The pathologically curvy Rio Grande Delta

I spent a summer in college staring at maps and aerial photographs of the Rio Grande delta in Texas and Mexico. Maybe now I can get some use out of it.  I was working with J.D.  Stanley at the Smithsonian’s NMNH and he pointed me to the apparently high sinuosity of deltaic channels on the Texas side of the Rio Grande delta.

According to my notes, the modern Rio Grande has a sinuosity of 2.075 in its delta, while Holocene channels have a sinuosity of 1.83, younger Pleistocene channels have a sinuosity of 1.81 and remnants of older Pleistocene channels have about 1.32. So our data suggests that the channels of the Rio Grande delta have gotten curvier over time. I also did a literature review of channel sinuosity in other deltas and found that the Rio Grande was indeed anomalously sinuous compared to many of the world’s major deltas.  In my review, only the Niger and Klangat Langat deltas were curvier. Unfortunately, we never came up with a good mechanism to explain why the Rio Grande was so curvaceous.

Indeed, if you look at the flash earth images (http://www.flashearth.com/?lat=26.07433&lon=-97.526349&z=10.4&r=0&src=msa)  below, you can see what caught our eye. One of the images is the majority of the delta (look for the anthropogenically straightened main outlet channel), one zooms in on the modern river mouth and area just to the north, one shows a portion of the southern, Mexico portion of the delta, and one shows the northern portion of the delta, which if I recall correctly has some of the oldest exposed deltaic deposits along with some eolian features (which can been seen in the image).