The Greenland Ice Sheet (GrIS) has been losing mass since the mid-1990s, with its contribution to sea level rise accelerating since the early 21st century. This mass loss is attributed to two main factors: acceleration of glaciers and changes in the surface mass balance, especially increased surface melting. Recent study, focused on the massive supraglacial lake on the Nioghalvfjerdsbræ Glacier (79° N Glacier, 79NG), provides valuable insights into how these processes are closely linked to a changing climate.

Before the mid-1990s, there was no lake in the study area. The transition from a lakeless area to frequent sudden drainage events is directly linked to the increase in atmospheric temperatures in the mid-1990s. For example, the Danmarkshavn meteorological station recorded a temperature increase of more than 1 °C at 2 m. Analysis of skin temperatures in the lake basin in the CARRA (Copernicus Arctic Regional Reanalysis) system showed that while mid-July temperatures changed little, temperatures rose significantly at the beginning and end of summerThis extends the melting season and thus the amount of meltwater available.

The drainage of supraglacial lakes through cracks is a critical process that delivers huge amounts of water to the base of the glacier within hours. The first recorded drainage of the monitored lake, with a volume of up to 1.23 × 10⁸ m³, occurred only in 2005/2006, approximately ten years after the lake began to form. In these early stages, extensive crack fields and triangular mouths of glacial wells (moulins) were formed, into which water flowed even after the main period of lake drainage. These triangular moulins, with openings tens of meters wide, can be reactivated in subsequent years, while their surface size remains unchanged for some time, which is consistent with viscoelastic modeling.

After 2015 – the year with the lake’s largest volume – the frequency of drainage increased and the lake’s volume decreased. For example, in 2019 and 2020, drainage occurred just a year after the previous event. 2023 saw the earliest recorded drainage, with the lake filling in just seven days and most draining between July 11 and 12. The frequent reactivation of previous drainage pathways suggests that it requires less mechanical loading than the formation of entirely new cracks.Even years after drainage, vertical displacement continues through cracks and sub-lithological features that change shape but remain detectable. A "blister" of water also forms beneath the lake, which is released over a period of several weeks.

These frequent and sudden drainage events are extreme disruptions to the hydrological system, which supply massive amounts of freshwater and lubricant to the seaward edge of the glacier. It is likely that the lake's development and frequent drainage in recent years have contributed to the formation of extensive subglacial channels further downstream. The study highlights that such an approach, combining different observational methods, is key to understanding the genesis of supraglacial lakes, the formation and closure of englacial pathways, and the response of the subglacial system to changing climate conditions. The question remains how this system will evolve in the future. JRi