What Kind of Continental Margin am I? Active or Passive?

• Utilize earthquake data to locate subducting slabs
• Examine topographic data to determine volcanic arc locations relative to trenches
• Integrate earthquake, volcano, and topographic data to distinguish between passive and active margins
• Introduce GeoMapApp, an easy-to-use mapping program focused on marine geology and geophysics

This exercise is designed for any introductory course addressing plate tectonics and continental margins (e.g., Physical Geology, Oceanography, Earth Science, etc.). It may be used as homework or a laboratory exercise.

The Assignment Handout is a ready-to-use exercise for students. Identical WORD and PDF versions are provided. The handout is given to students. Students take the handout to a computer connected to the internet and a printer to complete the exercise. Students must download GeoMapApp, a freely available mapping program that works on both Mac and PC platforms.
Student Handout for Continental Margin Exercise, WORD Version (Microsoft Word 166kB May29 09)
Student Handout for Continental Margin Exercise, PDF Version (Acrobat (PDF) 1.1MB May29 09)

Time Required & Class Setting
--Students will typically take less than an hour to complete this exercise.
--The exercise may be completed as homework or as a supervised in class or lab activity.
Stumbling Blocks
--Suggest to students that they attempt to download GeoMapApp well before the assignment is due. It should download without any trouble, but, as with any program, there can be glitches.
--One strategy is for the instructor to demonstrate GeoMapApp in class. Students may start the exercise in class, thereby decreasing the fear-factor associated with learning new software.
Misconceptions
--Volcanic arcs ARE NOT located at the trench but are typically on the order of 100s of km away from the trench on the overriding plate as shown by topographic profiles.
--Subducting slabs DO NOT stop just below the overriding lithosphere but typically extend deep into the asthenosphere as shown by earthquake locations and depths.
--Continental margins ARE NOT all active, corresponding to plate boundaries. 
What next?
--GeoMapApp has many interesting features. This exercise is meant, in large part, to introduce students to the software. There may be additional assignments where students will find it useful.
--After completing this exercise, consider using other MARGINS Mini-Lessons that use GeoMapApp:

• Profiling Earth's Surface using GeoMapApp, wherein students relate large-scale features on Earth's surface to lithospheric plates, the underlying asthenosphere, plate boundaries, earthquakes, and volcanoes http://serc.carleton.edu/margins/minilessons/17593.html.
• Margin Morphology: Does Form Follow Function?which focuses on continental margin morphology and earthquakes http://serc.carleton.edu/margins/minilessons/32510.html.
• Sediment Production and Distribution Across the Margins which explores erosion in large river basins and delta formation http://serc.carleton.edu/margins/minilessons/32033.html.
   

Students turn in a cross section and written work to be graded. After completing this exercise, students should be able to understand the following concepts:

• volcanic arc locations relative to trenches
• subducting slabs extend into the asthenosphere and host deep earthquakes
   
• passive continental margins coincide with plate boundaries and host earthquakes ± volcanoes
• active continental margins have a continental shelf and lack earthquakes and volcanoes
   

GeoMapApp Download

http://www.geomapapp.org/

Profiling Earth's Surface Using GeoMapApp MARGINS Mini-Lesson

http://serc.carleton.edu/margins/minilessons/17593.html

Margin Morphology: Does Form Follow Function? MARGINS Mini-Lesson

http://serc.carleton.edu/margins/minilessons/32510.html

Sediment Production and Distribution Across the Margins MARGINS Mini-Lesson

http://serc.carleton.edu/margins/minilessons/32033.html