Wednesday, September 14, 2011

Connecting the dots.

I've been working on my presentation for GSA - which is part of my developing research into the fluvial geomorphology of the Red Cedar River in western Wisconsin. The picture below represents some of what's occupying my mind right now. The dots represent the elevation of stream terrace surfaces along the river valley. The y-axis is elevation in feet above sea level and the x-axis is horizontal distance (in meters) measured from the mouth of the Red Cedar River. I obtained the measurements in GIS, getting the elevations from a LiDar dataset and using the "measure" tool to get horizontal distance. The orange and green lines represent some possible interpretations for correlating the different terrace surfaces.

You can see that the two interpretations are quite different in some aspects. The orange lines are my primary interpretation - I focused on emphasizing terrace elevations that were parallel with each other. But, while it's tempting to correlate terraces so that they are parallel with the modern stream profile (blue dots at the bottom), this may not be the case. So, as an exercise in "changing my perspective," I drew the green lines by "squishing" the plot horizontally (extreme vertical exaggeration). This emphasized the possible surfaces that were not parallel.

Those of you with some training in fluvial geomorphology may have noticed another interesting feature. The sheer number of terraces along a 20 km reach of a relatively small river. I have probably over-interpreted some of this data; fourteen terraces, some separated by only six feet is probably the high-end estimate. Even with a more "conservative" correlation, there are at least eight terraces along this stretch of river. I'll let further exploration of that point (as well as my take-home message about the terrace profiles) wait until GSA - if you want to get the full story, come to my talk on Tuesday afternoon.

No comments:

Post a Comment