Demonstration Do the following demonstration to simulate the nature of lava and the nature of tephra. Discuss how the nature of the material influenced the shape of the material built. Discuss what shape you would expect to get if you alternated a layer of cat litter with a layer of molasses. In the third pie plate, layer molasses and cat litter. 30 minutes Students locate some of the 1,500 active volcanoes on a world map.
Volcanoes are windows into how the Earth works.
They occur because the Earth's rigid outer shell, the crust and upper mantle, is broken into a mosaic of plates that are in constant motion. Most volcanoes occur along the boundaries of the Earth's tectonic plates. More than half of the volcanoes that are exposed on land form a chain along the converging plates that encircle the Pacific Ocean. After the students have completed their maps, lead a discussion. With a colored marker, trace the plate outlines.