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Introduction
Within the Auckland volcanic field there have been discovered over 50 significant lava tubes, however of these, the Wiri Lava Cave is the most impressive at over 290m in length. The Wiri Lava Cave is in fact considered the best example of a lava cave in New Zealand and is the only one that preserves the thin basalt-lined conduit through the scoria cone before passing down into the lava flow proper.
The Wiri Lava Cave embodies several features in their most perfect form. These are smooth, gas-flazed rock surfaces, lava stalactites, circular tube gas vents, ridging on the floors and contraction gaps at the base of walls. The cave is considered to be of international importance.
The lava that flowed to form the Wiri Lava Cave originated from the Manurewa volcano immediately to the south, which has been entirely quarried out of existence for it's useful scoria rock. The Manurewa volcano produced a scoria cone (now removed) and a pahoehoe lava field (also extensively quarried) with an area of about 2.5 square kms comprising alkalic olivine basalt.
Wiri Lava Cave has a variety of cross-sectional shapes, and many diverse flow features on the walls, floor and ceiling. The main gas-vent entrance to the cave lies within the quarry area and can be easily located, but it is sealed for safety and to prevent vandalism. A second, artificial entrance, from a public street is also sealed. Small mineral encrustations from within the cave have been identified as calcite.
A Cave Saved
Because lava flows and scoria in the Auckland region are sought after for quarrying aggregate, it took over 25 years to get legal protection of the unique lava cave near Wiri. The gazetting of the Wiri Lava Cave Scientific Reserve was signed in 1998 in the cave itself by the Minister of Conservation, who used the back of campaigner Les Kermode as a writing desk.
Severely threatened by the surrounding quarrying activity, particularly prior to it being assigned reserve status, the Wiri Lava Cave is considered of international significance. Fourteen other lava caves in the Auckland volcanic region are considered to be important for scientific or educational reasons.
This Earthcache
In order to log this earthcache, you will need to perform the tasks below. The answers to the questions must be emailed to the cache owner, while the required photo must be uploaded with your online log. DO NOT VISIT AT NIGHT!
The main entrance to the Wiri Lava Cave is accessible, with a minimal amount of difficulty, within the quarried area, east of the published coordinates. The easiest way in is via a track to the east of a small, seemingly abandoned, building on Wiri Station Rd. The approximate coordinates are listed below.
Please stay on the track, there is no need to actually go right over to the cave entrance. All we want you to do when you have identified where the cave entrance is, is the following:
1a. Take a photo towards the cave entrance, from the track, including your GPS unit. This photo should be uploaded with your online log.
1b. What is the elevation of this cave entrance from sea level? You don't need to go right over to the entrance to record this, just use your GPS unit to record the elevation on the track, when you feel you are about level.
Unfortunately, there's not much to see at the cave entrance, however, so that's why to learn about this area, we want you to visit the published coordinates - a much more accessible spot on the side of Roscommon Rd. You can't park right beside the spot, but you should be able to find some safe parking in the area a short walk away.
When you arrive at the spot you will see, in the road cutting, two very distinct layers. Please answer the following questions:
2a. Describe the two layers (upper and lower), in terms of colour, texture, and what you believe the two layers are (this should be fairly obvious).
2b. Estimate the height from the road level to the top of the lower layer, and the thickness of the upper layer.
You can log this cache straight away after you have emailed your answers to the cache owner, no need to wait for confirmation. Please include the name of this earthcache in the email - you'd be surprised how many people forget. Also, when contacting us with answers, if you want a reply, please include your email address. Any problems with your answers we'll be in touch.
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