Geology Test 3 study guide Section 1 Mass Wasting Mass wasting The downward slope movements of rock soil or sediment by gravity Materials involved rock soil or Earth mud debris Motions involved Examples of mass wasting Landslides mudslides avalanches fall free falling of detached material from a slide movement of rick debris down an incline ow moves as viscous uid with sediment water and sometimes air steep slope Landslide term for all slides ows and falls that occur at a fast or moderately fast rate Understand all the factors that effect mass wasting i e what factors in uence the stabilities of slopes and how they effect it Such factors include nature of materials consolidated vs unconsolidated materials consolidated materials are generally more stable resisting movement while the slope for unconsolidated materials can only be so steep before they start slipping down angle of repose maximum angle at which unconsolidated material is stable Steepness of slope gravity provides energy to move materials The steeper the slope the more likely for movement Rapid mass wasting occurs on steep slopes and slow mass wasting occurs on gentle slopes Water Reduces friction between bedding layers lubricating them However to a point the addition of water created adhesion of material adds weight which is instabliity Vegetation Holds unconsolidated materials together which reduces the likelihood of mass movement Removes water from the ground Presence and orientation of planes of weakness bedding joints cracks and metamorphic foliations assist in mass movement Climate Precipitation can saturate a surface and reduce adhesion causing mud ows a type of mass movement Freezing and Thawing cycles can also cause grain by grain movement As water between grains crystallizes to ice and expands a grain is pushed away from the surface of the ground On thawing gravity pushes the grain further downslope Think about some ways in which human activity can in uence these factors and what the results of such activity might be highway cuts excavations rock and soil material from a hill or mountain is cut to make way for a road This causes arti cial over steepening making the material unstable and move downslope Stripping of vegetation Because plants hold on to loose sediments stripping vegetation would increase the likelihood of material movement Natural processes that oversteepen slopes include stream erosion wave erosion tectonic uplift volcanic activity Mass wasting events are manifested in different ways and at different rates depending on the types of materials involved such as rock earth mud debris and the type of motion involved such as fall slide ow To what do the terms creep slump and avalanche refer what about the rates at which they occur Creep Materials involved are soil Earth Occurs at the slowest rate of mass wasting processes 1cm or less a year Creep is a grain by grain process It is the most damaging because it destroys foundations of buildings and such Slump material moves as a coherent mass along curved surfaces Slumps can be both slow moving and fast moving Fast moving ex La Concita slow moving ex Slumguillion earth ow Avalanche loose material moves rapidly down a slope in a chaotic or incoherent fashion Be familar with the details of creep and the structure geometry and behavior of slumps 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 of the slump The distal end toe of the slump moves along a less steep surface Often the toe of slumps move more as ows than as slides How can you recognize evidence of past mass wasting events The evidence of mass wasting can be observed on aerial photographs Scarps open ssures displaced tilted objects a hummocky surface and sudden changes in vegetation are features indicating former landslides Effects of erosion weathering and vegetation may however obscure evidence of past mass wasting events What if to lessen such mass Although events prevented engieneers to damage Because important role in many landslides one of the most effective and inexpensive ways to reduce to potential for slope failure or to increase existing slope stability is surface and subsurface drainage of a hillside It reduces the weight of the material likely to slide and increases the shear strength of the slope material by lowering pore pressure anything can be done the possibility of future events in areas prone to wasting most mast wasting usually cannot be geologists and can use various methods minimize danger and resulting from them water plays such an Section 2 Streams Recall that precipitation that does not evaporate either in ltrates the ground or runs off the surface Remember what factors effect the in ltration capacity of the ground in ltration capacity the max rate at which surface materials absorb water 1 2 Runoff is either in the form of sheet ow such as during oods or it is intensity and duration of rainfall condition of surface material loosely packed dry soil absorbs faster than tightly packed wet soil con ned to channels Channelized runoff is stream ow sheet ow continuous lm of water owing over a surface Stream ow surface runoff is con ned to trough like depressions Things that reduce the in ltration capacity of the ground results in more runoff and greater ooding potential Think of some natural and human activities that can increase the ooding potential of streams 1 Urbanization increases surface runoff because soils are compacted or covered by asphalt or concrete reducing in ltration capacity 2 Storm drains quickly carry water to nearby channels many of which ood 3 Deforestation soil without vegetation does not absorb water which increses more often then in the past runoff and ooding potential Streams erode the surface of the Earth picking up sediments they transport sediments and they deposit sediments There are erosional landforms produced by streams and there are depositional landforms produced by streams Erosional landforms landforms formed by erosion valleys are common landforms forming from the response to erosion by streams ex gullies canyons gorges Depositional landforms landforms formed by deposition alluvial fans deltas oodplains and levees terraces What factors effect the velocity of streams Understand how and why these factors effect velocity 1 Friction water moves more slowly and with greater
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