Nature Conservation Council

Information Booklet No. 28

Text by: Bruce W. Hayward, New Zealand Geological Survey; Beth Vaughan and Jack McConchie, Geography Department, Victoria University of Wellington.

Edited by Valerie Tait, Secretary, Nature Conservation Council.

Published by: Nature Conservation Council

PO Box 12-200

Thorndon

WELLINGTON

1988

ISBN 0-473-00603-0

It is widely acknowledged that population pressures and modem technology have had a detrimental effect on New Zealand's flora and fauna. Less readily appreciated is the parallel damage to landforms, soils, and geological features. Especially vulnerable are the more fragile, such as geysers, sand dunes, lava caves, fossil sites, fault traces, and unmodified lowland soils. Landforms of economic worth, such as estuaries and scoria cones, are also at risk.

It is important to have sites for education and research, as well as a wide diversity of landforms and features retained for aesthetic appreciation and recreational use. It is essential, therefore, to take stock of what there is, identify features and groups of features under threat, and take steps to protect the best remaining examples. This is what geopreservation seeks to do.

This booklet describes how the land that became New Zealand was formed, outlines its major landforms and geological features, and discusses their values. The booklet concludes with a brief description of the Geopreservation Inventory, a first step in preventing, or at least minimising, further loss or damage to this important part of our heritage.

New Zealand's present form emerged over a long period of time through the complex interplay of a wide variety of processes. These processes can be constructional (volcanoes delta formation, fault uplift) and destructional (stream erosion, wave attack, limestone solution, downtilting). Many of the processes are imperceptible and have been moulding New Zealand for hundreds of millions of years. Although they continue to transform the landscape, their impact appears slight when compared with the modifying forces of modern society.

The study of the composition, structure, and history of the earth and the processes that have given rise to its present state is called geology. Most of the clues to the geological history of New Zealand are still hidden in the rocks awaiting study and interpretation by geologists. Superimposed on the geology is a wide variety of landforms which contain a record of past and present processes that can be unravelled by geomorphologists.

The rocks and their contents tell us that the earth was formed about 4500 million years ago, that New Zealand's history began at least 680 million years ago, and that a complicated series of events since then has combined to produce the country we know today. These events not only produced the landforms and shape of New Zealand, but also played an important role in the development of its unique plant and animal life. The rocks can tell us a great deal about the past geographies and climates of New Zealand and their enormous influence on this flora and fauna.

Most of the processes that mould the landscape are strongly influenced by forces at work deep within the earth. The earth's S to 3S kilometre thick outer layer, known as the crust, is broken up into a jigsaw puzzle of jostling segments called plates. For hundreds of millions of years, movement in the molten mantle beneath the earth's crust has made the plates shift in different directions. Like ice floes on the sea, the plates jostle each other about, sometimes colliding and overriding one another, scraping sideways past each other, or pulling apart.

Until about 100 million years ago, the New Zealand region was on the margin of the huge Gondwanaland plate which included all the southern hemisphere continents grouped together. Then gradually Gondwanaland split into a number of separate plates and, between 85 and 60 million years ago, New Zealand split away from Australia and Antarctica, forming the Tasman Sea.

New Zealand owes much of its present shape and character to the constructional processes of mountain uplift, faulting, and volcanism that result from its position astride a collision boundary between the Indian and Pacific plates. For the past 30 million years tremendous forces have been concentrated within this broad collision zone. They have pushed up the high mountain chains, split the country in two, and slid the eastern part hundreds of kilometres south. In the north, the leading edge of the Pacific plate is being pushed beneath the Indian plate. As it descends, the crust melts and forms molten magma which rises to the surface and erupts as volcanoes in the North Island.

Following its origin some 4500 million years ago, the molten earth cooled on the outside to form a solid crust of rocks. Much of this was eroded by natural forces, the resulting fragments being carried by rivers and redeposited, mainly in the sea. Some of the rocks remelted at depth, then solidified again as they intruded up towards the surface. Many of the deeply buried crustal rocks were greatly changed by the intense pressures and heat.

These complex forces have produced a wide variety of rocks, classified by character and origin into three groups: igneous, sedimentary, and metamorphic. Study of these rocks provides clues to New Zealand's past.

