This lesson is an extension of the GEMS guide: “River Cutters” by the Lawrence Hall of Science (see note below). In the GEMS curriculum, students are introduced to erosion by modeling the formation of rivers in tubs of diatomaceous earth, a silt-like substance into which meandering river channels and deltas form. This lesson builds off of the River Cutters activities by using a combination of sediment types in the models. They observe how gravel and large particles of sand remain in place whereas silt is washed downstream in fast flowing river channels. In contrast, where the water velocity slows as it reaches the newly forming bay, a beautiful silt-covered delta forms. These observations lead students to the conclusion that fast moving water picks up the smaller sediment particles and eventually deposits them in places where the water slows. Students can then take this theory to test it out in real world conditions at a local creek in the Sediment Study Project, observing sediments and water velocity at different sites along a creek’s length. The concept of how sediments are deposited becomes a core feature of subsequent geology lessons and investigations in which the environmental conditions surrounding the formation of large particled conglomerates may be differentiated from small particled shales and siltstones.
Special Note: This lesson plan is written with the assumption that students have some experience using the river models in the GEMS guide “River Cutters”, written by Cary Sneider and Katharine Barrett and produced by the Lawrence Hall of Science. In this guide, students make observations of rivers carved in just silt (diatomaceous earth), sequencing events in time, noticing patterns, recording information, and acquiring the terminology necessary to describe common erosion patterns. My students completed the first 5 sessions of River Cutters although completing the first 3 lessons is sufficient. So as not to infringe upon the copyright of the GEMS unit, only the extension activity is described here.