Cracks in Greenland ice sheet are producing massive waterfalls
This is raising scientists’ concerns for sea level rise and their projections
A cerulean blue lake consisting of glacial melt water on the surface of the Greenland ice sheet, located about 18 miles from where the Store Glacier meets the sea in west Greenland, briefly became one of the world’s tallest waterfalls during the course of five hours on July of 2018.
The waterfall, like many others on the ice sheet’s surface, was triggered by cracks in the ice sheet. In the case of this one melt water lake scientists closely observed in July 2018, the water cascaded down more than 3,200 feet to the underbelly of the glacier, where the ice meets bedrock. There, the water can help lubricate the base of the ice sheet, helping the ice move faster toward the sea.
The observations of scientists, armed with aerial drones and other high-tech equipment, of the partial lake drainage that resulted could help researchers better understand how surface melting of the ice sheet could affect its melt rate, and improve global sea level rise projections.
Scientists are keenly interested in how melt water on the surface of the Greenland ice sheet — the largest contributor to global sea level rise — acts to speed up the movement of ice toward the sea by lubricating the underside of the ice surface. The new study, published Monday in Proceedings of the National Academy of Sciences, suggests that scientists are underestimating the number of melt ponds that partially, and rapidly, drain into the ice sheet each year. This means that tweaks may be needed to the computer models used to predict sea level rise from Greenland.
This is the first study to show that partial lake drainage can occur through cracks in the ice, rather than overtopping or other mechanisms, which was previously the assumption. This means even more water is reaching the base of the ice sheet than previously thought.
For example, rapidly draining lakes in fast-moving areas of the ice sheet could provide a timelimited burst of speed for glaciers to dump more ice into the sea. The new study showed a sudden but brief increase in ice flow as the lake drained, from seven feet per day to 16 feet per day, though it slowed down again thereafter.
Using computer models, the study found that the lake in question is what the researchers term a “trigger lake,” which can result in a chain reaction of sorts, causing more lakes as far away as 62 miles to subsequently drain.
The researchers observed a sudden, partial draining of the lake they termed “Lake 028” during a span of just five hours on July 7, 2018.
At its peak, the lake was draining the equivalent of one Olympic-size swimming pool every three seconds, according to study lead author Thomas Chudley of the University of Cambridge.
To put it differently, the melt water was enough to fill one U.S. Capitol rotunda every two minutes and 19 seconds.
The researchers measured the lake’s changes using about 900 photos collected by autonomously flying drones outfitted with GPS equipment. The images were stitched together to form 3-D surface elevation models.
Study co-author Poul Christoffersen said the study breaks new ground by detailing the mechanisms by which surface water is transported to the bed of the ice sheet in a rapidly flowing part of a glacier.