1. A river runs through it Erosion & rivers

2. River-related vocabulary  You may recall the following terms.  A tributary is a small stream that empties into a larger river.  A watershed is the land that water runs off from into a river.  A divide is an elevated region that separate watersheds.  The path a river follows is called the channel.  The lengthening and branching of a river is called headward erosion.

3. Stream Erosion  Rivers form when precipitation exceeds evapotranspiration.  The excess water then carries weathered soil and rock away, and forms a gully.  This also causes stream piracy, which is when one stream “captures” another and alters its channel.

4. Channel Erosion  The edges of a stream are called banks.  The flow of a stream is carrying other sediments – these are called loads.  The three types are suspended, bed, and dissolved loads.  The movement of these loads contributes to the erosion of sediments in the channel.

5. Discharge, gradient, and gaps  The discharge is the volume of water moved by a stream in a given time.  The gradient is the change in elevation of a stream from top to bottom.  A gap is a formation of a river through a mountain range, usually by the motion of isostatic adjustments.

6. River stages  A young river has a fast headward erosion, forming a V-shaped valley and waterfalls.  A mature river drains its watershed and usually only erodes its banks when it floods.  A mature river also bends and curves, and banks along these parts erode faster (these are called meanders). Abandoned meanders are called Oxbow lakes.

7. River stages  An older river has a lower gradient and lower discharge.  It usually deposits its loads along the bank and channel, forming a flat plain.  Movement of the earth’s crust can rejuvenate a river, and increase its gradient and/or discharge.

8. Reading and assignment  Now read pages 247-251. The following vocabulary will appear:  Tributaries, watershed, divides, channel, headward erosion, stream piracy, stream load (please also define suspended, bed, and dissolved loads), saltation, discharge, gradient, headwaters, water gap, wind gap, meanders, oxbow lake, rejuvenated.  Your homework will be to “glossarize” these words.