High-tech mini jet boat probes glacier secrets

Canterbury University geography technician Paul Bealing operates a miniature high-tech jet boat used to investigate Lake Tasman in the South Island. Photo: Heather Purdie

Scientists have deployed a high-tech, remote-controlled jet boat to solve long-standing mysteries about a New Zealand glacier.

The Tasman Glacier, which flows toward the Mackenzie Basin in the Southern Alps, has posed many curious questions to researchers because of its relatively uncommon underwater "ramp" of ice jutting out from the glacier's edge, or terminus, into the bed of Lake Tasman.

"Essentially, it's like a toe of ice that's getting left behind under the water as the glacier retreats," Canterbury University glaciologist Dr Heather Purdie said.

Little was known about what caused these underwater ramps to form, partly because there were few examples of them around the world.

But investigating the Tasman Glacier had been hazardous because of the risk of ice breaking off the glacier and dropping into the water.

This had meant researchers couldn't take boats close enough to the glacier edge to make precise measurements - until Purdie and her team came up with a novel idea.

They turned to a remote-controlled miniature jet boat which had previously been used by the university for river research and fitted it with an echo-sounder and a GPS system.

This allowed the researchers to drive it over the underwater ramp, collecting bathymetric data from 240 metres below the lake while tracking its location in real-time.

"We're being able to get data in a much high resolution than we ever have before, because we don't have that risk associated with it."

The miniature jetboat used an echo-sounder and GPS system to map out the underwater ramp of Tasman Glacier in Lake Tasman. Photo: Justin Harrison

The information had yielded new insights into how the ramp was forming as the glacier retreated, and what it was about the glacier's make-up that was contributing to carving events.

A study published last week in the journal Global and Planetary Change suggested that the effects of water draining out from under the glacier into the lake could influence where these underwater ramps do and don't form.

"We're also starting to look more carefully at debris, the ice can be full of rock particles so this may affect the strength of these ramps, how big they can get and what it actually takes to have one break off."

As glaciers around the world retreated under the effects of climate change, Purdie expected to see more of the same patterns in other inland spots around the globe.

"So anything that we can learn is going to be of real interest to other researchers all around the world.