lakes_cluster (Stevens et al., 2026)

Recreate figures and movies in Stevens et al. (2026): Ice-sheet hydro-fracture not advanced inland by lower-elevation lake drainages in Kalaallit Nunaat.

System requirements

This code requires MATLAB R2023B (or a more recent MATLAB release) to run. The code has been tested on MATLAB R2023B. To install, download this code repository to your computer (~900 MB). Also download the FigShare data deposition corresponding to this manuscript (~33 GB). A typical install/download time on a desktop computer should be <20 minutes, depending on internet speed.

Next, follow the instructions in each subsection below for running data-processing and figure-creation scripts. The expected outputs are reproductions of all quantitative results presented in the manuscript and the paper figures. A typical run time on a desktop computer will be a few minutes for each figure-producing script. The nevis subglacial-hydrology model (Hewitt, 2013) takes ~12 hours to run over a full melt season.

Probabilistic temporal-cluster analysis

Within homogeneous_poisson, scripts for counting up clusters of lake-drainage events, organized by drainage mechanism:

• hydro-fracture events (Fig. 3);
• moulin events (Fig. 4a–d); and
• overspill events (Fig. 4e–h).

Daily runoff accumulated at ice-sheet surface elevations within study region of interest courtesy of Noël et al. (2019).

GNSS-derived quantities

Within GNSS_derived, scripts for figures containing GNSS-observed and/or GNSS-derived estimates of:

• station horizontal and vertical positions (Supplementary Information);
• station horizontal velocities (Supplementary Information);
• station bed-separation rates (Supplementary Information);
• inter-station strain rates (Figs. 5 and 6; Supplementary Information); and,
• map of lake-drainage mechanisms, lake-to-lake supraglacial connections, and GNSS stations (Fig. 1).

Daily runoff courtesy of Noël et al. (2019).

Physical plausibility of hydro-fracture event clusters

Within physical_plausibility, scripts for physical plausibility of hydro-fracture event clusters C1–C6 (Figs. 7 and 8; Supplementary Information).

Subglacial-hydrology model

Within nevis_lakes_cluster, model-run and plotting scripts for the nevis subglacial-hydrology model (Hewitt, 2013), which is equivalent to the model version used in Stevens et al. (2022) nevis_helheim, save for parameter-value choices and the central west Greenland Ice Sheet model domain.

The model is forced by estimated rates of daily runoff courtesy of Noël et al. (2019). Model domain requires BedMachine Greenland v.5 (Morlighem et al., 2017; 2022). Ice-sheet basal velocities of the model domain are set to surface-velocity values observed by the 2022 MEaSUREs Annual Velocity Mosaic (Joughin et al., 2015).

• nevis: model code.
• Model run file for 2022: nevis_lakesix_noSK_300m_ub.m
• Model run file for 2023: nevis_lakesix_2023_noSK_300m_ub.m
• Surface runoff, subglacial discharge, and lake-drainage events in 2022 (Supplementary Information Movie M1).
• Surface runoff, subglacial discharge, and lake-drainage events in 2023 (Supplementary Information Movie M2).

Example subglacial-hydrology model output alongside mechanistic lake-drainage catalogue:

(The mechanistic lake-drainage catalogues are located in these two repositories: mechanistic_drainage_catalogue_2022 and mechanistic_drainage_catalogue_2023. The lake-drainage catalogues include figures of every image available for each lake identified by FASTER (Williams et al., 2018a; 2018b).)

Repository Figure 1. Surface runoff, subglacial discharge, and lake-drainage events on 2022/214. (upper panel) (blue colormap) Daily surface runoff $E$ for study region courtesy of Noël et al. (2019). Day of year of movie frame plotted as map title. (middle panel) (blue colormap) Modelled subglacial discharge $q$ forced by daily, distributed surface runoff inputs shown in upper panel. In both map-view panels, ice-sheet surface elevation shown with 100-m-elevation contours in grey (Morlighem et al., 2017; 2022). GNSS stations shown with solid black triangles. Black-outlined symbols show location and drainage mechanism of supraglacial lakes, with the symbol colour indicating whether the lake is (blue) filling; (goldenrod) initially draining; (green) continuing to drain; or (grey) an empty, dry, or frozen lake basin. Lake-drainage mechanisms are: (stars) hydro-fracture, (overturned triangles) moulin, (circles) overspill, and (square) no-exit, frozen. The location and drainage timing of (diamonds) water-filled crevasses are also shown. Lakes and water-filled crevasses are first plotted in time on the day of year in which they attain $v_{crit}$, their critical volume required to hydro-fracture to the ice-sheet bed. (bottom panel) (solid-blue line) Surface-runoff and (dashed-blue line) basal-melt inputs summed across the model domain; proglacial discharge exiting the model domain shown in yellow. Purple vertical bar tracks time.

License

This repository is licensed under the CC BY-NC 4.0 License. See the LICENSE file for more information.

References

Hewitt, I. J. Seasonal changes in ice sheet motion due to melt water lubrication. Earth and Planetary Science Letters 371–372, 16–25 (2013).

Joughin, I., Smith, B., Howat, I. & Scambos, T. MEaSUREs Greenland Ice Sheet Velocity Map from InSAR Data, Version 2. NASA National Snow and Ice Data Center Distributed Active Archive Center https://doi.org/10.5067/OC7B04ZM9G6Q (2015).

Noël, B., Van De Berg, W. J., Lhermitte, S. & Van Den Broeke, M. R. Rapid ablation zone expansion amplifies north Greenland mass loss. Sci. Adv. 5, eaaw0123 (2019).

Morlighem, M. et al. BedMachine v3: Complete Bed Topography and Ocean Bathymetry Mapping of Greenland From Multibeam Echo Sounding Combined With Mass Conservation. Geophysical Research Letters 44, (2017).

Morlighem, M. et al. IceBridge BedMachine Greenland, Version 5. NASA National Snow and Ice Data Center Distributed Active Archive Center https://doi.org/10.5067/GMEVBWFLWA7X (2022).

Stevens, L. A. et al. Tidewater-glacier response to supraglacial lake drainage. Nat Commun 13, 6065 (2022).

Stevens, L. A. Tidewater-glacier response to supraglacial lake drainage (v1.0). Zenodo. https://doi.org/10.5281/zenodo.7023662 (2022).

Stevens, L. A. et al. Elastic Stress Coupling Between Supraglacial Lakes. JGR Earth Surface 129, e2023JF007481 (2024).

Stevens, L. A., & S. Larochelle. Elastic stress coupling between supraglacial lakes (v1.2). Zenodo. https://doi.org/10.5281/zenodo.10650188 (2024).

Stevens, L. A. et al. Ice-sheet hydro-fracture not advanced inland by lower-elevation lake drainages in Kalaallit Nunaat. Nat Commun (2026).

Williamson, A. G., Banwell, A. F., Willis, I. C. & Arnold, N. S. Dual-satellite (Sentinel-2 and Landsat 8) remote sensing of supraglacial lakes in Greenland. The Cryosphere 12, 3045–3065 (2018a).

Williamson, A. Full source code for the Fully Automated Supraglacial lake Tracking at Enhanced Resolution ("FASTER") algorithm. Apollo - University of Cambridge Repository. https://doi.org/10.17863/CAM.25769 (2018b).

Correspondence

Have questions? Please address correspondence to L.A.S. (laura.stevens@earth.ox.ac.uk).