RELATIONSHIP BETWEEN THE BLUE MOUNDS AND THE SWIFT FALLS DELTA, POPE AND SWIFT COUNTIES, WEST CENTRAL MINNESOTA

The Blue Mounds are a band of parallel ridges, 10km long and 1km wide, that are composed of sand and gravel and the occasional large boulder. The ridges are oriented in a northwest to southeast direction and are geomorphologically and sedimentologically distinct from the Alexandria Moraine on which they were formed. The origin of the Blue Mounds is poorly understood. N.H Winchell and W. Upham in the 1880's suggested the Blue Mounds were deposited in a topographic low between ice sheet lobes. D.F. Reid (1979) proposed a supraglacial fluvial origin and Komai et al (2000) suggested a crevasse-fill origin. The goal of this project was to determine the origin of the Blue Mounds by determining if they formed contemporaneously with nearby, well understood glacial features, specifically: the Swift Falls Delta

The Swift Falls Delta is 12 kilometers south/south east of the Blue Mounds. The Swift Falls Delta formed in Glacial Lake Benson, a pro-glacial lake of the retreating Des Moines Lobe. Previous mapping in the Swift Falls area traced the upper and lower terraces of the East Fork of the Chippewa River (EFCR) northward from the Swift Falls Delta but neither terrace is preserved all the way to the Blue Mounds. The objective of this study was to map sediments in the EFCR drainage to determine if remnants of the terraces exist and thereby correlate the Blue Mounds with the Swift Falls Delta

To do this gravel pits in the EFCR were located and described, samples were collected and analyzed. Point counts and sieve analysis was done in order to correlate units. The results of these analyses show that there are numerous sedimentary units that have the same provenance but cannot be correlated on the basis of sedimentology. There are however very distinctive units (e.g. a boulder layer) found at individual sites that may be correlatable with additional mapping in the future.

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