DOI: 10.5061/dryad.rjdfn2zrc
title: Supporting data for: Rapid ice-marginal lake growth in Alaska driven by glacier retreat through bed overdeepenings

description: In this study, we mapped ice-marginal glacial lakes in Alaska in 2018 and
 2024 using Sentinel-2 optical imagery. We mapped glacier-bed
 overdeepenings using existing datasets and evaluated how much lake growth
 has occurred within these mapped overdeepenings as well as how much
 additional growth is possible. Here we provide seven supporting data
 products: i) a raster of mapped glacier-bed overdeepenings using best
 estimate of ice thickness, ii) a raster of glacier-bed overdeepenings
 using ice thickness plus uncertainty, iii) a raster of glacier-bed
 overdeepenings using ice thickness minus uncertainty, iv) a 2018
 ice-marginal lake shapefile, v) a 2024 ice-marginal lake shapefile, vi) a
 2024 ice-marginal lake shapefile joined to glacier-bed overdeepening area,
 and vii) RGI 6 glacier inventory joined to glacier-bed overdeepening
 area. 
description: Using an existing glacial lake inventory (Rick et al., 2022), we
 identified glacial lakes in Alaska greater than 0.5
 km<sup>2</sup> (n=211) for the period 2016 to 2019 (median
 year 2018). Using Sentinel-2 optical imagery from 1 May to 30 September
 2018 and 2024, we manually mapped lake extents at 1:10,000 scale for these
 two years in the open-source QGIS software program. We estimate error in
 lake area by multiplying the lake perimeter (in km) by half the Sentinel-2
 pixel resolution (5 m or 0.005 km). We also reviewed and updated the lake
 connection category, which describes the lake's spatial relationship
 to its source glacier. These categories include: proglacial (lakes at
 terminus of glacier, in contact with the ice), supraglacial (lakes on
 surface of glacier ice), ice (ice-dammed lakes found at ice margins or
 tributary valleys), detached (lakes fed by glaciers but not in contact
 with the ice), or unconnected (detached lakes that are not fed by
 glaciers). This study solely assesses ice-marginal lakes (n=147 lakes),
 defined as having contact with a glacier and thus excludes detached and
 unconnected lakes. To map glacier-bed overdeepenings in
 the region, we combined the Copernicus GLO-30 Digital Elevation Model
 (DEM) and previously modelled ice thickness estimates derived from
 observed ice velocities and the shallow-ice approximation (Millan et al.,
 2022). Imagery for GLO-30 was acquired between 2010 and 2015, while ice
 velocities used in Millan et al. (2022) are from 2017–18. The GLO-30 DEM
 was mosaicked, regridded to 50 m, and reprojected to NAD83/Alaska Albers
 (EPSG: 3338). The modeled ice thicknesses were mosaicked and reprojected
 and then subtracted from the surface DEM to generate a bed DEM. We created
 a filled bed surface using the “fillsinks” function in TopoToolbox in
 Matlab. In QGIS, we subtracted the filled bed DEM from the original bed
 DEM to map glacier-bed overdeepening spatial extents and magnitudes. To
 account for uncertainty in ice thickness estimates, we repeated the above
 workflow with revised ice thickness rasters that accounted for stated
 uncertainties.
