How long was the ice flow in the first tray? after the ice melted, how was the sand in the first tray different from the sand in the second tray? what was the sand depth in the first tray at the beginning of the experiment? what was the sand depth at the end? answer these questions for the second tray. did erosion take place in either tray? explain your answer. how do you think the results would change if the trays were propped up two inches?