ACKMA Journal No. 26. March 1997. Pages 5 – 9

Registrations for the Waitomo ACKMA Conference are flowing in and the organizing committee are busily preparing for the event, making sure that all the bases are covered.  Tourism Holdings Lid have now sold their interest in the Waitomo Caves Hotel to the Ruapuha Uekaha Hapu Trust.  The handover was made official on 6 February with a small ceremony.  The hotel will be the accommodation and meals venue for the Waitomo Conference and the Organizing Committee has been working with the new management to secure previous arrangements.

The proposed development plan being produced by Tourism Holdings Ltd including the Ruakuri Cave has still not been finalized for general release, no doubt the hotel sale negotiations have impacted on this process considerably.

The automated monitoring system in the Waitomo Glowworm Cave has been reviewed by a panel of scientists and the parameters have been established for the future of this system including the incorporation of new technology to gather samples.  The cave's new management has adopted the panel’s recommendation and the whole system will be the subject of one of the presentations at the conference.

The Waitomo Catchment Trust recently had an open day to inform the community of the extent and progress of works carried out which all benefit the waterway flowing into the Glowworm Cave.  This scheme will also form part of the field trips associated with the conference. 

A Planning Forum sponsored by the Waitomo District Council and facilitated by Di Lucas and Association of Christchurch took place over five days in mid February.  The process involved the whole community and culminated in a presentation of the findings to the Community at the Museum of Caves.  The Community expressed a strong desire to see the village atmosphere and rural outlook retained into the future with appropriate planning and design.  The planning covered basics such as housing, sewage treatment, parking and roading.  An observation by the Consultants, was just how little the village is presently impacted by 450,000 visitors annually to the Caves.  The tourist coaches travel through the village, the visitors are duly despatched underground into the Glowworm Cave, and the coaches, with visitors subsequently leave, once again passing through the village.  It is mostly the free and independent travellers and those experiencing the adventure tourism market that make up the bulk of visitors to the village.  The full report will be released by the Council to the Community.

The aftermath of the Cave Creek tragedy, where 14 people plunged to their death from a viewing platform almost two years ago is still impacting on the staff of the Department of Conservation. The Director General of Conservation has now resigned, hopefully the end of a succession of staff and the Minister, who have all had shortened careers as a result.  The department is presently  undergoing a full organizational review to provide a structure to better equip it to take on the new quality conservation management system that is under development.

The Waitomo Conference is shaping into an interesting event judging by the early abstracts and it will provide an excellent opportunity to reflect on the changes and progress with karst management and with ACKMA Inc. over the past ten years.

The following two papers, by Mike Mueller, on the Takaka Karst provide a great introduction to what ACKMA members will experience when attending the POST CONFERENCE STUDY TOUR.

THE DISAPPEARING WATER - THE TAKAKA KARST
Mike Mueller

Takaka Limestone and Arthur Marble are the main rock formations underneath the Takaka Valley and on the hills east and west of the valley.  Both rock types are soluble in water and at present, five kilograms of these carbonate rocks (CaCO3) dissolve every second in the catchment of the Takaka River (89Okm).  This surprising figure has been found by measuring the average flow volume and analyzing the calcium content of all water flows of the Takaka catchment into Golden Bay; i.e. Pupi Springs, Takaka River above Waikoropupu confluence, Motupipi River and adding estimates for the submarine springs.  For example the calcium content of the Pupu Springs water is 62 parts per million and the average flow is 15 cubic metres per second.  This equates to 2.2kg of dissolved limestone and marble pouring out every second; the calcium content of the Takaka and Motupipi River water is smaller but their combined flow volume is larger.

Dissolving of the limestone and marble occurs first along zones of weakness, such as bedding planes. fractures and fault lines.  Into these cracks water penetrates first and ever so slowly the cracks widen and cavities form within the carbonate rock.

This process has been happening for at least the last two million years in the Takaka catchment, since these rocks were exposed by erosion to surface waters.  There are indications that the same process was active in the Arthur Marble sixty to forty million years ago, but traces of these earlier events are obliterated by dissolution in the last two million years.