description: # Supporting data for: Rapid ice-marginal lake growth in Alaska driven by
 glacier retreat through bed overdeepenings Dataset DOI:
 [10.5061/dryad.rjdfn2zrc](https://doi.org/10.5061/dryad.rjdfn2zrc) ##
 Description of the data and file structure There are two glacial lake
 outline shapefiles : **Lake_Outlines_2018_102225** and
 **Lake_Outlines_2024_102225**. The shapefiles consist of a .shp file
 (feature geometry), along with supporting files (.shx - positional index
 of the feature geometry, .dbf - columnar attributes for each shape, .prj -
 project description, .cpg - used to specify the code page). Both are
 projected in EPSG:3338. Column Headers in these files include:
 **Lake_Outlines_2018_102225** Latitude: Latitude in decimal degrees in
 WGS84 format Longitude:  Longitude in decimal degrees in WGS84 format
 Area_2018:  Lake Area in km^2^ from Rick et al., 2022 Area_2018r: Revised
 Lake Area in km^2^ using 2018 Sentinel-2 imagery Dam_Type: Material
 damming lake; see Rick et al., 2022 for additional details Connection:
 Lake connection to glacier; see Rick et al., 2022 for additional details
 Perimeter: Lake perimeter in km^2^ Name: Glacier name from Randolph
 Glacier Inventory RGI6Id: ID from Randolph Glacier Inventory 6.0
 OutlineYr: Year of imagery used to generate lake outline Comments:
 Comments about lake status Incl_Analysis: Lakes marked 1 were included in
 analysis, lakes marked with 0 were not included in analysis for reasons
 stated in Comments column **Lake_Outlines_2024_102225** Additional columns
 in this outline: Upd_Conn: Updated lake connection if different in 2024
 RmvLakArea: Lake area [m^2^] for existing mapped lakes within outlines
 that need to be removed when calculating total area change Area_2024: Lake
 area in 2024 in km^2^ AreaChg: Lake area change between 2018 and 2024 in
 km^2^. This column does not account for the RmvLakArea values. Three
 raster (GeoTiff) files with the mapped glacier-bed overdeepenings were
 generated: i) using best estimate of ice
 thickness: **COP30_minus_IceT_rseries_COP30_orig_minus_filled_clipped.tif**, ii) using best estimate of ice thickness minus ice thickness uncertainty: **COP30_minus_IceT_minus_err_rseries_min_042125_orig_minus_filled_clipped.tif** and iii) using best estimate of ice thickness plus ice thickness uncertainty: **COP30_minus_IceT_plus_err_rseries_min_042125_orig_minus_filled_clipped.tif** These raster products are projected in EPSG:3338 with approximate pixel sizes of 50.05 m. Two additional shapefiles were generated: **Lake_Outlines_2024_joined_to_overdeepening_102225.shp** (and associated files). This shapefile is similiar in structure/column headers to Lake_Outlines_2024_102225 but has the addition of Over Area that is the area [km^2^] of mapped overdeepening attached to the lake. Multiple lakes can access the same overdeepening in this file (e.g., those lakes on Seward and Agassiz glaciers).  Lakes that are not connected to an overdeepening or where that overdeepening was less than 0.1 km^2^ in area are not included in this file.  **RGI6_zonalstats_merged_overdeepening_102225.shp** (and associated files).  This shapefile includes the same columns as the RGI 6 dataset ([https://www.glims.org/RGI/randolph60.html](https://www.glims.org/RGI/randolph60.html)) with the addition of five columns that summarize the mapped glacier-bed overdeepening within each glacier outline. PxCnt - the number of mapped glacier-bed overdeepening pixels within each glacier PxSum - sum of overdeepened pixel magnitudes (this is not volume and requires multiplying by pixel x and y) PxMean - mean of overdeepened pixel magnitudes [units of meters] GlOverArea - cumulative area of overdeepened ice by glacier [units of km^2^] GlOverVol - cumulative volume of overdeepened ice by glacier [units of km^3^] ## Access information Other publicly accessible locations of the data: * 
 
 Data was derived from the following sources: * Rick, B., McGrath, D.,
 Armstrong, W., and McCoy, S. W. 2022. Dam type and lake location
 characterize ice-marginal lake area change in Alaska and NW Canada
 between 1984 and 2019, *The Cryosphere*, **16**, 297–314,
 [https://doi.org/10.5194/tc-16-297-2022](https://doi.org/10.5194/tc-16-297-2022). * RGI Consortium, 2017. Randolph Glacier Inventory - A Dataset of Global Glacier Outlines, Version 6. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi: [https://doi.org/10.7265/4m1f-gd79](https://doi.org/10.7265/4m1f-gd79) * Millan, R., Mouginot, J., Rabatel, A. *et al.* 2022. Ice velocity and thickness of the world’s glaciers. *Nat. Geosci.* **15**, 124–129. [https://doi.org/10.1038/s41561-021-00885-z](https://doi.org/10.1038/s41561-021-00885-z) * European Space Agency, Copernicus Global Digital Elevation Model. *Distributed by OpenTopography* (2024). [https://doi.org/10.5069/G9028PQB](https://doi.org/10.5069/G9028PQB).