Why does Mount Everest make a terrifying noise at night? : Researchers led by glaciologist Yevgeny Podolsky

Once the sun sets in the Himalayas and temperatures drop, there is an eerie noise in the depths of the glaciers around Mount Everest.

The researchers, led by glaciologist Yevgeny Podolsky, found that the sounds of collapsing and fragmentation in high-altitude glaciers are caused by the sharp drop in temperatures after dark that causes the ice to crack.

The team determined the cause of the sounds in 2018 after spending more than a week trekking across the Nepalese Himalayas to test the seismic activity of the Trakarding-Trambau Glacier system there.

Dr. Podolski and his team spent three weeks shivering on the glacier, not sure what caused the nighttime sounds, but confirmed they were related to the extreme cold when they returned to sea level and checked the seismograph data.

Their research was the first to show such a large amount of seismic activity due to thermal rifting within the ice, based on a wide range of investigations into the behavior of glaciers as the effects of climate change continuously warm the planet.

Dave Haan, the leader of the expedition who completed 15 pods at the summit of Everest, spoke of hearing strange noises at night when he and his fellow climbers rested, including "falling ice and rocks in different places around the valley".

"It's hard to sleep," he added.

When Dr. Podolski and his team went to the Nepalese Himalayas to test the seismic activity of the Trakarding-Trambau glaciers, they landed about three miles above sea level, within sight of Mount Everest, which is about 29,000 feet high.

"It was a great experience because it's a great area to work in. Basically I'm having lunch looking at Everest," said Dr Podolsky, who works at the Arctic Research Center at Hokkaido University in Japan.

During the day, Dr. Podolski and his team can work comfortably in shirts.

But as night falls, the temperature may drop to around -15 degrees Celsius, or 5 degrees Fahrenheit.

After dark, he and his team heard "this noisy explosion," adding, "We have noticed our glacier cracking or bursting with cracks at night."

The team placed sensors on the ice to measure vibrations deep in the glacier, the same technique used to measure the magnitude of earthquakes.

The researchers collected seismic data on the vibrations and compared them with temperature and wind data, helping to establish a strong relationship between temperature fluctuations and nocturnal noise.

"Local ice has been shown to be very sensitive to this high rate of change," Dr. Podolski and colleagues write in the journal Geophysical Research Letters.

The research could help more teams of glaciologists and climate experts better understand the behavior of glaciers in remote regions such as deep in the Himalayas, which are home to one of the largest stores of ice on Earth.

The Himalayan glaciers are melting at a devastating rate, putting millions of people and the economies of South Asian nations at risk. The region's massive ice sheets have been shrinking 10 times faster in the past four decades than they have been in the previous seven centuries.

A 2021 study published in the journal Scientific Reports found that Himalayan glaciers have lost about 40% of their area in the past hundreds of years, or about 390 to 586 cubic kilometers of ice - enough to raise global sea levels from 0.92 to 1.38 mm.