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geology notes5 - surficial geology/geomorphology I: Streams...

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surficial geology/geomorphology I: Streams Important terms commonly used in surficial geology Surficial geology : study of rock, sediment, and erosional surfaces associated surficial processes, such as stream erosion and deposition, landslides, wave action, wind, and more. Geomorphology : study of factors influencing landscape evolution, and using landscapes and landscape elements as data to understand climate change and tectonism. Altitude : elevation above mean sea level. Topographic relief : difference in altitude between two points Potential energy in landscapes : mountain building creates topographic relief, therefore, the source of energy causing stream erosion is Earth’s internal heat via plate tectonics. Base level : the lowest altitude/level that a stream can erode to Base-level fall : any process that increases topographic relief between a stream network and its (local or absolute) base level. Stream incision : the lowering of the altitude of a stream bed as a consequence of erosion. Can be caused by base-level fall Streams: A stream is a channelized body of flowing water. Streams are links in the hydrological cycle, and are the fundamental landscape-sculpting agents. Streams are a part of the hydrologic cycle that exists because of topographic relief on Earths surface Stream Power: see <STREAMpower.pdf> The work a stream can do is dependent on channel slope and discharge, and discharge is mostly dependent on drainage basin area or catchment area (the terms drainage basin area or catchment area are similar to the term watershed , but watershed actually refers only to the drainage divide separating two drainage basins). Streams have concave up profiles because natural systems develop lowest-energy expenditure configurations. Base level Topographic relief : difference in elevation between two points . Causes water to flow! Base level : the lowest altitude/level that a stream can erode to. Absolute base level : sea level Local base level : a base level within a river network that is higher than absolute base level. An example a of local/temporary base level is a tributary junction
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Graded stream: a stream that is adjusted to its base level; over 1000-year time scales, it neither lowers nor raises it bed. A graded stream requires stable base level over 1000 year timescales. graded streams illustrate an important attribute of streams. Streams are inherently lazy, and when undisturbed by humans, streams will do as little work as possible. Stream transport of sediment and weathering products Stream power (revisited) : is expended on transporting sediment. Stream power in excess of that required to transport all sediment delivered to the channel is spent on lowering the channel bed by stream incision . stream power expenditure
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geology notes5 - surficial geology/geomorphology I: Streams...

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