Buenos Aires  - An Argentinian glacier, Perito Moreno, one of the world's few glaciers that have defied global warming and are actually growing, had a rare, massive mid-winter calf on Wednesday.

Water apparently had carved a tunnel under the front edge of the glacier, causing the huge ice mass to collapse in a thundering splash.

Since such spectacular "calving" - the term refers to the breaking off of massive pieces of a glacier - was unexpected during the South American winter, there were few tourists or locals nearby to observe.

For decades, the Perito Moreno has been pushing itself into the Lago Argentino lake, forced forward by the extreme weight of new ice and snow at the top of the glacier.

The process causes water to accumulate on top of the glacier, and has produced a lake water level that has varied as much as 30 metres. Every three to six years, the glacier tongue sticking into the lake breaks off, usually in the summer.

Over the past days, pieces of the 60-metre-high ice barrier had been breaking off and falling into the water, but the main barrier had held fast.

The last times the spectacle occurred were 2004 and 2006, when a huge calf fell with a long, ear-splitting crack, sending a huge tidal wave across the lake.

The glacier is 2,500 kilometres southwest of the capital Buenos Aires, in a thinly settled region. (dpa)