THE NATURE OF GLACIAL RIVER WARREN FLOW: A STUDY OF THE CHARACTERISTICS OF BOULDERS AND BEDROCK IN THE BIG STONE NATIONAL WILDLIFE REFUGE, WESTERN MINNESOTA, TO DETERMINE OUTLET FLOW RATES

Glacial River Warren, an outlet of Glacial Lake Agassiz, down cut through surficial sediments to form the Minnesota River Valley and, in the Big Stone National Wildlife Refuge (BSNWR), expose Precambrian crystalline bedrock. Previous studies of the geology of the BSNWR have resulted in two very differing models for the origin of the geomorphology of the area. The “catastrophic flow” model (Fischer, 2004) suggests that the bedrock was sculpted by high flow rates and the very large boulders were transported. The “corestone” model (Patterson and Boerboom, 1999) suggests that the boulders are corestones, which together with bedrock features, are the result of weathering. The purpose of this study was to determine the characteristics of the flow of Glacial River Warren by studying the relationships between bedrock and overlying boulders in the BSNWR.

The goal of this research was to: 1) determine if boulders within BSNWR were of local origin or transported; 2) identify geomorphologic evidence of catastrophic flow; and 3) determine the relationship between the orientation bedrock forms and flow direction in this portion of the Minnesota River Valley. The methods used included the measurement of boulder dimensions and orientation, analysis of fluvial erosional features, detailed determination of boulder and bedrock lithologies, and comparisons of the BSNWR boulder lithologies to boulder lithology suites upstream (in Browns Valley, MN), and downstream (in Appleton, MN) in the Minnesota River Valley.

The results of this study show (1) the boulders in BSNWR are overwhelmingly similar to the underlying bedrock; (2) the boulders up- and downstream did not share a similar lithology with the boulders in the BSNWR; and (3) both the bedrock and boulders in the refuge show fluvial characteristic such as, fluvial polish, pot holes, and streamlined forms. The boulders in the BSNWR are more than likely corestones from the surrounding bedrock. The relationship between the boulders in the BSNWR and Glacial River Warren however is ambiguous.

Research for this study was funded by a grant from the N.S.F.-R.E.U Program (NSF-EAR 0640575).