Lesson 1 Activity 2: Ring of Fire

• 30 minutes
• Students locate some of the 1,500 active volcanoes on a world map. Then by comparing their maps with a map of the world's tectonic plates, they discover that volcanoes occur because of the dynamic nature of the Earth's lithosphere - the crust and upper mantle.

Key

• 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. This chain is called the "Ring of Fire."

• Mount St. Helens is located in the "Ring of Fire."

Materials

• A photocopy of Activity Sheets 1.2a and 1.2b for each student
• Master Sheets 1.4 and 1.5
• Two 8 ½ " x 11" transparencies for overhead projection
• Colored pencils

Procedures

1. Make transparencies of Master Sheets 1.4-1.5.

2. Distribute Activity Sheets 1.2a -1.2b and ask each student to read the Activity Sheets.

Discussion

1. After the students have completed their maps, lead a discussion. Are there volcanoes on every continent? (yes) How many of the volcanoes on their map are located within the shaded area, "The Ring of Fire?" (14)

2. Show the class the transparency of Master Sheet 1.5, the "Plate Tectonics Map." With a colored marker, trace the plate outlines. Tell students that the outer layer of the Earth is broken into a series of 16 major plates and that the colored lines indicate the boundaries between these plates.

3. Next, superimpose the transparency of Master Sheet 1.4, "Volcanoes Map," on Master Sheet 1.5, the "Plate Tectonics Map."

4. Ask students to observe the location of the volcanoes in relationship to the plates. Where do most of the volcanoes occur? They should observe that most occur near plate boundaries. Is the "Ring of Fire" located near plate boundaries?

5. Use (poster fig. 2) to explain that rigid plates float on top of a softer layer of rock. As the plates move, they push together, pull apart, or slide past each other. Along two plate boundaries, magma comes to the surface and volcanoes can occur.

6. Explain that there are some volcanoes that occur in the interior of plates and not at plate boundaries. They occur over "hot spots" in the plates. Scientists do not know exactly why hot spots develop, but hot spots are places in the Earth's interior from which magma rises and erupts through the plate as it moves over the hot spot. Ask students which U.S. State is composed primarily of shield volcanoes? (Hawaii)

7. Is Mount St. Helens located in the "Ring of Fire"? (Yes)