Methodology:

By the 2018-07-07 lake drainage event, Lake 028 was instrumented with a GPS receiver, seismometer, and pressure transducer sensor. A dual-frequency GPS was installed ~600 m upstream of the lake in July 2017, and by July 2018 had advected into a position immediately south of the lake. A seismometer was installed in May 2018, and a water-level sensor on 2018-07-04. From this date, regular UAV surveys (See SI Appendix, Table S1 in associated publication) were performed over the lake and surrounding environments.

A detailed description of the data collection, quality control, processing and analysis is given in: Chudley, T.R., Christoffersen, P., Doyle, S. H., Bougamont, M., Schoonman, C. M., Hubbard, B., and James, M. (2019) Supraglacial lake drainage at a fast-flowing Greenlandic outlet glacier. doi:10.1073/pnas.1913685116

Data collection:

UAV: Custom-built Skywalker X8 fixed-wing UAV running ArduPlane autopilot software, collecting imagery with a Sony α6000 and GPS data with an Emlid Reach receiver. Images processed in Agisoft Metashape v 1.4.3.

Pressure Transducer: Solinst 3001 Levelogger

GPS: Trimble NetR7 GPS with Trimble Zephyr Geodetic III Antenna

Seismometer: HG-7 geophone recorded to a DiGOS DATA-CUBE

Data quality:

GPS data have been filtered with a two-pole, low-pass Butterworth filter with a 30-minute cutoff period. This 30-minute window was chosen based on a worst-case horizontal positional uncertainty of 0.035 m and a base ice velocity of ~650 m a-1, following from which assumptions the period over which velocities can be resolved is ~0.5 hours. Uncertainty was calculated based on a conservative estimate of the positional uncertainty of ±1 cm propagated through the velocity calculation.

Seismometer data were decimated to 100 sps and a 2-pole, zero-phase bandpass filter (10-50 Hz) was applied to eliminate instrument and high-frequency noise.

We assign UAV-derived orthophoto and DEM data uncertainties of ±0.12 m horizontally (~1.1x the ground sampling distance) and ±0.14 m vertically (~1.3x the ground sampling distance), following Chudley et al. (Cryosphere, 13, 955-968, 2019). Uncertainties in the velocity field were calculated based upon a displacement uncertainty of 0.17 m.

A detailed description of the data collection, quality control, processing and analysis is given in:

Chudley, T.R., Christoffersen, P., Doyle, S. H., Bougamont, M., Schoonman, C. M., Hubbard, B., and James, M. (2019) Supraglacial lake drainage at a fast-flowing Greenlandic outlet glacier. doi:10.1073/pnas.1913685116