Igneous rocks are formed when molten magma originating deep within the earth moves upwards through the crust. Sometimes it comes to rest in large underground chambers and eventually cools. Magma that solidifies in these chambers cools very slowly, allowing large crystals to grow and from coarse crystalline plutonic rocks, such as granite. The magma can also reach the surface through pipelike necks or fissures and erupt as hot lava. This cools quickly to form finer-grained volcanic rocks, such as rhyolite, andesite, and basalt.

Magma has been generated, volcanoes have erupted, and plutonic and volcanic rocks formed throughout the earth's history. The presence of volcanic rocks exposed in cliffs and riverbeds tells of eruptions going back throughout New Zealand's history. These rocks can also provide evidence of former plate splitting and collision events in the even more distant past. The matching of granites in New Zealand and Antarctica, for example, provides evidence of the geometry of Gondwanaland. Recognisable volcanic landforms can be seen only in the younger volcanoes that have erupted in the last few million years.

The study of ancient igneous rocks can also help in understanding the formation and occurrence of many metallic minerals. In New Zealand, deposits of tin, tungsten, molybdenum, copper, gold, and silver all occur in association with igneous rocks.

Sedimentary rocks formed from sediments, such as mud, sand and gravel, that accumulated in layers on the floor of the sea, lakes, or river valleys. These sediments have been compacted and often cemented to form rocks. Special kinds of sedimentary rocks include limestone, formed by the accumulation and cementation of shellbeds, and coal, formed from plant material that accumulated in peaty swamps and was compacted by burial.

Sedimentary rocks occur in layered sequences, or strata, that record the passage of time, the oldest layers on the bottom and successively younger ones on top. As more and more layers accumulated, the deeply-buried bottom ones were compressed into rock. Subsequently, many of these sequences have been disturbed by earth movements and the once horizontal layers tilted, broken into blocks by huge cracks called faults, or bent into vast folds. Some of these sequences have also been uplifted and partly eroded away before further layers have been deposited on top of them. The original, ordered structure of the layered sedimentary rocks is therefore often disrupted.

Sedimentary rock sequences may be exposed in coastal cliffs, river beds, bluffs on a hillside, or roadside cuttings. The best and most reliable information from the sedimentary rocks is obtained from good exposures of thick sequences. Studied in detail, they are often designated the "type sequence" for different units of rock and then used as a standard against which all the other less well-preserved exposures of rock in the area are compared. Type sequences are like chapters in a geologist's history book. Collectively, they contain the record of New Zealand's development which has the fewest number of missing pages. Several important type sequences are already legally protected, but a number of others are still under threat.

Detailed studies of sedimentary rocks can tell us a great deal - their age; what the particles of rock are made of, where they came from and how they were transported to their final resting places; and what kind of environment the rocks were deposited in, whether freshwater, intertidal or deep sea, a quiet backwater or storm-swept beach. When this information is combined with that from other layers and from other sequences throughout the country, geologists are able to determine what the past geography of the New Zealand region was like and how it has evolved.

Metamorphic rocks, such as schist, slate, and marble, are igneous or sedimentary rocks that have been greatly changed by enormous pressures and heat, usually as a result of deep burial or contact with super-hot magma.

Many metamorphic rocks have been pushed up from great depths by plate boundary collision forces and now form the landscape in many parts of the Southern Alps and Central Otago. Study of these rocks is important in understanding the forces deep in the earth that helped produce New Zealand. In addition, valuable minerals, such as gold, silver, and tungsten, can be found in ore bodies associated with metamorphic rocks.

Rocks are made up of various combinations of minerals, of which there are over 3000 known, but only about 150 commonly found. With most minerals occurring in characteristic geological settings, detailed studies are essential in understanding how and where they form and, for those with economic value, where they should be sought. For example, gold often precipitates from hot hydrothermal fluids at depth. Accumulating in quartz reefs, it may later erode out and concentrate in stream or river pools as placer deposits.

An understanding of how minerals form and alter can help resolve the history of the rocks of an area and also its past geography. Several New Zealand localities have been the sites of the first discovery and description of previously unknown minerals. Other sites show key associations and sequences of mineral formation. These sites provide invaluable material for scientific study and educational purposes.

