Newly available high resolution elevation data across North America and Europe have revealed previously unknown glacial landforms. This study focuses on the morphology and stratigraphy of a variation of tunnel channels with unique morphology that we have named parallel tunnel channels (PTCs). They are found in northeastern Indiana, northwestern Ohio, and southeastern Michigan, which were previously glaciated by the Huron-Erie Lobe (HEL) of the Laurentide Ice Sheet (LIS). PTCs are discontinuous, quasi-parallel pairs of depressions separated by a continuous central ridge that can extend upwards of 50 km, cross-cut multiple recessional moraines, and transition into standard tunnel channels. The PTCs range in width from 200 to 900 m, and the depressions range in width from 100 to 200 m and in depth from 3 to 10 m. Using water well logs and multiple electrical resistivity surveys, we determined that the stratigraphy beneath and surrounding the PTCs consists of a lower layer of sand and gravel (confined aquifer) and an upper layer of New Holland till, both of the Lagro Formation. A vibracore and multiple resistivity surveys reveal that depressions are filled with ~4 m of lacustrine sediment and occasionally are floored with gravel channel deposits. The depressions are erosional in origin, rather than a product of ice block melt-out and are cut into the upper surface of the New Holland till. We interpret the PTCs as subglacial, erosional landforms, similar to tunnel channels, which represent distinct pathways transporting subglacial meltwater from the interior to the ice margin. Identification of these landforms has several important implications for understanding the deglaciation of the HEL: 1) the major recessional moraines may not record the final deglaciation of the HEL (i.e., are palimpsest features); 2) a large portion of the HEL must have stagnated to preserve the subglacial landscape including the PTCs; and 3) the combined network of PTCs, tunnel channels, and proglacial spillways may represent a partially complete subglacial drainage network with distinct morphological changes as meltwater was transported from the interior to the margin of the HEL. An initial formational model is proposed for the formation of the PTCs by way of a supra- and/or subglacial lake draining through an ice-walled subglacial tunnel, but additional work is required to understand the distinct pattern of depressions observed.

北美和欧洲新获得的高分辨率海拔数据揭示了以前未知的冰川地貌。这项研究的重点是具有独特形态的隧道通道变化的形态和地层，我们将其称为平行隧道通道（PTC）。它们发现于印第安纳州东北部，俄亥俄州西北部和密歇根州东南部，这些地区先前曾被洛朗特冰盖（LIS）的休伦·伊利·洛伯（HEL）冰川化。PTC是不连续的，近似平行的凹陷对，由连续的中央隆起隔开，中央隆起可以向上延伸50 km，横切多个凹陷的，沟，并过渡到标准的隧道通道。PTC的宽度范围为200至900 m，凹陷的宽度范围为100至200 m，深度范围为3至10 m。通过水井测井和多次电阻率调查，我们确定了PTCs下方和周围的地层由砂和砾石（密闭含水层）的下层和New Holland直至Lagro地层的上层组成。震颤岩芯和多次电阻率调查显示，凹陷处充满了约4 m的湖相沉积物，偶尔还被砾石通道沉积物所覆盖。凹陷的起源是侵蚀性的，而不是冰块融化的产物，它们被切入纽荷兰的上表面直到。我们将PTC解释为冰川下的侵蚀性地貌，类似于隧道通道，代表了从内部向冰缘输送冰川下的融水的独特途径。识别这些地貌对理解HEL的冰消作用有几个重要意义：1）主要的衰退沟壑可能没有记录到HEL的最终冰消作用（即最薄弱的特征）；2）大部分HEL必须停滞以保护包括PTC在内的冰下景观；3）PTC，隧道通道和冰川溢洪道的组合网络可能代表了部分完整的冰川下排水网络，随着融水从内部向HEL边缘的转移，其形态发生了明显的变化。提出了一个初步的形成模型，用于通过冰上和/或冰河下的冰川湖排水的冰上和/或冰河下湖形成PTC，但是需要更多的工作来理解所观察到的凹陷的独特模式。