On Thin Ice MOUNTAINEERING IN A WARMING WORLD

BY DR HEATHER PURDIE

New Zealand mountaineer and glaciologist Dr Heather Purdie has been researching and teaching students about snow, ice, glaciers, and climate change for more than 15 years. An Associate Professor at the University of Canterbury / Te Whare Wānanga o Waitaha, Heather draws upon both her climbing and her research to explore how mountains are changing as the planet warms in this edited extract of her story “Revisiting the Nun’s Veil”. The full story appears in the anthology Adventures in Climate Science: Scientists’ Tales From the Frontiers of Climate Change, 2023, Woodslane Press.

There is a distinct satisfaction in listening to the rhythmic sound of your ice axe and crampons biting into a frozen snow and ice surface. Jason and I could not see much that morning. We had begun in the dark, the colder predawn temperature reducing the risk of rockfall. As the sun rose, the thick fog was almost a whiteout, and it engulfed the Nuns Veil in cloud as we systematically worked our way up the glacier towards the summit.

We were moving un-roped as it is not a difficult climb—a Grade 1+ for those who mountaineer—and one I had done six years earlier in 2007. The route follows the Nuns Veil Glacier up the southern flank of the mountain, rising in a series of gentle steps. Occasionally gaps would form in the swirling mist, revealing a glimpse of the summit.

My passion for mountains and glaciers was instilled at an early age. On one of our few family holidays we went to Aoraki Mount Cook National Park when I was seven years old. I remember long walks with my family and crossing the Hooker swing bridge. We also went to view the Haupapa/Tasman Glacier. There was no lake in front of the Tasman Glacier then, and it was blanketed in rock, though you could still see bits of ice poking out. I could hear the rocks and ice creaking and cracking as the glacier slowly flowed down from the distant mountains.

On that trip, I learnt that during the ice ages these amazing things called glaciers used to be much bigger, and that concept fascinated me. I imagined how it would have looked when the ice where I stood was so thick that only the tops of the mountains poked through.

Who knew then that 30 years later I would be standing on the same moraine explaining to a group of university students why the area I had once walked on, and where my sister and I had sat as children, was now a lake more than six kilometres long. These days, it’s getting difficult for the students to even see the glacier's terminus in the distance at the far end of the lake.

It’s not just the Tasman Glacier that is shrinking, of course. Glaciers gain and lose mass naturally as the climate varies, which is why they are such excellent indicators of climate change. They exist on the surface of the Earth in a very delicate balance; if temperatures increase, more snow and ice will melt, and if the climate gets colder, more rain will fall as snow. The Fox Glacier, for example, is now 3.5 kilometres shorter than it was in the 1800s when Europeans first started exploring there—shorter than any other time in recorded history.

People in these environments, for work or recreation, must be aware that the rate the ice is changing is so fast that you must be dynamic and learn to adjust based on year-to-year changes.

As Jason and I continued up the Nuns Veil, we reached the bergshrund. It can sometimes be wide