AEOLIAN DUNE STRATIGRAPHY REVEALED WITHIN NIOBRARA RIVER VALLEY, NEBRASKA SAND HILLS, USA

The vast region known as the Nebraska Sandhills is an area spanning approximately 57,000 square kilometers in central United States. The Sandhills are comprised of a variety of aeolian dune types. This study focuses on the linear dunes within the Niobrara Valley Preserve (The Nature Conservancy) in north central Nebraska. The linear dunes in this area were last active approximately 800 years ago, after which they were covered by vegetation and stabilized. Recent findings and LiDAR imagery suggest that many linear dunes in the study area are often found in pairs with a “Y” junction connecting them. The goal of the project is to enhance the understanding of the internal stratigraphy of these unique dunes to determine an accurate history of their formation. A Sensors and Software pulseEKKO GPR system was used with 100 MHz antennae to collect 12 lines at 8 different sites. The lines were shot with GPR antennae separated one meter and collected in 0.25 meter increments. The lines themselves were each approximately 200 meters in length and oriented south to north. In addition to GPR, we collected topographic profiles of the dunes at 2 meter increments using a Topcon laser level. The data was combined with the GPR lines in EkkoProject software to geometrically correct the data. With the 100 MHz antennae, we are able to see approximately 8-10 meters into the subsurface, allowing us to image the general dipping direction of the sediments within the dunes. Each dune studied varied in height and length ranging from 300-600 meters long and 6-10 meters in elevation change. We found that the stratigraphy within the dune pairs dip in opposing directions, indicating that wind patterns in the past were not unidirectional. By using GPR with imaging techniques such as LiDAR, we plan to generate a model to aid in better understanding how these linear dunes in the Niobrara Valley Preserve were formed through multiple wind patterns.