EVIDENCE FOR TUNNEL CHANNELS FROM HURON-ERIE LOBE IN NORTHEASTERN INDIANA

Recent releases of LiDAR data in northeastern Indiana have revealed a number of subtle glacial features in the area previously covered by the Huron-Erie Lobe of the Laurentide Ice Sheet. Several elongated, parallel troughs have been found in the area, extending upwards of 80 kilometers in some cases. These troughs are oriented NE-WSW at their eastern margins and curve to become oriented east to west at their western margins. At the western margins, many of the troughs converge to form a single pair of troughs and others dissipate. Many of the troughs cross one or more of the moraines associated with the Huron-Erie Lobe, including the Ft. Wayne, Wabash, and Salamonie moraines. This cross-cutting relationship suggests the troughs were eroded into pre-existing moraines. The troughs range in width from 100 to 350 m, and in depth from <5 to 15 m. Often, the troughs are deepest at moraine crests and shallowest in valleys between moraines. There is also a pattern of continuing for 6 to 10 km before becoming very shallow for a few kilometers then deepening again. A longitudinal profile of the longest parallel trough set over the Ft. Wayne and Wabash moraines undulates with a ~10 m amplitude over 50 km and an overall increase in elevation of > 30 meters. Between the troughs is a medial strip that is usually at a similar elevation to the surrounding topography, and on average measures between 350 to 500 meters in width. The troughs that end at the interlobate moraine are proximal to proglacial drainageways to the north. One set of parallel troughs connects with the lakes basins in the Chain O’Lakes State Park, which notably contains a number of eskers and kettle lakes, indicating a possible genetic association. These parallel troughs are most likely tunnel channels, subglacial erosional features indicative of pressurized subglacial meltwater flow. If these tunnel channels flowed from east to west, in the direction of ice flow, then the uphill flow could be explained by pressurized, subglacial flow. The medial strips could be esker like deposits partially infilling the tunnel channel, or be uneroded remnant stratigraphy.