ICE MARGINAL DRAINAGE DURING THE FORMATION OF THE BIG STONE MORAINE, WEST CENTRAL MINNESOTA: EVIDENCE FOR DES MOINES LOBE ICE DYNAMICS AND POSSIBLE ICE STREAM CONDITIONS

The Big Stone Moraine in west central Minnesota and eastern South Dakota, marks a pause of the late Wisconsinan Des Moines lobe prior to the formation of Lake Agassiz. The Big Stone Moraine is a moraine complex – deposited during multiple ice margin positions. The goal of this study is to analyze ice marginal drainage systems to reconstruct the history and dynamics of the Des Moines lobe (a possible ice stream) during the formation of the Big Stone Moraine.

Topographic maps and DEMs were used to map drainage system locations, paleo-gradients and paleo-channel widths. Two drainage systems: the Chippewa and Long Lake, formed on the easternmost side of the moraine were tributary to Glacial Lake Benson. The Pomme de Terre system, the next ice marginal system to the west, formed after Glacial Lake Benson drained and dissects the southernmost portion of the Big Stone moraine. Two additional drainages: Lighting Lake, and Griffen Lake appear to represent additional ice marginal drainage systems formed later in the formation of the Big Stone Moraine.

The relative age chronology of activation of ice marginal drainage systems which initially drain into Glacial Lake Benson and subsequently down cut through outer portions of the Big Stone Moraine, provide insight into the duration and extent of ice margin fluctuations during the construction of this complex moraine.

Research for this study was funded by a grant from the N.S.F.-R.E.U Program (NSF-EAR 1262945).