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NIU GEOL 120 - Volcanoes Continued

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GEOL 120 1st Edition Lecture 8Outline of Last Lecture I. VolcanoesII. Eruptions produce three main thingsIII. Secondary effects of eruptions includeIV. ViscosityV. Lava CompositionsVI. Basaltic Lava FlowsVII. Characteristics of mafic Lava FlowsOutline of Current Lecture I. Volcanic gasesII. Volcanic on climateIII. Volcanic architectureIV. Magma ReleasesV. Volcano TypesVI. Tectonic SettingsVII. Volcanic HazardsVIII. Predicting EruptionsCurrent LectureI. Volcanic Gasesa. Evidence of gas preserved as vesiclesb. Rapid expansion of gases can cause violent eruptionsi. Occurs during decompressionsii. Gas pressure increases….cannot easily escape…results in very high pressure. Then violent eruptionII. Volcanic influence on climatea. Aerosols and other gases can reach the stratosphere and reduce incident sunlightb. Cause global coolingi. Volcanic gases trapped in iceii. Correspond with thin tree ringsc. Massive eruptions implicated in Permian- Triassic extinction (250-200 million years ago)i. Ash restricted solar radiation on Earth’s surfaceii.CO2 emissions suffocated terrestrial life and acidified oceansiii.killed estimated 90 % of speciesiv. Resulting in geologic formation called: Siberian traps1. Enormous basalt piles in northern RussiaThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.III. Volcanic Architecturea. Volcanoes have characteristics featuresi. Magma chamber1. Located in the upper crusta. Usually an open cavity or area of highly fractured rockb. May contain a large quantity of magmac. May inflate and deflate2. Some magma cools here to form intrusive rock3. Some magma may rise to the surface to form a volcanoii. Fissures and ventsiii. Craters1. A bowl shaped depression atop a volcano2. Craters are up to 500 m across; 200m deep3. Form as erupted lava piles up around the venta. Summit eruption- located within the summit craterb. Flank eruption- located along the side of the volcanoiv. Calderas1. A gigantic volcanic depressiona. Once a ten kilometers across, larger than a craterb. Steep sidewalls and flat floors2. Form from massive eruptions3. The volcano collapsesa. Ex:i. Crater lake, Oregonb. Yellowstone national parkIV. Magma Releasesa. Some magma rises via conduit to the surfaceb. Magma may also erupt along a linear tear, a fissurei. Fissure eruptions may display a “curtain of fire”ii. Fissures may evolve into rift zonesV. Volcano Typesa. Volcano shape and internal structure is controlled by magma properties and vent stylei. Point style vents create volcanosb. Shield volcanoesi. Form from multiple layers of basaltic (fluid) lava flowsii. Low viscosity 1. Kilauea2. Killimanjaroc. Stratovolcanoesi. Form from alternating layers of lava and volcanoclastic debrisii. Subduction zones1. Exa. Mt fujib. Mt. saint helensd. Cinder conesi. Accumulated piles of tephraii. Small volcanoesiii. Low viscosity magma 1. Exa. Sunset createrb. CupulinVI. Tectonic Settingsa. Plate motion is a dominant control on volcanismb. Volcanic types are linked to tectonic boundaries1. Mid ocean rides- spreading axes.2. Convergent boundaries- subduction zones3. Continental rifts- incipient ocean basins4. Oceanic and continental hot spots- mantle plumesVII. Volcanic Hazardsa. Lava flowsb. Tephra fallsc. Pyroclastic flowsd. Laharse. Earthquakesf. TsunamisVIII. Predicting Eruptionsa. Earthquake activityb. Changes in heart flowc. Changes in shaped. Increases in gas emission and steamThese can’t predict the magnitude of eruption: all were recorded in the days of proceeding MT Saint Helens historic eruption, but nobody knew the catastrophe that would


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