# Constructive Forces of Mountain Building

## Activity Source:

Materials

• Computer with internet access

Procedure

1. Start the map at http://www.arcgis.com/home/webmap/viewer.html?useExisting=1.

2. Explore: Does North or South America have the biggest mountain range?

• Click Modify Map, and then click the Contents button.
• Click the Rocky Mountains bookmark, then click the Andes Mountains bookmark for closer examination.
• Compare and contrast the Andes and Rockies.
• Measure the Rocky Mountains and the Andes Mountains.
•  Which mountain range is longer: the Rockies or the Andes? The Andes is longer.
• What factors help make the Andes the longest continental mountain range? The long edge of the continent happens to move perpendicular to its long axis, creating a range along its entire length.

3. Explore: Where do mountains form?

• In the Contents pane, turn on Tectonic Boundaries.
•  Click the All Mountains bookmark. Mountains are “built up” through pressures on the Earth’s crust when plates collide.
• Where do mountain ranges occur in relationship to tectonic plates? Most form at the plate boundary edges because of collisions.

4. Explain: Do some plate boundaries produce mountains better?

• Count the number of mountains that occur near each boundary type.
• Based on this information, from which type of boundary are mountains more likely to occur? Convergent produces about 25, divergent produces about six, and transform produces about eight.
• Why would this plate boundary type be better at creating mountains? The greater relative velocity of converging plate crashes provides more energy for piling up mountains.

5. Elaborate: Are there exceptions to this rule?

• Turn on the Ranges Away From Boundaries layer.
• Find mountain chains that do not appear to be located near plate boundaries.
• Look at the Appalachian Mountains in the eastern United States.
• From what you are learning about how mountains form, which plate would North America have had to collide with to form these mountains? Europe — even the shape of how the continents appear to fit together hints at it.
• Is there evidence in Europe of this collision? Which range is it? The Scandinavian range was formed at the same time as the Appalachians. South America (Brazilian Highlands) also has a matching mountain range in Africa (Bie Plateau).
• Summarize why some mountain ranges are not located near plate boundaries. Many of these ranges formed from old plate boundaries that are no longer active.

6. Evaluate: What influences the height of the mountains?

• Turn on the Plate Motions (mm/year) layer.
• Think about how mountain heights might compare to the speeds of the colliding plates.
• With this in mind, rank which mountains you think are higher: Himalayas, Ural Mountains, and Rocky Mountains. Himalayas = 29,000 ft., Rocky Mountains = 14,400 ft., Ural Mountains = 6,200 ft.
• What is the relationship between the speed of plates and height of mountain ranges? The faster the plates are moving, the higher the mountain ranges.

Tech Tips

Measure

• At the top of the map, click the Measure button.
• Hover and click the Distance button.
• Click continuously along what you want to measure.
• Double-click to finish.

Bookmarks

• At the top of the map, click the Bookmarks button.
• Choose your bookmark; the map will take you there.

For more activities, visit http://www.esri.com/geoinquiries.