Using ultra-precise radar and decades of ice data, researchers have drawn the most detailed map yet of the ground beneath the Antarctic ice sheet, revealing unexpected hills, dramatic valleys and a colossal trench that could reshape what we know about future sea level rise.
What lies beneath two kilometres of ice
From space, Antarctica appears flat, white and almost featureless. That impression is wildly misleading. Beneath an ice sheet up to four kilometres thick sits a continent carved by ancient rivers, fault lines and mountains.
This new map shows that the subglacial landscape is far more uneven than thought. The study suggests there are roughly twice as many hills, ridges and knolls as previous models indicated, along with deep valleys where ice can slide faster toward the ocean.
The ground under Antarctica is not a smooth bowl of rock but a jagged, heavily sculpted terrain that controls how ice moves.
To produce this picture, scientists combined airborne radar observations, satellite measurements of ice height and motion, and advanced computer modelling. The project builds on earlier work such as “BedMachine”, but pushes resolution and coverage further, filling gaps in regions that had only sketchy data until now.
A giant hidden valley with global consequences
Among the standout features is a gigantic valley buried under the ice. It stretches for hundreds of kilometres and drops to depths of more than 3.5 kilometres below sea level in places, rivalling the deepest canyons on the planet.
Such valleys form natural highways for ice. Gravity pulls ice down these troughs, steering it toward coastal glaciers and floating ice shelves. Where the bedrock lies below sea level and slopes inland, warm ocean water can intrude and eat away at the ice from underneath.
The newly mapped valley acts like a funnel, guiding vast volumes of ice toward vulnerable parts of the Antarctic coast.
That geometry matters for sea level rise. If ice flowing through this trench thins or collapses, the knock-on effect could accelerate the loss of grounded ice further inland. Scientists are now feeding the updated topography into ice-sheet models to test how quickly those regions might respond to warming oceans.
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Twice as many hills, twice as many friction points
The discovery of roughly double the number of subglacial hills and bumps is not just a cartographic curiosity. Each rise or ridge affects how ice behaves above it.
- Hills increase friction and can slow ice sliding toward the sea.
- Ridges can pin ice shelves in place, stabilising them for a time.
- Low valleys and basins can collect meltwater, lubricating the ice base.
In some regions, the dense cluster of hills could act like a brake, giving coastal glaciers more resistance as the climate warms. In others, steep valleys might create fast-flow “ice streams”, where ice races seaward at several hundred metres per year.
This patchwork of roughness means that ice-sheet change will not be uniform. Neighbouring glaciers can respond very differently to the same temperature rise, depending on what lies beneath them.
How scientists mapped an invisible landscape
Because nobody can simply dig through kilometres of ice, researchers rely on indirect tools. The main instrument is ice-penetrating radar, usually mounted under aircraft. Radar waves pass through the ice, bounce off the rock below and return to sensors, revealing depth and shape.
Where radar flights are sparse, satellites help fill in the gaps. They measure tiny changes in ice surface height and horizontal motion. If surface ice speeds up or slows down over a known slope, computers can infer how rough or smooth the bed must be underneath.
The new map is essentially a best-fit solution: the only bedrock shape that matches all the observed ice thickness, speed and elevation.
This approach allows scientists to resolve features just a few kilometres wide over much of the continent, a sharp improvement on older global datasets that blurred many details.
Why this changes sea level forecasts
Antarctica holds enough ice to raise global sea levels by nearly 60 metres if it all melted. No one expects that to happen this century, but even a small fraction would hit coastal cities hard. The shape of the ground under the ice is one of the biggest sources of uncertainty in future projections.
Where the bedrock rises above sea level, inland ice tends to be more stable. Where it dips deep below the ocean and slopes inland, it becomes vulnerable to a process called “marine ice sheet instability”. Once warm water undercuts the ice front, the grounding line – the point where ice lifts off the bed and begins to float – can retreat rapidly.
The newly revealed giant valley includes long stretches of such inward-sloping seabed. That geometry can make retreat self-sustaining: as the grounding line moves into deeper water, flotation becomes easier and more ice is lost.
| Feature | Why it matters for sea level |
|---|---|
| Deep valleys below sea level | Allow warm ocean water to penetrate inland and melt ice from below |
| Dense fields of hills | Add friction, potentially slowing glacier flow |
| Steep bedrock slopes | Control whether grounding lines can retreat quickly |
| Subglacial basins | Can store meltwater and affect lubrication at the ice base |
A new testbed for climate models
Global climate models now link closely with ice-sheet models, which in turn rely on accurate bedrock maps. With the updated Antarctic map, modelers can run more realistic simulations of how different emissions scenarios might play out.
For instance, they can test how much extra melting occurs if Southern Ocean currents bring slightly warmer water under particular ice shelves. They can also evaluate whether some valleys might act as tipping points: once a threshold amount of ice is lost, retreat could proceed largely on its own.
Results from these experiments feed into projections used by coastal planners, insurers and governments. Slight changes in expected sea level rise by 2100 – for example, 60 cm instead of 40 cm – can drastically alter the cost-benefit balance of flood defences in cities such as London, New York or Shanghai.
Hidden geology and ancient rivers under the ice
The map is not just a climate tool; it is also a geological treasure. The pattern of hills and valleys hints at ancient river systems that once flowed when Antarctica was green and relatively warm, tens of millions of years ago.
Long, smooth valleys with branching shapes look like old river channels that glaciers later deepened and widened. Rugged mountain blocks trace past tectonic collisions and continental break-ups, tying the Antarctic plate into the broader puzzle of Gondwana and the southern continents.
Understanding this ancient landscape helps scientists reconstruct past climates. If Antarctica once supported forests and rivers, that tells us about greenhouse gas levels and ocean circulation in those epochs. Those deep-time analogues offer context for the rapid warming now driven by human emissions.
Key terms worth unpacking
Several technical phrases around Antarctic ice can sound abstract, but they describe very tangible processes:
- Ice shelf: the floating extension of a glacier or ice sheet, still attached to the land-based ice inland.
- Grounding line: the line where ice leaves the bedrock and starts to float; a critical control point for stability.
- Subglacial: anything located beneath the ice, including lakes, streams, valleys and mountains.
- Basal sliding: the motion of ice as it slides over rock or sediment, often lubricated by meltwater.
When climate projections mention the risk of rapid Antarctic change, these are the features and processes they have in mind. A small shift in grounding-line position along a deep valley, for example, can release far more ice than a simple surface melt event.
What this means for people living near coasts
For coastal communities from Miami to Mumbai, the new Antarctic map does not change the basic message: sea level is rising and will continue to rise. What it does offer is sharper insight into timing, pace and upper limits.
Planners can use that information to test different strategies. A city might model one future where Antarctic ice remains relatively stable, and another where retreat along the newly mapped giant valley accelerates. The range between those outcomes guides decisions on seawalls, zoning rules and insurance pricing.
On longer timescales – beyond 2100 – the shape of the Antarctic bedrock takes on an even larger role. Valleys that hold back ice today could, under sustained warming, become conduits for large-scale retreat. Knowing where those gateways lie helps humanity understand the long legacy of emissions made in this century.
Originally posted 2026-02-18 01:00:55.