A close encounter with glacier calving in Argentine Patagonia is a thrilling event, finds Paul Rush.
I'm deep in thought as I descend a series of steps through a serenely silent beech forest, wondering how one of Patagonia's greatest wilderness attractions can be so easy to reach.
Suddenly, a thunderous roar fills the air, resounding through the forest. I race down to the middle viewing platform just in time to see a billowing cloud of ice crystals glistening in the midday sun. Slowly, the cloud vapourises and reveals a swirling jumble of icebergs floating in a slurry of white water.
Towering above the icebergs is a 20 storey-high wall of solid ice, just a few hundred metres opposite where I'm standing. The fragmented ice wall is riddled with vertical cracks and deep fractures that expose the brilliant blue of old, heavily compressed ice.
Behind the five kilometre-wide wall I can see the rest of the glacier sweeping down from a high basin of snow-capped ridges and peaks enveloped in wispy clouds where ice and sky merge.
Hundreds of years of accumulated snowfall have been compacted into this majestic river of ice grinding its way down the valley. It's a truly mind-boggling sight. I find myself rooted to the spot in anticipation of another dramatic calving event.
I am viewing the terminal face of Perito Moreno Glacier, one of the most accessible and spectacular glaciers in the world.
It is named after one of Argentina's favourite sons, explorer and pioneer settler, Francisco Perito Moreno, who worked zealously to protect the Patagonian natural environment. The glacier spills out into a western arm of Argentino Lake, an hour's drive west of the tourist town of El Calafate.
Visitors are almost guaranteed to see a sizeable chunk of ice collapse under its own weight because the face is so massive. Just 10 minutes later, I hear a muffled groan, followed by a sharp crack as another column succumbs to gravity and slides down the face, exploding into the lake.
A shower of ice particles rises and disintegrates, leaving a new iceberg floating serenely down the narrow channel - the Canal de los Tempanos - into the main body of the lake.
I feel an irresistible desire to get closer to the great glacier. The walkway and steps run for 2km along the edge of the Magellan Peninsula, which faces the glacier.
People of many nationalities in mixed groups of all ages are hurrying down, calling out instructions and making earnest pleas for children to keep moving so they don't miss the main event - a major collapse of the face with its attendant thunder clap and tsunami.
Sadly, although I wait with mounting anticipation for a further 30 minutes, the colossal collapse does not happen this afternoon. Maybe it will come later. Maybe not at all today. The degradation of this unsung natural wonder of the world is not something to be hurried.
Later, our group boards a boat, which approaches within 300m of the glacier wall. We get a close up view of the deep fissures and openings where ice crystals glow in vivid blue colours. A wave of excitement sweeps through the boat as a one-tonne ice block dislodges and crashes down with a short peel of thunder.
A curious phenomenon occurs every few years when Perito Moreno Glacier advances and locks on to the peninsula, damming one arm of the lake.
The glacier is one of only two in South America that is refusing to subscribe to the popular concept of global warming and gracefully retreat. This is because the catchment area is a relatively low basin in the Andean Cordillera, which enables it to accumulate a huge amount of snow.
When the ice dam is in place, the trapped waters rise many metres, creating sufficient pressure to lift the front of the glacier off the bedrock. A few centimetres of space is enough to cause a current that undermines the ice sheet and forms a natural tunnel.
Eventually, there's a collapse and a barrage of ice explodes into the canal. People wait for many hours to see this dramatic spectacle.
Whisked by bus back to our hostel in the town of El Calafate, we relax over a beer and reminisce. Hostal de Glaciar is near the centre of town so we wander down Avenue del Libertador and find the best homemade pasta in La Cocina, one of several first-class restaurants in El Calafate.
Having seen glistening ice fields at a distance at Perito Moreno it's only natural to want to walk on a big glacier and touch it, taste it and feel its cold embrace. Next morning, we travel up to El Chalten and board a ferry to make a 30-minute crossing of Lake Viedma to the face of the Viedma Glacier.
This glacier has receded over recent years, which allows visitors to land on sculptured rock and climb to the deeply scarred surface. With crampons tightly fitted to our boots we join a large group, wending our way through a maze of obstacles, closely herded and corralled by four professional guides.
Crampons take a little getting used to so I concentrate on stamping down hard on the ice and keeping my feet apart. Negotiating narrow ledges, bordered by crevasses that plummet into the heart of the glacier, tends to sharpen the mind.
Our guides earnestly hack away at the ice, cutting steps up the most daunting slopes and we soon find ourselves in a surreal fantasy world of frozen sculptures, towers, caves and seracs.
A sharp wind is whistling over the frozen fractured landscape at 90km/h. We should be shivering in the bitterly-cold conditions but it's too exciting to worry about wind chill. Our guides invite us to literally embrace the glacier by leaning over the edge of a crevasse to photograph its electric-blue, tapering sides, while they hold us firmly. I click the shutter quickly and retreat. The abyss is too mesmerising for comfort.
The winding track over sharp ridges and down trickling streams appears to be chosen at random, but somehow we end up in an idyllic sheltered basin beside a translucent meltwater pool.
The chief guide announces that he has a surprise for us - a glass of Bailey's Irish Cream liqueur, chilled by small fragments of ice from a nearby sink hole. We gratefully propose a series of toasts - to the glacier, Argentina and our tour company, Viva Expeditions. We then head in single file back down to the rock platforms for lunch before the ferry arrives.
The monumental scale of the ice fields at Perito Moreno and Viedma is mind-boggling; they are almost three times the size of New Zealand's Tasman Glacier.
Whatever your taste in natural scenery and smooth liqueurs, the combination of blue ice and Irish cream at this end of the earth is breathtakingly exotic.
Getting there: LAN Airlines flies from Auckland to Santiago. Domestic flights connect Punta Arenas. Overland transport then takes you to El Calafate. Alternatively, Aerolineas Argentinas flies from Auckland to Buenos Aires, where domestic flights connect with El Calafate.
When to go: The best times are October/November and March/April. Temperatures are slightly cooler than the summer peak and there are fewer crowds.
The glaciers: Perito Moreno Glacier is located in Los Glaciars National Park in southern Argentina, 80km from the tourist town of El Calafate.
El Calafate: A lively tourist town on the shores of Lake Argentina, with lots of souvenir shops, cafes and restaurants serving excellent steak, lamb stew, pizzas and empanadas. There is over the counter banking, foreign currency exchange and ATM services.
Paul Rush travelled to Patagonia with assistance from Adventure World and Viva Expeditions.