Chapter 8

Chapter 8 - Chapter 8 I Obsidian is a very shiny natural...

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Chapter 8 I. Obsidian is a very shiny natural volcanic gas, usually of rhyolitic (felsic) composition and is typically black in color. Compared with window glass, obsidian is rich in iron and magnesium; tiny(<.005 mm) crystals of iron oxide within the glass cause its dark color. a. Produced when lava cools very quickly. The lava cools so quickly that no crystals can form. Glass, unlike crystals, has no regular structure and therefore fractures in smooth conchoidal (curved) shapes. When people make glass they melt silica rock like sand and quartz then cool it rapidly by placing it in water. Obsidian is produced in nature in a similar way. II. 13,000 volcanic forms recognized III. 800 active volcanoes IV. 50 erupt every year on surface and under earth. When recent we see feature like flows a. Moon and mars- not recent (10,000-5,000 years) aren’t exposed to a very active atmosphere V. Volcanic rocks easily weather and decay into plastic(clastic) pieces and dissolve away, that’s why volcanic structures disappear quickly. VI. Volcanic activity has fluctuated throughout history a. Collisions of earth with foreign bodies might cause volcanoes. Past 2 million years volcanic activity has been on the increase VII. 755 volcanoes that are active are below ocean VIII. Volcanoes bring new material to earth’s surface to form new minerals IX. Volcanoes alter climate by whet they erupt into the atmosphere- greenhouse gases, increase affect of solar radiation, cause climate cooling X. Water, vapor, and carbon dioxide, raise climate temperature XI. Sulfur dioxide can cool climate XII. 1783, Franklin—volcanic effect on climate, introduction of particles in earth’s atmosphere. XIII. 1860- year without a winter, snowed in July on blue ridge a. Dropped by 2 degrees f in global temperature XIV. Pinatubo Phillipines a. 1991 after 600 years of dormancy
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b. 15-20 million tons of ash and sulfuric acid blasted 16-25 km into the atmosphere c. 12 km3 of materials ejected d. 60 days after the eruption about 42% of the globe was affected e. Increase in atmospheric albedo of 1.5% f. Lowered n. hemisphere temp (9F----.5 C) XV. Magma (below)- molten rock, minerals grains and gases below the surface XVI. Lava (above)- composistion is primarily silicon (most dominant element in earth’s crust) a. Affects viscosity (how easily a liquid flows (high viscosity, slow flow), nature of volcanoes, types of rocks that form i. The less silicon the less stick/viscous the magma is ii. Temp has effect on viscosity (hotter the magma, the less viscous) iii. Viscosity affects nature/violence of eruption (silicon, temp) b. All rocks from magma= igneous XVII. Volcanic gases are .2-5% of magma. 98% of hases are (1) H2O, (2) CO2, (3) Sulfur gasses. Others include N2, CI, and Ar a. Gasses other than H20- can be toxic and can cause destruction to life surrounding has b. More gas magma contains- more violent the eruption XVIII. Kinds of Magma a. Mafic- (Ma)- magnesium is high (Fic)- iron is high Silicon dioxide is lowest 50%-
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This note was uploaded on 11/23/2008 for the course EVSC 101 taught by Professor Blum during the Fall '08 term at UVA.

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Chapter 8 - Chapter 8 I Obsidian is a very shiny natural...

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