Factors Influencing Mass Wasting and Stream Behavior: Understanding Geology and Hydrology , Study notes of Geology

Download Factors Influencing Mass Wasting and Stream Behavior: Understanding Geology and Hydrology and more Study notes Geology in PDF only on Docsity! Mass Wasting Understand all the factors that effect mass wasting (i.e. what factors influence the stabilities of slopes) and how they effect it. Such factors include:  nature of the materials (unconsolidated sediment-soil or consolidated rock)  steepness of slope  water  vegetation  presence and orientation of planes of weakness (bedding, joints, metamorphic foliations (i.e. potential slide surfaces)  heights  climate (in addition to precipitation, freeze-thaw cycles are important) Some 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, flow). To what do the terms creep, slump, and avalanche refer; what about the rates at which they occur? -creep: slow movement (1-10mm/year) -slump: slow slide that travels as a unit -avalanche: fast movement downward "Landslide" is a general term refering to all slides, flows (even falls) that occur at a moderately fast rate. Be familar with the details of creep and the structure, geometry, and behavior of slumps. -creep: downhill movement of soil and debris -slumps: slump slips along a basal surface that forms a concave-upward shape, like a spoon How can you recognize evidence of past mass wasting events? -if it looks like the earth has moved downwards with gravity What (if anything) can be done to lessen the possibility of future such events in areas prone to mass wasting. -avoid construction in areas prone to mass movement -build in a way that does not make naturally stable slope unstable -control water drainage to prevent strata to become water saturated and prone to fail Streams Recall that precipitation that does not evaporate either infiltrates the ground or runs off the surface. Remember what factors effect the infiltration capacity of the ground. Runoff is either in the form of sheet flow (such as during floods) or it is confined to channels. Channelized runoff is stream flow. Things that reduce the infiltration capacity of the ground results in more runoff and greater flooding potential. Think of some natural and human activities that can increase the flooding potential of streams? -construction *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. *What factors effect the velocity of streams? -Stream gradient, channel shape, and roughness of the channel. It is a common misconception that the velocities of streams with steep gradients are faster than velocities with lesser gradients, or that the velocity of upstream reaches of a river, where its gradient is steep (think of the "long profile") is greater than its velocity downstream, near its mouth. However, the other velocity controlling factors are important. Down stream, a river generally has a wider, deeper, smoother channel, and a greater discharge. It is carrying the waters supplied by tributaries. It is true, however, that along a given segment or reach of a stream, if its gradient is increased (such as by construction of a meander cutoff of comparable channel size), the velocity will be increased - albiet as a temporary condition, because equilibrium will be restored eventually. *What determines the competence and capacity of a stream? -channel slope What is meant by "base level"? How does the longitudinal profile of a stream vary along its length? How does the longitudinal profile of a stream evolve through time? - the lowest point to which it can flow, often referred to as the 'mouth' of the river. For large rivers, sea level is usually the base level, but a large river or lake is likewise the base level for tributary streams - the longitudinal profile of a stream can reveal whether a stream has achieved a graded state, whether over only a part or the entire stream. The curved profile of a graded stream exhibits a steeper slope upstream giving way to a gentle slope in the down valley direction *Thoroughly understand the concept of a graded stream and how they behave and respond to change. -A graded stream is a system in equilibrium, one in which there exist a balance of the erosional and depositional processes. It is a stream that is transporting just that amount of sediment it is capable of, for its velocity and discharge. While a graded stream might be both picking up new sediment by erosion and depositing sediment, there is no net erosion or net deposition. While it might be argued that a With this knowledge you can understand the relationship between topography and the geometry of the water table, how the table is effected by drawdown, and what might be its recovery rate. Be familar with those ground water problems that face some areas of the country and world; problems such as depletion, contamination, saltwater intrusion, subsidence (and land rising) Karst features such as sinkholes and caverns, hydrothermal waters “Cheat Sheet” Relative rates of different types of mass wasting processes Velocity of ground water - Q = KIA Factors influencing runoff/infiltration – amount of water in the ground Factors influencing the rate of recovery of a depressed aquifer (i.e. one that has been drawn down or had the water table lowered) – aquifer properties Factors influencing the stability of slopes – the material they’re made out of and the water content An aquifer vs aquclude – aquifers are permeable, aqucludes are not Something about sinkholes – kiss my ass How dams, cutoffs, levees and other things might affect a stream – obstruct flow Things that might help control slumping and things that can cause slumping – add more material or add a supporting material How a cone of depression forms and how the water table can recover – when discharge exceeds recharge Levees – a slope that regulates water levels How rivers increase their lengths - erosion Factors affecting stream velocity, competency and capacity Effects of urbanization of forrested land on mass wasting, streams and groundwater Understand graded streams Some important groundwater problems that can occur