Nigel Atkinson

Discovery of relict subglacial lakes and their geometry and mechanism of drainage

Recent proxy measurements reveal that subglacial lakes beneath modern ice sheets periodically store and release large volumes of water, providing an important but poorly understood influence on contemporary ice dynamics and mass balance. This is because direct observations of how lake drainage initiates and proceeds are lacking. Here we present physical evidence of the mechanism and geometry of lake drainage from the discovery of relict subglacial lakes formed during the last glaciation in Canada. These palaeo-subglacial lakes comprised shallow (<10 m) lenses of water perched behind ridges orientated transverse to ice flow. We show that lakes periodically drained through channels incised into bed substrate (canals). Canals sometimes trend into eskers that represent the depositional imprint of the last high-magnitude lake outburst. The subglacial lakes and channels are preserved on top of glacial lineations, indicating long-term re-organization of the subglacial drainage system and coupling to ice flow.

The periodic topography of ice stream beds: Insights from the Fourier spectra of mega-scale glacial lineations

Ice stream bed topography contains key evidence for the ways ice streams interact with, and are potentially controlled by, their beds. Here we present the first application of two–dimensional Fourier analysis to 22 marine and terrestrial topographies from 5 regions in Antarctica and Canada, with and without mega-scale glacial lineations (MSGLs). We find that the topography of MSGL-rich ice stream sedimentary beds is characterized by multiple, periodic wavelengths between 300 and 1200 m and amplitudes from decimeters to a few meters. This periodic topography is consistent with the idea that instability is a key element to the formation of MSGL bedforms. Dominant wavelengths vary among locations and, on one paleo ice stream bed, increase along the direction of ice flow by 1.7±0.52% km-1. We suggest that these changes are likely to reflect pattern evolution via downstream wavelength coarsening, even under potentially steady ice stream geometry and flow conditions. The amplitude of MSGLs is smaller than that of other fluvial and glacial topographies, but within the same order of magnitude. However, MSGLs are a striking component of ice stream beds because the topographic amplitude of features not aligned with ice flow is reduced by an order of magnitude relative to those oriented with the flow direction. This study represents the first attempt to automatically derive the spectral signatures of MSGLs. It highlights the plausibility of identifying these landform assemblages using automated techniques and provides a benchmark for numerical models of ice stream flow and subglacial landscape evolution.

Landscapes of the Alberta Oil Sands

Alberta’s oil sands underlie about 142,000 km2 of the Athabasca, Cold Lake and Peace river areas in northern Alberta. Up to 80 % of this deposit is buried too deeply to be recoverable by traditional mining techniques. However, shallow bitumen deposits in the Athabasca oil sands area north of the city of Fort McMurray have been extracted within open-pit mines since the mid-twentieth century. The surface mineable area occupies approximately 4800 km2 of lowlands flanking the Athabasca River. The morphology of these lowlands largely reflects a fluvial landscape, superimposed by sediments and landforms relating to advance and retreat of the Laurentide Ice Sheet and the subsequent effects of deglacial meltwater drainage. Oil sand within this area is currently mined using electric and hydraulic shovels and transported to processing facilities where it is mixed with hot water and diluent to separate the bitumen from the sand. Water and sand are then transferred to settling basins and storage facilities that are impounded by tailings dams. To date, up to 844 km2 of land has been disturbed by development activities, making this one of the largest mining developments in the world. This chapter reviews the pre-development landscape of the Athabasca oil sands area and the geomorphic impacts of current landscape modification, as well as comments on future changes to the landscape associated with post-mine closure and reclamation.