Mapping a Local Dune Field and Estimating Paleowind Speed and DirectionDonald T. Rodbell, Union College
Intended Audience: Undergraduate geomorphology course.
Pinebush dune field, eastern New York State (approximately 20 minutes from Union College campus).
This lab exercise is conducted just after we spend approximately 1.5 weeks talking about eolian processes and landforms in lecture. For this exercise, students map one large hairpin parabolic dune in the Pinebush Preserve. They also profile the slopes on both proximal and distal sides of the dune. As a group, we take an ~ 2m long core of the dune sand to sample the sand beneath the soil profile. In the lab, students measure the particle size distribution of their sand samples, map the whole dune field from aerial photographs and a DEM, and estimate paleo-wind speed and direction. They then compare these data with modern wind data (available from the web) to answer the question of just how different conditions were when the dune field was deposited. This activity uses online and/or real-time data, addresses student fear of quantitative aspect and/or inadequate quantitative skills, and uses geomorphology to solve problems in other fields
Students use data they collected in the field and lab to address a paleoclimatic question: how different was wind speed and direction (relative to modern values) when a large body of sand was deposited in eastern NY State. The initial reaction of students is that it must have been really windy, and very different from today! I play this up a bit. Invariably, when students do some calculations to estimate possible paleowind speeds and compare these with modern values, they find that there is plenty of wind today to move the dunes. Students must then decide what was really different when the dunes were deposited (answer: the sudden draining of Glacial Lake Albany, and the exposure of delatic and shoreline sands in the mouth of the Mohawk Valley. This activity also aims to improve oral and writing skills by requiring students to make oral and written reports.
Assessment and Evaluation:
The quality of lab reports, ability to select a logical parameter of their grain size data to use in the calculations of past wind velocity, quality of their dune maps, and for the students who present their labs orally, the quality of these presentations determine whether or not the goals are met.