A HANGING TUNNEL CHANNEL/ESKER/MEGADRUMLIN/HUMMOCKY TERRAIN COMPLEX ON THE HIGH PLAINS OF ALBERTA

Hanging valleys dissecting the Hand Hills, Alberta, with upstream ends about 70 m above the prairie surface are identified as hanging tunnel channels. Hanging tunnel channels, which have not been previously described in the literature, provide evidence for extreme subglacial meltwater discharges. The hanging channels were probably formed during the waning stages of a flood that overtopped the Hand Hills and sculpted them into streamlined megadrumlins. Erosion steepened the proximal slopes of the Hand Hills, formed hummocky terrain at the foot of these slopes and scoured a deep trough around the northwest slopes. To the east and southeast, a zone of hummocky terrain was eroded from the bedrock, preglacial and glacial sediments. The hummocky complex is punctuated by enormous sichelwannen (up to 1.8 km wide and 2.2 km long). Eskers occupy the main tunnel channel and are superimposed on the hummocky terrain at the mouth of the valley. Shattered quartzite clasts in the esker indicate loading by thick ice resulting from reduced meltwater pressure and recoupling of the ice to the substrate. The array of landforms and sediments most likely result from a regional-scale sheet flow of subglacial meltwater and its waning stage evolution. Due to rerouting and temporally dependency of the cross-section area during waning flows, instantaneous discharges are difficult to estimate. Tentative estimates of peak discharges vary between 10⁶ and 10⁷ m³s ^-1.