Characterizing Plate Boundaries
College of the Siskiyous
Students examine maps showing four different types of geologic data along three specific plate boundaries, and document the patterns in the data along each boundary. Next, they compare their observations to the patterns of seismicity, volcanism, etc. they would expect to find along different types of boundaries based on their reading in order to decide which type of boundary each of the three they examined is most likely to be. The exercise's strengths are that (1) it promotes careful observation and (2) asks students to interpret their observations in terms of an understanding of some more general principles (processes at plate boundaries and isostasy).
This assignment is used in three introductory geology courses for (mostly) non-majors: Environmental Geology, Geology of the National Parks, and Geology of California.
Skills and concepts that students must have mastered
Students must be able to locate features on a map and interpret differences among them using the legend.
Students must be able to recognize whether properties are uniform or variable in space, and whether patterns of variation are symmetrical or asymmetrical. (This may sound trivial, but many of my students do not initially understand these concepts.)
In order to interpret their observations, students must have a basic understanding of the physical processes that occur at divergent, convergent, and transform plate boundaries and of how the elevation of the lithosphere is related to its composition (oceanic vs. continental) and temperature through the principle of isostasy.
How the activity is situated in the course
This activity is a stand-alone exercise that is assigned early in the semester, but because plate tectonics is a unifying theme in each of these courses it is an activity that I expect students will refer back to repeatedly throughout the term.
Content/concepts goals for this activity
Accurate description of the distributions of geologic features on maps with several different themes
Higher order thinking skills goals for this activity
Correlation of the observed patterns of seismicity, etc. at plate boundaries with those inferred from a basic understanding of the processes operating at these boundaries
Other skills goals for this activity
Ability to collaborate with other class members by posing and answering well-thought out questions on a discussion board
Description of the activity/assignment
To prepare for this exercise students read about the processes that operate at plate boundaries and how they are related to the distinct patterns of seismicity, volcanism, surface elevations (e.g., ridges versus trenches), and seafloor ages characteristic of different boundary types. During the week the assignment is available online, students have access to:
(1) an index map that locates three boundaries they are to study; and
(2) four maps from Sawyer's Discovering Plate Boundaries website that provide the data mentioned above.
Student tasks are to:
(1) document patterns in each type of data along the three targeted boundaries; and
(2) use these observations in conjunction with their understandings of the processes that operate along different types of boundaries to decide whether each of the targeted sites is most likely to be a divergent, convergent, or shear boundary.
This activity gives students practice in map reading, interpreting the likely tectonic setting of a boundary by pulling together constraints from several types of data, and collaborating with their classmates in an online environment. The activity also provides a foundation for understanding a wide range of phenomena that are discussed later in the semester in the context of plate tectonic processes.
Modifications on this activity from the community
Adaptations that allow this activity to be successful in an online environment
Sawyer's Discovering Plate Boundaries is a jigsaw exercise in which students collaboratively develop an empirical classification of plate boundaries by first studying an individual data set (e.g., seismicity) and then working as part of a multidisciplinary team to develop a composite classification for the boundaries of a single plate using several types of data. In order for the classification to be truly empirical, students are not introduced to the "traditional" classification of plate boundaries till the end of the exercise.
In adapting this assignment to the online environment I have:
(1) asked students to prepare by becoming familiar with the standard classification of plate boundaries and the processes that operate at them;
(2) limited their work to three targeted boundaries of different types; and
(3) provided guidance about which features to look for in the each data set. I have found that these modifications help online students, who often work alone "on their own schedules", to avoid getting "lost" and frustrated with the assignment and to compensate for the lack of collaborative input they would receive in a classroom setting.
Elements of this activity that are most effective
The success of this exercise is really seems to depend on how well a student follows the directions. If a student learns about the geologic differences among plate boundaries, makes careful observations, and thoughtfully compares his or her observations to the expected patterns he or she typically does quite well based on answers to the follow-up questions. If, on the other hand, a student simply looks up the types of the targeted boundaries on a map and then attempts to "back out" the observations that he or she thinks should fit, the result is often inconsistency and a poor score on the questions. (I can often tell which approach a student is taking based on the queries they post to the discussion board, but rarely seem to be able to get those who are trying to work backwards through the assignment to change direction.)
Recommendations for other faculty adapting this activity to their own course:
To date my experience developing an engaging online exercise to help students learn the principles of plate tectonics has only been partly successful. I think that having such an exercise is critical, however, because this topic provides the framework for so much of what we learn in the geosciences. Based on my efforts to adapt elements of Discovering Plate Boundaries to an online environment I would offer three recommendations.
(1) Provide examples. Confronted with an unfamiliar map students are sometimes confused when asked to decide if seafloor age, for example, is uniform or variable along the length of a boundary. Showing them what you mean using snapshots from a map can often clear questions like this up quickly. Similarly, for written work a single example that gives them a clear sense of "what you're looking for" and can often head off a lot of questions.
(2) Choose the boundaries you ask students to study carefully. The scarcity of documented volcanism along a mid-ocean ridge or the burial of seafloor age belts by sediment along a trench can result in student observations that are correct, but problematic for correctly assessing the nature of a boundary.
(3) Stay on top of student questions and comments, and be prepared to make well-publicized "mid-course corrections" if something you thought was clear turns out to be misunderstood. These minor corrections happen naturally in face-to-face classes but can require real diligence to catch and correct in the online environment.
Determining whether students have met the goals
Students are assessed based on their answers to a series of ten questions that address both the accuracy of their observations and their ability to make interpretations that depend on both their data and their understandings of plate tectonic processes. A link to the follow-up questions used for evaluation is given below.
Teaching materials and tips
Solution Set: Follow-up Questions for Plate Boundary Exercise (Text File 3kB Jun11 10)
Dale Sawyer's original Discovering Plate Boundaries exercise