According to the Ministry for the Environment, glacier ice volumes in 1978 were above 50 cubic km.
In 2014, it dropped to slightly more than 35 cubic km.
University of Otago department of geography lecturer in hydrology Sarah Mager said last year that ice loss observed at the famous Tasman Glacier was likely a natural readjustment to climate changes.
Melting ice had formed a terminal lake.
The glacier was losing more ice volume than was being naturally replaced through snowfall and ice accumulation, Mager said.
The terminal lake is now 7 kilometres long and deeper than Lake Pukaki due to the glacier's ice loss, and was expected to grow much larger.