Thwaites Glacier Is Melting More Aggressively Than Expected

Scientists already knew that Thwaites Glacier was retreating, losing ice and contributing to global sea-level rise. New observations reveal a more troubling detail: ocean water may be penetrating farther beneath the glacier and with greater force than many earlier models represented.

The finding does not mean Thwaites Glacier will collapse tomorrow. It does mean that some processes controlling its retreat are more dynamic and difficult to predict than satellite images alone can show.

Thwaites is one of Antarctica’s largest and most closely studied glaciers. It drains a substantial portion of the West Antarctic Ice Sheet into the Amundsen Sea, where ocean-driven ice loss has accelerated in recent decades. Its popular nickname, the “Doomsday Glacier,” is a media label rather than an official scientific classification. The name reflects the glacier’s potential importance to future sea-level rise and its role in supporting neighboring ice.

Researchers are examining three central questions: how far warm water can travel beneath Thwaites, how that water affects the grounding line, and whether ice loss could destabilize a larger part of West Antarctica.

What Is Thwaites Glacier?

Thwaites Glacier lies in West Antarctica and flows from the Antarctic Ice Sheet toward the Amundsen Sea. Its exact dimensions vary depending on how scientists define its boundaries, but it covers an area comparable to that of a large region or country.

The glacier is remote, heavily crevassed and difficult to access. Some sections rest on bedrock, while others extend over seawater as floating ice. Thick ice, severe weather, deep ocean cavities and an uneven seafloor make direct observation difficult.

Key terms include:

• Ice sheet: A continental-scale mass of land-based ice.
• Glacier: A moving body of ice that flows under its own weight.
• Ice shelf: Floating ice attached to a glacier or ice sheet.
• Grounding line: The boundary where ice resting on bedrock begins to float.
• Calving front: The seaward edge of floating ice where icebergs break away.

The grounding zone is especially important because small changes there can alter the glacier’s flow into the ocean.

Why the grounding line matters

A grounding line is not necessarily a fixed or visible boundary. It can move as tides lift and lower floating ice, as the glacier thins and as seawater melts its underside.

When the grounding line retreats inland, more of the glacier becomes afloat. Floating ice no longer rests directly on the seafloor, reducing friction that helps slow inland ice. The glacier can then discharge ice into the ocean more quickly.

Retreat can also expose thicker ice to the ocean. If the bed beneath the glacier slopes downward inland, the grounding line may enter deeper water as it retreats. A thicker ice column at the grounding line can increase the amount of ice flowing toward the sea, creating a feedback that makes retreat harder to stop.

This process is associated with marine ice-sheet instability. It is not an automatic collapse mechanism, but it is one reason West Antarctica is considered vulnerable to long-term retreat.

Why scientists monitor Thwaites

Thwaites is already losing mass. Its direct contribution to global sea-level rise is measured in millimeters over longer periods, but the loss accumulates and could increase if the glacier accelerates.

Its floating ice shelf also acts as a buttress. It does not hold the glacier in place like a wall, but contact with the seafloor, internal ice strength and the shelf’s shape can slow inland ice.

As the shelf thins, fractures and loses contact with underwater ridges, that restraint weakens. The concern extends beyond Thwaites itself: major retreat could change stresses across neighboring glaciers and contribute to wider West Antarctic ice loss. Source 1

The New Finding: More Aggressive Melting

Warm seawater is reaching farther beneath the glacier

The word “warm” is relative. Seawater beneath Thwaites remains extremely cold by everyday standards. It is warm because its temperature is higher than the local pressure-adjusted melting point of the ice.

In a 2024 study, researchers reported that seawater intrusion reached roughly 12 kilometers upstream from the grounding line during parts of the tidal cycle. The result suggested that the ocean can access areas previously treated as more isolated from direct ocean circulation. Source 2

Melting does not need to occur across the entire underside at an extreme rate to weaken a glacier. Water entering a strategic part of the grounding zone can affect ice thickness, buoyancy, flow and the stability of the transition from grounded to floating ice.

The study also indicated that ocean-driven melting associated with this intrusion could be higher than estimates from models that exclude or simplify the process. It does not establish one final melt rate for the entire glacier. It shows that some models may underestimate localized melting where seawater is actively pumped beneath the ice.

Melting is not uniform

Thwaites is not melting at one consistent rate across its underside. Important areas include crevasses, channels, fractures and the grounding zone.

A smooth, flat underside is easier to represent in a computer model, but the real glacier is more irregular. Its underside contains cavities, ridges and pathways that can direct water toward particular sections.

Narrow openings can allow seawater to travel farther inland than a broad-average model predicts. The water can then melt ice at the base and alter the shape of the cavity. The changing cavity may affect currents and create new pathways for heat transport.

Localized melting can have structural consequences disproportionate to its area. A channel near a grounding-zone pinning point may matter more for glacier stability than a larger amount of melting in a region that provides little resistance to ice flow.