All rocks are susceptible to great pressures in the earth which may pull them apart along faults or compress them into series of folds. Sometimes several episodes of folding and fracturing can be recognised, each possibly recording a major collision event in the history of the area. Some of the folds and faults are small and can be seen in exposures of rock the size of a car, but many are much larger and only become apparent when data from many exposures are combined.

Fossils are traces or remains of ancient plants or animals preserved in rock. Most fossils consist of the hard parts of an organism, such as seashells, teeth, bony skeletons, or woody branches. Macrofossils are large and easily visible (seashells, bones and leaves), while microfossils are small and microscopic (pollen, spores, skeletons of algae, and protozoa). Macrofossils occur in abundance in sedimentary rocks in many parts of New Zealand. In some places, for example limestone areas, the rocks are composed entirely of them. Microfossils, although difficult to see, are even more common and occur in vast numbers in most sedimentary strata.

Fossils have a unique place in New Zealand's natural heritage. They link the biological and earth sciences by providing the only reliable evidence of the beginnings of life in the region, as well as the only tangible material for the study of evolution. New Zealand fossils record the development of life from early forms, such as trilobites and graptolites, through ammonites and dinosaurs to the appearance of flowering plants, birds, and finally humans.

Fossils also provide valuable clues about the region's climate and geography over the last 500 million years. They can tell us how warm, cold, wet, or dry it was and also of the presence of former forests, lakes, swamps, estuaries, beaches, shallow harbours, or deep ocean basins - all vital information in piecing together the history of this changing land.

The most important use of fossils is in dating the rocks in which they occur. Through studying fossils in the sequences of sedimentary strata geologists have been able to determine the processions, or evolution, of life through geological time, so that now the ages of rocks can be deduced from their fossil content. Ages are quoted in terms of the succession of life forms, for example age of dinosaurs, age of trilobites. In recent years the ages of rocks have been calibrated against an absolute time scale (millions of years) that has been determined using the known rate of decay of certain radioactive elements present in the rocks.

The study and understanding of New Zealand geology requires accurate dating of rock sequences. Because of its geographic location, New Zealand does not have many of the detailed successions of fossils used for dating in other parts of the world. So geologists here have had to study a unique succession of fossils in great detail. They have divided geological time in the region into as many easily recognisable time periods as possible. As with sedimentary rocks, these detailed studies require well-exposed, thick sequences of fossil-bearing strata. The best of these have been designated type sequences for selected intervals of geological time in New Zealand.

Erosion has removed the characteristic form of most volcanoes extinct for more than about a million years. In New Zealand, the younger volcanoes with preserved landforms are all in the northern and central North Island, where the Pacific Plate is being pushed under the Indian Plate.

Volcano shapes and types of eruption depend on the character of the magma and whether the eruptions are onto land or through water. Magmas rich in silica produce the most viscous lava and often the most violent eruptions; those low in silica produce the most fluid lava and usually the quietest and most predictable eruptions. Magma is a mix of liquid rock, crystals, and dissolved gas. Magma with low gas content erupts as lava flows or squeezes up as viscous domes. It may be full of dissolved gases which, on reaching the surface, are released explosively, blowing the lava into fragments that are ejected into the air as ash, pumice, or scoria.

This wide variety of magma types and physical settings produces a diversity of volcanic landforms - the large cones of Egmont and Ruapehu, the vast volcanic plateau of Mamaku and Kaingaroa, the collapsed giant craters of Lakes Taupo and Rotorua, the small scoria cones of Auckland and Whangarei, and the explosion craters of Orakei Basin and the Tama Lakes.

Hot springs, fumaroles, geysers, and mudpools are all hydrothermal features formed by the surface discharge of hot water or steam that has been heated to high temperatures by a heat source deep in the earth. These features are often found in association with recently-active volcanic centres. Hot, mineral-rich water flowing out of the ground at springs may deposit silica in the surrounding area and slowly build up sinter terraces. An outstanding example of these were the Pink and White Terraces which were destroyed in the Tarawera eruption in 1886. Bright yellow sulphur crystals often precipitate around the mouths of hot fumaroles, algae produce orange, yellow, and green colours in the cooling discharge waters.

