One of world's largest glacier floods triggered in Greenland

Imagine an enormous bathtub atop a mountain filled with water equivalent to three times Denmark’s annual water consumption, and then suddenly bursting. This is essentially what happened when the massive Catalina Lake in East Greenland released 3.4 cubic kilometers of meltwater – 3,000 billion liters – into the Scoresby Sound fjord.

The enormous volume places this event among the top three largest of its kind ever documented. The meltwater outburst flood occurred between September 23 and October 11, during which the lake’s water level plummeted 154 meters. The dramatic phenomenon was observed for the first time in real time using satellite imagery by scientists from the University of Copenhagen’s Niels Bohr Institute.

"We have previously found traces of similar outburst floods, but due to polar night and clouds obstructing the potential for satellite observations, this is the first time that researchers have been able to monitor an event and measure the water volumes in real time," explains Niels Bohr Institute climate researcher Aslak Grinsted.

Animation of the 324-meter Eiffel Tower standing in Catalina Lake, while the water level fell 154 meters. Animation: Aslak Grinsted.

Threatens millions of people

The outburst flood in East Greenland occurred because meltwater from Catalina Lake had been accumulating over the past twenty years. The lake is situated in a valley blocked by the massive Edward Bailey Glacier. As the lake filled, the water began to lift the glacier, carving a 25-kilometer-long tunnel beneath the ice, through which the water eventually burst into the world’s largest fjord, Scoresby Sound.

This phenomenon, where a glacial lake gradually fills and then releases its water in a sudden flood, is known as a Glacial Lake Outburst Flood (GLOF). Such events have become increasingly frequent over the last three decades due to rising global temperatures and climate change.

“The danger from glacier-dammed lakes is increasing due to global warming. It’s vital to improve our understanding of this phenomenon to issue timely warnings should there be an imminent risk,” says Grinsted.

Before and after photo-swipe of Catalina Lake.

While glacial lake outburst floods can be catastrophic in populated areas like the Himalayas, where they often destroy villages, this particular outburst caused no harm due to Greenland’s sparse population. However, a 2023 study concluded that 15 million people worldwide live under the threat of deadly glacial floods.

“I expect that we will witness outbursts from even larger ice-dammed lakes as Greenland’s ice sheet retreats in coming centuries. At the end of the last Ice Age, Lake Missoula had an outburst that was 2,500 times larger than the recent Catalina event. To understand these massive forces, we must study the largest outbursts when they occur,” says Aslak Grinsted.