Huge ice falls at Argentina's Perito Moreno glacier stir awe and concern

The deep cracking sound bursting from within the ice signals the dramatic fall about to happen. Seconds later, a block of ice some 70 meters (230 ft) tall - the size of a 20-story building - collapses from the face of the Perito Moreno glacier into the aquamarine water below.

The sight has attracted visitors to Argentina's most famous glacier for years. Standing on platforms facing the ice, they wait for the next crack to split the cool Patagonian air.

But recently the size of the ice chunks breaking off - a process called "calving" - has been starting to alarm local guides and glaciologists, already anxious at a prolonged retreat by Perito Moreno, which had bucked the trend in recent decades by maintaining its mass even as warmer climates spurred faster glacial melting worldwide.

"Ice calving events of this size haven't been very common at the Perito Moreno glacier over the past 20 years," said Pablo Quinteros, an official tourist guide at Los Glaciares National Park in the southern province of Santa Cruz.

"It's only in the last four to six years that we've started to see icebergs this big," he told Reuters during a visit in April.

The face of the glacier, which flows down from Andean peaks to end in the waters of Lake Argentina, had for decades held more or less steady, some years advancing and others retreating. But in the last five years, there's been a firmer retreat.

"It had been in more or less the same position for the past 80 years. And that's unusual," said Argentine glaciologist Lucas Ruiz with state science body CONICET, whose research focus is the future of Patagonian glaciers in the face of climate change.

"However, since 2020, signs of retreat have begun to be seen in some parts of the Perito Moreno glacier's face."

He said that the glacier could rebound as it has done before, but that for the moment it was losing between one and two meters of water equivalent per year, which if not reversed could lead to a situation where the loss accelerates.

A state-backed 2024 report, co-authored by Ruiz and presented to Argentina's Congress, showed that while Perito Moreno's mass has been overall stable for half a century, the period since 2015 has seen the fastest and most prolonged loss of mass in 47 years, on average losing 0.85 meters per year.

Glaciers around the globe are disappearing faster than ever, with the last three-year period seeing the largest glacial mass loss on record, according to a UNESCO report in March.

'YOU CAN'T GRASP THE IMMENSITY OF IT'

Ruiz said instruments his research team used to monitor the glacier had shown an increase in air temperature in the area of around 0.06 degrees Celsius per decade and precipitation decreasing, meaning less accumulation of snow and ice.

"The thing with Perito Moreno is that it took a while, so to speak, to feel the effects of climate change," Ruiz said. Now, however, the accumulation of ice at the top of the glacier was being outpaced by melting and calving at the bottom.

"The changes we are seeing today clearly show that this balance of forces... has been disrupted, and today the glacier is losing both in thickness and area."

For now, the glacier remains an awe-inspiring attraction for travelers, who board boats to see the calving and the huge icebergs floating around the lake up close.

"It's insane. The most incredible thing I've ever seen," said Brazilian tourist Giovanna Machado on the deck of one of the boats, which have to be careful of sudden ice falls.

"Even in photos, you just can't grasp the immensity of it, and it's perfect. It's amazing. I think everyone should come here at least once in their lifetime."