The most spectacular hydrothermal features are geysers that periodically shoot boiling water and steam into the air through a narrow vent. As slight modification of the vent of a geyser or of ground water levels can be sufficient to stop eruption, geysers are rare and precious. Known only in seven countries, they are easily accessible only in the United States, Iceland, and New Zealand. Indeed, New Zealand's geysers, rivalled only by those at Yellowstone in the USA, are the most impressive in the Southern Hemisphere.

Because of New Zealand's location on a plate boundary, it is the site of active earth deformation caused by stresses between the two colliding plates. The crustal rocks accumulate this stress, which results in earthquakes when it is periodically released by the failure or breaking apart of large areas. The failure usually occurs along faults which break through at the surface, forming lines of breakage called fault scarps (banks or cliffs) that cut across the landscape.

Study of these fault scarps shows how often they have moved in the recent past. Information on past movements gives an indication of how soon faults may move again and result in a devastating earthquake. These faultlines also play an important part in the development of the landscape, upthrusting hills on one side and downthrowing valleys on the other.

Other obvious earthquake-related features include raised and tilted beaches and raised and displaced river terraces. Softer rocks may not fracture along faults in this brittle fashion, but, as strain accumulates, they may buckle upwards to form active folds that can be seen as warped surfaces of formerly fat terraces.

Geomorphology is the study of landforming processes and the mechanisms which drive them. These processes lead to the rearrangement of materials, building up or wearing down landform features over millions of years or, in the case of eruptions or earthquakes, in just a few seconds.

A physical system cannot be separated from the social, cultural, and economic attitudes and conditions of the people living in the area. Applied geomorphology looks at these interactions of landform, process, and society. Societies are not only affected by natural events, but can themselves manipulate the environment and influence natural processes and their effects, either beneficially or catastrophically. In a more passive way, societies have always made use of naturally-occurring landforms, settling usually in river valleys or adjacent to harbours.

There are a number of reasons why New Zealand's landforms and geological features should be valued and, in some cases, given legal protection.

Aesthetic and Recreational Values The wide variety of landforms and geological features found in New Zealand gives us a rich and varied natural environment. Tourism, one of New Zealand's largest and fastest-growing industries, depends to a great extent on this diversity of landforms in a relatively small area. The many outdoor activities enjoyed by New Zealanders and overseas visitors, from picnicking to mountaineering, also need a variety of areas available throughout the country.

Physical features associated with the landscape give people a sense of place, a means of orienting themselves within the natural world. Spectacular and inspiring natural features like mountain ranges, fiords, glaciers, and geysers have intangible but nonetheless important values. Many smaller features, too, because they are unusual or scenically attractive, provide a more stimulating, interesting environment.

As more and more people live in towns and cities, outdoor education is becoming increasingly important. Many people enjoy studying the natural world, either individually or with organisations or clubs. The study of natural resources plays an important part in the education system, too, particularly in science and geography. It also helps people become aware of the relationships between their activities and natural systems and of the fact that many resources needed by modern societies could well run out.

A wide range of accessible and easily interpreted landforms and geological features must be set aside for educational use. These protected examples would help us to see ourselves in perspective. They preserve evidence of a grand process which preceded humans, has affected their history, and will shape their future.

Landform features and geological exposures are the essential ingredients of almost all earth science research - research that is required to understand the processes that have 'formed the world, continue to modify it, and sometimes threaten human lives and property. It also tells us where resources such as petroleum, natural gas, silica, road aggregate, concrete, soils, iron, aluminium, and coal can be found and in what quantities.

While larger and more robust landforms and geological features can withstand the impact of natural processes and human activities with little effect, many smaller scale and more fragile types cannot. Examples of features threatened with total destruction include estuaries, spits and tombolos, sand dunes, moraines, kettle lakes and tarns, fault traces, limestone topography, scoria cones, geysers, mud pools, fossil and mineral sites, and small rock exposures.

Erosion and weathering are slowly eating away at most features, but they are also responsible for maintaining systems such as sand dunes, deltas, moraines, and badlands in a healthy state. Unless natural erosion has been modified by human actions and now threatens significant features, there seems little justification for interfering with nature's course.

