Researchers may have finally solved a mystery surrounding the Rink Glacier on Greenland, and in the process have discovered a new way in which ice flows through and is subsequently lost in glaciers.

The Rink Glacier is known to typically lose around 10 billion tonnes (11 billion tons) of ice every year, as the glacier steadily flows into the ocean. But in 2012 the river of ice lost an extra 6 billion tonnes (6.7 billion tons) that could not be explained by any conventional ideas of how glaciers behaved. Nothing appeared to have changed and, using satellites, researchers could see that the thickness had not altered, either. This made the origin of the extra ice loss a complete mystery.  

But a GPS sensor situated on the bedrock near to Rink Glacier may have the answer. In 2012, it recorded a depression in the Earth’s crust over a period of four months. The researchers think that this disturbance represents a wave of ice flowing down the interior of the glacier, traveling at a rate of around 4 kilometers (2.5 miles) a month for the first three months, before speeding up to around 12 kilometers (7.5 miles) in the final month. For comparison, Rink Glacier usually flows at a rate of just a few kilometers a year.

Interestingly, they saw the same pattern of disturbance from the sensor in 2010, although from the surface of the glacier nothing would be visible. “You could literally be standing there and you would not see any indication of the wave,” explained NASA’s Eric Larour, who co-authored the paper published in Geophysical Research Letters. “You would not see cracks or other unique surface features.”

While the researchers aren’t entirely sure what caused the wave – they’re not even sure what it was made from, but suspect a mix of ice and water – they do have a theory. The pulse was observed in the wake of the 2012 melt, which saw up to 95 percent of the snow and ice on top of the glacier turn to liquid, creating pools and lakes on the surface.

They think that this water may have made its way into the cracks and crevices of the glacier, working its way to the bottom, and flowing outward. This may have lubricated the bottom and the sides of the glacier, allowing the wave to slide through it, unseen to the casual observer. It is this extra mass that depressed the Earth’s crust more than is already occurring due to the main body of the glacier, and allowed it to be picked up by the GPS sensor.

Even though this is newly described behavior for a glacier, the researchers suspect that we will be experiencing it more often as the climate continues to warm.