It's a bit like approaching a sleeping giant. You're not sure when it will wake up but, despite the anticipation and danger, you want to get closer. Perhaps even close enough to touch it.
The Tasman Glacier is a living beast that shifts, twists and growls like a teenager tormented by growing pains. It's always been that way, certainly since the river of ice was created two million years ago.
But New Zealand's largest glacier (26km long, as much as 3km wide and 600m thick) is changing faster than at any other time in its history. Over 18 months it has shed 800m in length - on top of several kilometres lost over the past 30 years. And it doesn't look like slowing down any time soon.
In this era of climate change uncertainty, there's a perception that higher temperatures are the chief cause of the glacier's retreat. Although that is a factor, it is the the terminal lake - which formed in 1991 - that has precipitated such huge change.
So accelerated is the melting process, that large chunks of ice have broken off and sit atop the frozen lake.
No amount of snow at the head of the glacier - there is as much as 70m a year - can compensate for the melting effect of the lake and there are concerns that the glacier could retreat beyond the Ball Glacier, another 10km up the valley.
It's disturbing and fascinating seeing icebergs close up.
Husband and wife Elayne and Vernon Reid, of Discovery Tours, operate tours up the glacier and even they are surprised by the daily changes.
Although menacing winter weather prevented us skiing the magnificent Tasman Glacier, the world's longest ski run, it didn't stop us hiking up to Tasman lake. There we discovered a moonscape - grey rock strewn everywhere and a lake with a distinctive blue glow. Sediment in the water creates a weird, sci-fi luminosity. The icebergs are of all shapes and sizes - jagged ones, round ones, dirty ones, spotty ones - and made of ice that's taken about 500 years to travel from the neve at the top of the glacier.
Come summer, clusters of kayakers and tour boats explore these wonderful creations as they drift in the prevailing winds. In winter, as long as the glacier lake ice is thick enough, you can walk or ski around them. Up close you get a great perspective of the glacier's foreboding size even if it is shrinking.
The glacier flows down the eastern flank of Aoraki/Mt Cook, starting just five metres from the peak of our highest mountain - one that's been a popular climbing destination since the late 1800s.
Sir Edmund Hillary was a regular who developed his great love of climbing in the area and used it as a training ground before knocking off Mt Everest in 1953.
The mountains here rise up almost vertically from the Tasman and Hooker valleys, appearing razor-sharp. Aoraki/Mt Cook at 3755m, is the undoubted daddy of them all.
From his vantage point he overlooks the Tasman Glacier seemingly checking its progress.
The river of ice is a sleeping giant now but, like the giant in Jack And The Beanstalk, it might soon be cut down to size.
- Detours, HoS