Experimental modeling of pressurized subglacial water flow: Implications for tunnel valley formation

Abstract

Tunnel valleys are elongated hollows commonly found in formerly glaciated areas and interpreted as resulting from subglacial meltwater erosion beneath ice sheets. Over the past two decades, the number of studies of terrestrial tunnel valleys has continuously increased, and their existence has been hypothesized also on Mars, but their formation mechanisms remain poorly understood. We introduce here an innovative experimental approach to examine erosion by circulation of pressurized meltwater within the substratum and at the ice/substratum interface. We used a permeable substratum (sand) partially covered by a viscous, impermeable, and transparent cap (silicon putty), below which we applied a central injection of pure water. Low water pressures led to groundwater circulation in the substratum only, while water pressures exceeding a threshold that is larger than the sum of the glaciostatic and lithostatic pressures led to additional water circulation and formation of drainage landforms at the cap/substratum interface. The formation of these drainage landforms was monitored through time, and their shapes were analyzed from digital elevation models obtained by stereo-photogrammetry. The experimental landforms include valleys that are similar to natural tunnel valleys in their spatial organization and in a number of diagnostic morphological criteria, such as undulating longitudinal profiles and "tunnel" shapes. These results are consistent with the hypothesis that overpressurized subglacial water circulation controls the formation of tunnel valleys.Tunnel valleys are elongated and overdeepened hollows, up to hundreds of kilometers long, several kilometers wide and hundreds of meters deep, and their formation is generally attributed to subglacial meltwater erosion [Ó Cofaigh, 1996;Huuse and Lykke-Andersen, 2000]. They are generally exposed at the emplacement of former ice sheet margins

Conceptual hydrogeological model of the Yonge Street Aquifer, south-central Ontario: a glaciofluvial channel–fan setting

“…Hence, other identified Thorncliffe channels across the region are likely part of a network of north-south to northeastsouthwest-trending channel-esker-fan systems (Table 3; Schomberg, Nobleton, 15th Ave., 16th Ave., and at Holt on the eastern flank of the YSA). The inferred array of fans has a likely spacing of 5-15 km (e.g., Sharpe et al 2017), which effectively drained excess water from the ice sheet (Lelandais et al 2016). This estimate of eskerfan spacing is based on an exposed network of eskers in treeless terrain of northern Canada (Aylsworth et al 2012).…”

Microsedimentological evidence of vertical fluctuations in subglacial stress from the northwest sector of the Laurentide Ice Sheet, Northwest Territories, Canada

“…[Colour online.] Lelandais et al 2016). This porewater drainage could have resulted from an increase in the stress on the underlying sediment, which caused localized brecciation, evidence for which can be seen in the large number of voids observed directly below the porewater flow structure (Fig.…”

Ribbed bedforms in palaeo-ice streams reveal shear margin positions, lobe shutdown and the interaction of meltwater drainage and ice velocity patterns

“…Three-dimensional numerical modelling of bedforms remains a challenging enterprise however, and investigation is far from complete, mostly because the involved components show drastically distinct thermo-dependent and strain-rate dependent rheologies, and therefore temporal 200 scales of activity (Paterson, 1994). To circumvent the challenge of numerically modelling these complex interactions, Lelandais et al (2016Lelandais et al ( , 2018 developed a physical laboratory model able to simulate simultaneously ice flow, subglacial hydrology and subglacial erosion/transport/sedimentation/deformation. This model contributed to better constrain the link between subglacial meltwater drainage and the lifecycle of ice streams, but subglacial bedforms did not arise.…”