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Los Angeles - Intro : Activity 1 : Activity 2 : Activity 3 :

Activity 2: Creating a Topographic Model

Purpose

Students often have difficulty visualizing topography from two dimensional contour maps. In this activity, students will build a topographic model of Shields Canyon and the area south into La Crescenta. They will be able to see and feel the steep slopes in the area and the sharp change in topography from the San Gabriel Mountains to the nearly flat valley where the population is concentrated.

Materials

Each group will need:

  • Topographic map of model area (Teacher Packet page 4),
  • Thick cardboard boxes,
  • Scissors,
  • Tracing paper, and
  • Glue.

Procedure

  1. Begin by deciding what kinds of models the students will create. They could work in groups to construct models by using different vertical exaggerations (2:1, 4:1, 1:1) or, you may want to divide the map into smaller areas and have each group construct a model of an area. After constructing the individual models, students would then assemble the models and create a model of the entire area.

    You may want to invite your students to devise their own method of making a three-dimensional representation of the area. They may want to use modeling clay, Styrofoam, or sheets of acrylic. The model-making activity explained below uses heavy cardboard.

  2. After deciding what area students will create a model of, explain the model-building process to the students. They will begin by tracing the outlines created by individual contour lines, starting with the lowest elevation. Using the traced shape as a template, students will then cut out cardboard to match the shape. Students will trace each subsequent (and higher) contour, reproduce the shape in cardboard, and stack it on top of the last cardboard shape. Students should glue each piece in place. They will need to refer to the topographical map to see how to place each layer of cardboard.

  3. Once they have built the models, have the students compare the topographic map to their model. Comparing the model to the map will help students see that when the topography is steep, the contour lines are close together. When the topography is relatively flat, the contour lines are far apart. Ask students if the model surprises them in any way. Ask students to focus on the Shields Canyon area. Can they now see why in Shield's Canyon the contour lines make upside down v's.

  4. Ask students a variety of questions that will help them interact with the model. Have them place markers on the map to represent the schools in the focus question. Ask them to indicate the necessary path of a debris flow.

  5. Have students locate the debris retention basins on their models. Ask students to consider the following questions:

    • Why were the basins placed where they are?
    • What areas do the basins protect?
    • What developed areas are not protected by a debris-retention basin?


  6. Have students measure the slopes in their model area by using the clinometer they constructed in Activity 1 or a contact goniometer. How do the slopes in the model compare with the slopes of their sand castles? If the slopes in the model are steeper than the ones in the sand castle, ask students to explain why.

  7. Display the models prominently during this unit. Have students refer to the models as they answer the Focus Question.

Extension

  • Students could construct a series of topographic profiles, which are perpendicular, then connect the profiles.

  • Students could pick new sites for debris retention basins that would protect development upstream, from existing basins.

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