The carbonate rocks are found in about 21Okml of the catchment.  At the measured dissolution rate of 5kg/s, the thickness of the limestone and marble is reduced by 0.277mm every year.  This may not appear much but over a period of two million years this adds up to more than 500m.

Theoretically it takes only 17,000 years to dissolve one cubic kilometre of marble and limestone in the catchment and create cavities of that volume.  But this is counteracted by the fact that much of the dissolution occurs near the surface of the marble (Takaka Hill) and no actual cavities are formed.  Furthermore caves in the subsurface become after a while too large and they collapse.  These cave collapses are often printed through to the surface as can be observed in Hamama and West Takaka.  The water entering the cave systems often contain, during periods of high rainfall, mud, silt, sand and pebbles which fill up part of the cave system.  This sedimentation is counterbalancing the volume loss by the dissolution process.  As a result of all these events the present day cave volume underneath the Takaka Valley is about 1.5kml. That is only the caves which are permanently filled with water.

Caves in the hills east and west of the valley are above the water table and are dry for most of the time.  In these caves some of the calcite precipitates and stalactites, stalagmites and other decorations form.  The caves above and below the water table are distinctively different – called vadose and phreatic.  The dissolving potential of water depends on its temperature, acidity, carbon dioxide content and the presence of other dissolved salts.  Carbon dioxide is the most important dissolving agent.  It is present to some degree in the atmosphere and in the rainwater. But most originates from bacterial activity in the top soil through which rainwater percolates.

The outcome of all this dissolving activity, and underground cave formation, is that Kitty Creek, Dry River, Rameka Creek, Gorge Creek, Scott Creek, Craigiebum Creek, Washaway Creek and Stony Creek go underground and disappear into the cave system as soon as they meet the limestone and marble rocks on their course.  Only at very high flows some of the water spills down the lower parts of the creeks.  The Takaka River is connected to the cave system between Lindsay’s Bridge and Gorge Creek, over a distance of 4.5 km.  About ten cubic metres of the river flow disappear in this stretch of the river every second into the subterranean system.  At times the flow of the Takaka River above Lindsay's Bridge is less than 10ml/s and subsequently the river falls dry below Lindsay's Bridge.

This is little observed as the course of the Takaka River is not visible from S.H. 60 between Payne's Ford and Lindsay's Bridge.  Near Hamama artesian springs, the Spring Brook Springs, are discharging into the river and the river starts flowing from there again.  Further artesian  Springs are present on the right bank of the river in East Takaka.  In the summer of 1986/87 I walked from Hamana to Lindsay’s Bridge through the dry river bed for a distance of 10km, somehow an eerie feeling.  The water level can fall as much as 20m below the river bed level.  The total depth of the aquifer within the marble can be as much as 300m below the valley floor.  One Bore in East Takaka showed that freshwater flows in limestone exist 84 metres below sea level.

The Cobb Hydro Electricity scheme operates only during peak demand periods and releases up to 7M3S. These water pulses can be traced through the cave aquifer system and be noticed for example 13 hours later in the Pupu Springs as a slight increase in flow of about 70 litres per second.  The new Catchment Board water test bore at Hamama records all these water level and flow changes and gives excellent information on the aquifer which might become important for future horticultural development.

The water flow speeds in the aquifer are on average about 2 metres per hour and the water reappearing in the Pupu Springs is about two years old.  The submarine outflows of this aquifer are not studied at present.  My assumptions are that these outflows are contaminated by seawater intrusion into the aquifer and are not suitable for pumping onto ships to be exported to California.

Salt water is heavier than freshwater and replaces it in the lowermost levels of the aquifer system.  This salt water wedge is estimated to reach about ten kilometres inland and be present underneath Takaka township (at great depth).  An indication for this salt water intrusion is the slight salinity of the Pupu Springs which discharge about 50 litres of sea water every second. This water is presumably brought up by venturi mixing effects when the freshwater flows towards the sea over the lower salt water wedges.

MARBLE, LIMESTONE AND WATER - THE TAKAKA KARST
Mike Mueller

Many articles have been written in the Community News on the subjects of local history, native plants and horticulture. I thought it to be complemental to add some notes on the rocks of Golden Bay. For me, the most interesting rocks are the marble and limestone because they influence all groundwater movements in the Takaka Valley.  They are the reason that all tributaries of the Takaka River are dry for most of the year.

