“It was so unexpected, we thought there was an issue with our data,” said Jade Bowling, senior author of the study which has turned scientific knowledge of Greenland’s ice sheet hydrology on its head. During the summer of 2014, a subglacial lake in north Greenland dumped 90 million cubic meters of meltwater in a span of 10 days, breaking through almost 300 feet of solid ice and blasting into the surface with an unprecented force in the area. The flood dug an 85-meter-deep, 2-square-kilometer crater, tossed 25-meter-high blocks of ice, and scoured an area nearly double the size of Central Park.
The mechanics of this phenomenon were against existing models. Subglacial lakes bodies of liquid water that are confined between bedrock and ice are known normally to drain slowly, with meltwater migrating downward to the ocean. Satellite data from ESA’s CryoSat, Copernicus Sentinel-1 and Sentinel-2, NASA’s ICESat-2, and surface models from ArcticDEM showed an upward migration. The water, held under intense pressure, broke through the ice above and burst upward vertically a phenomenon, as Georgia Tech’s Winnie Chu explained, that “requires some extremely unique conditions.” More astonishing still, the eruption occurred in a region where basal thermal models should have seen a frozen bed, indicating that powerful hydraulic pressure can overcome thermal limits and cut new paths of drainage.
The hydrological intricacy beneath the ice sheet at Greenland is only now being charted. Airborne radar surveys revealed 54 new previously unknown subglacial lake prospects, some lasting decades under ice cover up to 3,200 meters thick. The majority are in equilibrium, but a minor portion only 6.7% have signs of active drainage. The 2014 event close to Harder Glacier is now recorded as one of the largest subglacial floods ever in Greenland, and its upward rupture adds a mechanism missing from existing climate and ice flow models.
The physics of these outbursts are grounded in subglacial hydrology and fracture mechanics. When meltwater is built up, either from surface supply or geothermal melting, basal water pressure is increased. If that pressure becomes greater than the overburden pressure of the ice, fractures may extend upward, a process similar to hydrofracturing in supraglacial lakes but from below. Numerical modeling of drainage in Antarctic analogs indicates that even minor perturbations like small surface elevation changes or incremental water input can induce episodic drainage. In Greenland, the steeper hydraulic gradients and more limited lake sizes make predictions more challenging, but the 2014 flood proves that catastrophic drainage can result with no apparent precursors.
Remote sensing played a key role in reconstructing the event. Multi-mission altimetry measured the instantaneous surface lowering, whereas optical images showed the downstream fracture zone and smoothed ice surfaces of the deluge. Radar, laser altimetry, and high-resolution DEMs synergistically allowed researchers to measure both the volume and geomorphic effect of the flood. As Lancaster University’s Mal McMillan pointed out, “Satellites represent an essential tool for monitoring the impacts of climate change, and provide critical information to build realistic models of how our planet may change in the future.”
The consequences are far-reaching. The ice sheet in Greenland is losing mass at an increasing rate NASA estimates a 12.2% decadal growth in ice loss and makes a substantial contribution to world sea level rise. If more frequent upward-draining subglacial floods do occur, they may destabilize ice in unmodeled ways, potentially accelerating the release of ice to the ocean. The coupling of such floods with outlet glacier dynamics, as suggested by Harder Glacier’s anomalous calving and flow responses during the 2014 event, is an immediate concern for investigation.
In answer to such uncertainties, some researchers are investigating geoengineering ideas to slow polar ice loss. They include proposals for underwater buoyant curtains to deflect warm ocean currents off glacier fronts, to marine cloud brightening to reflect solar radiation. Though such concepts remain controversial raising logistical, ecological, and ethical concerns they highlight the imperative to develop adaptation strategies in addition to ambitious emissions cuts.
For the present, the 2014 Greenland flood is a scientific surprise and a warning sign. It reveals an unsuspected vulnerability in the plumbing system of the ice sheet, upends ingrained beliefs in basal hydrology, and introduces a volatile new factor into the arithmetic of sea level rise in a warming world.
