Los Glaciares National Park

Listen first. Somewhere ahead of you, a deep crack rolls across the water, like distant thunder. Then comes a heavy splash, and a slow wave spreads across the grey-green lake. The wind here smells of cold stone and wet ice. Under your feet, the ground is hard and dry. A few metres away, a wall of blue-white ice rises from the water. Welcome to Los Glaciares National Park, in the far south of Argentine Patagonia.

The park sits in Santa Cruz Province, along the eastern edge of the southern Andes. Argentina created it in 1937, partly to protect this remote frontier region. In 1981, UNESCO added it to the World Heritage list. That status recognises one main thing: ice. This is a land shaped by glaciers. The glaciers carved its valleys, filled its lakes, and still move through it today, slowly, a few metres at a time.

Most of that ice comes from one source. To the west lies the Southern Patagonian Ice Field. It is one of the largest bodies of ice on Earth outside Antarctica and Greenland. Picture a frozen plateau high in the mountains, fed by snow from storms off the Pacific Ocean. From that plateau, dozens of glaciers flow downhill. Many of them end here, in the long, cold lakes of the park.

The largest of those lakes is Lago Argentino. It is the biggest lake that lies entirely inside Argentina. Its water has a strange, milky colour — turquoise in sunlight, pewter under cloud. That colour comes from glacial flour. When glaciers grind over bedrock, they crush the stone into a very fine powder. The powder hangs in the water and scatters the light. So the colour of the lake is, in a real sense, the colour of mountains turned to dust.

The glacier in front of you, if you are on the walkways, is the Perito Moreno. It takes its name from Francisco Pascasio Moreno, a nineteenth-century Argentine explorer and scientist. The word perito means expert. Moreno earned the title for his work on the border between Argentina and Chile, a long and difficult dispute. He also gave land that later helped start Argentina's national park system. He never knew this glacier would become so famous.

Here is the first surprise. Around the world, most glaciers are shrinking. The Perito Moreno has stayed remarkably stable for decades. It pushes forward, breaks off at the front, and pushes forward again. Scientists still study exactly why. Its balance between new snow and melting ice is unusually even. Recent years have shown signs of change, however, so researchers watch it closely. For now, you are looking at a glacier that is still very much alive.

Watch the front of the ice for a while. It is several kilometres wide, and it stands as tall as an apartment block. Every so often, a piece breaks away. This is called calving. Sometimes it is a small shower of ice. Sometimes a section the size of a house falls into the lake. Often the sound reaches you a moment after the movement. Many visitors stand here for an hour, simply waiting for the next fall.

Now the second surprise. Every few years, the glacier advances until it touches the land on this side, the Magallanes Peninsula. When that happens, it blocks one arm of the lake, called Brazo Rico. Water builds up behind the ice dam. The level on one side rises far above the other. Then the water begins to cut a tunnel through the ice. An arch forms. Eventually, the arch collapses. Crowds gather for days in the hope of seeing that moment.

Why is the ice so blue? Old glacier ice is very dense. Over many years, the weight of new snow squeezes out the air bubbles. Dense ice absorbs the red part of sunlight and lets the blue pass through. So the deepest cracks look the brightest blue. On cloudy days, the colour often looks stronger, not weaker. Look at the fresh scars where ice has just fallen. They are usually the bluest places on the whole face.

The Perito Moreno is only one part of the park. Boats travel across Lago Argentino to other glaciers, such as the Upsala and the Spegazzini. Far to the north, near the small town of El Chaltén, the landscape changes again. Granite towers rise above the forest. The tallest is Mount Fitz Roy. Its peak is often wrapped in cloud. The Tehuelche people, who lived on these plains, called it Chaltén, a name usually translated as smoking mountain.

The European name honours Robert FitzRoy, captain of the ship that carried Charles Darwin around South America. Near Fitz Roy stands Cerro Torre, a thin needle of rock coated in ice. Both mountains are famous among climbers for their difficulty. The weather changes fast. Winds come over the ice field with great force. Even on the hiking trails below, many walkers learn to lean into the wind and wait for it to pass.

Life here has adapted to that wind. Low forests of southern beech grow in the sheltered valleys. On the open steppe, you may see guanacos, wild relatives of the llama. Andean condors ride the air currents above the cliffs, often without moving their wings. The park also protects the huemul, a rare deer of the southern Andes. In the gateway town of El Calafate, locals share a saying. Eat the small, dark calafate berry, and you will return to Patagonia.

Before you leave, stay still for one more minute. Look at the line where the ice meets the water. Notice how the lake moves after each fall. Listen for the small creaks and cracks inside the glacier itself. That ice formed from snow that fell long before anyone here today was born. Now it is slowly reaching the lake. As you walk back along the path, the thunder will follow you for a while... and then the wind will take its place.