Maps showing the thickness of sediments above the bedrock (depth to bedrock, or DTB) are important for many geoscience studies and are necessary for many hydrogeological, engineering, mining, and ...forestry applications. However, it can be difficult to accurately estimate DTB in areas with varied topography, like lowland and mountainous terrain, because traditional methods of predicting bedrock elevation often underestimate or overestimate the elevation in rugged or incised terrain. Here, we describe a machine learning spatial prediction approach that uses information from traditional digital elevation model derived estimates of terrain morphometry and satellite imagery, augmented with spatial feature engineering techniques to predict DTB across Alberta, Canada. First, compiled measurements of DTB from borehole lithologs were used to train a natural language model to predict bedrock depth across all available lithologs, significantly increasing the dataset size. The combined data were then used for DTB modelling employing several algorithms (XGBoost, Random forests, and Cubist) and spatial feature engineering techniques, using a combination of geographic coordinates, proximity measures, neighbouring points, and spatially lagged DTB estimates. Finally, the results were contrasted with DTB predictions based on modelled relationships with the auxiliary variables, as well as conventional spatial interpolations using inverse-distance weighting and ordinary kriging methods. The results show that the use of spatially lagged variables to incorporate information from the spatial structure of the training data significantly improves predictive performance compared to using auxiliary predictors and/or geographic coordinates alone. Furthermore, unlike some of the other tested methods such as using neighbouring point locations directly as features, spatially lagged variables did not generate spurious spatial artifacts in the predicted raster maps. The proposed method is demonstrated to produce reliable results in several distinct physiographic sub-regions with contrasting terrain types, as well as at the provincial scale, indicating its broad suitability for DTB mapping in general.
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 extent of proglacial lakes following the initial separation of the southwest Laurentide Ice Sheet from the Cordilleran Ice Sheet and its eastward retreat from the Canadian Rocky Mountains has ...been reconstructed across regions of Alberta at a range of scales. However, to date, no studies have integrated all available geological information to produce a province-wide deglacial reconstruction that considers the evolution of proglacial lakes as components of the ice-marginal system.
In this paper, we utilize a geologically constrained shoreline projection method with a high resolution digital elevation model to reconstruct the evolution of the ice-marginal system along the southwest LIS during the last deglaciation. This method provides new details on the configuration, volume, drainage history and routing of ∼240 proglacial lakes as they migrated across Alberta and establishes a succession of paleogeographic reconstructions that can place geological evidence of regional and local ice-flow reorganizations into a spatiotemporal context. These reconstructions demonstrate that although the evolution of proglacial lakes was largely driven by the topography of the emerging landscape and the configuration of the ice margin, positive feedbacks in the ice-marginal system, particularly where margins transitioned from terrestrial to subaqueous settings played a major role in deglacial ice dynamics. Narrow, ribbon-shaped lakes that paralleled the ice margin induced relatively minor changes in style and rate of deglaciation, whereas the evolution of progressively larger, longer-lived lakes extending obliquely to the ice margin promoted surging and subsequent rapid retreat.
•The retreating Laurentide Ice sheet dammed proglacial lakes over much of the Alberta area.•By using an outlet projection method we reconstruct proglacial lakes over the region.•We reconstruct the pattern of deglaciation from the relative sequence of proglacial lakes.•In the south relatively small proglacial lakes drained through spillways that formed along the lobate ice sheet margin.•In the north, larger proglacial lakes developed, promoting surging and subsequently rapid retreat of the ice sheet.
The Empress Group in Alberta, Canada Hartman, Gregory M.D.; Pawley, Steven M.; Utting, Daniel J. ...
