Margin Morphology: Does Form Follow Function?

The primary goal of this mini-lesson is to orient students to the geomorphology of a variety of continental margins. For each margin investigated, students will collect data related to depths and distances along portions of the margin, and they will make additional observations regarding other features that may appear on the profiles generated. The secondary goal is for students to relate geomorphologic variability to the distribution and magnitude of recent earthquakes (>4.0). Through the process of making observations among multiple variables, students will make interpretations about the relationships between margin morphology and seismic activity. Ultimately, students will create a series of general statements that will then allow them to answer the question, "Does form (i.e., the geomorphology) follow function (i.e., the seismic activity)?"

This mini-lesson would be a good introduction to the geography and geomorphology of continental margins of the North American and South American continents. Students generally have not spent a great deal of time looking at the earth in detail! Even fewer have studied the ocean and its physiography, and geography skills are often somewhat lacking for introductory geology students. The phrase "Form Follows Function" is common in the world of architecture and engineering design. Students are asked to consider if Earth's form follows how the margins are functioning in terms of seismic activity.

• The mini-lesson can be used for an introductory oceanography, geology and/or environmental science classes.
  
• The students are not required to have strong background in science, as the lesson is designed to be exploratory (guided inquiry).
  
• The students will need to have access to computers and become familiar with GeoMapApp.
  
• Students will also need to have access to Excel to compile their data in a spreadsheet
  
• The students will need to have access to computers and become familiar with GeoMapApp.
  
• Students will also need to have access to Excel to compile their data in a spreadsheet
  

This activity could be assigned as a group project, where the first example exercise could be introduced during a class or lab period. Each profile and its set of observations made will take a student approximately 1/2 an hour. If students work in groups, they will need to share profiling responsibilities and consolitdate their data, discussing the complete suite of observations (for the 10 sites) as a group. The interpretations paragraphs should be completed outside of the classroom and handed in as an assignment.

This activity uses GeoMapApp with an overlay of earthquake epicenters. Students use the magnitude and location of earthquakes to make observations related to the continental margin geomorphology.

Students may want to view an online video tutorial to learn how to generate profiles:
http://www.geomapapp.org/tutorials/profile_tool/profile_tool_20080812/profile_tool_20080812.html

Students may work alone or in small groups to examine and create bathymetric profiles for a series of continental margins (10 suggested sites are provided). They then create a data table (on a separate spreadsheet), recording their observations regarding the geomorphology along each of the profile. Observations may include description of the topography of the continent near to shore and of features along the profile, width of the shelf, depth of the shelf break, steepness of the upper slope, distances to various water depths, etc. Observations related to the nearby earthquake concentrations and magnitudes are also recorded in the table. A complete list of data table items is included in the student page. The students can be instructed to use all or some of these.

Following data collection and data table creation, students are then asked to make interpretations based on their observations. They write brief paragraphs to address the following comparative studies:

• Select several margins that have similar characteristics (both geomorphology and seismic activity). Sort similar margins into different groups. Then, define the group(s) and use your observations to make interpretations about the processing occurring on the collective margins.
  
• Compare and contrast a single pair of margin sites that show the greatest dissimilarity in both geomorphology and seismic activity. Interpret why these margins are so different.
  
• Based on your observations, which margins would you classify as being seismically "Active" and which would be "Passive"? Are there geomorphologic similarities to each of your classified margins? Support your answer with your observations. Summarize your findings with a brief description of an Active Margin and a Passive Margin.
  
• The phrase "Form Follows Function" is common in the world of architecture and engineering design. Generally, does the geomorphology (i.e., form) of continental margins follow the margin's seismic activity (i.e., function)? Explain your answer and provide examples.
  
• Compare your interpretations to those of others in your class. Defend any differences you might have. This is what science is all about: using your observations to defend your interpretations!
  

The Student Pages can be found at Student Pages for "Margin Morphology" (Microsoft Word 59kB May28 09)

The Excel Spreadsheet can be found at Data Spreadsheet (Excel 28kB May29 09)

The images of the maps and profiles for each of the 10 Margin Sites can be found at Site Images (Microsoft Word 173kB May29 09)

Students may work alone or in small groups. Each student could create a few profiles.

Ten suggested Margin Sites are provided. Each site is identified as a single Longitude/Latitude location and students are instructed to generate the profile from this point to the deep ocean (to at least 4000m or deeper where trenches occur). Once students find the location, they determine the lengths of their profiles, therefore profiles of one location may not be the same for each student. However, as long as students plot the profiles shore-normal, there should be general consistency among student observations.

A JPEG image of each Margin Site will be included (soon!) that the instructor may use as guidelines for what students will generate. The image is a screen grab of the map with earthquake magnitudes, the white profile line and the graph.

Students could be asked to find additional margin areas to profile to build a larger database for comparative analyses.

An excellent follow-up activity would be ____________ (by E. Beutel), where students examine the focus depths of earthquakes along many active continental margins, in order to make interpretations about plate processes associated with the margins.

Any introductory oceanography text will cover the general continental margin geomorphology.

Also recommended: The Open University "The Ocean Basins: Their Structure and Evolution". Chapter on continental margins.