Fluvial supraglacial landscape evolution on the Greenland Ice Sheet

Abstract

Supraglacial stream networks incise via thermal erosion of underlying ice, reflecting a balance between localized fluvial incision and dynamic topography from underlying ice flow. We analyze high‐resolution digital elevation models of the ice surface and bedrock in the southwest Greenland Ice Sheet from 1000‐1600 m elevation to quantify the importance of fluvial erosion. At wavelengths greater than ice thickness, bedrock dominates surface topography so supraglacial drainage basins are fixed spatially. At smaller wavelengths, fluvial erosion significantly affects topography. Stream longitudinal profiles exhibit positive mean curvature and consistent power law scaling between local channel slope and drainage area, suggestive of adjustment toward topographic steady state. We interpret these observations with a model for fluvial thermal erosion on top of a flowing ice substrate that predicts concave up steady state longitudinal profiles, where average concavity is most sensitive to melt rate and the relative magnitudes of ice flow and fluvial erosion.

Flow Routing for Delineating Supraglacial Meltwater Channel Networks

“…With topographic data, Rippin et al (2015) [4] used drone imagery to produce high-resolution (0.01 m) surface Digital Elevation Models (DEMs) of an alpine glacier in Svalbard, and identified channels using an iterative elevation threshold. DEMs have also increasingly been used to delineate channels through flow routing methods modified for use on ice surfaces [10,[34][35][36][37].…”

“…As such, this study is focused on Greenland's southwestern margin where there is a coincidence of multispectral and topographic datasets. The study area displays extensive supraglacial channel development [2], and has been the focus of previous studies on the GrIS's surface meltwater systems (e.g., [2,7,10,30]). A total of seven meltwater catchments were delineated through flow routing on the ice surface.…”

“…Data availability and overlapping spatial extent for the MS and FR datasets limit the spatial extent of our study area and restrict the temporal resolution of our data choices. However, numerous observations suggest that supraglacial meltwater channels (particularly high-order, mainstem channels) perennially re-occupy the same spatial location [1,2,48], even as abandoned channels are advected down-glacier [10]. Furthermore, Lampkin and VanderBerg (2014) [29] observe that the extent of the supraglacial network on the GrIS, observable at 15 m resolution, did not change significantly between early July and early August 2007.…”

“…They are of intrinsic interest to researchers as unique fluvial systems as well as for the important roles they play in glacial hydrology. As fluvial systems, researchers have been interested in their morphometrics and controlling processes (e.g., [1,[5][6][7][8][9]), and in how their form may encode landscape processes [10]. Hydrologically, supraglacial meltwater channels influence the spatial and temporal distribution of surface water inputs to en-and sub-glacial hydrological systems [3,[11][12][13], which in turn have been shown to influence glacier and ice sheet dynamics (e.g., [3,14,15]).…”

“…Yang et al (2015) [34] tested an automated sink retention size threshold (termed a "depression area threshold"), but advised caution when using flow routing over moderate resolution (30-40 m) DEMs to delineate supraglacial channels. To overcome the limitations of automated moulin detection, non-automated sink preservation has been used by Andrews (2015) [37] and Karlstrom and Yang (2016) [10], in which manually identified moulin locations are preserved as sinks during flow routing over moderate-(25 m, resampled from 10 m) and high-resolution (2 m) DEMs, respectively.…”