VISUALIZING SURFACE PROCESSES THROUGH GEOLOGIC TIME BY REPEAT PHOTOGRAPHY, REVISITED

Students often have difficulty gaining a sense of the summative result of incremental effects of earth surface processes on exposed rocks. Repeat photography provides a visual method to help students sense how small changes can impact earth materials. To assist students in introductory geology courses gain a sensory appreciation of these effects, I began a repeat photography project which has lasted 35.3 years. Since the most common occurrence of rocks observed by the average student is a road cut, I chose a fresh cut through Pennsylvanian strata in eastern Kansas. The results were originally discussed after eight years of repeat photography (Reams, 1981). Repeat photography through 2009 provides a unique opportunity for students to visualize and interpret how a road cut through limestone and shale responds to surface processes. Vegetation changes are apparent, as well as freeze-thaw release of limestone blocks. As shale becomes covered by vegetation and littered with limestone fragments, the student may realize how different rocks respond to weathering. Strong contrasts in weathering and vegetation development on the north and south facing road cuts are also obvious. In addition to gaining an appreciation for the incremental changes through time, students understand why we have a distorted perception of rock abundances, due to their unique responses to weathering. The slides provide a useful segue to a discussion of geologic time.