We left the sandbox uncovered under last week’s heavy rain, and the result was a new perspective on erosion, sedimentation and the evolution of landforms.
Nice, sharp, hand-sculpted valleys were smoothed out by the raindrop splatters. The beautifully steep sided fjord on the lower left, in particular, eroded into the gentler slopes of a fluvial surface.
This process is diffusional. Sand moves from high peaks to fill in the low valley floors, evolving toward a softer, flatter land surface in the same way dye in pan diffuses from the high concentration droplet to a more uniform distribution.
There was enough rain that water pooled, for a little while, at the lower end of the sandbox. This allowed the formation of a beautiful little delta from the main river, which was most remarkable to observe while it was raining because the channel bifurcated at its mouth with running water to the left and right of the depositional landform.
The standing water in the “ocean” also caused the islands to partially erode at the edges to create steep bluffs overlooking sandy beaches.
And finally, if you looked carefully at the sides of the river channel you could see where the water was beginning to cut into the banks, a little offset on either side, to start the formation of meanders.
