GENESIS OF GLACIOFLUVIAL HUMMOCKS IN SUBGLACIAL MELTWATER CORRIDORS OF THE SLAVE GEOLOGICAL PROVINCE, NWT, CANADA

The Slave Geological Province in Northern Canada was affected by the Keewatin sector of the Laurentide Ice Sheet during the last glaciation. A distinctive record of this is a network of ‘subglacial meltwater corridors’ (SMCs), consisting of relatively continuous, narrow, sub-linear tracts where till has been eroded, bedrock is commonly exposed, and glaciofluvial landforms were deposited. SMCs are parallel to sub-parallel with deglacial ice flow directions and have undulating longitudinal profiles. Till dominates in intervening areas. Here we discuss the origin of SMC’s and genesis of the landforms within them.

Eskers make up a small proportion of glaciofluvial features in most SMCs, more common are variably shaped depositional landforms referred to as ‘hummocks,’ composed of sandy diamicton. Hummocks typically occur in groups of tens but can number in the hundreds. Features range from individual mounds to irregular complexes with multiple high points. Sample transects from unmodified till into the SMC’s indicate the hummocks are much sandier than the regional till. In some SMCs, the hummocks are streamlined. Limited morphometric analysis shows that individual features have a mean length-to-width ratio of 1.8. The average mound elongation direction usually parallels the final ice flow that affected the area.

These results and mapping relationships suggest the corridors were formed from subglacial meltwater flow. SMCs likely formed late during deglaciation because in most areas, the hummocks and eskers that they contain do not appear significantly affected by ice flow. In SMCs that contain both eskers and hummocks, depositional relationships indicate esker ridges were deposited after the glaciofluvial hummocks. We hypothesize that transient subglacial meltwater flow events sourced from supraglacial lakes that drained in catastrophic pulses resulted in erosion and transport of till to form SMC’s. Glaciofluvial hummocks formed from the rapid deposition of eroded till while eskers likely formed further downflow during the waning stages of these flow events. SMC’s and related landforms likely formed in short segments in a time transgressive manner. It is possible that SMCs are the Quaternary landscape record of lake-drainage events similar to those that occur presently in Southwest Greenland.