Figuring out what’s happening under a kilometer (more than half a mile) of solid Greenland ice isn’t easy for scientists, but the rise and fall of ‘water blisters’ could offer some vital insights into the deep flow of water and ice, accordingly. for a new study.
These blisters form between the ice sheet and the underlying rock, and they form when lakes of natural meltwater at the surface flow through fractures in the ice and fill cavities. From there the water seeps into the drainage system under the glacier.
What researchers have now discovered, through a combination of field measurements, modeling and lab experiments, is that these blisters can push the ice up as it forms and cause it to sink again as it recedes.
This means they can be used to estimate permeability — the efficiency of water systems that form between the ice and the underlying rock beneath — and to better understand how increased melting caused by climate change affects the overall stability of the ice sheet.
«We know that as the climate warms in the future, the surface melt zone could expand and move to higher altitudes than is currently observed,» Geologist Cheng Yao Lai says: from Princeton University.
«The big question that still needs to be answered, however, is how much permeability can be increased indoors.»
Lai and her team looked at five lake drainage events from 2006 to 2012, using methods including GPS tracking to monitor drainage volume, surface displacements, and blister formation occurring under the ice.
The time it took for the ice to sink down as the blisters disappeared varied greatly, indicating key differences in the subglacial drainage system beneath them.
After developing analytical models to match the field observations they had seen, the researchers conducted experiments in the lab using a silicon sheet deformable as ice and a porous material as bedrock. These tests helped them improve their models even more.
«The system is small enough to hold in one hand and the material is transparent, so we were able to directly observe bubble shape and drainage in the porous substrate over time,» Mechanical Engineer Daniel Chase says: from Princeton University.
When water flows through the ice and forms blisters, it can act as a lubricant between a glacier and the ground it sits on. Evidence suggests that this instability is likely to worsen as temperatures rise and melt increases.
With the new model now available, scientists should be able to measure this potential perturbation more accurately, by analyzing the permeability and how it changes over time.
The next step is to apply these results to get a better understanding of what is happening under the Greenland ice sheet — especially in the inland and higher regions, where current data is incomplete and it becomes very difficult to take readings.
«The potential effect is that the link between surface melt and the development of the subglacial water system could be activated not only at lower altitudes, as is currently observed, but also at higher altitudes,» Lay says.
«Further observations of seasonal changes in subglacial permeability in response to surface melt will be needed to understand what might happen when melt migrates to higher altitude regions.»
The search was published in Nature Connections.