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.