REVISITING THE HURON-ERIE LOBE: GEOMORPHOLOGIC INSIGHTS FROM LIDAR AND THEIR IMPLICATIONS FOR THE DYNAMICS OF THE ICE SHEET

The Huron-Erie Lobe was the dominant lobe of the Laurentide Ice Sheet in Indiana, covering most of the state during the last glacial maximum. The general chronology of the Lobe in Indiana has been studied, but the details of the Lobe’s marginal positions are not well known. Specifically, northeastern Indiana has puzzled glacial geologists as the unconsolidated sediment here exceeds depths of 350 feet, and large, broad recessional moraines dominate the region. The longstanding chronology consists of the Lobe advancing to the Wisconsinan limit of Indiana at the last glacial maximum (~24 ka) and depositing a large portion of the unconsolidated sediment in the area. The Lobe then retreated to an unknown location outside of Indiana during the Erie Interstade (~19 ka), and readvanced to the Union City Moraine during the Port Bruce Stade (~18 ka). The Lobe then slowly retreated, depositing the large recessional moraines of the area, Mississinawa, Salamonie, Wabash, and Fort Wayne, in that order.

New high-resolution LiDAR data across the Midwest have illuminated landforms that complicate previous interpretations, but provide an insight into the Lobe’s dynamics. Newly found landforms in the area such as tunnel channels, eskers, and so called “paired tunnel channels” point towards a possibility that the large recessional moraines of the area are palimpsest features and were simply overrun by the Lobe without being eroded. Numerous small morainic ridges have been found between the larger moraines, and the small moraines indicate a flow direction oblique to the larger moraines. Proglacial lake deposits with subaerial drainage ways between them have also been found between the larger moraines, with a flow path parallel to the smaller moraines.

This new data calls into question some longstanding ideas about the dynamics of the Lobe in Indiana. The last advance of the Lobe appears to have been only erosive in localized locations (i.e., tunnel channels) and deposited very little sediment overall. It also appears to have flowed in a direction unrelated to the large recessional moraines. This indicates that the recessional moraines are palimpsest features from an unknown number of advances and retreats, perhaps even pre-Wisconsinan in age.