TERRACES (CONTINUED)

This photograph shows two terraces on the Little River near Tifton, GA.  The small stream and its floodplain are below the bridge by several meters.  The bridge and the road in the near foreground are built on a lower, depositional terrace.  The first rise in the background is onto a higher terrace where the road levels again.  This is an erosional terrace created by lateral erosion when base level was higher than at present.  The final rise takes the road out of the river's valley and onto the original surface into which the valley was eroded (an "interfluve").

Larger streams, with their higher erosive power, accomplish more lateral erosion than do small streams like the Little River.  Where GA 32 crosses the Flint River the road also crosses two terraces, but they are so broad that both cannot easily be seen in the same photograph.  The left-hand photo below shows the lower terrace.  Again, the level of the river and floodplain are several meters below the bridge shown, which crosses only a backwater slough of the river.  The bridge and road are on the level of the first terrace.  It is depositional.  Notice the cars almost beyond sight in the background.  They are on the second terrace, probably also a depositional one.  The right-hand picture was taken from approximately that point, facing in the same direction as the left-hand.  The rise in the distance takes the road out of the valley and onto the interfluve.

 

The final photograph was taken at the bottom of Providence Canyon.  Base level in the canyons there has changed for reasons unrelated to sea level change, but they have changed many times.  The reddish level surface in the upper left-hand part of the diagram lies on sediment deposited by this small creek during a time of aggradation.  As base level for the stream dropped, the stream incised itself downward and began laterally eroding at approximately its present position.  The reddish surface is therefore a depositional terrace.

 

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