Scientists from the University of Copenhagen, Denmark, have for the first time observed a rare natural phenomenon - glacial flooding in Greenland. More than 3 trillion litres of meltwater poured out of a lake in the eastern part of the island over several weeks. The study highlighted the "enormous and potentially dangerous forces" that meltwater can unleash. Catalina Lake in East Greenland holds three times the annual water consumption of the whole of Denmark. It dumped 3.4 cubic kilometres of meltwater into the Scoresby Sound fjord.

The event was one of the three largest on record. The release took place from 23 September to 11 October and lowered the lake level by 154 metres. The energy released was equivalent to the capacity of the world's largest nuclear power plant, which operated for 22 days. Previously, experts had found evidence of glacial flooding, but were unable to observe it because of the polar night and high cloud cover. In the case of Catalina Lake, it was possible for the first time to track the events in real time using satellite imagery and to measure the volume of water discharged.

The meltwater in Catalina Lake had been accumulating for 20 years. It lies in a valley covered by the massive Edward Bailey Glacier. As the lake filled, the water began to lift the glacier, forming a 25km-long tunnel under the glacier. Through this, the river rushed into the fjord. Such a catastrophe is known as a glacial lake outburst. Over the past 30 years, the frequency of these events has increased due to global warming. Scientists have warned that if such an event were to occur in a densely populated region such as the Himalayas, the consequences could be catastrophic. In total, 15 million people live in areas threatened by glacial flooding, according to the University of Copenhagen.

Earlier, it was revealed that warming has turned the Greenland glacier into the world's largest dam. Huge amounts of meltwater are falling from the surface to the base of the ice sheet. In the process, energy is converted into heat. Similar processes take place in hydroelectric power plants. Studies have shown that in the summer of 2014, up to 82 million cubic metres of meltwater flowed into the glacier bed every day.