARIES (plates pulling apart) - ex: submarine eruptions along mid-oceanic ridge, Iceland Fig. 2.1 Pillow lavas when lava comes up and cools quickly Convergent plate boundaries (plates subducting under each other) !  Fig. 7.22 - Pacific "ring of fire" - Mt. Pinatubo - Cascade Volcanoes (mt. st. Helens) •  HOT SPOTS - not associated with plate boundaries (ex: Hawaii) Fig. 2.39 •  Related to mantle plumes, narrow columns of hot mantle rock •  Plume is stationary, plates move Chain of •  produced -volcanic islandson fringing reefs the sides Fig. 2.42 Which is the youngest Hawaiian island? Guyots are old volcanic islands under the waters surface e.g. Hawaiian islands Fig. 2.43 - Youngest Hawaiian Island b/c its the biggest, all other are older/eroding - eroding by wave action to form seamounts Fig. 2.36 Why do hot spots develop in certain places? - Hot Spots related to mantle plumes - Hawaii - over plume - rocks have isotopic characteristic of core Silica content of magma is critical •  Affect style of eruption and type of volcano produced –  •  Silica rich (felsic) lavas - Very viscous, flow slowly - gases cannot escape easily - violent eruptions, explosive - ex: rhyolite • Silica-poor (mafic) lavas - low viscosity, flow easy - gases escape easily - quiet eruptions, lava flows - Basalt • Intermediate lavas (ex: andesite) •  3 main types - shield, conder cone, composite - Shield Volcanoes: broad, sloping cones, low viscosity lava flows, non-violent eruptions (mafic) e.g. Hawaiian Islands Pahoehoe - ropey (hot lava) •  Basaltic lavas flow easily •  Two types –  - Pahoehoe - Aa Aa - sharp, jagged (cooler) Form on shield volcanoes • Splatter cones: trapped in cooling lava when gas is Apillie, pyroclastic cones build up and you get a little cone volcano •  Pyroclastic Cones: made of pyroclastic debris; steep slopes; small - Felsic or intermediate lavas - formed when gas escapes - ex: Sunset Crater, Arizona • COMPOSITE VOLCANOES - alternating lava flows and pyroclastic debris - intermediate steepness - form over a long time - can be very large e.g. Mt. Garibaldi, B.C. Fig. 7.21 •  - m ostly associated with intermediate lavas (andesitic), violent eruptions ex. Mt. St. Helens, Mt. Etna, Mt. Vesuvius Table 7.2 What kinds of hazard are produced by volcanoes? •  Lava Flows -- destructive to property, roads, etc Pyroclastic debris - volcanic bombs, ash pyro --> Fire clastic --> broken Mt. St. Helens's -- volcanic ash microscopic ash ASH - tiny glass shards •  PYROCLASTIC FLOWS - nuee ardente, mixture of hot gases and volcanic debris - tavels at >100km/h - very dangerous - St. Pierre, Martinique, 1922 Mayon Volcano, Phillipines, 1984 flow of hot gas/ashes •  Debris flows (lahars) - mudflows, flow along valleys - hot mud flows 1985 eruption: Lahars caused 23,000 deaths TOXIC GASES - Water vapour, CO2, CO, hydrogen sulphide, sulphur dioxide - heavier than air move along topographic depression Lake Nyos, Cameroon August 21, 1986 1700 people killed by CO2 •  Steam explosions Island arcs –-  seawater seeps into rock and comes into contact with magma - steam produced and blows up volcano (phreatic eruption) e.g. Krakatoa, 1883 silica is sticky; traps gas, causes l arge explosion •  Krakatoa (1883) –  sound heard 3000 miles away –  40 m high tsunami killed over 36,000 people –  huge ash clouds produced ) What is the effect of huge ash clouds - l ower temp - effects on climate - global temperature reduced 0.5'C for 10 yrs after Krakatoa eruption, cooling after Pinatubo ? What is a rock? a ROCK is a naturally • material composed of formed,ofconsolidated grains one or more m inerals What is a mineral •  a MINERAL is a naturally occuring, inorganic, crystalline solid that has a definite chemical composition Volcanic Rocks also called igneous rocks •  - -form from solidified magma volcanic plug; volcano eroded away •  either at the Earth's surface (extrusive) or underground (intrusive) How do we classify igneous rocks? by Texture (coarse and fine) by mineralogy (composition of magma) Intrusive Igneous rocks Under what conditions would these form? How would this affect their characteristics? •  Cool slowly ( > 1 million years), under pressure •  - Coarse grained (large crystals) - granite (quartz, feldspars) - Gabbro (Ferromagnetism, feldspars) gabbro granite INTRUSIVE IGNEOUS ROCKS - formed at depth are called plutonic rocks •  INTRUSIONS - bodies of i nstrusive rock - plutons, sills, dykes Fig. 6.2 e.g. Ship Rock, New Mexico Fig. 6.8 DIKES Extrusive Igneous Rocks How do these differ from intrusive igneous rocks? •  •  Cool rapidly as lavas or tephra (rock fragments) Mostly fine-grained (small crystals) intrusive extrusive EXTRUSIVE ______________ _______________ Intrusive igneous rocks •  Either Silica rich, light coloured (ex. rhyolite) •  Or rich in ferromagnetism minerals, dark coloured (ex. basalt) basalt rhyolite Extrusive Igneous Rocks •  may be glassy (ex: osidian) - extremely rapid cooling •  may contain vesicles, or holes (ex: pumice) Can rocks float? Yes – if they are pumice! •  Read Chapters 6 and 7 in textbook –  Igneous rocks, intrusive activity –  Volcanism and extrusive rocks •  Answer this question: What are phenocrysts? ...
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This note was uploaded on 11/28/2011 for the course ENV SCI 1G03 taught by Professor Padden during the Fall '11 term at McMaster University.

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