A Greenland glacier is cracking open in real time

After forming in 1995, the lake did not remain stable. "From the time of its formation in 1995 until 2023, the lake's water repeatedly and abruptly drained through channels and cracks in the ice, causing massive amounts of fresh water to reach the edge of the glacier tongue towards the ocean." Researchers identified seven major drainage events in total, with four occurring within just the last five years.

Unusual Ice Fractures and Giant Vertical Channels

As these sudden drainages took place, the glacier surface began to fracture in unexpected ways. "During these drainages, extensive triangular fracture fields with cracks in the ice formed from 2019 onwards, which are shaped differently from all lake drainages I have seen so far," Humbert said. Some of the fractures developed into large vertical shafts known as moulins, with openings that can span several dozen meters.

Even after the main lake drainage ends, water continues flowing through these moulins. This allows enormous volumes of meltwater to reach the base of the ice sheet within just a few hours. "For the first time, we have now measured the channels that form in the ice during drainage and how they change over the years."

Why the Glacier Cracks and Then Heals

Following the lake's formation in 1995, its surface area gradually shrank as cracks began to appear. In recent years, however, drainage events have happened more frequently. "We suspect that this is due to the triangular moulins that have been reactivated repeatedly over the years since 2019," Humbert explained.

This behavior is linked to how glacier ice responds to stress. Ice flows slowly like an extremely thick (viscous) fluid as it moves over the ground beneath it. At the same time, it behaves elastically, meaning it can bend and partially return to its original shape, similar to a rubber band. This elasticity makes it possible for cracks and channels to form. Meanwhile, the slow flowing nature of the ice helps those channels gradually close again after a drainage event.

"The size of the triangular moulin fractures on the surface remains unchanged for several years. Radar images show that although they change over time inside the glacier, they are still detectable years after their formation." The data also shows that the glacier contains a connected system of cracks and channels, providing multiple routes for water to escape.

Meltwater is lifting the glaciers

Aerial images revealed shadows tracing many of the surface cracks. In some cases, the ice on either side of a fracture appeared uneven. "In some cases, the ice at the fracture surfaces has also shifted in height, as if it were raised more on one side of the moulin than on the other," Humbert noted.

The most dramatic vertical movement was observed directly beneath the lake. Huge volumes of water had flowed into fractures below the glacier, collecting there to form a subglacial lake. Radar data from inside the ice shows what appears to be a blister beneath the surface, pushing the glacier upward at that location. Remarkably, surface cracks from the earliest drainage events remain visible more than 15 years later.

Tracking the Water and the Future of the Glacier

To conduct the study, researchers combined several types of observations. Satellite remote sensing data and airborne survey measurements were used to monitor how the lake fills and drains, as well as the paths water takes inside the glacier. Viscoelastic modeling helped determine whether drainage channels close over time and how long they persist.

These findings raise a key question. Has the glacier been pushed into a new long term state by repeated drainage events, or can it still return to normal winter conditions despite such extreme water input? "In just ten years, recurring patterns and regularity have developed in the drainage, with massive and abrupt changes in meltwater inflow on a timescale of hours to days," said Humbert. "These are extreme disturbances within the system, and it has not yet been investigated whether the glacial system can absorb this amount of water and is able to influence the drainage itself."

Why These Cracks Matter for Ice Sheet Models

The study delivers valuable data for improving ice sheet models by directly incorporating how cracks form and evolve. Researchers at AWI are collaborating with scientists from TU Darmstadt and the University of Stuttgart to better simulate these processes.

Accounting for fractures is especially important when examining the lake on the 79°N Glacier. As atmospheric warming continues, cracks are forming farther uphill, affecting increasingly larger sections of the glacier. Understanding how these fractures behave will be critical for predicting how Greenland's ice will respond in a warming world.