A new study has revealed how fractures in the mass of Greenland glacial ice cause huge quantities of surface water to be transferred beneath the ice. This has a significant impact on ice sheet dynamics.
The Greenland ice sheet, the vast body of ice covering about 80 % of the island, is rapidly melting, contributing to global sea level rise and increasing coastal flooding risk. Having lost 3.8 trillion t of ice between 1992 and 2018 according to a study in the journal ‘Nature’, Greenland is the single largest contributor to global sea level rise.
Partially supported by the EU-funded RESPONDER project, researchers have shown that the Greenland ice sheet is becoming unstable due to fractures from under meltwater lakes. Conducting the research at a camp on Store Glacier in north-west Greenland, the team used drones to observe how one fracture extended 500 m down into the ice. In multiple drone flights, the researchers documented the flow of water into the fracture and the water’s subsequent pathway under the ice.
Their study revealed that about 5 million m3 of water (the equivalent of 2 000 Olympic-sized swimming pools) was drained to the bed of the kilometre-thick Greenland ice sheet in just 5 hours – enough to lift it up by over half a metre. The findings were published in the journal ‘Proceedings of the National Academy of Sciences’. “Partial drainage events have previously been assumed to occur slowly via lake overtopping, with a comparatively small dynamic influence. In contrast, our findings show that partial drainage events can be caused by hydrofracture, producing new hydrological connections that continue to concentrate the supply of surface meltwater to the bed of the ice sheet throughout the melt season.”
A news item by the University of Cambridge summarises the research. “The drone footage supports computer models used by the same team of researchers to show that drainage of melt lakes in Greenland can occur in a chain reaction. The new study provides an insight as to how these chain reactions might be triggered, via lakes that can drain through existing fractures.”
Quoted in the same news item, first study author Thomas R. Chudley says: “It’s possible we’ve under-estimated the effects of these glaciers on the overall instability of the Greenland Ice Sheet.” The news item notes that the drone footage is utilised “to identify ‘hotspots’ where the ice sheet behaves sensitively.” It adds: “Using drilling equipment, the team is now exploring how the water is accommodated in the basal drainage system and how the ice sheet may change over the coming decades as the climate continues to warm.”
The RESPONDER (Resolving subglacial properties, hydrological networks and dynamic evolution of ice flow on the Greenland Ice Sheet) project will run until September 2021. The RESPONDER team is examining the dynamics of the Greenland ice sheet to understand how physical properties and hydrological networks evolve over seasons and over multiple years, and how this evolution affects the flow of the ice sheet when water from the surface is transferred to the bed. The project website states: “By employing multiple, complementary approaches, ranging from geophysical imaging techniques to direct exploration in kilometer-deep boreholes, the project is collecting an unparalleled stream of observational data from the basal environment which is rarely studied, yet responsible for making Greenland glaciers flow faster than glaciers anywhere else on Earth.”
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