NASA Maps 1,943 Hidden Valleys Beneath Greenland's Ice Sheet

NASA cryospheric scientist Joe MacGregor and colleagues have mapped 1,943 valleys buried beneath Greenland's ice sheet using satellite data, NASA said Monday, revealing geological features that extend far deeper into the island's interior than scientists previously knew.

The findings come from a NASA-led paper published in Geophysical Research Letters. The team used a technique called Ice Flow Perturbation Analysis, which works by reading faint signals on the ice surface. As ice moves over a buried valley or ridge, the hidden terrain leaves subtle bumps and dips on the surface above it. Satellites can map those surface variations in fine detail, and scientists can work backward from them to reconstruct the shape of the rock below.

The result is the most detailed picture yet of the landscape beneath the Greenland Ice Sheet, which NASA describes as spanning 1.7 million square kilometers and reaching more than 3 kilometers thick at its deepest point.

About a third of the 1,943 valleys the team identified are newly discovered, according to the NASA page describing the research. The rest were already included in BedMachine Greenland, a high-resolution terrain dataset, but the new analysis found that roughly half of those known valleys extend farther inland than BedMachine shows. In some cases, NASA said, the true extent reaches hundreds of kilometers beyond what the existing map indicated.

That is the detail that changes the picture. Scientists had a map. The map was incomplete, and not by a small margin.

Some of what the new map shows fits the existing understanding of how Greenland's terrain formed. Many valleys appear to originate in the southern and eastern highlands, where the ice sheet is thought to have first developed, according to the NASA account. Near the eastern highlands, the map reveals a buried mountain range with interconnected valleys and relief that increases toward the coast. NASA said these alpine-style landforms may have survived under the ice since at least the Pliocene.

Other features are harder to explain. A large number of valleys in the west-central region are long, straight, and consistently aligned in a southwest-to-northeast direction. That kind of regular orientation points toward tectonic forces rather than simple erosion by water. "That's a riddle to us," MacGregor said in the NASA account. "Greenland is justifiably usually treated as a rigid block of old rock that is simply translated as needed to accommodate the motion and interactions of other tectonic plates."

The branching angles of the valleys add another layer to the puzzle. According to NASA, the relatively wide angles at which valleys meet suggest that surface water alone did not carve them. A widespread groundwater network, seeping upward through the rock before the ice sheet existed, likely played a role as well.

The valleys are not just geological curiosities. They shape how the ice sheet behaves today and how it will behave as it retreats.

Ice flow concentrates in valleys, NASA explains, forming glaciers that move toward the coast and eventually break off into the ocean. The process feeds itself: ice funneling into a valley grows thicker, thicker ice moves faster, and faster movement carves the valley deeper still. MacGregor compared the result along western Greenland to the glacially carved landscape at Yosemite, describing Greenland's western coast as "El Capitan after El Capitan," according to the NASA account.

Because ice tends to follow existing valleys, scientists expect that pattern to continue as the ice sheet shrinks. The valleys that exist now will guide where flow concentrates in the future. "The better we understand the topography now," MacGregor said in the NASA account, "the better sense we'll have of what it will look like in the longer term, beyond the next decade or two, as faster ice flow propagates into Greenland's interior."

That matters for sea level projections. Ice sheet models depend on accurate terrain data. If the valleys are longer and deeper than the models assumed, the models will produce different answers about how fast ice moves and how much melt reaches the ocean.

The work is aimed in part at improving future versions of BedMachine Greenland, the terrain dataset the research community uses as a foundation for ice sheet modeling, according to NASA. The map was built by Lauren Dauphin using data from Chartrand et al., as credited on the NASA Earth Observatory page. The paper itself is published in Geophysical Research Letters.

What the team does not yet know is why the west-central valleys align so consistently in that southwest-to-northeast direction. MacGregor called it a riddle, and the NASA account leaves it as one.

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