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| | Harwoods Hole
CAVE SYSTEMS
On the south-west edge of the park are several spectacular cave systems, including an extraordinary pothole, Harwoods Hole. Fully 370 metres in depth, the hole is among the deepest of its kind to have been explored, although the Nettlebed system, under Mt Arthur, is certainly very much deeper.
The likely presence of cave systems is hinted at by the marble outcrops so much a feature of Takaka Hill. Marble (together with limestone, dolomite and gypsum) is particularly soluble in natural water. "Secondary" cave systems such as these are formed by water dissolving rock and they contrast with "primary" cave systems, formed during the cooling of lava. "Secondary" systems form the most extensive and best-known of the world's cave systems. Where they occur they can permit surface runoff to drain directly underground, instead of forming small tributary valleys. Occasionally streams may disappear through open "swallow holes", to reappear elsewhere (e.g. Pupu Springs, near Takaka).
The systems here are still the subject of exploration. Harmless coloured dyes poured into the water help ascertain links between various systems, and where these are located, speleologists may try to follow the tell-tale fluorescent trails, using the techniques of both mountaineer (in descending and ascending sheer rock faces) and diver (to explore underwater lakes and streams).
Within the caves themselves are insects adapted to live in a perpetually dark environment.
The utmost care is called for when visiting Harwoods Hole, and one should not attempt to look down it as the surrounding rock scree is most unstable. Indeed, a slip killed a caver in 1959 while he was being winched to the surface. Harwoods Hole may be reached from the end of Canaan Rd on Takaka Hill, off Highway 60. The 45-min walk is signposted. The Nelson Speleological Club has been co-ordinating the exploration of the cave systems. Ngarua Caves are open to the public; signposted on Highway 60. |
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