GEOL 101 1nd Edition Lecture 20 Outline of Last Lecture I Hydrologic Cycle II Running Water III Stream Flow Outline of Current Lecture I Stream Valleys II Other Stream Features III Floods Current Lecture Stream Valleys Floodplain deposits Natural levees form parallel to stream channel by successive floods over many years Back swamps marshy lands between the levels and the valley walls Yazoo tributaries small streams that run parallel to the main river situated between the levee and the valley wall Stream Valleys Consists of stream channel as well as surrounding terrain The shape of a typical stream valley changes from the headwaters to the mouth The gradient is steeper at the headwaters which causes valley deepening Result valley is V shaped Downward erosion dominates and develops features like rapids and waterfalls Towards the mouth of the river the gradient is more gentle allowing for valley widening Stream begins to meander side to side This widens the valley and develops features such as floodplains oxbows yazoos etc These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Meanders bends in a stream or river Cut bank and point bar Cut bank outside of a meander erosion is active Point bar inside a meander deposition is active Cutoffs and oxbow lakes As the streams mender part of meander can be cut off from the rest of the river These segments can form oxbow lakes Incised meanders Caused by a drop in base level or uplift of the region by tectonic forces Meanders are carved in steep narrow valleys Common in the Colorado Plateau Terraces Remnants of a former flood plain River has adjusted to a relative drop in base level by downcutting Drainage patterns are formed by the network of streams in a given area Common drainage patterns Dendritic irregularly branching tributaries o Most common type Radial streams diverge from a center point o Typical streams flow off of volcanoes Rectangular streams bend at right angles o Caused by fractures in the bed rock that are perpendicular to each other Trellis rectangular pattern where tributary streams run roughly parallel to each other o Form in areas of alternating resistance and less resistant bedrock Flood any event where the amount of water in a stream is too much for the channel to hold Floods are the most common and most destructive geologic hazard Floods may vary depending on the terrain of the land and the intensity and duration of the rainfall Types of floods Regional floods o Caused by a long duration precipitation o Flood waters cover a large geographic area Flash floods o Caused by intense short duration precipitation o More localized areas Commonly narrow canyons act as funnels Urban areas do not allow for infiltration so runoff is maximized Ice jam floods o Ice flowing along partially frozen rivers may block part or all of the channel o The ice creates a dam causing water to flood over its banks Dam failure o Man made and natural dams may fail under any number of circumstances o Too much water from previous floods earthquakes etc
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