Assesing the angle of subduction using GeoMapApp

Rory McFadden, Science Education Resource Center

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This activity has students determine the angle of subduction using GeoMapApp. Students use datasets available within GeoMapApp to examine the influence of the age of oceanic lithosphere and convergence rate on the angle of subduction. These datasets include: earthquakes (depth, magnitude, etc), subduction interface (based on earthquake data), convergence rate, and age of oceanic lithosphere.

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This activity is designed for a plate tectonics course at the sophomore/junior level. It can be easily modified for a senior level course.

Skills and concepts that students must have mastered

This activity will work best if students have been introduced to benioff zones and the role of density and buoyancy in subducting lithosphere. In addition, this activity is enhanced if students have been introduced to types of accretionary orogens. No prior knowledge of GeoMapApp is necessary (directions are provided).

How the activity is situated in the course

This activity is a homework assignment that ties together the topic of subduction zones in a plate tectonics course. This would also work well as a lab assignment.


Content/concepts goals for this activity

Content goals for this activity are examining the relationship between subduction angle, age oceanic lithosphere, and convergence rate.

Higher order thinking skills goals for this activity

This activity requires the formulation of hypotheses, analysis of large datasets, and the synthesis of ideas.

Other skills goals for this activity

Another goal of this activity is that students develop the ability to access online databases and mapping programs integral to geoscientific inquiry.

Description and Teaching Materials

This activity is a homework assignment that students complete after discussing subduction zones in lecture. The crux of the assignment is to use GeoMapApp to examine datasets from four different subduction zone systems (Tonga-Kermadec, Java-Sumatra, Central America, and Chile-Peru). Students work through a directed assignment and then answer accompanying questions that aid in interpreting the data they have collected. This assignment requires only access to the internet and the attached Word document. Depending on class size and level, there could be many interesting tweaks to this assignment. As an example: Each student could study one subduction zone and report back to the class. Then, students could compare data and come up with a rationale for distinguishing characteristics of subduction zones.

Updated_SubductionAngle_PlateTectonics_McF (Microsoft Word 43kB Jul14 23) (updated file includes directions after GeoMapApp revised data organization)

Subduction_Angle_PlateTectonics_McF (Microsoft Word 41kB May4 12)

Teaching Notes and Tips

If students have not had structural geology, they have difficulty in properly determining the angle of subduction from the profile of the subduction interface.
Also, to create the subduction interface profile it is necessary to already have added the subduction interface data (seems obvious, but of course it's not).


This activity is assessed by students submitting a completed homework assignment with answers to homework questions and images from GeoMapApp that show their collected and organized data from each subduction zone.

References and Resources

Syracuse and Abers (2006): Global compilation of variations in slab depth beneath arc volcanoes and implications