When the glacier advances fast enough, this channel closes.
Part of a set of photographs taken at or near the Perito Moreno Glacier in Los Glaciares National Park in the south west of Santa Cruz province, Argentina.
The glacier feeds into Lake Argentino. Every few years the glacier blocks off part of the lake, acting as a dam. The resulting difference in water levels eventually causes a catastrophic collapse of the ice, in a spectacular rupture event.
The glacier is part of the en.wikipedia.org/wiki/Southern_Patagonian_Ice_Field - a suspension of fine particles created by the grinding of the bedrock by the massive glacier.
The image is a scan of a slide / transparency. As much as is possible with film, the colours are real, the exaggerated blue of the ice being an example of glacial blue ice.