Surface expression of the Cary Age Drift (Des Moines lobe of Iowa) exhibits a pattern of intersecting linear ridges and depressions, known as swell-swale or "minor moraine" topography. Linear ridges, as mapped from air photos, are aligned either parallel or approximately transverse (45° to 90°) to associated end morainal systems. Both parallel and transverse ridges appear genetically related, range in height from 5-20 feet and are composed predominantly of till. Ridge intersections produce "T", "offset" "step" and "box" patterns. The irregular shape and high dip of crossbedding of small sand bodies and the dip of small faults and joints suggest a controlled ice disintegration origin. Alignment of till fabric with glacier flow is indicative of a lodgment till or ground moraine. The current hypothesis that the "minor moraines" represent "annual" recessional moraines does not explain the lack of outwash, the origin of transverse ridges, till fabric, the number of moraines and their geographic distribution. Alternate hypotheses for the observed pattern are: 1) crevasse fill 2) ice marginal thrust 3) basal crevasse "squeeze" and 5) boundary wave phenomenon.
Proceedings of the Iowa Academy of Science
©1969 Iowa Academy of Science, Inc.
Foster, John D. and Palmquist, Robert C.
"Possible Subglacial Origin for "Minor Moraine" Topography,"
Proceedings of the Iowa Academy of Science, 76(1), 296-310.
Available at: https://scholarworks.uni.edu/pias/vol76/iss1/41