Volume loss in New Zealand glaciers is dominated by 12 large glaciers. The NIWA glacier monitoring program has noted that volume of ice in New Zealand’s Southern Alps has decreased 5.8 cubic kilometres, more than 10% in the past 30 years. More than 90% of this loss is from 12 of the largest glaciers in response to rising temperatures over the 20th century. Three of these glaciers are the Tasman, Mueller and Hooker Glacier. Mueller and Hooker Glacier are one valley west of the Tasman Glacier and end in the same valley ending just 3 km apart. Description of the retreat and the role of glacier lakes in accelerating the reteat of Tasman Glacier is discussed in detail in Dykes et al (2011). If we look back to the 1972 Mount Cook Map no lakes are evident at the terminus of Hooker (H), Mueller (M) or Tasman Glacier(T), pink dots indicate terminus location, top image. In 2011 the Landsat image illustrates that this has become a new lake district, bottom image.. Mueller Glacier drains the eastern side of Mount Sefton, Mount Thompson and Mount Isabel. The lower section of the glacier is debris covered in the valley reach from the terminus at 1000 m to 1250 m. A comparison of the Mueller Glacier in a sequence of three Landsat images below from 2000 (top), 2004 (middle) and 2011 (bottom), indicates that the lake at the end of Hooker Glacier had developed by 2000. The lake at the end of the Mueller Glacier was just forming length of 400 meters. By 2004 the Mueller Glacier Lake had expanded to a length of 700 meters. By 2011 the lake had reached 1400 meters in length. The 1000 meter retreat from 2000-2011 will continue in the future as the lower section is stagnant. . A closer look at the lower Mueller Glacier indicates that the lower 2 km is stagnant as indicated by the formation of supraglacial lakes and considerable surface roughness (green arrow) that does not occur when a glacier is active and moving. The glacier has been fed by three different glaciers flowing off of Mount Sefton. Two of them Tuckett and Huddlesoton (pink arrow) are no longer delivering significant ice to the Mueller, only modest avalanching now spills onto the Mueller Glacier. Only the Frind Glacier (yellow arrow) is contributing to the Mueller Glacier. The result is that the end of truly active ice is at the purple arrow, this will develop into the terminus of the Mueller Glacier. In the 2011 image of the glacier the yellow-burgundy arrow indicates the snowline on the Frind Glacier is at 1900 meters, yielding too small of an accumulation zone to support the valley tongue of the Mueller Glacier. This is similar to the situation on nearby Murchison Glacier. Further the lack of ice connection from Huddleston and Tuckett Glaciers to Mueller is again evident, pink arrow. The lake will continue to expand through minor calving and downwasting. The lake has not been surveyed, but seems to lack the depth at the current terminus of Tasman Lake where calving can be more important.
Murchison Glacier drains southeast from the Mount Cook region, one valley east of Tasman Glacier. The end of the glacier terminates in a lake that is rapidly developing as the glacier retreats. This retreat will become rapid as 2010 imagery indicates other proglacial lakes have now developed 3.5 km above the actual terminus. These lakes are at a higher elevation and may not endure but do help increase ablation, and in the image below show a glacier that is too narrow to provide flow to the lower 3.5 km. The increased retreat has been forecast by the NIWAand Dykes et al (2009) This lower section is debris covered, stagnant, relatively flat and will not survive long. The demise of the lower section of this glacier will parallel that of Tasman Glacier. The glacier has retreated 2200 meters from the moraines at the south end of the lake. There was not a lake in the 1972 map of the region. A comparison of 2006 and 2010 imagery indicates the decrease in glaciated area in the lake basin. The bottom image is from NASA after the Feb. 2011 earthquake near Christchurch that led to a major calving event of a portion of the rotten stagnant terminus reach of the Tasman Glacier. There is no evident calving event from Murchison Glacier. The lake on the western margin of the valley, separated from the main lake has since April 2010 expanded notably. The glacier still has a significant accumulation area above 1650 m to survive at a smaller size. The lower debris covered tongue is 6 km long and extends from the terminus at 1050 meters to 1200 meters, a very low gradient to supply healthy flow from the accumulation area. The ongoing retreat is triggered by warming and a rise in the snowline in the New Zealand Alps observed by the NIWA.