The Thwaites Glacier, a massive, fast-moving river of ice in West Antarctica, holds an outsized significance for future sea levels. Due to its potential for a catastrophic contribution to global oceans, it has earned the ominous nickname, the “Doomsday Glacier.” This ice stream, over 120 kilometers wide, is part of the larger West Antarctic Ice Sheet (WAIS) and is currently undergoing an accelerated phase of melt and retreat. Covering approximately 192,000 square kilometers, the glacier’s sheer volume is a primary factor determining the stability of the entire West Antarctic region.
Thwaites Glacier Context and Scale
Before its current period of rapid change, Thwaites Glacier was a relatively stable, though vulnerable, feature of the WAIS. Ice thickness near the coast typically measures between 800 and 1,200 meters. The glacier performs a mechanical function by acting as a geological buttress, slowing the flow of ice from the interior of the WAIS. This ice sheet is considered the “weak underbelly” of Antarctica because a large portion of it rests on bedrock that lies far below sea level.
The stability of the system is governed by the grounding line, the precise point where the ice stream lifts off the bedrock and begins to float as an ice shelf. Historically, the grounding line was positioned further seaward on a shallower part of the continental shelf. The grounded ice acts as a plug that slows the flow of ice, and the floating ice shelf provides an additional buttressing effect. Retreat of this boundary onto deeper bedrock represents a loss of mechanical resistance, which is crucial for predicting the glacier’s fate.
Drivers of Instability
The primary mechanism driving the rapid destabilization of Thwaites Glacier is the inflow of warm ocean water beneath its floating ice shelf. This water mass, known as Circumpolar Deep Water (CDW), is relatively warm, typically over 1.0 degree Celsius. The unique, deep-trough geometry of the continental shelf in the Amundsen Sea allows this CDW to flow directly onto the shelf and access the deep cavity beneath the ice shelf. This inflow causes basal melt, which is the melting of the ice from below by the ocean water.
The penetration of CDW into the sub-ice cavity significantly raises the melt rate, the speed at which ice is lost from the underside of the glacier. While ice shelves in calmer regions melt at rates of centimeters per year, melt rates in the Thwaites grounding zone have been measured up to 250 meters per year in some areas. This high rate of melting thins the ice shelf, reducing its buttressing capacity and allowing grounded ice to flow faster toward the sea. The situation is exacerbated by the bedrock beneath the glacier, which slopes downward toward the continent’s interior, known as a retrograde slope. This slope creates a positive feedback loop: retreat onto deeper bed exposes a thicker column of ice to the ocean, increasing ice flow and leading to further retreat.
Observable Changes
The difference between the glacier’s historical and current state is visible through measurable changes in its physical properties and movement. Prior to the mid-1990s, the glacier was relatively stable, but satellite monitoring has documented an accelerating shift since then. The flow of the main ice stream has dramatically accelerated, with ice speeds now exceeding two kilometers per year near the grounding line. This increase in velocity is directly linked to the loss of stability caused by warm ocean water.
The grounding line has been in rapid retreat, monitored using satellite altimetry data and airborne radar. In some sections, the grounding line retreated by as much as 14 kilometers between 2009 and 2017 alone. Sustained retreat rates of up to 700 meters per year were observed in certain areas between 2010 and 2022. This retreat is accompanied by significant ice thinning, which was observed to be lowering by approximately 10 centimeters per year in the interior of the basin during the 1990s.
The Thwaites Eastern Ice Shelf (TEIS), which stabilizes the eastern portion of the glacier, is showing signs of structural failure. This floating extension is held in place by a pinning point, a section of ice temporarily grounded on an underwater rise. Satellite imagery documents increased fracturing and weakening of the ice shelf, and the grounded area of the pinning point has been greatly reduced since 2014. If surface lowering rates persist, the TEIS could completely unpin and disintegrate within the current decade, further accelerating the flow of grounded ice behind it.
Global Impact and Future Projections
The changes observed at Thwaites Glacier are already contributing to global sea level rise, currently accounting for about four percent of the total annual increase. If the entire Thwaites Glacier were to collapse, it would contribute approximately 65 centimeters of sea level rise worldwide. The glacier’s true importance lies in its role as a gatekeeper for the entire West Antarctic Ice Sheet (WAIS).
The destabilization of Thwaites Glacier could initiate Marine Ice Sheet Instability (MISI), where the retrograde slope causes a self-sustaining and irreversible retreat. A full collapse of Thwaites could trigger a runaway destabilization across the entire WAIS, which holds enough ice to raise global sea levels by over 3.3 meters. While the collapse of Thwaites itself is projected to take centuries, with ice loss accelerating through the 22nd century, a widespread WAIS collapse is a long-term projection for the 23rd century in some models. Scenarios of rapid, catastrophic collapse within this century, based on Marine Ice Cliff Instability, are considered less likely by recent high-resolution modeling. However, the continued rapid retreat driven by ocean warming and MISI remains a significant threat for the coming centuries.