An Antarctic lake holding twice the volume of water as San Diego Bay in California has vanished. An international team of scientists used satellite imagery to show that on the Amery Ice Shelf in East Antarctica, a lake containing an estimated 600 to 750 million cubic meters (21 to 26 billion cu ft) of water drained through the ice and into the ocean during the 2019 Antarctic winter.
Unless it involves dams breaking, one doesn't expect something like a full-size lake to simply disappear. However, the Antarctic ice cap isn't a normal place by everyday standards. Though the popular image of the region is one of unending snow and ice, lakes filled with meltwater form on the surface during the Antarctic summer.
According to the team, the lake in question was formed by decades of meltwater accumulating under a layer of ice that developed on the lake's surface in the winter darkness. It then underwent a process called hydrofracturing. That is, the weight of the growing body of water pressed down on the ice, causing it to fracture and allowing the water to quickly drain away into the ocean below. The surface ice layer then collapsed into the empty crater, known as an ice "doline", or sinkhole.
Such an event is rare, but not unheard of. However, this one is unusual not only because of the size of the lake but also because such water draining through ice as thick as 4,590 feet (1,400 m) is uncommon.
The event was observed by images from NASA's Landsat 8 and ICESat-2 satellites. The latter's green-light laser instrument transmits photon pulses and records the reflection point of each photon it receives back from Earth. This data allowed the team to calculate how far the ice layer collapsed and how the floating ice shelf rose by up to 118 ft (36 m) as the weight of the lake was removed.
In addition, the rising area created another lake, which drained directly into the crater at a rate of a million cubic meters (35.3 million cu ft) per day.
As well as being a curiosity, the vanishing lake also sheds light on the danger of widespread hydrofracturing resulting from a warming climate, which could cause ice shelves to collapse, releasing more meltwater to add to rising sea levels. The data gathered from the event could provide a better understanding of the frequency and evolution of deep lakes on the ice.
"It is exciting to see ICESat-2 show us details of processes that are occurring on the ice sheet at such fine spatial scale," says Helen Amanda Fricker, a glaciologist at Scripps Institution of Oceanography. "Since surface meltwater on ice shelves can cause their collapse which ultimately leads to sea-level rise when grounded ice is no longer held back, it’s important to understand the processes that weaken ice shelves."
The research was published in Geophysical Research Letters.
Source: Scripps Oceanography
