High above the Arctic Ocean, one of Greenland’s last great floating glacier tongues is flexing, fracturing and draining in dramatic bursts offering scientists a rare, real-time window into how climate change can destabilise massive ice structures.
On Greenland’s remote northeast coast lies the Nioghalvfjerdsbræ better known as the 79°N Glacier. It is one of only three remaining large floating glacier tongues in Greenland, making it critical for understanding future sea-level rise.
A Lake That Vanishes Overnight
In 1995, satellite imagery revealed a vast meltwater lake sitting atop the glacier tongue a 21-square-kilometre basin formed by rising air temperatures. Since then, researchers from the Alfred Wegener Institute (AWI) have tracked its unusual behaviour.
The lake does not simply freeze and thaw. Instead, it drains suddenly and violently sometimes within hours leaving behind complex fracture systems etched into the ice. Scientists have now documented seven major drainage events, four of them in the past five years alone.
Each drainage sends enormous volumes of freshwater plunging through vertical shafts known as moulins near-vertical tunnels carved by meltwater that funnel water more than a kilometre down to the glacier’s base.
Triangular Fractures and Hidden Water Blisters
What makes this glacier different is the geometry of the fractures left behind. Since 2019, researchers have observed large triangular crack fields radiating outward from the drained lake basin patterns unlike the circular sinkhole shapes seen on other glaciers.
These fractures act like giant funnels, guiding water into openings tens of metres wide. Radar and aerial imaging show that after major drainage events, water can accumulate beneath the glacier tongue, forming pressurised subglacial lakes.
In some areas, that trapped water physically lifts the ice above it, creating what scientists describe as a “blister” beneath the glacier. Surface measurements indicate uplift of several metres evidence that the glacier is not just cracking, but being pushed upward from below.
Why This Matters
When meltwater reaches the glacier’s base, it reduces friction between the ice and the underlying rock or sediment. Lower friction can allow the glacier to slide more rapidly toward the ocean particularly during or shortly after drainage events.
The dual nature of ice complicates matters. Over long periods, glacier ice flows like a very thick liquid. Over short timescales, however, it behaves elastically bending, cracking and rebounding under stress. This viscoelastic behaviour means fracture systems can persist for years, reopening each summer when new meltwater arrives.
Researchers are now investigating whether repeated drainages have pushed the 79°N Glacier into a new, less stable state one where cracks and internal channels remain semi-permanent, primed for rapid reactivation.
Although this system revolves around a single lake on a single glacier, its implications extend far beyond northeast Greenland. The 79°N Glacier acts as a buttress, slowing the flow of inland ice toward the sea. If its floating tongue weakens or breaks apart, ice discharge into the ocean could accelerate.
At the same time, warmer ocean waters are thinning the glacier from below, while surface melt and lake formation weaken it from above a double stress that may shorten the lifespan of this critical ice barrier.
Climate models have historically struggled to incorporate sudden drainage events and evolving fracture systems. The detailed satellite observations, radar data and viscoelastic modelling from the AWI study now provide rare empirical data that can improve projections of the Greenland Ice Sheet and its contribution to global sea-level rise.
As Arctic warming intensifies, scientists expect melt seasons to lengthen, lakes to form earlier, and drainage events to become more frequent.
What is unfolding at 79°N Glacier is not just a local curiosity. It may be an early signal of how large floating ice tongues long considered relatively stable respond when surface melt and ocean heat work together.
The glacier is cracking. The water is draining. And researchers are watching, in unprecedented detail, as a once-stable system begins to change.