NZICESCAPES IMAGES

Does Franz Josef Glacier retreat or advance?

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 20th 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

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