Secrets of Greenland's Vanishing Lakes Revealed

In the past few years, some of the large lakes that sit atop the Greenland ice sheet mysteriously drained billions of gallons of water in just matter of hours. It was earlier discovered that giant hydro-fractures or water-driven cracks were to blame, Live Science notes. But exactly how these cracks were formed remains unknown, until recently.

Reuters reports that a team of U.S. researchers has already figured out the cause of the crack, as well as its effect on sea levels.

The new study, published June 3, 2015 in the journal "Nature", used GPS technology to discover the hydro-fractures or water-driven cracks formed underneath the lake basin. It was found out that the cracks were due to tension-related stress caused by the shift on the ice sheets. These movements are triggered by dripping water from the melting of the ice.

16 GPS stations were placed around the North Lake for the study. The GPS recorded two types of movements -- the uplift and slip -- which happen during and after annual drainages. The scientists found out that these movements create tension on the ice sheet where cracks are formed.

"We found that before we get the main expression of the lake drainage, there is a period of time (about six to 12 hours) where uplift and slip increase," lead author Laura Stevens explained, as quoted by Live Science. "That motion is enough to take the surface of the ice sheet and put portions of it in high tension that allows cracks to start forming." 

According to the study, the vertical shafts in the ice sheet, known as moulins or crevasses, funnel down the melt water especially during summer. This prompts a decrease in the surface area of the ice sheet, making the bedrock soft, and causing it to move horizontally. The cracks beneath the supraglacial lakes are what cause them to be emptied or drained rapidly in just hours or days.

On the other hand, the draining of the lakes proportionally accelerates the sea level as the large volume of water flows in to the ocean, while lubricating the flow of ice offshore. But, the study shows that only lakes at lower and warmer altitudes on the ice sheets, where there's a prevalence of moulins, are more vulnerable to this phenomenon.

"Our discovery will help us predict more accurately how supraglacial lakes will affect ice sheet flow and sea level rise as the region warms in the future," Stevens said.

With more than 600,000 squares miles of ice sheets covering Greenland, the study is a step forward towards the growing concern of rising sea levels.