Nikau Cave
Monday 8 April 2013

Nikau Cave is a privately owned and operated tourist cave with an associated cafe – Nikau Cave and Cafe web site. It's located south west of Mercer near the Auckland/Waikato boundary.

The operation seems reasonably well set up, with helmets and torches for those paying for a cave tour, but unfortunately a couple of us drew blood before even getting into the cave. It turns out that fence railings around the cafe are (um, were) just nailed on to the posts instead of being securely bolted. With even a moderate load (for example, a single boy) the nails started to pull out. A railing several of us were sitting on for a photo came off completely at one end, catching the back of one boy's foot underneath it. After the Cave Creek disaster this lax attitude to robustness should be completely unacceptable. These railings are not just for decoration.

The cave itself is quite well decorated, with many stalactites and glowworms. There is at least one good "bacon" drapery and there are even a few small helictites (stalactites that go sideways).

The home page of their web site gives an indication of the pace they say the tour sets:

The one and a half hour tour through Nikau Cave is personal and unhurried.

However, we found that for people wanting to admire the formations, with or without photography, that simply isn't true. The tour runs too fast. From their FAQ:

We find that if people are taking photos they miss out on the experience and are also not sufficiently aware of their surroundings to be safe. It is also inconsiderate for one person to delay the group.

Maybe we'll actually miss out on the experience they want us to have, which doesn't involve hanging around long enough to properly take in the beauty of the formations. After all, they have another tour to push through the cave.

The repetitive commentary from the guide that the stals only grow 1 mm every hundred years was tiresome; her claim that touching a stal can kill it is just wrong. Indeed, it would be rather unverifiable if they really did grow that slowly (as we muttered at the back of the group). It can leave permanent marks, however, so should definitely be avoided.

The actual rate of stalactite formation varies hugely, and depends on a number of factors like water flow. The formation rate at Nikau Cave is very unlikely to have actually been measured.

Touching a formation will not kill the formation. The bat in the picture at right (not from Nikau Cave) didn't kill the stalagmite it landed/fell on. The bat was presumably dead at the time; it got covered with calcite so rapidly it didn't have time to rot and fall off.

This article mentions how fast formations actually form (emphasis in original):

Strangely, there seems to be little or no systematic measurement of stalagmite growth rates. Why should one bother, the thinking seems to go, when all one has to do is take the radiometric ‘age’ and divide it by the stalagmite’s length to get the rate?

However, where growth rate has been measured in show caves (which are not necessarily the fastest growing), it varies from 0.1 to 3 mm (four thousandths to 1/8 of an inch) each year. Thus, to grow 2 m (7 ft), a stalagmite could take anywhere from 700 to 20,000 years.

The minimum actually measured rate is ten times faster than the rate our cave guide claimed!

The cave was first mapped in 1970 as a result of cavers being asked to help search for the bodies of Jeanette and Harvey Crewe – murders still unsolved almost 43 years later (at time of writing). The cave is 713 m long.

After visiting the cave we took a walk (or jog) through native bush to have a look at a nearby waterfall, about 10 m high at a guess, with free falling water the whole way. The bush is great, with supplejack vines making for awesome dodging as we ran through the bush. The signage to the waterfall could do with improving.

My thanks to the Hallidays for this great day.