30 Aug 2017

What causes sink holes?

From Jesse Mulligan, 1–4pm, 1:30 pm on 30 August 2017

Another sink hole in Waihi has left a 20 metre wide shaft on a council reserve.

The sink hole appeared yesterday and is on land adjacent to the Martha open pit mine. The collapse is into an old mine which was left partially filled.

Residents in Waihi have become used to sink holes, but they have cropped up around more urban areas in Auckland this year during heavy rain and flooding.

GNS Science Engineer Sally Dellow explains how sink holes form.

A large sink hole which opened up in Matatua Road, Raumati in 2015

A large sink hole which opened up in Matatua Road, Raumati in 2015 Photo: RNZ/Charlotte Gendall