Gravity is a subtle but ubiquitous force that influences nearly all geologic processes from the formation of ores to the flow of glaciers and rivers. Gravity also determines the path some materials take as they flow down volcanoes. Lava flows, mudflows (also called lahars), and pyroclastic flows are three such materials. Understanding the factors that influence their path is critical to protecting lives and property. In this lesson, we focus on mudflows and demonstrate simple ways for students to predict their paths using 3-D clay models. Students are then asked to transfer their new knowledge to a real volcano.