The two rocks are easily distinguished: the limestone is light grey to cream and the marble in most cases dark grey-blue; fossils are very common in the limestone and absent in the marble; freshly broken limestone has a dull surface and marble sparkles in the sunlight.

Both rocks have formed in a shallow sea with a tropical climate where the seascape looked similar to the Great Barrier Reef in Australia.  Corals and other organisms extracted calcium from the sea water to build their skeletal structures of Calcium Carbonate (CaCO3).  The remains of these organisms accumulated over a period of time, and with continuing subsidence of the sea floor great masses of carbonate piled up.  These early limestones were buried under hundreds of metres of sand and clay.  Tectonic earth movements carried the compacting rock even further down until solid limestone formed.

If this sinking is continued to a depth of several kilometres, the rock will heat up to several hundred degrees and at the same time be subject to intense pressure.  Under such conditions the limestone compacts even further and partially melts.  At this point the limestone metamorphoses into marble.  All fossils are destroyed and a new crystalline structure forms in the rock.

In the Takaka Valley both rock types are present and they originate from different ages.  The Arthur Marble formed in the Silurian, 420 million years ago (700m thick).  The Takaka Limestone in the Tertiary, Oligocene, 25 million years ago (60m thick).  The marble had gone through a period of deep subsidence, whereas the limestone after shallow subsidence was redirected to the surface by the vagrancy of underground molten rock currents.

Both rocks are soluble in water which makes them different from any other kind of rock (CaCO3+H2O+CO2 = Ca (COH3)2).  As soon as these rocks are in contact with groundwater they react and a dissolution process starts along fissures, joints and bedding planes.  Over periods of time large cave systems are thus formed within the carbonate rocks.  Sometimes these caves collapse and circular depressions of 2m to 100m diameter form on the land surface above.  Many of these depressions can be observed right and left of SH 60 between Hamama and Upper Takaka.

Underneath 5 to 70m thick gravel in the Takaka Valley a large cave system, with a volume of about 1.5km3 exists in the Arthur Marble and Takaka Limestone.  Into these caves disappears all the water from Scott Creek, Gorge Creek, Rameka Creek, Dry River, Kitty Creek, Stoney Creek, Washaway Creek, Craigieburn Creek.  Sometimes even the Takaka River runs dry in its middle course.  Downstream of Lindsay's Bridge, 10m3 of water disappears every second into this karst aquifer underneath the Takaka River.  Most of the water comes out again in the Motupipi Springs near the Dairy Factory, and in the Pupu Springs.  Further outflows of this aquifer are artesian springs on the banks of the Waingaro and Takaka River, and submarine springs in front of the Takaka River mouth.

The cave system within the carbonate rocks is more than 200m deep, and is thought to have formed mainly in the early Tertiary, 60 million years ago.  After a long period of subsidence below sea level it was reactivated during the ice ages of the Pleistocene, when sea levels were much lower (-270m).

This process of dissolution is ongoing and water analyses from the Pupu Springs have shown  that 62ppm calcium are present in the spring water.  The water outflow rate of the springs is on average 15m3/s.  This translates to the fact that during one year 70,000 tons of dissolved carbonate rock pour out of the springs.  Taking these calculations to the extreme, and considering other analyses and water outflow rates, one arrives at the conclusion that, every second, 5 Kilograms of marble and limestone dissolve in the catchment of the Takaka River (277m3/year/km2 of).

The rock outcrop on the Pikikiruna Range, east of Motupipi and East Takaka, are mainly marble. The lower slopes are covered with limestone and a band of Motupipi Coal Measures.  Marble is most easily accessible at Hamama and West Takaka and of course on the top of the Takaka Hill. The area around the Limestone Works, The Grove and Paynes Ford give the best outcrops for limestone.

These dry creeks, artesian springs and sinkholes could only have developed because the landscape of the Takaka Valley is made up of large thicknesses of soluble marble and limestone. This situation is unique for New Zealand and rare in other parts of the world.  The closeness to the sea creates other special circumstances and a parallel is only found in Yugoslavia.  The submarine springs show that the cave system continues beneath the sea.

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