Peter Lea

Bowdoin College

Undergraduate majors course in sedimentary geology.

Prior to the exercise, students should have a descriptive introduction to bedforms and formative flows in unidirectional, oscillatory and combined flows.

The activity is presented as a field exercise early in the course, setting the stage for later projects on quantitative aspects of bedforms and bedload transport, and for studies of sedimentary structures in outcrop.

The activity gives students direct experience in recognizing, describing and mapping bedforms and relating them qualitatively to formative flows. Students become familiar with a diversity of bedforms within lower- and upper-flow regimes, as well as ripples formed by waves and by wind.

During the prediction exercise, students essentially make hypotheses based on their current understanding of bedforms (i.e., without direct field experience). By comparing their predictions with observations and reflecting on differences, students critically evaluate their evolving understanding of bedforms and flows.

Students gain experience with GPS units and digital cameras, and learn how to take effective field photographs of bedforms.

To prepare for this activity, students receive background on bedforms and flow regimes in class and practice identifying and classifying bedforms from field photographs. Students are then given a map of a barrier beach/inlet/tidal delta complex in mid-coast Maine and asked to predict what bedforms they expect to find in specific sub-environments. During a subsequent field trip to the area, students observe, classify and map bedforms and relate them qualitatively to formative flows. Qualitative description and classification are supplemented by quantitative measurements of bedform morphology and orientation, and by GPS-located digital photographs. After the trip, students compare their predictions and observations of bedforms in the sub-environments, reflecting on the reasons for the differences and the evolution of their thinking. The exercise also serves to set the stage for subsequent quantitative studies of bedforms and bedload transport, as well as interpretation of sedimentary structures and clastic depositional environments in the geological record.

Evaluation comprises checking field descriptions for accuracy and completeness, as well as reviewing students' assessments of the differences between their predictions and observations. Such comparisons commonly allow me to track the evolution of student's thinking, such that I can reinforce conceptual advances and/or correct persistent (or new) misconceptions. Asking for a synthesis of major flow patterns evaluates whether students can recognize the larger picture ("forest") from compilation of the details ("trees").