Man-sized boulders crashed down the cliff and on to the beach recently, flattening trees and tussock on the Aramoana Recreational Reserve.
The cliff had been known to crumble occasionally but it was the first time in many years such a big fall had occured, nearby resident Bradley Curnow said.
''This is by far the biggest. I didn't even hear it, which is unusual,'' he said.
Luckily, it just missed the traps set by Aramoana Conservation Trust volunteers to protect the penguins and their nests, but it did knock down a sign informing people it was a nesting area and not to bring dogs into the area.
He believed the rockfall was the result of the recent rain and snow combined with frosts.
Doc ranger Jim Fyfe said the rockfall was a natural process and ''by luck'' it had not affected the yellow-eyed penguins.
