Geomorphology

1997 Edition

Aggradation

  • Rhodes W. Fairbridge
Reference work entry
DOI: https://doi.org/10.1007/3-540-31060-6_3
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A process of physical geology, aggradation means to fill up with sediment (first used by Salisbury in the last century, 1893, p. 103; see Fig. 1). It is thus the opposite of degradation (q.v.). Aggradation may occur along a river valley (see Alluvium), at the foot of a slope, in a lake basin, bolson depression, on a desert, or in the ocean.
FIG. 1

Diagrammatic cross section of an aggraded valley in which the stream shifted its course many times in the process of aggradation, as depositing streams are known to do. The coarser materials in the various positions, from below upward, represent the successive sites of the channel, two channels being represented in the last stage. In nature, the shiftings of the channel are much more frequent than represented here, so that the coarse materials marking the temporary sites of the channels do not remain so distinctly separated from each other (from Salisbury, 1893, p. 104).

W. M. Davis (1899) applied the term in a more specialized way to the talweg and valley of a river; where the erosional or degradational sector ends, the sedimentational or aggradation stage begins.

Mackin (1948), however, points out that the usual state of a stream is that of “grade” (as first proposed by Davis), and thus “degrading” or “aggrading” are both special cases where the equilibrium is shifting. “Regarding” refers to a simultaneous alteration in both senses in different sectors (Johnson, 1932). Short-term changes (scour and fill) should not be included in these terms, which refer to the general regime.

An “aggraded valley floor” (according to Cotton, 1952, p. 193) is a broad alluvial flat that is thicker than the depth of the stream channel.

References

  1. Cotton, C. A., 1952, Geomorphology, sixth ed., New York, John Wiley & Sons, 505pp.Google Scholar
  2. Davis, W. M., 1899, The geographical cycle, Geograph. J., 14, 481–504 (also Geographical Essays, New York, Dover, reprint, 1954).Google Scholar
  3. Johnson, D. W., 1932, Rock planes of arid regions, Geograph. Rev., 22, 656–665.CrossRefGoogle Scholar
  4. Mackin, J. H., 1948, Concept of the graded river, Bull. Geol. Soc. Am., 59, 463–512.Google Scholar
  5. Moody, A. E., 1907, Aggradation and degradation of valleys, Ohio Nat., 8, 191–197.Google Scholar
  6. Salisbury, R. D., 1893, Annual Report (for 1892), Surface geology, New Jersey Geol. Surv., 37–166.Google Scholar

Cross-references

Copyright information

© Reinhold Book Corporation 1968

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  • Rhodes W. Fairbridge

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