Earth Changes at the Lake Outlet Mill

Clues Where the Lake Becomes a River

At an old mill, water leaves a lake and enters a river. The mill no longer runs, but visitors can follow a marked path past its stone foundation. A class studied the caretaker's photographs and measurements instead of approaching the water. During winter, the caretaker photographed water in stone cracks. After several nights below freezing, fresh chips lay beside those cracks. Water takes up more space when it freezes. The chips remained beside the foundation until a later rainstorm. Then flowing water carried some chips toward the river.

Other photographs followed two stone cracks from spring to fall. A crack containing a growing root widened from 2 millimeters to 5 millimeters. A nearby crack without a root stayed 2 millimeters wide. The photographs showed the root becoming thicker. Near the path, fine roots formed a network through soil. After rain, soil remained tangled among those roots, while a nearby bare patch had a shallow channel. On a dry, windy afternoon, the caretaker watched loose sand travel from the bare patch onto a marked paving stone.

Breaking rock into smaller pieces is weathering. Carrying loose rock or soil to another place is erosion. To investigate water erosion, the class made model slopes. Each tray held 600 grams of the same soil. The trays had equal sizes and slopes. Students poured 300 milliliters of water from the same height. For a slow pour, they spread the water evenly over 60 seconds. For a fast pour, they spread it evenly over 15 seconds.

Students waited two minutes after each pour finished. They collected the soil that left each tray with the water, let it dry, and measured its mass. They completed two trials for each pouring time, using fresh soil for each trial. The graph shows their results. These small models helped the class investigate one cause of soil movement without disturbing the mill site.