A river of shingle rock flowing down Terrible Gully has left eight farms cut off from town in Rakaia, near Canterbury's Mt Hutt.

Incredible video of the "rocky river" was captured by Donna Field of Cleardale Station as she surveyed the damage from former Cyclone Gita on Wednesday.

The flow of careering shingles closed Double Hill Run Rd which services the farms in the South Island region. It's an event that has become a regular occurrence for the farmers in the area.

DONNA FIELD The shingle river sounded like when a "gravel truck tips all its load".

"But it's never been this bad before," Field said.

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"For a long time it was quite stable, but the last 2.5 - 3 years it has become a lot more active."

DONNA FIELD Donna Field and her son captured the flowing shingles following former Cyclone Gita.

Field and her son Joe - who had to shout at each other due to the noise and strong winds - were in the right place at the right time to watch the incredible flow of cascading rock begin to form.

"It was really loud [and] sounded like when a gravel truck tips all its load, but if you were right underneath it."

Cleardale is a 1250ha station situated up the Rakaia Gorge, where they run Merino, English Leicester, Halfbred and Quarterbred studs as well as an Angus stud.

Supplied Professor Tim Stern of Victoria University's School of Environment and Earth Sciences.

On Cleardale's Facebook post it said the liquid flow of rocks travel like a river from the mountains and are deposited in a fan shape where the land flattens out.

Field said there were no injuries to people or livestock, but the eight farms isolated by the landslide would have to wait until the road was cleared.

"They'll wait it out, this isn't the first time its happened."

Professor of Geophysics at Victoria University Tim Stern saw the video and thought it was an impressive sight.

"You wouldn't want to be trapped by it - it's a scary example of how vulnerable our environment is to be destroyed by weather," he said.

New Zealand has one of the highest erosion rates in the world, alongside the eastern Himalayan syntaxis, he said.

"This [video] exemplifies that and shows the effect heavy rainfall has on New Zealand's weak greywacke basement rocks, which are much weaker than other basement rocks, like in Australia."

Monsoon rains, in combination with rocks pushed up very quickly by tectonic uplift, means they are vulnerable to erosion.

"The rain is what weakens them and causes it to erode very quickly, it's why we have one of the highest erosion rates in the world."