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This 3 page Class Notes was uploaded by Mrs. Gardner O'Keefe on Thursday September 17, 2015. The Class Notes belongs to GLY 1000 at Florida State University taught by A. Leroy Odom in Fall. Since its upload, it has received 23 views. For similar materials see /class/205588/gly-1000-florida-state-university in Geology at Florida State University.
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Date Created: 09/17/15
MASS WASTING Mass wasting is the down slope hill movement of rock soil or sediment under the influence of gravity Mass wasting events occur in different ways and at different rates depending on the types of materials involved such as rock soil or earth mud debris and the motion involved fall slide flow What types of motion are involved in creep slump and avalanche What about the rates at which they occur quotLandslidequot is a general term that applies to all slides flows and falls that occur at a fast or moderately fast rate Economic cost The economic cost in the USA of damage by landslides is well over a billion dollars per year The cost for damage done by the far less spectacular process of creep is much greater The slow downhill movement of ground surface by creep destroys the foundations of buildings highways railways underground pipelines and utilities Understand all the factors that influence mass wasting ie the factors that affect the stability of slopes and how they affect it Such factors include nature of materials involved rocks sediments soil ect steepness of slope water vegetation heights climate such as freezethaw cycles presence and orientation of planes of weakness such as joints bedding foliations some human activities think of examples Some processes that oversteepen slopes include stream erosion wave erosion volcanic activity tectonic uplift human construction Human cost Mass wasting poses serious threat to many people in the world Read about the fate of Armero in the path of a mudflow that was triggered by a volcanic eruption Earthquakes have likewise triggered disasterous mass wasting events In 1970 the mountain Hauscaran in the Peruvian Andes was shook by a large earthquake A great mass of rock and glacial ice became detached and started its long fall to the valley below As it moved downward more debris and ice were picked up and the falling slab broke apart The mass turned into a debris avalanche with a speed approaching 300 miles per hour Reached the valley and the town of Yungay The devastation of Yungay was complete Within 45 minutes ofthe time the rock and ice broke loose high in the mountains only 94 ofsome 20000 people were alive Among the debris the avalanche carried were boulders up to 700 tons in weight The dashed red lines trace the surface displacement at top of slump See drawing belowleft This drawing shows the geometry of a typical slump such as the photo above In slumps material moves as coherent mass along curved surfaces This motion results in a slightly backward rotation of blocks Note that the ground surfaces on the intermediate blocks dip slightly toward the master sole ofthe slump The distal end toe of the slump moves along a less steep surface Often the toe ofslumps move more as flows than as slides The 1994 La Conchita slide oooh see La Conchita move began as a fast moving slump Toward its toe it moved as an earthflow Note the steep back wall sliding surface of the slump and how the material closest to the camera has the appearance of an earthflow At Frank Alberta in 1903 90 million tonnes of limestone detached from Turtle Mountain and buried part ofthe coal mining town of Frank resulting in the deaths ofabout 75 people Some ofthe vegetation on the ground over which the limestone traveled on its air cushion was hardly damaged While the Amero mudflow the Thistle landslide and the Yungay debris avalanche were very fast moving events and the La Conchita was a moderately fast moving slump there are a few documented cases of perhaps even more spectacular events where immense slabs of rocks breakofffrom high in mountains and fall or sai downward trapping a cushion ofair beneath and riding this cushion across almost flat valley floors A prehistroic example is the Backhawk slide that now lies out on the Mohave Desesrt floor The Slumgullion earthflow is a good example ofa slow moving and long lasting event
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