Canadian journal of earth sciences,
01/2024, Letnik:
61, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Basal gravel and sand mantling the bedrock floors of buried valleys throughout the Canadian Interior Plains, and conformably overlying proglacial lacustrine sediment, comprise the Empress Group. ...While previously conceptualized as stratigraphically equivalent deposits of preglacial rivers prior to the first and most extensive continental and montane glaciations, subsequent stratigraphic studies indicated that buried valley basal gravel must have been deposited between, or during, progressively more extensive continental glaciations and could not be stratigraphically equivalent throughout the buried valley network. However, in the general absence of formation-rank stratigraphic description of basal gravel units that might better inform the geologic history of the deposits, most workers simply consider Empress Group sediments time-transgressive. In this paper, we examine basal gravel at provincial and regional scales to understand its genesis and geologic history. At the provincial scale, we map basal gravel in three dimensions using a novel machine learning approach. At the regional scale, we formally define basal gravel formations at either end of the largest buried valley system in Alberta, which informs its glacial history and physiographic development and shows the importance of formation-rank stratigraphic description. Our results indicate that the buried valley network across Alberta is palimpsest in genesis and basal gravel units within it are chronostratigraphically intercalated between tills. We advocate that the Empress Group definition be extended across Alberta with modifications to improve its clarity and utility, and formally define the Old Fort, Unchaga, Ipiatik, and Winefred formations as part of the Empress Group.
Government geological survey maps and research publications have portrayed the distribution of glacial landforms associated with the advance and retreat of the Laurentide and Cordilleran ice sheets ...across Alberta at a local, regional, and continental scale. To date, this information has not been systematically synthesized into a single compilation at a consistent scale. Although this original work provided valuable information to constrain reconstructions of former ice sheet extent, configuration, and flow geometry, its derivation primarily from the interpretation of aerial photographs and the Shuttle Radar Topography Mission 90 m digital elevation model (DEM) may result in methodological inconsistencies and spatial biases. These biases, together with challenges associated with geomorphic mapping in densely forested areas of western and northern Alberta limit the usefulness of previous mapping when applied to inversion-based ice sheet reconstructions, which have specific input data demands. Recently, light detection and ranging (LiDAR) DEMs have become increasingly available throughout Alberta. Hill-shaded imagery of these data provides unprecedented geomorphic detail beneath the forest cover and reveals that that the glacial geomorphology of northern and western Alberta is more complex than previously recognized. In this paper, we describe the methodology and geomorphic criteria used to produce a glacial landform map of Alberta using previously published data, supplemented by comprehensive new analysis of high-resolution (2-25 m) DEMs. These include 306 624 km2 of LiDAR imagery, with which it is now possible to verify and where necessary augment previous mapping, particularly across areas with a dense forest cover.
Any process that causes a sudden brittle failure of material has the potential to cause earthquake-like seismic events. Cryoseisms represent an underreported class of seismic event due to their ...(often) small magnitudes. In this paper, we document the phenomenon of some of the largest magnitude lake-associated icequakes (ML 2.0) yet reported. These events occurred nearly simultaneously (within ∼2 h) on geographically separate lakes in Alberta, Canada, starting 1 January 2018. We conjecture that these events were caused by the sudden brittle failure of lake ice due to thermal expansion; the effects of the thermal expansion were compounded by the lack of insulating snow cover, high lake water levels, and a rapid onset of atmospheric warming. These factors also contributed to ice-jacking - a repeating process in which thermal contraction produces tensile cracks (leads) in lake ice that are then filled with water that is frozen during the cooling cycle. Thus, any subsequent thermal expansion must be accommodated by new deformation or brittle failure. This ice-jacking process caused creeping ground deformation after the initial brittle failure and again two weeks later following a second warming period. In many cases, the resulting ground deformation was significant enough to cause property damage.
Glaciofluvial corridor hummocks (GCHs) within the Walker Lake map area, Canada, were examined in order to determine the character and genesis of these geomorphic features and their associated ...deposits. Located south of the Chantrey Moraine and north of the Keewatin Ice Divide, these corridors occur within a belt extending approximately 120 km east–west and approximately 60 km north–south. They are spaced 5–10 km apart and are hundreds of metres to several kilometres in width. They have undulating longitudinal profiles, abrupt material boundaries with the surrounding till and occur in valleys and over interfluves. Hummocks were investigated using longitudinal and perpendicular ground‐penetrating radar (GPR) surveys in conjunction with pit excavations. From these analyses, the hummocks comprise a single lithofacies consisting of coarsely stratified, matrix‐supported gravely sand to a depth of approximately 10 m. This sediment is similar to that of a ‘sliding bed facies’ observed in esker sediments and hyperconcentrated flow deposits, both of which are attributed to high meltwater discharges. Therefore, we hypothesize that the Walker Lake GCHs formed from sedimentation in cavities at the base of the ice sheet by a rapid influx of meltwater.
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