diatomaceous earth with glacier expirement

I recently conducted an experiment on the affects of glacier runoff being related to erosion of earth and the creation of rivers. to test this my group members and I used a giant ice cube and a plastic tub with about a quarter inch layer of diatomaceous earth at the bottom. we hypothesized that the runoff would only create one small river. We started the experiment by propping the tub up at one end and placed the ice cube on it. we started waiting and soon enough we had runoff creating one large river down the middle, and several smaller tributaries along the way.