Visualizing inclined contacts using Google Earth

Barbara Tewksbury (Hamilton College)

Chahar Gas, Iran, mapping area small
Doubly plunging anticline near Chahar Gas, Iran (31 54 22.30N, 56 38 59.91E)

Although it seems silly to teach geologic map interpretation starting with the most complicated case of inclined units in areas with topographic relief, the powerful 3D viewing capability of Google Earth allows students to visualize relationships easily. For the second homework assignment of the semester, students create a geologic map and sketch a topographic profile before they have learned about units and contacts or strike and dip.

Although many areas in the world contain Google Earth imagery suitable for this kind of assignment, few in the US are as fabulous as the images from the folded terrain in the Dasht-e Lut in eastern Iran, at right, with detail for mapping below.

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The assignment

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Students fly around the area in Google Earth and create their own geologic map of a small portion of the structure (above) by
  • defining mappable units based on outcrop color and features that they see in Google Earth.
  • drawing lines separating the map units they have defined.
  • drawing blue lines down the centers of major valleys.
  • drawing red arrows that point in the direction that the layers are tilted into the ground.
  • sketching a topographic profile.

Click image to enlarge.

The results

  • Students have no trouble defining mappable units, although different students define different units.
  • Because students can see the third dimension in Google Earth 3D view, they seem to have little trouble grasping that the color bands are actually tilted layers that extend below ground. This is, quite frankly, an enormous break-through over previous approaches that I've used, where many students see map units as 2D paint stripes.
  • Even though students don't yet know what dip is, they have no trouble drawing arrows in the direction that the layers are tilted into the ground as they see them in the 3D view.
  • Students have little trouble making a sketch of the topo profile.

Follow-up in class

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  • In class, students look at each other's maps to see how their choices differ. We also discuss areas where they had problems, such as what to do about areas where the bedrock is covered by alluvium.
  • I introduce the concept of a vertical cross section, and students sketch cross sections of their maps along the topographic profile, using Google Earth 3D view to help them visualize relationships.
  • They then infer age relationships and add legends to their maps.

Go to the next step:
Visualizing strike & dip

Go to Visualizing inclined contacts - Visualizing strike & dip - Visualizing vertical contacts - Visualizing horizontal contacts - Visualizing folds - Other mapping projects