Lava cave found in Auckland every month

One of the many lava caves in Auckland.
One of the many lava caves in Auckland. Photo credit: Supplied

Researchers and Auckland Council are working collectively to completely map a field of hundreds of lava caves under the City of Sails.

Auckland is well known for being built on an active volcanic field - with 53 active volcanoes and hundreds of lava caves - which could pose a risk to construction and development.

A collective project by Toka Tū Ake EQC, Auckland University, DEVORA, and Auckland Council, aimed to create a full database on the caves.

The Earthquake Commission said homeowners and developers are finding approximately one new lava cave every month.

University of Auckland researcher Jaxon Ingold said the caves were created in very particular circumstances.

University of Auckland researcher Jaxon Ingold.
University of Auckland researcher Jaxon Ingold. Photo credit: Supplied

"The type of lava and the speed of the flow will determine if the outside layer cools down fast enough to harden. This creates a tunnel for the lava to flow through, and when the lava drains away a cave is left behind," he said.

Ingold was tasked with collating all known information on the lava caves and mapping new ones.

Previously, there had never been a complete database where all information on Auckland's lava caves was being kept.

"Many people know there are lava caves all over Auckland, but the exact information is spread around lots of different groups, like local iwi, the council and experts who have been investigating and mapping some of the network," Ingold said.

Toka Tū Ake EQC said the database will be used by "planners, engineers and relevant people in order to protect them and to strengthen our understanding of lava caves and lava flows in Tāmaki Makaurau".

Auckland Council geoheritage expert Kate Lewis said the caves had long been important to iwi heritage, and even those which had not surfaced could be significant.

Because of this, Lewis said many caves were considered 'Outstanding Natural Features' and each one found to be more than one metre wide would need to be investigated and potentially protected.

She urged anyone who found a lava cave on their property to report it.

"There are several reasons why this information could be sensitive, so we want to reassure people we will treat that information appropriately," Lewis said.

The last of the caves were formed approximately 600-700 years ago when Rangitoto Island erupted.