Scientists undertaking the annual glacier snowline survey over the South Island later this month are keeping a watchful eye on a lake that has been forming and disappearing at the junction of the Tasman and Hochstetter glaciers.
NIWA principal scientist Dr Andrew Lorrey, who leads the annual end-of-summer survey, says the lake appears to have been periodically forming and then disappearing since about October.
"We suspect it may build to a certain size and is then siphoned away, possibly underneath the Hochstetter glacier, into Tasman Lake. What we are seeing from preliminary satellite images is a potential hazard forming that could increase ice calving off the glacier," Dr Lorrey says.
NIWA and Victoria University of Wellington scientists complete the annual end-of-summer snowline aerial survey of 50 South Island glaciers once a year, taking thousands of photographs to evaluate the snowline altitude and build 3D models of the glaciers. These are then used to assess how much of the previous winter’s snow has remained covering each glacier to contribute toward long-term glacial ice accumulation.
The snowline survey began in 1977 and provides a valuable long-term record of how New Zealand’s glaciers have retreated over time due to climate change.
In recent years the impact of marine heatwaves and record temperatures has been harsh. Dr Lorrey said he was expecting to see a good blanket of snow over the Southern Alps this year but said that would only be masking the true extent of the overall ice loss - which amounts to about 30% since surveying began.
"The snowline may be sitting pretty close to normal at the moment, but the overall health of the glaciers is completely different."
Dr Lorrey said that the formation of an ephemeral lake on the left flank of the Tasman Glacier terminus was predicted by Dr Trevor Chinn, who was part of the glacier survey since its inception. He died in 2018.
The Hochstetter and Tasman Glaciers join together upstream of Tasman Lake, but Dr Lorrey said cumulative ice loss would eventually mean they become two separate entities.
The aerial survey will take place later this month.
