23 Jan 2015

Glacier retreat changes valley

11:52 am on 23 January 2015

The retreat of Fox Glacier on the South Island's West Coast is having a dramatic effect on the landscape around it.

An annual Massey University survey of the glacier valley has found the valley floor has risen by more than 1 metre in the past two years.

Fox Glacier in 2005

Fox Glacier has retreated rapidly from its level in 2005 Photo: SUPPLIED / Ian Fuller

The glacier in 2015.

Ten years later, in 2015, changes to the Fox Glacier geography are clearly visible. Photo: SUPPLIED / Ian Fuller

The ice has been melting since 2008, following decades of steady growth and tour operators can no longer take visitors through on foot.

Massey University researcher Sam McColl said the glacier normally helped make the surrounding hill slopes more stable, but as it had retreated parts of the slopes had collapsed.

"Dramatic phases of retreat, like the one the glaciers are experiencing now, remove the buttress effect provided by the glacier - essentially a door stop that makes the surrounding hillslopes more stable," he said.

"Without it, the hill slopes are more unstable and likely to fail which leads to more sediment being delivered down-valley.

"At Fox Glacier, this extra sediment is what has resulted in the valley floor rapidly increasing in elevation."

Dr McColl said with the pace of change the whole valley could look drastically different in 100 years' time.

Until a couple of years ago people could walk straight up to the Franz Josef Glacier, and before April last year it was the same on Fox Glacier. But as both retreat visitors are now only permitted to tour the West Coast attractions by air.

Dr McColl said this was the first time in 11 years the annual field trip they lead for students was unable to access the glacier, but it did not prevent them carrying out their detailed study of the adjoining valley.

Get the RNZ app

for ad-free news and current affairs