Slope Development on a Mississippi River Bluff in Historic Time

• Published in: The Journal of geology 1973-09, Vol.81 (5), p.576-598
• Main Authors: Brunsden, Denys, Kesel, Richard H.
• Format: Article
• Language: English
• Subjects: Bank erosion; Cliffs; Fluvial erosion; Lithology; River ports; Sediments; Silts; Talus slopes; Terraces; Water erosion
• ISSN: 0022-1376; 1537-5269
• DOI: 10.1086/627908

Using a space-time transformation, hillslope development was examined along a segment of the Mississippi River bluff at Port Hudson, Louisiana. The entire bluff segment was being undercut by a meander of the Mississippi River in 1722. Since that time, the meander has migrated downstream progressively, abandoning the river bluff. A space-time calibration of the hillslopes along the bluff was done by determining the position of the river along the bluff base from historic maps and aerial photographs. In plan, the bluff was divided into three segments: high, intermediate, and low intensity according to processes acting along the base of the bluff. The high-intensity zone represents a zone of active undercutting by the river, while the intermediate zone is characterized by basal scour and the low-intensity zone by basal aggradation. The present rate of retreat for each segment was calculated to be 75, 1.0, and 0.63 feet/year, respectively. The slope profiles within the three zones represent a sequential change reflecting the change in basal conditions. Hillslopes grade from the high-intensity zone, where profiles have a mean slope angle of 44° and a well-developed cliff face, to the concave profiles of the low-intensity zone. The latter profiles lack the cliff face and have a mean slope angle of 19.5°. Processes which cause these changes in slope profile are discussed. It is concluded that slope profiles in each of the zones reach a steady-state condition. It is estimated that a steady-state condition for slopes subjected to subaerial processes can be achieved in slightly more than 90 years.