LOS GLACIARES NATIONAL PARK, Argentina - The face of Perito Moreno Glacier resembles a colossal fortress, its jagged spires of ice towering about 200 feet above a lake dotted with icebergs.
It is Patagonia's most-photographed glacier, yet as we stand before it I realize that images can only begin to capture its grandeur: the panorama of ice that fills our field of vision, the thunderous cracking sounds that echo from within the glacier as it slowly shifts and advances.
My wife and I have come with our two children to southern Argentina to see and experience its glaciers and mountain landscapes. We are among hundreds of visitors who stand watching from a network of raised walkways on a slope facing the glacier.
Suddenly, the cracking sound grows louder and a cascade of ice tumbles down the sheer snout of the glacier. A column the size of a 20-story building slowly begins to tip away and collapses in a giant splash about 500 yards from where we are standing.
Then other pieces break off and fall in a series lasting more than a minute, leaving a dozen new icebergs floating away.
"Woo-hoo!" my 6-year-old son shouts. "It's just like sand."
The calving glacier reminds him of sand cascading down a steep dune he had climbed a few days before on the Argentine coast.
Perito Moreno is among the most accessible large glaciers and remains relatively intact even as glaciers all over Patagonia have been retreating in the past few decades.
During that trip earlier this year, we all stood gazing at the glacier, leaning on the wooden railing and silently waiting for the next ice fall.
Along the section of glacier that had just calved, the newly revealed wall glowed deep blue, indicating the ice had been tightly compressed during its long journey down the mountain slope.
We had heard and read that waiting for a big ice collapse could require patience, so we felt fortunate to have witnessed the spectacle within minutes of arriving. We lingered on the walkways, enjoying the cool air and seeing the glacier from different angles.
The next day, we took a boat tour of the glaciers that border Lake Argentino.
There are dozens of glaciers in the area fed by the Southern Patagonian Ice Field, which blankets a wide swath of the Andes between Chile and Argentina. Huge quantities of meltwater flow into Lake Argentino, and then down the Santa Cruz River to the Atlantic.
We started at the port of Punta Bandera and set out aboard a catamaran carrying nearly 200 people. The wind was very cold, so we started out inside the cabin, then put on wool hats and scarves and went out on deck for a better view.
The icebergs were a gemlike radiant blue, contrasting with the charcoal-colored mountainsides behind them.
As we headed toward Upsala Glacier we encountered more and larger icebergs, and the boat stopped once we faced a barrier of floating ice. Some passengers posed for photos at the boat's railing with craggy masses of ice floating behind them.
Guides announced over the loudspeaker in Spanish, English and French that Upsala Glacier could be seen in the distance. They didn't mention that it has shrunk dramatically over the past century, nor did they discuss how the glaciers have fared overall in the face of global warming.
I later learned that according to a recent study by British and Swedish scientists who analyzed about 350 Patagonian glaciers, all but two of the glaciers have receded significantly since the late 1800s, and have been shrinking at a faster rate during the past three decades.
Still, Patagonia's mountain glaciers are so colossal, and fed by so much snowfall each winter, that scientists believe they are in no immediate danger of vanishing in the coming centuries.
"Those glaciers aren't going to disappear, that's for sure. They might get smaller, but they're not going to disappear," said Neil Glasser, a British glaciologist and one of the authors of the study, which was published in April in the journal Nature Geoscience.
Motoring on in the lake, we soon reached smaller Seco Glacier, which is aptly named "dry" and has been in retreat.
We moved to the bow as the boat neared the Spegazzini Glacier, a steep, dramatic icescape that curves down a mountainside and ends in the lake.
Our boat slowed down and stopped, and two crewmen tossed a rope over the bow and lassoed a briefcase-sized chunk of ice. They broke off a small chunk with an ice pick and passed it around.
After two days visiting the southern part of Los Glaciares National Park near El Calafate, we set out for the town of El Chalten and scenic Mount Fitz Roy.
After driving for about 20 minutes, the dramatic view of Mount Fitz Roy appeared on the horizon under a clear sky, its sheer granite faces flanked by smaller jagged peaks. Measuring 11,072 feet, the mountain is a world-class destination for trekking and climbing.
The next day, the weather was calmer near the base of Fitz Roy, and we hiked along streams and through forests where grass glowed in patches of sunlight.
On the last afternoon of our stay, the weather was cloudy and drizzly, and we walked farther along the same trail toward Fitz Roy. After more than an hour of hiking, we stopped at a clearing.
Even from a distance across that mountain valley - and now from a distance of several months - the glaciers of Patagonia have left a powerful impression on us.
If You Go
Los Glaciares National Park www.losglaciares.com/en/parque/index.html
• Seasons: Southern Hemisphere summer in Argentina, which is also the peak tourism season, runs from December through February.
• Getting there: Aerolineas Argentinas offers flights from Buenos Aires to various locations in Patagonia, including El Calafate. Rental cars may be reserved through various agencies and picked up at El Calafate airport. From El Calafate, it is a 48-mile drive to Perito Moreno Glacier. Taking another road out of El Calafate, it is a beautiful 136-mile drive across open country to El Chalten and Mount Fitz Roy.
• Glacier tours: Inter Habit Travel Network offers boats tours to glaciers on Lake Argentina. The daylong "Complete Glaciers Tour" costs $122 per person and includes pickup by bus from hotels in El Calafate, http://bit.ly/runcB8