Lahar erosion reason for Mt Taranaki dust clouds

Dust clouds rising from Mt Taranaki are the result of widespread erosion caused by last year's series of powerful lahars.

The plumes of smoke-like cloud near the skifield on Tuesday caused concern for some Tariki residents who thought part of the mountain had collapsed.

However, the Department of Conservation's Dave Rogers confirmed yesterday the dust was coming from the highly eroded valleys – especially near the Maketawa catchment – where last year's lahars had ripped out all vegetation. "There's now huge areas of sand and gravel there, and the wind just funnels straight up the valley walls and the clouds look like plumes of smoke," Mr Rogers said.

"We've been to dozens of these call-outs now."

Massey University earth sciences professor Vince Neall, who has done a study on the April 2008 lahars, said in places the near-solid rivers of mud had torn out vegetation from nine metres up the valley walls.

"That was only 18 months ago so there has been no opportunity for the vegetation to recolonise," he said.

"As we approach summer that's a big supply of dust to blow up."

Professor Neall said he had seen the same problem on the other side of the mountain in the Pyramid Stream catchment.

"Those windy westerlies whip around there and pull up all the loose sand."

Taranaki Fish and Game's Allen Stancliff said although the lahars had dumped a large amount of debris in the Maketawa main stream – which had had significant adverse affects on the aquatic life – he did not think the dust clouds would have the same effect.

"It will be only minor in comparison to the main event," Mr Stancliff said.

However, he did note that although the habitat had substantially recovered by April this year, apart from having more sand than usual, the trout population had not yet been able to fully recover.

- © Fairfax NZ News