How Slab Dip Affects the Location of Volcanoes

Erin K Beutel
Dept. of Geology and Environmental Geosciences
College of Charleston, Charleston, SC
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Summary

In this module students will be provided with data regarding the depth of subduction zone earthquakes (from the approximate top of the slab) and surface volcano locations for Central America, they will then plot this data on a map and develop a hypothesis regarding their relationship. As part of this exercise students will create a cross-section of some of the earthquakes, and determine the dip of the slab. The students will then be asked to look at a map of subduction zone earthquake depths for another location and predict where they would expect the volcanoes to be located. They will compare their results with the location of the actual volcanoes in the region. The students will then create a cross-section of the new subduction zone (Tonga) and determine the slab dip for that location. Finally, students will develop a hypothesis regarding slab dip and the distance volcanoes are from the trench (marked on both the Central America and Tonga maps) and test that hypothesis on the Cascadia subduction zone.

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Learning Goals

Critical Thinking
Hypothesis Testing
Data Analysis
Model Development
3-D Thinking
Mapping
Graphing
Basic Math

Context for Use

Level: Undergraduate (lower and upper)
Pre-Concepts: Students should understand earthquakes, the general idea behind what goes on in subduction zones, what a volcano is.

Description and Teaching Materials

There are two sections for people to use; one is the activity itself with the questions for the students, two is a file of the maps the students and teacher are likely to need. The images include the maps for the students to work on and then the answer keys for the professors.
Assignment handout including data table for plotting. (Microsoft Word 59kB Apr21 09)
Images used for the activity and for the teacher (answer key images are marked as such) (Acrobat (PDF) 4.9MB Apr21 09)

Teaching Notes and Tips

  1. This module is probably best done in pairs so that the students can talk to each other and work out the problems.
  2. It is important to remind students that if they aren't plotting earthquakes precisely they will have trouble with the rest of the activity.
  3. This can be expanded significantly with melting curves, more subduction zones, and even be blended into a discussion regarding bowen's reaction series.

Assessment

If the students truly understand the activity they should be able to predict the location of the volcanoes on the Figi-Kermadec trench and at other subduction zones worldwide. They should be able to discuss how close to the trench the volcanoes will be if simply given the slab-dip.

References and Resources