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Earth Science - Final Exam Terms.docx

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Earth Sciences
Sergei Basik

Pyroclastic Flows and Volcanic Surges  Pyroclastic flow: mixture of hot volcanic ash and steam that pours downslope because it is too dense to rise  Can be referred to as an ash flow, glowing avalanche or ignimbrite deposit  Flows develop when rapidly erupting steam carries large volume of ash in a column that rises high above the volcano  When the rush of steam slows, part of column collapses and the cloud of ash pours down the flank of the volcano  Main flow hugs the ground  Less dense part billows above as loose ash is stirred into the turbulent air  Fast-moving flows tend to hug valley bottoms but their high velocity can carry them over intervening hills and ridges  Destroys everything flammable in their path (including forests and people)  Surge: high-speed ash-rich stock wave  Can race across ground ahead of a pyroclastic flow  Commonly originate as lateral blasts of ash and steam in the first stage of an ash-flow eruption  Because of their large proportion of steam they are generally less dense than standard pyroclastic flows Sinkholes: Three Main Types (Dissolution, Cover Subsidence, Cover Collapse) Dissolution  Soil cover is thin and highly permeable so acidic groundwater seeps through it and dissolves the underlying limestone along fractures  Upper parts of fractures widen to form a lumpy or jagged karst surface  Overlying soil slowly percolates or ravels down into fractures to creat surface depression  Where groundwater level is high or fracture plumbing is clogged with sediment  depression may fill to form a pond  Depressions are shallow and not dangerous Cover Subsidence  Tens of meters of sandy and permeable sediment exist on top of limestone bedrock so numerous sinkholes can form as the soil slowly fills expanding fractures and cavities in the limestone  Depressions generally form gradually Cover Collapse  Overlying sediments (overburden) contain significant amounts of clay  Cover will be more cohesive and less permeable  Does not easily ravel into underlying cavities in limestone  Can allow a soil cavity to grow large and unstable leading to a sudden collapse of its thinning roof  Lack of warning makes these steep-sided sinkholes destructive and dangerous  Can collapse taking parking lots, roads, cars and houses/buildings into them Tsunami (earthquake-generated tsunami)  Occur most commonly by displacement of the ocean bottom on a reverse or thrust-fault movement on a subduction-zone fault  (Occasionally occur on normal fault)  Subduction zone: oceanic lithosphere slide under continental lithosphere  Boundary between two plates sticks for many years  Where they stick, the continental edge is pulled downward toward the continent as the subducting plate moves under it  Causes overlying plate to flex upward in a coastal bulge  When stuck zone finally ruptures in an earthquake, edge of the continent snaps up and ocean-ward  Suddenly displaces huge volume of water creating tsunami waves that move in both directions from location where they are generated (toward and away fro continent) El Nino  Every 6 years (on average) Pacific Ocean circulation reverses  Major high-pressure area develops in equatorial latitudes over Indonesia and northern Australia in western Pacific  Major low-pressure cell develops near Tahiti in central pacific  Rising moist air over Tahiti and descending dry air over Indonesia and northern Australia: o Weakens trade winds o Allow warm ocean currents to flow eastward toward Ecuador and Peru  Results in extreme weather and weather-related hazards  Causes: o Rains and floods in western South America, Mexico an California o Droughts and widespread fires in Australia, Indonesia and Southeast Asia o Increased rainfall to normally dry areas of Peru Tornado  Tornadoes: narrow funnels of rapidly rotating intense wind  Tornadoes form when there is a shear in wind directions (ex. surface winds approaching from the south-east with winds from the west higher in the atmosphere)  Shear can create a roll of horizontal currents in a thunderstorm as warm and humid air rises over advancing cold air  Currents are dragged into vertical rotation axis by an updraft in the thunderstorm to form a rotational cell  Cell sages below cloud base to form a slowly rotating cloud wall  Tornadoes derive energy from the latent heat released when water vapor in the atmosphere condenses to form raindrops  Heat released creates instability in atmosphere that can fuel tornadoes  Tornadoes usually form toward trailing end of a severe thunderstorm Lightning  Results from strong separation of an electric charge that builds up between top and bottom of cumulonimbus clouds  Charge separation increases when updrafts carry water droplets and ice particles toward top of cumulonimbus clouds where they collide with downward moving ice particles or hail  Smaller, upward-moving particles acquire a positive charge  Larger, downward-moving particles acquire a negative charge  Top of cloud has a strong positive charge  Bottom of cloud has a strong negative charge  Strong negative charges near bottom of clouds attract positive charges toward ground surface (tall objects – buildings, trees, radio towers, etc.)  Eventually electrical resistance in air cannot keep opposite charge apart and positive and negative regions join with electrical lightning strike (Diagram would help) Hurricane  When a large tropical cyclone occurs in the North Atlantic and eastern Pacific  Hurricanes begin to develop over warm seawater  In tropical latitudes, temperatures are high and air-pressure gradients are weak  Air rises by localized heating  Without winds to dissipate them: o Convection chimney’s form and strengthen when air rises to high elevations o Warm, moist air over ocean rises
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