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23 Cards in this Set
- Front
- Back
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Basic Parts of a Volcano?
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Crater, Summit (central) vent, Flank vent, magma chamber
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How does a volcano work?
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Magma chamber feeds volcano, magma rising up conduit to erupt out a vent(summit or flanks). A crater is often found at the top.
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Shield volcanoes...
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very large, made of many layers of basalt flows with gentle slopes.
minor explosive activity + many major flows |
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Composite/strato-volcanoes...
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built of alternating layers of lava flows and pyroclastic flows (explosive).
steeper |
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Calderas...
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big holes in the ground where a volcano used to be.
ground collapsed after magma chamber emptied. |
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Cinder Cones
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built of scoria. very small.
usually from 1 relatively short-lived eruptive phase. |
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magma erupts in 2 ways...
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Effusive: dominated by flowing lava
Explosive: dominated by pyroclastics blasted through the air. Magmas rich in dissolved water and other gases. |
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Crater vs. Caldera
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crater forms when material is ejected and accumulates around vent.
caldera forms when material around vent collapses into vent or magma chamber.Much larger and have lava lakes. (shield) |
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Fissure Eruptions..
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occur when magma flows up through cracks in the ground and leaks out onto the surface.
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Pahoehoe def.
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hot, fluid lavas. smooth "skin" and flexible
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aa def.
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Rough lava flows.
as it cools, solid skin gets thicker and less flexible. breaks into pieces. moves like a tank tread. |
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What caused the lateral blast at Mount St. Helens?
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rising blob of magma caused the bulge to grow.
the growing bulge caused a huge part of north side to collapse. this uncorked a part of the magma chamber, and this directed a powerful lateral blast. debris avalanche. |
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Mafic vs Felsic lavas...
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Mafic: LOW silica and HOT temps give LOW viscosity. LOW volatile concentrations.
Felsic: HIGH silica and COOL makes lavas with generally HIGH to VERY HIGH viscosities. HIGH volatile concentrations. |
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How do silica and temperature affect viscosity?
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SILICA tetrahedra tend to link up. High silica = high viscosity.
TEMP - cooling causes rapid increases in viscosity. ex. honey |
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How does viscosity affect the length & thickness of lava flows and the types of volcanoes produced?
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mafic flow freely & make thin flows (shield)
Intermediate flow less freely & make thicker flows (composite) Felsic hard flow, make wart-like domes (lava domes) |
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Why are bubbles important & how do they produce explosive eruptions?
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Volatiles cause bubbles in magma/lava.
Pressure keeps volatiles dissolved in magma, as it rises - pressure drops. When near/at surface - pressure drops enough to allow volatiles to exsolve = bubbles. Bubbles suddenly increase in volume and forces the magma to shoot out of the volcano. |
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How does volcanic ash form? What are volcanic bombs?
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When small bubbles pop/rapidly cool, ash forms.
When larger bubbles pop, droplets and stringy clots of material fly into air. Droplets form cinders, clots form VOLCANIC BOMBS. |
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Explain how volcanic ash can go so high? How does magma viscosity determine whether there is a huge ash cloud or not?
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Many bubbles = very small ash particles = rapidly heating a large volume of air. Hot air rises quickly and carries ash with it.
Mafic = big bubbles going small distance (no ash cloud) Felsic = tiny bubbles (ash cloud) |
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How does pumice form? Mafic or felsic?
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"rock foam" = bubbles formed and expanded but did not rip the rock apart. blasted out of vent.Felsic.
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Where does obsidian form, is it mafic or felsic? Diff. between pumic and obsidian in terms of composition?
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Gas poor felsic eruptions like lava domes.
Main diff - pumice had gas |
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Why is obsidian glassy?
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Rhyolite cools too quickly to form crystals and makes obsidian.
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Lahars definiton...
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volcanic mudflows. many volcanoes are covered with glaciers.
small eruptions = mudslides |
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What causes pyroclastic flows?
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Bubbles cause debris to be hurled into the air and ash clouds.
Collapsing lava domes. Can cause landslides and searing ash clouds. Very dangerous. |
