Comment: 04:30 - 05:47 (01:17)
Source: Annenberg/CPB Resources - Earth Revealed - 20. Running Water II: Landscape Evolution
Keywords: "Douglas D. Rhodes", landscape, mature, uplift, stream, valley, slope, youthful, energy, erosion, "base level", degradation, floodplain, peneplain, "old age"
Our transcription: During the earliest stages after uplift, streams were predominantly cutting downward incising their valleys and creating a steep sided landscape.
Davis referred to this as "youth."
As this process continues, the streams gradually spent some of their energy carving from side to side, wandering back and forth across the valleys.
The valleys then cease to be V-shaped, become somewhat more flat floored, and eventually all of the original upland surface is consumed by erosion from tributaries, so that all of the landscape is now in hill slopes.
This is what Davis considered to be the stage of "maturity."
Finally, as the stream works down, it reaches near base level or the limit to which it can erode downward.
And then does very little vertical erosion, expending almost all of its energy eroding from side to side, and as it does so, these valley bottoms become more and more broad.
The tributary streams erode their slopes eventually creating flood plains of their own.
Finally, virtually all of the material that was uplifted is destroyed and brought to an equal level, which Davis referred to as a "peneplain," as the ultimate stage in the cycle of erosion, which he thought ended in "old age."
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