New Zealand; limestone cave

New Zealand has been under the sea for millions of years during the past eons. It is up and down based on the pressure being applied to the edges of the continental plates of which it is part. Actually New Zealand is at a junction of two plates and it slides, bumps, jumps, and changes its elevation over time. Mountains are being built on New Zealand’s west coast (South Island) as you read this page and those same mountains are being eroded away at an equal speed. There are dozens, if not hundreds, of earthquakes every day. It is a geologically exciting place to live but perhaps not a great place to display a collection of fine China.

The undersea portion of New Zealand’s existence has allowed for the formation of a great deal of lime-based rock. The ocean oozes shells and calcium rich bits that form layer upon layer on the ocean floor. The layers reach a certain weight and undergo a chemical and physical change. This divides the build-up of ooze into what look like separately formed layers of calcium carbonate (the mineral calcite). Some day, millions of years in the future, those “layers” are/will be lifted above sea level. Being a rather wet part of the world these limestone edifices are rained on a great deal. The fresh water seeps down into the myriad of cracks and through the layers of calcite eroding the limestone and carrying off an aqueous solution rich in calcium. Picture that happening for tens of thousands of years and you have a subterranean cave. New Zealand has  miles and miles of such caves. The drips will sometimes evaporate before dripping – this leaves behind the calcium which can create a structure on the walls or ceiling of the cave.

Many of these limestone caves still have running water in them and these have sometimes been turned into tourist attractions. Rafting and walking through these caves is big business. The image above shows the scope of the Ruakuri Cave. There is a very safe and modern (and environmentally sensitive)  walkway at the base and motion-sensitive lights. It is a wonderful visit. the lower part of the image shows the blurry group walking ahead and to the right. The “layers” or seabed sediments show well in the middle center.
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Most of the cave was formed by water running laterally along cracks between the layers. However, there are a few places where the cave has collapsed creating an amphitheatre and other place with chimneys reaching up into the darkness.
There are thousands of stalactites in the Ruakuri Cave. There is also good representation of “coral”, “curtains”, and stalagmites. One of the few animals in the cave is the Glow Worm. This is a small insect (actually a fungus gnat, a Diptera which includes what we call flies?
Before looking at the glow-worm a bit closer here is a nice “curtain” with tiny stalactites growing, drawn by gravity, from it.
I have dozens of images of the glow-worm snares. They all look pretty much like this. It is pitch black in the caves and we don’t bother the larva too much with lights. So I take what I can. I have had pretty good luck with an iPhone rather that an expensive Nikon; however if I had a quiet time in the cave with a chance for long exposures I’d try again with the Nikon. These snares are gooey and hand down from the hammock in which the glow-worm larva. resides. Pretty cushy life but not much in the way of food. When, and if, some tiny insect flies into the cave and is drawn toward the “stars” that are actually bioluminescent glow worm larva and then gets entangled in a snare it is drawn upward and eaten by the larva. They shed several times and eventually pupate. The adults emerge and the females will lay a few hundred eggs, in bunches of about 40, and then she dies. The male dies after mating. Neither adult feeds. In the darkness of the cave the glowing larva, pupa, and adults can look like a beautiful starry night. The Maori people named them after the reflection of their glow in the cave waters below.


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