Structural Control of Giant Rock Avalanches in Argentina
Barbara J. Tewksbury
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Students analyze the influence of bedrock structures on the locations of giant rock avalanches in Argentina. Activity is available in two versions: 1) short case example that can be used as an in-class activity or as an exam question and 2) in-class jigsaw with homework prep.
undergraduate required structural geology course for majors
Skills and concepts that students must have mastered
Students must be able to read geologic maps and interpret stereonets. In-class case example assumes familiarity with mass movement deposits, joints, structural weaknesses in rocks. The jigsaw version has a preparatory homework that provides this background and could be used with the in-class case example version.
How the activity is situated in the course
This jigsaw version is one of many combined homework assignments/in-class activities that students do over the course of the semester; I have used the short case example version as both an in-class activity and as an exam question.
Content/concepts goals for this activity
influence of structural weakness in bedrock on occurrence and location of mass movement events; relevance of structural geology to environmental problems; practice with structural terminology, stereonets, and geologic maps; bedrock geology and tectonics of another area of the world.
Higher order thinking skills goals for this activity
analysis of data to solve a problem
Other skills goals for this activity
peer teaching, oral communication of ideas.
Description of the activity/assignment
Jigsaw version: To prepare, students do background reading on landslides and rock avalanches and read the introductory portion of Hermanns and Strecker's 1999 article on rock avalanches in Argentina. In class, students receive data (assembled from figures in the article) on bedrock geology and physiography, as well as stereonets showing orientations of prominent joint sets, bedding, and foliations in the bedrock. Their task is to answer the question of why gigantic rock avalanches occur is some places but not others in this part of Argentina. Each student receives one of four possible data sets and works with a team to analyze the data and solve the problem for the team's area. Each team member must then individually explain his/her analysis to a group of three other students, one from each of the other teams, and the group then compares the four locations for similarities and differences. The activity gives students practice in interpreting geologic maps, using stereonets, and peer teaching. The activity also connects structural geology to another geoscience discipline.
Short case example version: This is an abbreviated version of the jigsaw activity described above and focuses on only one of the rock avalanche areas.
Determining whether students have met the goals
Jigsaw activity: I check each team to make sure that their interpretations are reasonable before they have a chance to teach other students about their area. Once each student has had a chance to learn about the other areas and data sets from three other students in the class, I draw straws to select students to present brief oral presentations to the class about one of the areas other than their own and about similarities and differences among the areas. This allows me both to reinforce points and to determine whether students learned from their peers.More information about assessment tools and techniques.
Short case example activity: After students have worked in pairs on the activity, I draw straws to select students to present portions of the analysis, much as I would do in the jigsaw. I have also use this shorter case example as an exam question.
Teaching materials and tips
Short case example version (Microsoft Word 2007 (.docx) 461kB May8 12)
with associated kmz file (KMZ File 715bytes May8 12)
; can be used either as an in-class activity or as an exam question.Version 2:
in-class jigsaw activity (Microsoft Word 2.6MB May8 12)
, with preparatory homework assignment (Microsoft Word 33kB May8 12)
Hermanns, Reginald L. and Strecker, Manfred R., 1999, Structural and lithological controls on large Quaternary rock avalanches (sturzstroms) in arid northwestern Argentina: Bulletin of the Geological Society of America, v. 111, no.6, p. 934-948.