Department of Geography and Geology
Master of Science
Removal of vegetation and subsequent erosion in karst regions such as central Kentucky or southeastern Alaska often leads to increased sedimentation in karst features such as caves and dolines. This sedimentation can impact the ground water by altering flow paths and the bio-geochemistry of the karst aquifer itself. Various methodologies have been used to obtain quantitative erosion and sedimentation rates for surface areas in karst and non-karst settings, but few quantitative studies have taken place in caves. The purpose of this study is to examine the effects of timber harvesting and development upon the caves and karst of southeastern Alaska by determining the recent (post 1954) sediment accumulation rates. Cesium 137 from open-air nuclear testing was is used to determine the age of the sediments in caves, surface karst features and undisturbed areas. Sediments generated from surface land disturbances and deposited in caves and karst features since 1954 may have positive cesium activities, whereas sediments deposited in caves and karst features before 1954 (the beginning of 137Cs deposition in the environment) will have little or no cesium activity. The method was successfully tested in the main river passage of Big Bertha Cave in south-central Kentucky before fieldwork commenced in Alaska. Samples collected from sediment berms in the study areas were analyzed for 137Cs on the EG and G High Purity Germanium detector at the Western Kentucky University Applied Physics Institute for a period of 12 hours. Results from each site were obtained in terms of peak area (net counts) and then converted into international units (Bq/Kg). Vertical profiles of cesium activity were constructed for each site and a minimum sediment accumulation rate (in cm per year) calculated. This sedimentation rate represents a minimum rate of sediment accumulation since it does not take into account the removal and re deposition of sediment during flood events. The Alaskan caves and karst areas selected for this study are all within or downstream from areas of significant development and /or timber harvesting, and cesium 137 is present at all locations. Recent sedimentation rates in the sampled caves and karst of southeastern Alaska range from approximately 1.5 cm/year to over 6 cm/year, and it appears that recent timber harvesting has had a significant effect upon sedimentation in these areas.
Curry, William, "Using Cesium 137 to Understand Recent in Cave Sedimentation in the Tongass National Forest, Southeast Alaska" (2003). Masters Theses & Specialist Projects. Paper 589.