Lesson 2 Activity 2: Mapping Mount St. Helens

• 30-minute demonstration
• 45-minute work session
• Students use topographic map skills to interpret the impact of the May 18, 1980, eruption of Mount St. Helens on the volcano's topography.

  This activity is divided into an introduction, a demonstration, and a student work session.

  In the demonstration you
  (1) introduce students to topographic maps and contour lines and
  (2) construct a simple three-dimensional model of Mount St. Helens before the May 18, 1980, eruption.

  In the work session, students draw profile views of Mount St. Helens before and after the May 18, 1980, eruption. Students use these profiles to interpret the changes in the mountain's topography that were caused by the eruption.

Key teaching points

• Because volcanic eruptions both create and destroy landforms, they cause changes on the surface of the Earth's lithosphere. The May 18, 1980, eruption of Mount St. Helens destroyed a significant portion of the mountain that had been created by previous eruptions.

• Within a few minutes of the start of the eruption, the mountain lost 400 meters (1,312 feet) of its height and a gaping crater 625 meters (2,050 feet) deep, 1.7 miles (2.7 kilometers) long, and 1.3 miles (2 kilometers) wide opened on its once nearly symmetrical cone.

• The changes to Mount St. Helens' landscape have been recorded on topographic maps. Topographic maps represent the three-dimensional features of a landscape on a two-dimensional surface.

Materials

• Master Sheet 2.2
• Play-doh®
• Scissors
• Activity Sheet 2.1 Map A and 2.1 Map B

Procedures

Begin this activity by showing the class the photograph on the poster of Mount St. Helens taken before the 1980 eruptions (poster fig. 10). Remind students that Mount St. Helens began erupting about 40,000 years ago, but most of its height formed over the past 2,500 years from repeated eruptions. At the time of the May 18, 1980 eruption it was 2,780 meters (9,677 feet) high. Some eruptions can destroy part of the mountain that earlier eruptions have built. Look at the photograph (poster fig. 11) taken after the May 18, 1980 eruption. Ask students what they think the impact of the May 18, 1980 eruption was on the shape and size of Mount St. Helens. Tell students that they will use topographic maps of Mount St. Helens before and after the May 18, 1980 eruption to verify or refute their observations. Use a transparency of Master Sheet 2.2 to explain that a topographic map shows topography - the highs and lows of a given area. Topographic maps use special lines called contour lines to show the shape and elevation of the land. On this map, each contour line represents 100 meters (330 feet) change in elevation. With your finger trace the "2,000" meters contour line. Tell students that if they were walking on this imaginary line, they would never go up or down. To walk up or walk down, they would have to change lines-much like walking up or down steps.

Demonstration

1. Make a transparency and 4 photocopies of Master Sheet 2.2 (topographic map of Mount St. Helens before the 1980 eruptions).

2. Use the transparency to show students the topographic map of Mount St. Helens before the 1980 eruptions.

3. Tell your students that you will use this topographic map to "build" Mount St. Helens before the 1980 eruptions. (fig. 3)

4. Cut along the 1,400 meters contour line to make a pattern. Roll out Play-doh® about ˝ inch thick and place the cutout on top of the Play-doh®. With a sharp point, trace along the contour line to form your first layer.

5. Cut along the 1,600 meters contour line to make a second pattern. Roll out Play-doh® about ˝ inch thick, place the pattern on top of it, and trace along the contour line to make your second layer. Stack layer 2 on top of layer 1, like building a tiered wedding cake.

6. Repeat this process for the 1,800, 2,000, 2,200, 2,400, 2,600, and 2,800 meters contour lines.

7. Give students an opportunity to look at the model. Have them pay special attention to the side view, or profile, as a preparation for their work session.

Work session: Drawing profile maps

1. Hand out Activity Sheets 2.1. Map A is a topographic map of Mount St. Helens before the 1980 eruptions. Map B is a topographic map of Mount St. Helens after the eruptions.

2. Following the directions on their Activity Sheets, students use topographic maps to draw a profile (side view) of Mount St. Helens before and after the 1980 eruptions.

3. Students compare the completed profiles to see how the eruption changed the size and shape of Mount St. Helens.

4. As a class, calculate how many meters in elevation Mount St. Helens lost as a result of the May 18, 1980, eruption. (400 meters/1,312 feet)