Observations beneath the ice changed the picture

Satellite data can track surface elevation, ice speed and grounding-line movement, but they generally cannot measure the detailed temperature, salinity and circulation of water inside an ocean cavity.

Scientists combine several tools:

• Autonomous underwater vehicles: Map ice-shelf cavities, seafloor topography and water properties.
• Oceanographic instruments: Measure temperature, salinity, pressure and currents.
• Radar surveys: Estimate ice thickness and map the bed beneath grounded ice.
• Satellite observations: Track surface motion, elevation, fractures and grounding-line changes.
• GPS and seismic instruments: Detect movement, tidal flexing and structural changes.

The 2024 observations came from instruments placed near Thwaites’ grounding zone. They revealed tidal movement of seawater beneath the ice and helped researchers estimate how far the water could penetrate. Source 2

How Ocean Water Melts Ice From Below

The melting point of ice decreases slightly under pressure and changes with salinity. At the base of a thick glacier, seawater can therefore melt ice even when its temperature is below 0 degrees Celsius.

The key comparison is between the water temperature and the local pressure-adjusted melting point of the ice, not between the water and room temperature.

Antarctic glaciers near the Amundsen Sea are exposed to relatively warm deep water that can move onto the continental shelf. When that water enters an ice-shelf cavity, it transfers heat to the ice. Melting can be slow in some places and rapid in others, depending on current speed, cavity geometry, turbulence and the temperature difference between water and ice.

Tides pump water into the cavity

Floating ice rises and falls with the tides. That movement can open and close pathways beneath the ice and force seawater inland and seaward.

This tidal pumping transports heat into cavities that might otherwise receive less ocean circulation. It also makes melting dynamic rather than steady. The amount of water entering the cavity can change throughout the tidal cycle.

As the ice lifts, seawater may move beneath areas that appear grounded at lower tide. The intrusion can spread heat across the glacier base and increase melting near the grounding line.

Channels and crevasses amplify damage

Water can travel through channels beneath an ice shelf. Surface meltwater may also enter fractures, although the importance of surface-driven processes varies across Antarctica and must be measured rather than assumed.

Channels focus ocean circulation. Crevasses weaken the ice shelf and can connect basal melting to surface cracking. An ice shelf affected by both thinning and fracture becomes less able to transmit stress and resist flow.

Basal melting therefore has two effects: it removes ice directly and can weaken the structure that helps restrain inland ice. Those effects are not always captured by a single average melt rate.

Why Earlier Models May Have Underestimated the Risk

Scientists cannot continuously observe the entire underside of Thwaites. Models fill the gaps by representing ocean circulation, ice flow, cavity shape and grounding-line movement.

Simplifying assumptions may produce lower melt estimates if they represent the underside as smooth, restrict water access beneath the glacier or treat ocean circulation as relatively uniform. A model may also hold the grounding line in a more stable position than the real glacier does.

These limitations do not make models useless. Models are essential for estimating future behavior, and their results improve when researchers add direct measurements of water movement, ice geometry and seafloor shape.

An average melt rate can also conceal important differences. A high rate beneath an isolated section may have limited influence on ice flow, while a lower rate near a grounding-zone ridge, fracture or pinning point may weaken a feature that helps slow the glacier.

Scientists distinguish among:

• Ice-volume loss: The amount of ice removed.
• Structural weakening: The loss of strength caused by thinning and fracture.
• Grounding-line retreat: Inland movement of the boundary between grounded and floating ice.
• Loss of buttressing: Reduced resistance to inland ice flow.

These processes interact but are not identical. A glacier can experience modest average thinning while becoming more structurally unstable.

What Happens If Thwaites Continues to Retreat?

Thwaites will not produce an immediate worldwide flood. Ice-sheet change generally unfolds over years to centuries, although individual calving events can occur suddenly.

Continued retreat could bring:

• More ice discharge into the ocean.
• A growing contribution to sea-level rise.
• Greater stress on nearby ice shelves.
• More fracture development.
• More frequent calving.
• Further inland migration of the grounding line.

Annual changes may appear small, but their importance comes from accumulation over decades and the possibility that ice loss accelerates.

Scientists are also concerned that Thwaites could influence neighboring parts of the West Antarctic Ice Sheet. A possible sequence would involve a weakened floating shelf, faster inland ice flow, changing stresses across adjacent glaciers and continued regional retreat.

That sequence is a risk scenario, not a guaranteed timeline. Its extent and speed depend on the bed beneath the ice, ocean conditions, ice-shelf geometry, fracture processes and future climate forcing.

The International Thwaites Glacier Collaboration was established to improve observations and projections because the glacier’s future cannot be determined from a single satellite image or one melt measurement. Source 1

The complete loss of Thwaites Glacier would contribute significantly to global sea-level rise, but it would occur over a long period rather than overnight. The wider West Antarctic Ice Sheet contains far more potential ice loss than Thwaites alone.

