Tasman Glacier is dying and I am floating in its cold, milky grey blood.

On a cheery yellow boat my fellow Glacier Explorers and I putter through shrouding mist and stinging wind across the Tasman Glacier terminal lake in Aoraki Mt Cook National Park. The greyness of the day, mirrored in the bleak water, is punctured by stunningly stark white icebergs - flotsam of New Zealand's largest glacier.

The presence of these house-sized icebergs, the frequency with which they are falling from the glacier's face, and the very fact that there is a lake on which to wend around these brilliant bergs are all indicative of the Tasman Glacier's demise.

Thirty years ago, this lake didn't exist. Thirty years ago the ice that crumbled from the solid face of the Tasman would hit the dry, rocky ground, melt and disappear into the sky to repeat the cycle of evaporation. But then, 30 years ago the words 'global warming', 'climate change' and 'irreversible damage' weren't uttered every day.

"These icebergs are about 500 years old," says our guide Jo as she steers the boat around the glittering islands of ice that crowd the lake. Up close the dripping icebergs comprise thousands of smooth, oddly shaped chunks of ice stacked together so intricately they resemble a huge 3-D glass jigsaw puzzle.

At Jo's insistence we reach out and touch Mother Nature's elaborate artwork, snapping off pieces of ice and eating them. My 26-year-old teeth crunch deftly through the 500-year-old ice. My tongue stings from the cold shards and the roof of my mouth sieves out miniscule granules of silt - those which make the terminal lake its uninviting wishy-washed colour. I'm eating rock particles and water and a part of the world that has been around longer than any material thing I can fathom. I suddenly feel very young and very, very insignificant.

I am just a passing guest in this age-old, ever changing landscape. If I return - even tomorrow - nothing about the lake will be the same. The icebergs I see now will be gone. Melted. The lake will be larger or deeper. The air will have worked its magic on the glacier's terminal face, breaking off new icebergs in unique sizes and shapes. The wind will have pushed them around the lake into new, transitory positions (as it has done today, blocking our way to the glacier's face where most Glacier Explorer trips go). Then the sun will bear down upon them, morphing and melting the icebergs and adding volume to this rapidly growing lake.

Of course, this process has happened before. In its two million year history the Tasman Glacier has advanced and retreated a number of times. One of the glacier's many travels back and forth saw it carve out an enormous bowl in the Earth, its formidable might akin to a very large, excruciatingly slow bulldozer. When the glacier eventually melted, this bowl filled with water and became what is now Lake Pukaki.

Jo pulls the boat in close to a small, curved hump of an iceberg. She leaps out, secures the vessel with a rope and a rock and invites us onto her icy island. The boat sways as I stand and teeter towards the front. Swinging my legs over the edge, my feet crunch down on the complex layers of ice crystals which are scattered with dark rocks. Given its size and apparent fragility I expect the iceberg to begin bobbing and listing as six of us climb aboard. But it remains still. We crunch about, picking up pieces of jagged ice and cold rocks that are emerging from their frozen haven for the first time in 500 years.

As we perch on the iceberg the wind spikes us with its southerly force. Murky clouds hunker down, eliminating all views and enveloping us in an eerily beautiful grey and white world. Suddenly ice is falling from the sky. Stinging particles of hail redden our faces and hands. It is an odd sensation, simultaneously standing on and being pelted with ice - such a transitory thing.

I wonder if this driving ice might settle at the top of the glacier, become compacted and begin a slow downhill crawl. Maybe in the next few hundred years it will melt away, or perhaps it will be the beginning of a reformation - a new glacier. Maybe in 1000 years one of these tiny particles of hail will finally reach the glacier's terminal face, break off and begin bobbing about in a newly formed terminal lake. And maybe someone just like me will arrive by boat and climb upon it and feel like nothing more than an infinitesimal speck, a transient and insignificant spectator to the mighty life cycle of the Tasman Glacier.

Amelia experienced Glacier Explorers courtesy of Mount Cook Mackenzie Tourism.

Amelia is Content Editor for the New Zealand travel and tourism website, www.fourcorners.co.nz.