From the sky, it looked like an eruption on the western side of Mt Taranaki as huge clouds of dust billowed into the sky.
But while the mountain is overdue for an eruption, yesterday's spectacle was put down to erosion "on a massive scale".
Taranaki Daily News photographer Cameron Burnell, who flew over the scene yesterday, said it looked as though geothermal activity was taking place on the mountain's slopes. "There's a large dust cloud pouring out from a very large gorge that looks to have just appeared," he said. "That's a very large natural event that is happening up there."
An Okato man, who did not want to be named, said it started about 7.30 yesterday morning. "Then there was a big collapse at 11am. It's quite common but this is the biggest one I have ever seen," he said.
The area above the headwaters of Stony River is unstable and has been a scene of constant erosion ever since a series of big storms about 13 years ago.
Taranaki Regional Council rivers manager John Philpott confirmed yesterday that the erosion appeared to be getting worse. "The thing is we can't do anything about it," he said. "This is a natural event taking place on a massive scale. So it's not as if you can plant trees to stop the erosion. All we can do is manage the effects of it so there is as little impact on the local community as possible."
Millions of tonnes of rock and sand have collapsed, creating massive gorges and canyons in the landscape.
Engineers and geologists are concerned about the long-term effects.
It has turned Stony River – once Taranaki's premier trout fishery – into a "dead" river, because of the loose sand and rock material pouring down the waterway. This is in turn leading to concerns about the security of the State Highway 45 bridge near Okato.
Two years ago the regional council warned that the western side of the mountain was literally falling to bits. It said canyons were rapidly developing that were up to 40 metres deep. When it was dry and the wind blew, it created clouds of ancient volcanic ash – as was happening yesterday.
- Taranaki Daily News
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