Even a few centimeters of global sea-level rise matter. Higher baseline sea levels increase the reach of storm surges and make coastal flooding more frequent. They also worsen erosion, saltwater intrusion and pressure on drainage systems, roads, ports and protective barriers.

The Intergovernmental Panel on Climate Change identifies ice-sheet loss as a major source of uncertainty in long-term sea-level projections. Source 3

What the Findings Do Not Mean

Thwaites will not suddenly collapse tomorrow

New observations show a more active melting process than some earlier models represented. They do not establish an immediate collapse date.

Thwaites is retreating and becoming less stable, but the timing of major changes remains uncertain. Headlines that turn increased scientific concern into a precise near-term catastrophe go beyond the evidence.

Thwaites is not the only driver of sea-level rise

Global sea-level rise also results from thermal expansion of seawater, mountain glacier loss, Greenland Ice Sheet loss and changes in other Antarctic glaciers.

Thwaites matters because it can amplify regional ice loss. It is not the sole cause of future coastal flooding.

Better measurements can improve projections

New observations may cause projections to move higher or lower. Scientists still need better data on ocean circulation, cavity geometry, grounding-line behavior and ice-shelf fracture.

Uncertainty is a reason to improve monitoring and prepare coastlines, not a reason to delay action.

How Scientists Are Studying the Glacier

Autonomous underwater vehicles and oceanographic instruments can enter cavities that ships and satellites cannot directly observe. Researchers measure water temperature, salinity, current speed, ice geometry and seafloor topography.

Satellites track ice velocity, surface elevation, crevasse growth, grounding-line movement and changes in ice-shelf thickness. Airborne radar maps ice thickness and the bed beneath the glacier. Together, these surveys place local field measurements within the larger glacier system. Source 4

Thwaites requires international cooperation because it is too large, remote and technically difficult for one institution to monitor alone. Researchers share field campaigns, satellite records, radar maps and model results. Long-term observation is essential because the glacier’s most important changes may emerge over decades rather than during one expedition.

What Can Be Done About the Risk?

Reducing greenhouse gas emissions remains the main way to limit future warming of the atmosphere and oceans. Lower warming reduces the likelihood of continued ocean heat reaching vulnerable Antarctic ice.

Emissions cuts will not immediately reverse existing glacier retreat, but they can reduce the severity and duration of future warming and improve the chances of limiting long-term ice loss.

Coastal communities can use updated flood maps and long-range sea-level projections to guide decisions. Adaptation measures include stronger defenses, restored wetlands, restrictions on high-risk development, improved evacuation plans and resilient water, power and transportation systems.

Researchers also need more direct measurements beneath ice shelves, better seafloor maps, improved simulations of tidal pumping, stronger models of ice-shelf fracture and longer satellite records.

Conclusion

Scientists already knew Thwaites Glacier was losing ice. New evidence shows that the process beneath it is more complex and potentially more aggressive than broad-scale models suggested.

Relatively warm seawater can reach the glacier’s underside. Tides can pump that water beneath the ice. Channels and irregular cavities can carry heat inland toward the grounding zone. Melting and fracture can weaken the ice shelf’s ability to slow the flow of inland ice.

Thwaites is a serious long-term risk, but its collapse is not an immediate certainty. Better measurements can reduce uncertainty, emissions reductions can limit future ocean warming and coastal preparation can reduce the damage from higher seas.

The broader lesson is clear: processes hidden beneath Antarctic ice may help determine the future shape of coastlines around the world.

FAQ

Why is Thwaites Glacier called the “Doomsday Glacier”?

The nickname refers to Thwaites’ large size, rapid ice loss and potential influence on neighboring parts of the West Antarctic Ice Sheet. It is not an official scientific term and does not mean the glacier will collapse suddenly.

How is Thwaites Glacier melting?

Relatively warm seawater flows beneath the floating ice and melts it from below. Tidal movement, channels and fractures may allow the water to penetrate farther inland than earlier models assumed.

Will Thwaites Glacier collapse soon?

Scientists have not established a precise collapse date. The glacier is retreating and becoming less stable, but major ice-sheet changes generally unfold over years to centuries.

How much sea-level rise could Thwaites Glacier cause?

The amount and timing depend on how quickly the glacier retreats and whether its loss destabilizes nearby ice. Thwaites alone contains enough ice to produce substantial global sea-level rise, while the connected West Antarctic Ice Sheet contains much more.

Can Thwaites Glacier’s melting be stopped?

Reducing greenhouse gas emissions can limit additional atmospheric and ocean warming, but it may not immediately reverse existing changes. Coastal adaptation and continued research are also necessary.

Why are scientists still uncertain about the glacier’s future?

Much of Thwaites is remote, submerged or covered by thick ice. Researchers cannot directly observe every process near the grounding line. Underwater instruments, satellites, radar surveys and computer models are reducing—but not eliminating—the uncertainty.