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As ice sheets load Earth's surface, they produce ice‐marginal depressions which, when filled with meltwater, become proglacial lakes. We include self‐consistently evolving proglacial lakes in a glacial isostatic adjustment (GIA) model and apply it to the Laurentide ice sheet over the last glacial cycle. We find that the locations of modeled lakes and the timing of their disappearance is consistent with the geological record. Lake loads can deflect topography by >10 m, and volumes collectively approach 30–45 cm global mean sea‐level equivalent. GIA increases deglaciation‐phase lake volume up to five‐fold and average along‐ice‐margin depth ≤90 m compared to glaciation‐phase ice volume analogs—differences driven by changes in the position and size of the peripheral bulge. Since ice‐marginal lake depth affects grounding‐line outflow, GIA‐modulated proglacial lake depths could affect ice‐sheet mass loss. Indeed, we find that Laurentide ice‐margin retreat rate sometimes correlates with proglacial lake presence, indicating that proglacial lakes aid glacial collapse.

Ice‐shelf basal channels form due to concentrated submarine melting. They are present in many Antarctic ice shelves and can reduce ice‐shelf structural integrity, potentially destabilizing ice shelves by full‐depth incision. Here, we describe the viscous ice response to a basal channel—secondary flow—which acts perpendicular to the channel axis and is induced by gradients in ice thickness. We use a full‐Stokes ice‐flow model to systematically assess the transient evolution of a basal channel in the presence of melting. Secondary flow increases with channel size and reduces the rate of channel incision, such that linear extrapolation or the Shallow‐Shelf Approximation cannot project future channel evolution. For thick ice shelves (m) secondary flow potentially stabilizes the channel, but is insufficient to significantly delay breakthrough for thinner ice (m). Using synthetic data, we assess the impact of secondary flow when inferring basal‐channel melt rates from satellite observations.

Subglacial lakes are bodies of water that form at the base of ice sheets and glaciers. Ice‐surface elevation above these lakes responds to water volume changes, providing one of few ways to monitor subglacial hydrological systems. Here, we use numerical models to compare surface elevation‐derived estimates of subglacial‐lake length, water‐volume change, and highstand or lowstand timing with their true values. Because ice flow influences the surface expression of lake‐volume change, the correspondence between these estimates and their true values depends strongly on ice thickness, volume‐change rate, and basal drag coefficient. For many realistic combinations of these factors, viscous relaxation of the ice‐sheet surface can render lake volume‐changes unobservable with altimetry. Our results highlight the need for new estimation methods that account for the effects of ice flow, as well as improvements to current resolution limitations that render some events unobservable with altimetry.