Create a landscape of mountains, rivers and plains out of sand. Turn a hair dryer on it to create wind, changing its position and speed to simulate how real wind might behave. Observe how the "wind" moves the sand. Sprinkle water over the mountaintops to see how water erodes a landscape. Slowly increase the amount and force of the water to observe the effects of flooding. Next create an extended slope of sand with a depression at the lower end filled with water. Use the palm of your hand to create waves that lap up against the shore and observe what happens.
Build a dirt mountain 3 feet high in an outdoor area where it will not be disturbed. Measure the height and observe the shape of the mountain once a week for three months. Keep weather data during the same time period, especially noting precipitation and wind. As the weeks pass, have students interpret both sets of data they are collecting. Primary-grade students can note how windy or rainy days affect the mountain. Intermediate-aged children can make more complex observations such as how much precipitation wore down how much of the mountain. Some might estimate how long the mountain will remain given the area's annual precipitation.
Measure the dimensions of a small sandstone rock. Weigh it and have students draw it or photograph it from various angles. Place the rock in a plastic jar filled halfway with clear water. Secure the lid and shake the jar 1,000 times. Observe how the water has changed. Shake the jar another 1,000 times. Remove the rock and compare it to the original drawings, dimensions and weight. Pour the water through a coffee filter and discuss the material that remains. Challenge the students to predict and then figure out how much the material weighs.
Build a landscape of a mountain and a meadow out of modeling clay. Lightly press flat rocks onto the mountaintop and put pebbles, soil and sand on the mountainsides and meadow. Starting at the top, gently rub an ice cube down the mountain. Observe how it either picks up or moves loose debris. Discuss how the cube is like a glacier and ask students to think about how ice might reshape the area over several years. Further demonstrate ice's power by filling the cracks of rocks with water and freezing the rocks. Repeat the experiment until the rocks crack.