DUNITE DUST AND DELTAS: COMBINING STREAM TABLES, HIGH-TECH PARTICLE ANALYSIS, AND THE WEB TO HELP GEOMORPHOLOGY STUDENTS EVALUATE LANDFORM EVOLUTION

New labs developed for geomorphology classes at WWU help introduce students to concepts of landform evolution, hypothesis testing, and quantitative grain-size analysis. The three sequential labs allow geomorphology students to combine qualitative observations with quantitative measurements, using cutting-edge analytic equipment, to critically evaluate their own hypotheses of delta formation.

In the first lab, students visit a stream table, the upstream half of which contains a ~4-cm thick layer of sediment, the other half of which is filled with water to the level of the edge of the sediment (forming a “lake”). The sediment is unsorted crushed dunite (from a local quarry) that ranges in size from fine sand to clay (a range compatible with our particle size analyzer). The students are asked to hypothesize how a delta will form through time once the water is turned on and flows across the sediment into the “lake.” They also predict how and why the grain sizes might change across and within the delta. Two web cams, attached to a computer, provide (1) a live feed to the web so the students can watch the delta form in real-time over ~2 days between labs, and (2) a time-lapse MPEG of the delta forming.

In the second lab, the “lake” is drained, and the delta is sectioned and sampled for particle size analyses to test the students’ original hypotheses. With instructor guidance, the students design a strategy to sample the topset, foreset, and bottomset beds. Samples are then analyzed on a Malvern Mastersizer 2000 laser particle size analyzer with an automated sample stage. Through the Integrated Laboratory Network at WWU, students are able to drive the analyzer themselves, remotely from the classroom, and to see grain-size distribution graphs of each sample as they are analyzed. The graphs are posted to the course Blackboard web page. Students then compare the results to their original predictions, and assess the differences.

The third lab is a field trip to a local gravel pit in a stranded Pleistocene delta. By comparing and contrasting this natural delta to the one studied in the first two labs, students gain an appreciation for the benefits and limits of models when studying natural landforms. Student assessment of the labs indicates they feel improved understanding of and interest in landform development.