Structural Control of Giant Rock Avalanches in Argentina

Barbara J. Tewksbury

Hamilton College

undergraduate required structural geology course for majors

Students must be able to read geologic maps and interpret stereonets.

This activity is one of many combined homework assignments/in-class activities that students do over the course of the semester.

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.

analysis of data to solve a problem

peer teaching, oral communication of ideas.

To prepare for this case study, 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.

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.

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.