Lesson 1 Slow Changes to Earth’s Landscape – We learned slowing down steep slopes cut into the valley floor and carry material down-slope forming a V-shaped Valley. Over time, erosion and deposition of rock material widen the valley walls and floor decreasing the slope of the river. The longer these processes continue the wider the valley becomes. As the river slows down deposition becomes greater than erosion, and the valley becomes very wide with a gentle slope.