What role does elastic deformation play on the 79° N glacier?
This week our GROCE colleagues from subproject 2 in Nature Communications Earth and Environment published a new exciting research article, full of surprising findings: "Elastic deformation plays a not insignificant role in Greenland's exit glacier flow".
What was the key question that inspired this research?
It is well known that the velocity of ice streams in Antarctica is modulated by tides up to 80km inland. They wanted to study whether this takes place at the 79°N Glacier (79NG) too, and aimed to understand the mechanism behind it.
November 12, 2021
Which methods did you use?
The essential method is a viscoelastic simulation – that means, we are modelling the ice of the glacier not only as a viscous fluid but also with elastic characteristics which are most important on short time scales. That becomes even more complicated by ice sliding across the bed and subglacial water acting as lubricant. Subglacial water is in contact with the ocean and thus modulated by tides, too. We have run three different models to simulate this complex interaction.
What is most exciting of your result?
The fact that the simulations fit so well to the observational data was also for the field glaciologists in the team a surprise. For the modellers, the most exciting part is to have the chance to use this model system as a tool to understand in detail which process acts how on the motion. This way we found, that tides can only act that far upstream as the subglacial hydrological system allows – the hydraulic properties cannot change fast enough to progress the signal further inland.
Additionally, we gained some interesting new insights by investigating at which places the elastic contribution is particularly high. Even locations that are at places out of reach for the tidal signal, show effects of elastic components! The reason is that subglacial hills and mountains are changing stresses at the base and with the high flow velocities of the outlet glaciers at the margins of the ice sheet an elastic deformation is formed. That was an a-ha! effect and we were wondering if we can transfer this to entire Greenland ice sheet? To this end, we conducted another simulation, this time for pan Greenland and found that the region of high elastic components matches areas of massive crevasses. That is exactly what we would expect, as cracks are the characteristics of a solid and arise from elastic stresses.
What does that mean for the future?
Usually, one tries to simplify the system as much as possible if one conduct simulations. We took the opposite approach and tried to represent the complexity of the system as much as we could. That was a mad ride, but it opened us the opportunity to understand many causal relationships. Einstein said ‘Everything should be made as simple as possible, but no simpler.’ and our study is a good example of it. Keeping in mind that crevasses are playing a special role in Greenland as they are a pathway of seasonal melt water to the glacier base, it becomes clear, that in future we need to aim at making this type of simulation the standard – which is quite an endeavour.