MAPPING SURFICIAL FEATURES IN THE MISSOURI RIVER VALLEY

During the summer of 2008, a group of students and faculty studied part of the Missouri River valley in an effort to map the movements of the Missouri River during the Holocene. The study was part of an REU granted by the National Science Foundation to the University of Texas-Arlington (supervised by John M. Holbrook, Ph.D.) and the University of Nebraska-Lincoln (supervised by Ronald J. Goble, Ph.D.). The research area included southeastern South Dakota and northeastern Nebraska.

This part of the larger study involved mapping of surficial features in an area near Ponca, Nebraska and Elk Point, South Dakota. Methods employed included analysis of: a) features visible on aerial photos; b) elevations detailed on topographic maps; c) data compiled by drilling test holes with a manual (Dutch) auger; and d) first-hand observations made in the field. We were also able to collect samples of sand for Optically Stimulated Luminescence (OSL) dating.

Aerial photos reveal scars where the river flowed prior to its present location. Elevations on both sides of the river provide evidence of at least one paired terrace with the west side downstream from the right side by approximately three miles. Core samples from our drill sites confirm the location of old channels and point bars, which we have mapped. We also mapped several splays that were identified by aerial photos and analysis of core sample data.

Analysis of the data indicates that the most recent changes in the Missouri River valley, near Ponca, Nebraska and Elk Point, South Dakota, reflect a response to a change in climate. The progressive drop in the elevation of the valley in this area is evidence of the decreasing discharge of the river as the glaciers receded. Changes from braided to meandering channels were also observed in the surficial record demonstrating climatic variations.