March 24, 2016
Terminus of Tasman, Mueller and Hooker Glacier terminus in Mount Cook 1972 map, no lake present.
Progalcial lakes forming in front of Tasman, Mueller and Hooker Glacier in 1990 above and 2015 Landsat images below.
Red arrows are the 1990 terminus and yellow arrows the 2015 terminus locations.
The Southern Alps of New Zealand are host to over 3000 glaciers that owe their existence to high amounts of precipitation ranging from 3 to 10 m (Chinn, 1999). The list below examines the changes of 12 glaciers examined in a separate post. The NIWA glacier monitoring program has noted that volume of ice in New Zealand’s Southern Alps has decreased by 36% with the loss of 19.0 km3 of glacier ice, from 53.3 km3 in 1978 to 34.3 km3 in 2014 (New Zealand Govt., 2015). Volume loss in New Zealand glaciers is dominated by 12 large glaciers (Salinger and Willsman, 2008). More than 90% of this loss is from 12 of the largest glaciers in response to rising temperatures over the 20th century (Chinn, 1999). In the 1972 map of the region there is no lake at the terminus of the Tasman Glacier, Mueller Glacier or Hooker Glacier; each are substantial in size by 2015. Each lake continues to expand and as glacier retreat continues .From 1977-2015 NIWA has conducted an annual snowline survey, in six of the last nine years the snowline has been significantly above average and three years approximately at the average (Willisman et al., 2015). This has driven the widespread glacier retreat underway. In each case the retreat of the largest glaciers has been enhanced by the formation and expansion of lakes, in this newly developing lake district. Dykes et al., (2011) identify the role of glacier lakes in accelerating the retreat of Tasman Glacier. The retreat of these glaciers has until recently been slowed by debris cover and the long low slope ablation zone segments (Chinn, 1999). Glaciers that lack debris cover and have a steeper slope have a more rapid response time, such as Fox Glacier and Franz Josef Glacier (Purdie et al., 2014). These two glaciers have been in the news of late due to rapid retreat causing glacier tours of the lower reaches of the glacier unsafe. NIWA reported that February of 2016 was the second warmest month of any month in New Zealand, which will drive snowlines higher and enhance glacier melt this year.
Many New Zealand glaciers are important for hydropower: Lake Tekapo and Lake Pukaki are both utilized for hydropower. Hooker Glacier, Mueller, Murchison and Tasman Glacier drain into Lake Pukaki, where water level has been raised 9 m for hydropower purposes. Water from Lake Pukaki is sent through a canal into the Lake Ohau watershed and then through six hydropower plants of the Waitaki hydro scheme: Ohau A, B and C. Benmore, Aviemore and Waitaki with a combined output of 1340 MW. Meridian owns and operates all six hydro stations located from Lake Pūkaki to Waitaki. The reduction of glacier area in the region will reduce summer runoff into Lake Pukaki and this hydropower system.
Gunn Glacier in, 2006 above and 2012 below,Google Earth image. Red arrows the 2006 terminus position yellow arrows 2012 terminus location. The glacier lost 25% of its area in six years.
Donne Glacier from 2003-2012 in Google Earth images. Red arrow is the 2003 terminus and yellow arrow the 2012 terminus. A seven hundred meter retreat in a decade.