Known as “Doomsday Glacier” – Antarctica’s Thwaites Glacier is one of the most rapidly changing glaciers on Earth, and its future evolution is one of the biggest unknowns when it comes to predicting global sea level rise.
The eastern ice shelf of Thwaites Glacier is supported at its northern end by a ridge of ocean floor. However, over the past two decades, cracks in the upper reaches of the glacier have increased rapidly, weakening its structural stability. Up-to-date test by the International Thwaites Glacier Collaboration (ITGC) provides a detailed record of this gradual collapse process.
Scientists from the Earth Observation and Science Center at the University of Manitoba in Canada analyzed observational data from 2002 to 2022 to track the formation and propagation of cracks in the ice shelf shear zone. They found that as cracks grow, the connection between the ice shelf and the mid-ocean ridge weakens, accelerating the flow of ice upstream.
A crack in an ice shelf is expanding in two stages
The study shows that ice shelf weakening occurred in four distinct phases, and crack growth occurred in two stages. In the first phase, long cracks appeared along the ice flow, gradually extending eastward. Some exceeded 8 km in length and covered the entire shelf. In the second phase, numerous compact transverse fractures, less than 2 km long, formed, which doubled the total length of the fractures.
Analysis of satellite images showed that the total length of cracks increased from approximately 165 km in 2002 to approximately 336 km in 2021. Meanwhile, the average length of individual cracks decreased from 3.2 km to 1.5 km, with a marked enhance in compact cracks. These changes reflect a significant change in the stress state of the ice shelf, i.e. the interaction of forces in its structure.
Between 2002 and 2006, the ice shelf accelerated as it was pulled by nearby, fast-moving currents, creating compressive stress at the anchor point that initially stabilized the shelf. After 2007, the shear zone between the shelf and the western ice tongue collapsed. The stresses concentrated around the anchor point, leading to vast cracks.
Since 2017, these cracks have completely penetrated the ice shelf, severing the anchor connection. According to researchers, this process has accelerated upper ice flow and turned anchoring into a destabilizing factor.
Breakdown of the feedback loop
One of the most crucial findings of the study is the existence of a feedback loop: cracks accelerate the flow of ice, and this increased speed causes modern cracks to form. This process was clearly recorded by GPS devices that the team deployed on the ice shelf between 2020 and 2022.
In the winter of 2020, the upward propagation of structural changes in the shear zone was particularly observable. These changes occurred at a rate of approximately 55 kilometers per year across the ice shelf, showing that structural breakdown in the shear zone directly affects the upstream flow of ice.