New Greenland map connects valleys hidden beneath the ice sheet

NASA Earth Observatory has published a new map connecting valleys beneath the Greenland Ice Sheet that earlier maps missed or showed only in fragments. Researchers say the fuller picture of the buried terrain could help them understand where ice flows as the sheet changes, while the map also raises questions about how Greenland’s landscape formed.

The researchers manually mapped 1,943 valleys, according to NASA’s September 28 report. About a third were newly identified. NASA also says roughly half of the valleys shown in BedMachine Greenland, particularly near the ice sheet’s edge, extend farther inland than that map indicated—in some cases by hundreds of kilometres. Those counts come from NASA’s account of the work.

Reading the landscape through the ice

The team used a method called Ice Flow Perturbation Analysis. As ice moves across a buried valley or ridge, the terrain leaves a faint pattern of bumps and dips on the ice surface. Researchers use observations of surface elevation and ice velocity to infer the shape of the bedrock below. The valleys are therefore mapped from the ice’s behaviour, rather than seen directly across the ice sheet.

The peer-reviewed study, led by Allison M. Chartrand and published in Geophysical Research Letters on July 16, describes an island-wide network connected to valleys already mapped near Greenland’s margins. Its abstract says an earlier method, based on the principle of mass conservation, improved mapping around those margins but cannot be applied to the slower-flowing interior, where ice-thickness observations are sparse.

BedMachine Greenland remains a substantial mapping resource. The National Snow and Ice Data Center describes its current version as a 150-metre-resolution dataset combining mass conservation, multibeam measurements and other techniques. It includes bed elevation, ice thickness and surface elevation. The new valley map is intended to inform future versions of BedMachine, NASA says; it does not mean the existing dataset was a direct view of every part of the buried landscape.

What the valley shapes suggest

NASA highlights long, straight valleys in west-central Greenland. Some were mapped for the first time; others appear to run farther inland than previously known. Their consistent southwest-to-northeast alignment suggests a possible tectonic influence on where water travelled and valleys formed, according to NASA. The pattern does not by itself establish the valleys’ origin.

Joseph A. MacGregor, a NASA cryospheric scientist and study co-author, called that apparent pattern “a riddle to us.” NASA quotes him explaining that Greenland is generally treated as a rigid block of old rock in accounts of plate movement. The alignment gives researchers a question to investigate, rather than a settled account of past tectonic activity.

The study’s abstract also points to Greenland’s southern and eastern highlands as possible starting areas for the ice sheet, based on the network’s shape. NASA describes a mountain range and interconnected valleys beneath the eastern highlands. It says some alpine-style landforms may have survived under the ice since at least the Pliocene, an interpretation of their form rather than a direct observation of when they formed.

The angles where valleys branch offer another clue. NASA says their relatively wide angles suggest surface water was not the only force involved: groundwater moving through the landscape may also have helped erode rock before the ice sheet formed. The study abstract likewise identifies groundwater flow and Greenland’s tectonic history as possible influences on the network. Neither explanation is presented as a direct measurement of those ancient processes.

Why the map matters for ice research

The terrain beneath an ice sheet helps determine how ice moves above it. NASA explains that flow gathers in valleys, forming glaciers that can reach fjords at the ice sheet’s edge. Ice concentrated in a valley can grow thicker and move faster, deepening the valley over time. NASA says this carving effect is particularly apparent in western Greenland.

Researchers expect existing valleys to keep concentrating flow if the ice sheet retreats. MacGregor told NASA that a better account of today’s bedrock topography could improve understanding of longer-term changes as faster flow reaches farther into Greenland’s interior. That is a reason to refine the map, not a measured forecast of how much ice Greenland will lose or when.

The map supplies a more connected picture of a landscape hidden beneath ice that covers about 1.7 million square kilometres, according to NASA. Its most distinctive shapes may also provide tests for ideas about ancient water flow and the island’s geology. Establishing those histories, and translating better terrain maps into future ice-flow projections, remains further scientific work.