White mud and saline water have covered about 1.2 hectares in the Waimata Valley after a mud volcano eruption last month.

Gisborne District Council integrated catchments manager Dr Murry Cave said while mud volcanoes were uncommon in New Zealand, there were a number in the Tairawhiti region which were part of an ongoing study being undertaken by the the council.

"In our region mud volcanoes occur from the Hangaroa Valley in the south to near East Cape in the north.

"A mud volcano erupted on the Waimata Valley mud diapir."


A diapir is a domed rock formation in which a core of rock has moved upward to pierce the overlying strata.

"This area showed significant signs of movement after the Te Araroa earthquake in September 2016 where the land was uplifted by about half a metre," said Cave.

"Although the eruption doesn't appear to be associated with any significant seismic shaking, the Institute of Geological and Nuclear Sciences (GNS), together with researchers from Imperial College (UK), installed sensitive seismographs in the area last summer as part of the Hikurangi margin project.

"It's hoped the data from these seismographs may help provide a better understanding of mud volcanoes."

This month the council plans to map the feature using high resolution drone aerial photography.