Tasman Glacier and its terminal lake with icebergs and icy debris after massive terminal face calving in 2010 under sunset, Mt. Cook National Park, Mackenzie Country, World Heritage Area, New Zealand

Glaciers around the world are melting and disappearing from World Maps. We are not immune to it as this sad reality is hitting New Zealand as well, and it’s not a nice sight.
The Southern Alps are becoming more and more unstable for alpine activities with increased rock avalanches as the warmer temperatures are melting rock binding ice in lower altitudes then in past.
All this rock avalanche debris falls on the shrinking and narrowing glaciers in valleys below, covering their gasping for breath remnants under layers of rocks.

In case of Tasman Glacier, this is even more evident, as with it’s lengths of 27km now, it is New Zealand’s longest and mightiest glacier…but how long for when its retreat is today estimated to be close to 1 km each year.
In 2010 massive calving event occurred, littering Tasman Glacier terminal lake, non-existent 40 years ago, with tons of ice debris and icebergs.

It’s not every day when event like this happens so I went to check it out myself. When I arrived at the terminal lake near sunset time, the sky suddenly closed up, clouds rolled over my head and it started to snow. The light of the setting sun was penetrating this gentle snowfall, and all Tasman Valley got dressed up in this beautiful pinkish pastel colours…very eerie, moody scene with all the icebergs in the lake…how lucky I was to witness this alone…

Tasman Glacier with its terminal lake after calving at sunset, Mt. Cook National Park, Mackenzie Country, World Heritage Area, New Zealand

Taken with Nikon D300 and Nikkor 24-70mm f2.8 lens

A terminal moraine (foreground) left by retreating Franz Josef Glacier around 14.000 years ago.

If the current average temperature were just 4° C lower, we would be living in an ice age. During the last, 18, 000 years ago, Franz Josef Glacier stretched its tongue some 10km beyond the present coast line. In this period the sea level was around 100m lower than today, as an immense amount of water was locked up in the glaciers all around the world. On the West Coast there were not many visible mountain valleys as the majority were filled with ice. The western side of the Alps was literally one massive white sheet of ice with rock ridges sticking out, and stretched from the alpine tops all the way to the sea. The life of the glacier is represented by its repeating advance and retreat leaving traces in forms of terminal and lateral moraines. These moraines are particularly visible from the air and some of them can even be observed from the ground.

As with all the rest of the glaciated world, New Zealand is also losing ice mass at a rapid rate, with 61% lost since 1850 (Hoelzle et al. 2007), and 11% in the last 30 years (T. Chinn, pers. comm.).

Most of this loss is from the large glaciers calving into pro-glacial lakes, such as the Tasman Glacier. This lake formation is the result of glacier thinning in response to climatic warming in the 20^th century. As well as these large dynamic changes in glacier volume, there are smaller annual changes in volume due to changes in the amount of snow accumulation and snow and ice melt. An idea of how much mass is lost or gained each year throughout the Southern Alps is given by measurements of the end-of-summer snowlines since 1977. These measurement indicate that there have been positive mass balances at times during this period balance (Chinn et al. 2008) and the very sensitive and responsive Franz Josef and Fox Glaciers have advanced as a result.

The advance of Ka Roimata o Hine Hukatere Franz Josef Glacier since 1984 has been extraordinary given the global pattern of receeding glaciers during this period. Recent work has confirmed the very sensitive nature of this glacier – that is it advances or retreats a large amount for a small change in climate (Anderson et al. 2006; Anderson et al. 2008). Combined with its very short response time this explains the large variations in glacier length observed in the last decade.

All of the indications are that Franz Josef Glacier has lost mass in recent years, particularly in 2008, and 2010. We do not have enough measurements to calculate an annual mass balance, but the combination of thinning in the accumulation area and lower amounts of net accumulation observed indicate a negative mass balance. This makes it likely that the recently-started retreat will continue.

This is an excerpt from a full report researched and written by one of the leading New Zealand glaciologists Brian Anderson/Victoria University Wellington.

Text ©Brian Anderson