Trekking ice in Los Glaciares National Park

Perito Moreno Glacier, viewed from nearby Bahia de las Sombras. Perito Moreno forms part of the Southern Patagonian Ice Field, the world's third-largest reserve of fresh water. It is one of only three stable glaciers in Patagonia.

The final approach to Perito Moreno involves a boat trip over the Brazo Rico branch of Lago Argentino, Argentina's largest freshwater lake. The icebergs, broken off from Perito Moreno's constantly collapsing edge, will last just a few weeks before melting away.

Taking a minute to admire Perito Moreno from the beach. At a maximum depth of over 1,600 feet, the waters surrounding the glacier are deeper than any of the Great Lakes.

It's a quick hike along the shore to get to the glacier's base. There, hikers don crampons before beginning the climb to the top.

Following the path stamped out by previous groups' bootprints to avoid crevasses.

Guides instruct first-time crampon users to go "up like a duck, down like a monkey" - toes turned out on ascent, feet straight and knees bent on descent.

The top of the glacier is a maze of tooth-like spurs and cracks, formed by erosion and the glacier's constant movement. Without sunglasses, the sun's reflection off of the compacted ice is almost blinding.

Dotted with ponds and flooded crevasses, eroded by running water from the glacier's spring melt.

Though they may appear shallow, the crevasses can be hundreds of feet in depth. The wells often lead to cave-like systems of horizontal chambers and passages, formed where the melt water reached a layer of ice too hard to penetrate.

Guides keep harnesses, ropes, and other rescue equipment cached in barrels at various points around the trail.

Hikers celebrate a successful trek with a whiskey toast. Appropriately, it's served on ice.