Constructing a Cross Section
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Constructing a cross-section to help students visualize subsurface conditions is the objective of this module. This module provides the data and background materials to help instructors convey geologic principles to students so that they can both create and geologic cross-section and interpret of the materials in the cross-section would affect flow to the wells at the Woburn site.
The basic skills for constructing a cross-section should be the end result of this module activity. Students should have an appreciation of the value of selecting appropriate scales and cross-sectional alignments, identifying geologic boundaries, and the importance and limitations of using vertical exaggeration.
Context for Use
This activity was developed for an introductory level, mock-trial class centered around the Woburn, MA groundwater pollution trial. It is also appropriate for an introductory level structural geology or groundwater hydrology class.
Description and Teaching Materials
The teaching materials are presented in Learning Module 3:Constructing a Geologic Cross Section
. Files presenting a base map, lithologic logs and template for a geologic cross section of the Aberjona River Valley are included in the learning module. The files are intended to provide students with an all resources necessary to construct a geologic cross section, along with questions intended to help with the interpretation of the cross section.
Teaching Notes and Tips
It is probably best to use a visual demonstration of the layout and construction a cross section. An effective way to do this is to use an overhead projector and a pre-made scaled page to walk students through the setup of geologic logs on the scaled page, correlation of like units and the actual interpretation of the geologic history of the units. As part of the assessment review it may be helpful to have an in class discussion regarding the hydrologic properties of the various little logic units presented in the cross-sections. This may help students understand how groundwater preferentially flows through higher permeability units and how this may actually affect the migration of contaminants.
Students hand in the cross section they develop as well as the question set. The instructor may want to grade the cross section more qualitatively than the questions (credit for "reasonable effort" or "on the right track.").
References and Resources
Chute, N.E. (1959) . Glacial geology of the Mystic Lakes-Fresh Pond area, Massachusetts. U. S. Geological Survey Bulletin 8755-531X; B 1061-F, 187-216.