Geopreservation of Lava Caves in Auckland: A Lack-of-Progress Report
Introduction
In 1983, the Geological Society of New Zealand, in association with other earth sciences societies, recognised that some of the unique features of New Zealand's distinctive landscape were threatened with destruction. Years earlier, Lands and Survey Department, the government department then responsible for national parks and scenic reserves, had spent time and money, attempting to identify landscape features that were representative of each region. In addition, a few regional councils had provided some legal protection concepts in their planning schemes. However, no nationwide listing of representative sites was established, and it thus became difficult to advocate for the protection of the most threatened geological heritage sites. An ambitious Geopreservation Inventory was commenced by the Geological Society, and hundreds of earth scientists contributed by identifying and listing more than 3600 geological and geomorphological features and sites in New Zealand, that were of scientific or educational value. These sites and features were accepted as being worthy of preservation, and, if possible, legal protection. The existence of public access was not a controlling factor in the selection of the sites. A great diversity of earth sciences values were included, and in the early lists the compilers did no nationwide co-ordination or evaluation. Fifteen subject category lists, such as "caves and karst", and "Quaternary volcanoes of Auckland" were compiled and published. After comments on these lists had been received, twelve regional inventories were prepared and published.
ACKMA conferences focus on the management of caves and karst terrains which are two classes of geological features that have intrinsic earth sciences values worthy of being managed in a sustainable way. However, there are also caves in terrains other than karst, and these also must be protected and enhanced by sound principles of cave tourism and management.
Auckland Lava Caves
The greater Auckland urban area is the only district in New Zealand that is known to have lava tube caves. Many small cavities and short tube segments have been found within lava flows from fourteen of the small, geologically very young, basalt volcanoes that are part of Auckland Volcanic Field. Excavations for construction sites within the city have uncovered, and destroyed, many small cavernous features. No large or long lava caves have been discovered. About 40 of the caves are greater than 20m in total length, and all the lava tubes are within 8m of the ground surface. Wiri Cave, imminently threatened by quarrying activities, is rated of international significance, and sixteen other lava caves are considered to be of national importance for scientific or educational reasons. Over several decades speleologists have explored the Auckland lava caves and produced simple outline plans, but few scientific or educational reports with photographs have been published. No regional studies of lava cave biota have been undertaken.
Field discussions with foreign volcanospeleologists have brought some objectivity into the processes of geoheritage assessment, but no spectacular lava caves of world record status have been revealed. There are lava tube caves in other countries (Hawaii, Tenerife, Korea, Kenya, Japan, Australia, United States, etc.) that rank more highly for their length, diameter, or uniqueness of flow features.
RANGITOTO volcano is a circular island within Hauraki Gulf Maritime Park. It has an area of about 23km2 (about one seventieth of the area of Undara Volcano, Queensland), and consists mainly of rubbly lava flows. A cratered scoria cone rising to 260m above sea level caps this 600 year old volcano.
Southern Cave is the most frequently visited lava cave in New Zealand. It is one of the main group of five lava caves near the rim of the lava crater at about 150m above sea level. Southern Cave is a straight downslope segment of a closed lava trench, about 60m long, that has no humanly devised modifications, such as boardwalks or artificial lighting. Visits are strictly do-it-yourself. The upper and lower entrances are natural roof collapses into lava tubes or trenches, and a third central entrance is a natural skylight surrounded by a raised spatter rim.
In 1996 the Department of Conservation prepared some explanatory display panels for this cave, but they have not been erected. Display panels for other park features have been installed and used by tens of thousands of visitors. The administration seems not only to suffer from the all-pervading lack of financial resources, but also from a bureaucratic reticence that fears infringement of new government health and safety legislation, or intimidation by the current safety expectations of the public in general. Can there be risk-free cave adventure trips?
THREE KINGS volcano is within a residential suburb of Auckland. About 20,000 years ago a large explosive eruption produced a tuff ring (about 1200m across) in which several scoria cones formed. Lava was initially confined within the tuff crater, but it later overtopped the rim, filled an adjacent valley, and advanced about 10 km from the source vent, out on to an ancient river plain that is now the main Auckland Harbour. The lava flows cover an area of about 6.4km2.
Stewart's Cave is close to the point where lava flowed out over the tuff ring rim at about 70m above sea level, and now lies beneath privately owned residential properties. The landowners who have the only unblocked natural entrance within their boundaries control access to the cave. This lava tube system is about 180m long with two converging levels that connect with a third tube. It contains flow features, surge level marks, kerbs, a short cave-in-cave, and a large terminal lobe. The floor is mainly rough and rubbly, or, in places, covered with blocks fallen from the ceiling. A detailed cave plan and longitudinal sections were published in 1870. The cave is easy to enter and mostly easy to negotiate. The entrance, a natural roof collapse, has been modified slightly. The future existence of this lava tube cave could be threatened by groundworks associated with residential redevelopment, even although it is, at present, designated for protection.
Auckland City Council planning department had interpreted the geopreservation inventory to mean that all the geological sites listed were to be accessible to the public, and therefore specified facilities and safety features were to be installed. Such a proposal did not please the landowners, who responded by prohibiting all visits to the cave until the ill-conceived provisions of the plan were waived.
MANUREWA volcano produced a scoria cone that is now almost totally quarried away, initially by the Government Railways. An extensive lava field with an area of about 2.5km2 has also suffered similar destruction.
Wiri Cave is located at what used to be the northern foot of the now demolished scoria cone. The main (upper) entrance is 45m above sea level. The cave is an unbranched lava tube 290m long, with a variety of passage shapes and many diverse flow features on the walls, floor, and ceiling. Some of the most interesting flow features are on the floor. This is New Zealand's longest and most important educational lava cave, and therefore, is of international significance. The main entrance (an old volcanic gas-vent) has been sealed for safety reasons, because it is within an operating quarry. A second permanent, artificial entrance from a public street is also sealed. Most of this well-documented cave is easily negotiated from the main entrance, but is extremely difficult to negotiate from the second entrance. A cave plan with cross-sections has been published. Destruction of this cave by quarrying is a constant threat. It was last inspected in 1996.
Although Wiri Cave is located within a large quarry, it has been listed in the regional and district plans as a geological heritage feature of national importance. Protection by legislation has been sought, and the Parliamentary Commissioner for the Environment has criticised the bureaucrats for their inertia. However, local, regional, and central governments are still reluctant to accept responsibility for the cave's preservation.
After nearly 30 years of procrastination by central government and local politicians, the quarrying nearby continues to move closer and go deeper. This brittle lava tube with many natural cooling cracks throughout its length is very likely to disintegrate because of excavation-induced ground settlement into the enormous hole in the sensitive, wet sediments beneath the volcanic deposits. A precise monitoring programme has been agreed to, not in order to protect the cave, but to evade the responsibility for damage or destruction of the cave if litigation ensues. Perhaps the consciences of the dithering bureaucrats have been stirred, at least until the next staff restructuring.
Conclusions
Three lava caves in Auckland are awaiting effective legislative protection, and the development of appropriate management strategies. Several local territorial authorities have uncritically taken sections from the geopreservation inventories and incorporated them directly into their planning schemes, but such actions are contrary to the concept of the inventory, and are proving to be counter-productive. Eventually it is hoped that many of the geological heritage sites and features will become available to the public, and then sustainable use will become a conservation issue rather than remaining a scientific preservation issue. Tourism in lava caves is always a possibility, but is not essential. It might not even be desirable.