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Extreme melt and rainfall events can induce temporary acceleration of Greenland Ice Sheet motion, leading to increased advection of ice to lower elevations where melt rates are higher. In a warmer climate, these events are likely to become more frequent. In September 2022, seasonally unprecedented air temperatures caused multiple melt events over the Greenland Ice Sheet, generating the highest melt rates of the year. The scale and timing of the largest event overwhelmed the subglacial drainage system, enhancing basal sliding and increasing ice velocities by up to ∼240% relative to pre‐event velocities. However, ice motion returned rapidly to pre‐event levels, and the speed‐ups caused a regional increase in annual ice discharge of only ∼2% compared to when the effects of the speed‐ups were excluded. Therefore, although late melt‐season events are forecast to become more frequent and drive significant runoff, their impact on net mass loss via ice discharge is minimal. Plain Language Summary: Extreme melt and rainfall events can cause the flow of ice on the Greenland Ice Sheet to accelerate, potentially causing more ice to move to lower elevations, where temperatures are warmer and melt rates are higher. In September 2022, there were multiple unprecedented melt events. Their intensity caused some glaciers on the ice sheet to speed up by 240% relative to pre‐event speeds. Despite these accelerations, our analyses show that these events had only a minimal long‐term impact on how much ice was moved to lower elevations due to the short duration of the speed‐ups. As a result, while these melt‐induced speed‐ups are expected to become more common in a warmer climate, their effect on the amount of ice transported toward the ice margins is minimal. Key Points: September 2022 saw multiple melt events over the west Greenland Ice Sheet, with the largest daily runoff of any late melt‐season since 1950Large quantities of surface‐generated meltwater overwhelmed the subglacial drainage system causing brief increases in ice velocityLate‐season runoff‐induced speed‐ups have only minimal impact on the mass balance of the Greenland Ice Sheet via dynamical processes [ABSTRACT FROM AUTHOR]

Subglacial meltwater landforms found on palaeo‐ice sheet beds allow the properties of meltwater drainage to be reconstructed, informing our understanding of modern‐day subglacial hydrological processes. In northern Canada and Fennoscandia, subglacial meltwater landforms are largely organized into continental‐scale networks of subglacial meltwater corridors (SMCs), interpreted as the relics of subglacial drainage systems undergoing variations in meltwater input, effective pressure and drainage efficiency. We review the current state of knowledge of bedforms (hummocks, ridges, murtoos, ribbed bedforms) and associated landforms (channels, eskers) described along SMCs and use selected high‐resolution DEMs in Canada and Fennoscandia to complete the bedform catalogue and categorize their characteristics, patterning and spatial distributions. We synthesize the diversity of bedform and formation processes occurring along subglacial drainage routes in a conceptual model invoking spatiotemporal changes in hydraulic connectivity, basal meltwater pressure and ice‐bed coupling, which influences the evolution of subglacial processes (bed deformation, erosion, deposition) along subglacial drainage systems. When the hydraulic capacity of the subglacial drainage system is overwhelmed glaciofluvial erosion and deposition will dominate in the SMC, resulting in tracts of hummocks and ridges arising from both fragmentation of underlying pre‐existing bedforms and downstream deposition of sediments in basal cavities and crevasses. Re‐coupling of ice with the bed, when meltwater supply decreases, facilitates deformation, transforming existing and producing new bedforms concomitant with the wider subglacial bedform imprint. We finally establish a range of future research perspectives to improve understanding of subglacial hydrology, geomorphic processes and bedform diversity along SMCs. These perspectives include the new acquisition of remote‐sensing and field‐based sedimentological and geomorphological data, a better connection between the interpreted subglacial drainage configurations down corridors and the mathematical treatments studying their stability, and the quantification of the scaling, distribution and evolution of the hydraulically connected drainage system beneath present‐day ice masses to test our bedform‐related conceptual model. [ABSTRACT FROM AUTHOR]

Predicting the amplitude and distribution of surface undulations on ice sheets and glaciers is useful because of their influence on surface mass and energy balance, atmospheric boundary layer processes, and supraglacial meltwater routing. We develop an approximate method of calculating the surface elevation response due to spatial perturbations in basal topography and slipperiness, on two‐dimensional flow sections whose thickness, surface slope, and basal slip ratio vary along flow. Our main result is an integral expressing nonuniform transfer of basal variability to the surface. It uses published Fourier transfer functions derived through perturbing plane‐slab Stokes flow but circumvents the need to subwindow the spatial domain to estimate the response. We test the method on ice flow synthesized by a finite‐element model of Stokes flow with constant viscosity and known basal topography and slipperiness perturbations; in this case, it predicts the observed size and shape of the surface undulations well, capturing more than 90% of their variance. Application of the method to the central flowline of Columbia Glacier, Alaska, and a flowline on the Greenland Ice Sheet ending on Nordenskiöld Glacier, using knowledge of the approximate bed topography and ignoring the unknown slipperiness forcing, yields less faithful prediction of their surface undulations (40–50% of their variance) but demonstrates the method's potential to reproduce their qualitative features. We discuss the factors limiting the method's performance on real flowlines. Key Points: We present an extended mathematical theory of how ice flow transfers basal variations upward to form undulating surface topography, for nonuniform flow in two dimensionsWe formulate an integral transform method for calculating such transfer along flowlinesValidation of the method on synthetic flowlines informs its application to flowlines on valley glaciers and ice sheets [ABSTRACT FROM AUTHOR]