The Tasman Glacier tastes of nothing. I crunch through a morsel of the 25km long ice river and feel the frozen fragment melting across my tongue. Granules of silt wash across my teeth.

A visual feast, the glacier's intense arctic blue colour and frosting of thick grey dust made me think I'd taste something - even dirt. But the glass-clear ice chunk I consume is so pure it's untainted even by flavour.

"This ice is around 500 years old," explains Vernon, our guide and owner of Discovery Tours Ltd. He has just hauled an armload of mini icebergs from the frigid waters of the grey Tasman Glacier Terminal Lake here in Aoraki Mount Cook National Park. Across the silt-tinged water crowds of angular grey icebergs, some the size of Mt Cook's famed Hermitage Hotel, float serenely. Vernon clambers back towards us across a jumble of smooth boulders - once a part of the glacier themselves - and hands round his haul; his fingers red with cold.

"Take a bite," he enthuses as our group marvels at Mother Nature's intricate ice sculpting skills.

Here in the Tasman Valley, everything is an acknowledgement to the mighty Tasman Glacier. All around, the glistening snowy peaks that career towards the electric blue sky remind us of whence this glacier came. We perch upon a moraine wall, high and solid and formed entirely by the glacier as it bulldozed its way through this valley hundreds of years ago. And off to our right, the wandering braided rivers lead our eyes across the barren riverbeds, onwards to the startlingly blue glacial-formed Lake Pukaki.

It is this, the epic tale of the Tasman Glacier's existence, which creates the essence of Discovery Tours' Ultimate Glacier Discovery - a 3.5 hour 4WD and walking tour in the glacier's vicinity.

After meeting Vernon in Mt Cook Village we trundle along a rock-strewn gravel road, roving where just smatterings of tourists as well as the first conquerors of Mt Cook, and the Tasman Glacier itself have travelled before us.

Through signposted 'avalanche zones' we journey into an increasingly moon-like landscape. Mammoth rocks dotted with lichen and tinged red with iron ore lie in a jumbled mass for kilometres on end. We are dwarfed and isolated by the magnitude of the snowy peaks, bush clad hills and rocky moraine walls that rear up all around us. There is not another person in sight.

"This landscape is continuously changing," comments Vernon as he takes us on a verbal time trip to Gondwanaland, 83 million years ago. In words, he etches out the development of this peculiar scenery and the Tasman Glacier. In straight-forward terms he explains the process of 'freeze/thaw' and the effect of the local tectonics. It soon becomes apparent that Vernon's knowledge of and infectious passion for this topic is almost as deep and complex as the glacier itself.

Vernon and his wife Elayne set up Discovery Tours in 2001. For nine years prior they lived in Mt Cook village working in a range of jobs including park ranger roles for the Department of Conservation. Elayne's qualification in ecology and the pair's passion for the outdoors were the driving forces behind the establishment of the company, which offers guided wilderness hikes, Lord of the Rings movie set tours and heli-biking tours as well as their informative glacier trips.

Their focus is on providing small, quality tours that explore the unique features of the Mt Cook and Mackenzie regions. But at the same time, the pair are providing for the increasing market of travellers who want to learn about the environment and its changing face.

"Glaciers are thermometers, basically," explains Vernon as we amble up a moraine wall to peer down at the glacier. "They react to whatever our climate is doing - whether that reaction takes 10 years or 100 years.

"In the last 20 years, this glacier's lost 4km in length," continues Vernon.

"14,000 years ago, the glacier created Lake Pukaki. Now, the same system that created that lake is repeating itself and creating a new lake - the 'brand new Tasman Lake', as it's known."

Although our musings about climate change reach no conclusion, Vernon, Elayne and their staff are all taking strident efforts to minimalise the company's impact on the climate and the delicate environment in which their business operates.

This includes everything from walking single file on alpine tracks so as not to disturb the new moss growing on the near-uninhabitable terrain, to meeting Green Globe standards and actively seeking out conservation opportunities to be a part of.

"Glaciers can tell us what's been happening in our environment for thousands of years - wind, rain, summer dust levels, seasonal melt...

"But, history can't tell us yet what impact we are actually having on our climate," reasons Vernon.

"So until we know, I figure it's best to be as cautious as we can."

Amelia experienced the Ultimate Glacier Discovery courtesy of Discovery Tours (www.discoverytours.co.nz) and http://www.fourcorners.co.nz/.