Today is an exciting day because I finally have some concrete results to share! These revelations have been hiding among large spreadsheets of MATLAB output matrices for the past couple of weeks, but only after plotting up over 100 graphs of various model parameters (channel slope, width/depth ratio, vertical erosion rate, minimum and maximum erodibility, and others) were Dr. Hancock and I able to understand why the graphs of times to equilibrium I posted last time differed so significantly between weathering and non-weathering model runs.

The answer seems to lie in the existence of a continuum between weathering and erosion. When the baselevel lowering rate in a channel is high, the erosive power of the stream is also generally very high. When a channel has a low baselevel lowering rate, the erosive power of the stream is also fairly low. In my set of model runs, all runs that increased the baselevel lowering rate showed very similar response times for weathering and non-weathering channels. Runs that decreased the baselevel lowering rate showed significantly lower response times for weathering channels than for non-weathering channels. However, once the baselevel lowering rate was decreased by a factor of .175 or below, the times to equilibrium began to quickly rise again. My explanation for this trend is that for the mild reductions in baselevel lowering rate, the reduction in erosive power allowed the rock in the channels to weather from the minimum erodibility to some value below the maximum erodibility. Once the baselevel lowering rate was reduced enough, the rock weathered to its maximum erodibility and weathering could no longer have an effect.

Aside from these trends, I ran into a small hiccup with some of the lowest factor model runs. The channel slope, which was my proxy for my equilibrium graphs, had reached equilibrium, but the width/depth ratio and vertical erosion rate had not. Therefore, the final 3 data points are erroneous and will have to be determined with new model runs set to 300,000 or 400,000 years. Oh well, c’est la vie!