School sitting on buried treasure

Hebron Christian College students take a look inside the lava cave uncovered by their Mt Albert school grounds. Photo / Brett Phibbs

Children at an Auckland school will not have to go far to learn about geology, with the rediscovery of a lava cave running under their playing field.

The cave, which is about 40m long and 2m high in places, starts in the lower corner of Hebron Christian College's grounds, and runs across the lower field.

Some staff were aware the old cave existed but no one had been inside as it was blocked with debris.

But Peter Crossley, a lava cave enthusiast, said he entered the cave about 30 years ago before it was covered over and has revisited the site for a project to map Auckland's 200 lava caves.

After removing the dirt and debris during a visit last week, Mr Crossley and some colleagues entered the cave to find it was still in good condition - although he was shocked to find some new additions.

"The only thing that's changed is all the rubbish that's in there. I was shocked at how much is in there - it was pretty disgusting." That rubbish included old paint tins, softdrink bottles, the wheels of a pram and spouting - which Mr Crossley believes may have been dumped before the cave was covered when the school took over the site in 1980.

Now, the school's staff and students are keen to explore inside the cave too.

"The children have been running on top of this cave for years, not knowing it was there," said principal Geoff Matthews.

Now that the children do know it's there, they think it's pretty neat.

"The lava flowed down there, it's cool," said 6-year-old Davina White. Her classmate Jacqueline Jiang, also 6, was disappointed there was rubbish inside the cave. "There was litter, plastic bottles. It's a bad thing."

Mr Matthews said he was keen to join Mr Crossley when he returns to take another look inside and starts to remove the rubbish in the next few weeks. He'd also like to see the cave opened up for students in the future - if they are brave enough.

"I'm keen to allow the kids down there. It's safe, it's not like a dirt roof that's going to collapse or anything but if you get claustrophobic ... it might be a bit scary for some."

Mr Crossley said another large cave across the road from the school, underneath the New North Rd BP petrol station, had no access as the entrance had been concreted over long ago.

He said the size of Auckland's caves vary greatly with the largest, in Wiri, being about 300m long.

"Some of them you would be crawling through, some you could drive a double- decker bus through."

He said though most Aucklanders knew there were lava caves under the city, few knew their exact location.

LAVA CAVES

* Formed about 50,000 years ago when the surface of flowing lava crusted over, leaving a cave when the interior drained away after the eruption.

* Unique to Auckland - in other parts of the country flowing lava is too sticky to form caves.

* Almost 200 documented in Auckland but only about 50 are still accessible. Most have been covered by concrete or buildings; some have been destroyed.

Hebron Christian College students in the photograph
From left: Veronika Bilos, Suhyun Kim, James Taylor-Dayus, Isaiah Fale, Nevaeh Brown and Jordan Polglase.