Scientists have mapped 1,943 valleys carved into the bedrock beneath the Greenland Ice Sheet, and about a third of them had never been identified before. The new map links those valleys into an expansive network that earlier surveys missed or left fragmented, according to a NASA-led study highlighted by NASA Earth Observatory on September 28.

The work also found that about half of the valleys in BedMachine Greenland, the standard dataset of terrain beneath the ice, extend farther inland than that map shows, in some cases by hundreds of kilometers. The study, by A. M. Chartrand and colleagues, was published in Geophysical Research Letters.

Why should anyone outside Greenland care about buried valleys? Because they help steer the ice. Where valleys run, ice concentrates and flows faster toward the sea, so a better map of the ground beneath the ice sheet can sharpen projections of how it will change. That does not mean the new map changes sea-level forecasts on its own, a point the researchers are careful about.

Reading the Ground Through the Ice

Greenland's ice sheet spans about 1.7 million square kilometers (656,000 square miles) and measures more than 3 kilometers (1.9 miles) at its thickest point. No one has seen the land beneath it directly. Scientists have relied on airborne radar and other measurements, which leave large gaps across the slow-moving interior.

The new map comes from a method called Ice Flow Perturbation Analysis. As ice flows over a valley or ridge, the buried terrain leaves a faint signature of bumps and dips on the ice surface. Satellites map that surface in fine detail, and researchers can use the subtle patterns to infer the shape of the landscape below. NASA lists its ICESat-2 laser altimeter among the instruments behind the work, and the researchers mapped the valleys manually.

The aim is practical. The team says the work is intended to improve future versions of BedMachine Greenland, the dataset that ice sheet models draw on.

A Landscape Older Than the Ice

Many of the valleys appear to begin in Greenland's southern and eastern highlands, where scientists think the ice sheet first formed. Near the eastern highlands, the map reveals a mountain range beneath the ice, 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, an epoch that ended about 2.6 million years ago.

Other features are harder to explain. In west-central Greenland, many valleys are long, straight and consistently aligned from southwest to northeast, a pattern that suggests a tectonic influence creating preferential pathways for water to flow and valleys to form. "That's a riddle to us," said Joe MacGregor, a NASA cryospheric scientist and co-author, who noted that Greenland is usually treated as a rigid block of old rock.

The angles at which the valleys branch offer another clue. Their relatively wide branching suggests that surface water did not act alone, and that a widespread groundwater network seeping upward and eroding rock likely helped carve them before the ice sheet formed.

Valleys That Steer the Ice

Ice follows the terrain. Flow concentrates in valleys, where it forms glaciers that eventually calve into fjords at the edge of the ice sheet. That creates a reinforcing cycle: ice funneling through a valley gets thicker, thicker ice flows faster, and faster flow carves the valley deeper. MacGregor likened western Greenland's glacially incised coastline to Yosemite, describing it as "El Capitan after El Capitan."

Because that relationship is well understood, scientists expect that as the ice sheet retreats, flow will keep concentrating where the valleys already are. "The better we understand the topography now," MacGregor said, the better sense researchers will have of the longer-term picture as faster ice flow propagates into Greenland's interior.

That is a statement about long-term flow pathways, not a new estimate of sea-level rise. The study maps terrain; it does not project how much ice will be lost or how quickly.

Stakes for Distant Coastlines

Greenland's ice sheet is one of the largest contributors to global sea-level rise, which affects coastal communities from Miami and New Orleans to New York and San Diego. Projections of that rise depend partly on how well models represent the ground beneath the ice. Better maps of where ice can flow fastest help researchers narrow uncertainty, even if they do not change today's forecasts.

For coastal residents and planners, the practical guidance remains the same: rely on official sea-level projections from agencies such as NOAA and from local planning bodies, which incorporate new research as it is reviewed and built into models. A single mapping study, however striking, is an input to those projections rather than a replacement for them.

The next steps are technical. The authors intend the valley network to inform updated versions of BedMachine Greenland, and other research teams can test the tectonic and groundwater explanations the map raises.

A NASA-led team mapped 1,943 valleys beneath Greenland's ice, about a third of them new, revealing a connected network that shapes how ice flows. The finding improves the foundation for future projections, but it does not by itself change estimates of sea-level rise.

What Readers Want to Know

What did scientists find beneath Greenland's ice?

They mapped 1,943 valleys in the bedrock beneath the Greenland Ice Sheet, about a third of them newly identified, forming an expansive network across the island.

How can scientists map land under miles of ice?

They used Ice Flow Perturbation Analysis, which infers buried terrain from subtle bumps and dips in the ice surface measured by satellites.

Does this change sea-level rise projections?

Not directly. The map improves understanding of where ice will flow as the sheet retreats, and the researchers intend it to feed into future terrain datasets and models.

How old are the valleys?

Many formed before most of the current ice existed. NASA said some alpine landforms may have survived beneath the ice since at least the Pliocene.

Why are some valleys so straight?

Long, straight valleys in west-central Greenland suggest a tectonic influence, which study co-author Joe MacGregor called a riddle for researchers.

Where was the study published?

In Geophysical Research Letters, with results highlighted by NASA Earth Observatory on September 28.