Known as the angle of repose, this threshold limits the height of the castle for a given volume of sand. Extension Discuss how the sand castles could be designed to prevent them from slumping. Ask students what methods they have observed of preventing walls from slumping. They might recall seeing retaining walls or terraces along rivers, streams, or highways. Build castles using other earth materials, then compare the height of these castles to the sand castles.
Students can bring samples of soil from home.
Explore how the rate of water flow affects erosion. Activity 2 Creating a Topographic Model Purpose Students often have difficulty visualizing topography from two dimensional contour maps. In this activity, students will build a topographic model of Shields Canyon and the area south into La Crescenta. They will be able to see and feel the steep slopes in the area and the sharp change in topography from the San Gabriel Mountains to the nearly flat valley where the population is concentrated. Procedure Begin by deciding what kinds of models the students will create.