29. Mississippi River Delta, Longshore Current

This October 1985 photograph of the Mississippi Delta, taken with the 250-mm lens, shows why this is called a “birdfoot” delta. Its spread, scrawny, narrow toes look just like a chicken foot reaching out to the Gulf. This photograph also helps to explain what was seen in the Seasat image (slide #28) taken two-and-a-half years earlier. The use of natural color film helps to unravel the tale told by the black-and-white radar image.

We can clearly follow the color of the main stream of the Mississippi as it disperses into its many distributaries and out into the Gulf. The long, thin curves (displayed in white on the radar image) mark the point where the dispersing river waters are turned sharply south and westward as they confront the wind-driven longshore current in the open Gulf. The strength of the wind and the direction from which the wind is blowing can be deduced by comparing the very choppy wave surface at the bottom right of the frame with the smooth, unruffled sea surface to the left of the frame where the waters to the west of the delta are protected from the wind by the land mass. Notice also that the outflow from the major western distributary can be distinguished flowing freely for a greater distance out into the Gulf than the outflow on the eastern side of the delta, because the water discharging to the west is flowing with the longshore current.

STS-61A, October-November 1985. Picture #61A-42-051

Right click here to download a high-resolution version of the image (8.82 MB)