Tourists watch as a massive chunk of ice breaks off Argentinian glacier [Video]

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 tall — the size of a 20-storey 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 …