The largest extractive industry in New Zealand is aggregate quarrying for building, road making, and railway lines. Its impact on river beds has vastly altered the natural erosional and constructional processes. Elsewhere, such as in Auckland city, whole volcanic cones have been quarried away.

Sluicing, dredging, and mining for alluvial gold continue to have a major effect on fluvial and terrace features in Central Otago and on the West Coast.

Increased peat harvesting is threatening New Zealand's remaining undrained peatlands, such as those on the Hauraki lowlands.

Major works like dam construction, irrigation schemes, airports, refineries, and smelters also damage landforms and geological features. When such projects are being planned, important physical features should be given as much consideration as flora and fauna values and economic benefits.

Geothermal fields in the central North Island are an important part of New Zealand's heritage and are particularly significant in Maori culture and tradition.

Last century, there were over 130 geysers regularly active in five major hydrothermal fields in the Rotorua-Taupo area. Since then, one field has been buried by the Tarawera eruption, Orakeikorako drowned by damming the Waikato River, Wairakei and Spa fields destroyed by exploitation of steam for electricity generation, and a number of Whakarewarewa geysers have ceased because of over-use of the hot water. Today, fewer than 15 geysers remain active. Eight of these, including Pohutu, the most spectacular and regular, are at Whakarewarewa.

In 1979, the Nature Conservation Council commissioned an assessment of the remaining values of the 88 hydrothermal areas in New Zealand. This was undertaken by the Geological Society of New Zealand. Their subsequent report recommended complete protection of Whakarewarewa, Waimangu, Ketetahi, and White Island fields and also the deferral of any exploitation of seven others which had significant discharge features. Government policy now largely follows these recommendations.

As cities spread, the irregular beauty of the countryside is levelled by large, earth-moving machines to accommodate housing, motorways, railways, water, gas, sewage, and electricity reticulation. In the process, a wealth of geomorphic information and the aesthetic values of a diverse and interesting landscape are destroyed.

Agriculture and horticulture have had a substantial impact on New Zealand's landforms and geological features. Forest clearance for farmland accelerated erosion, modifying natural watercourses and steep mountainsides and rapidly infilling swamps and lakes. Almost all of New Zealand's natural freshwater wetlands have been drained to provide more land for production. The natural soil profile has been disturbed over vast areas, making it extremely difficult to find unmodified lowland soils for baseline studies.

Many valuable exposures of rock have been produced during roadmaking and quarrying. Well-intentioned efforts to rehabilitate these scars by spraying road cuts with grass seed or backfilling quarries with rubbish have destroyed many cuttings that were of scientific and educational importance.

Exotic forests now cover large areas of New Zealand. Planting processes disturb the natural soil profile and bulldozed forestry tracks scar many landscapes. More significantly, in many coastal areas, forest planting has threatened the very existence of representative examples of active dune systems.

The erection of barriers to slow the rate of coastal or river erosion often obscures valuable rock exposures and can also interfere with natural erosional and depositional systems. Stabilising foredunes behind a beach, for example, may cut off the sand supply to an important, active dune system further inland.

Reclamation of land from the sea constitutes another threat to valuable landforms. The provision of rubbish tips, sports grounds, industrial development, and farmland has meant the destruction of thousands of hectares of estuaries, salt marshes, mangrove swamps, and natural coastline.

Rare mineral specimens, fossils, and natural artifacts are all vulnerable to overcollecting by scientists, rock hunters, and commercial operators. Some specimens should be deposited in museums where they can be studied in detail and interpreted in displays for the public's benefit, but in many instances they are best left in the rocks so that information about their settings can also be obtained.

While it is in New Zealand's economic interest to protect those natural assets that draw the tourist dollar, it is equally important to be aware of the damage increased human impact can do to some features. For example, with more people visiting the Waitomo caves, increased carbon dioxide levels in the passageways may affect delicate stalactite structures. Tourist facilities, such as skifields, marinas, and walking tracks, all need careful planning to minimise damage.

Many people take landforms and geological features for granted and often exploit them. A small number of scientifically important or obviously spectacular features are now legally protected; but no systematic regional or national assessment has been made of where they are, how many others are threatened, and how many need further protection.

To ensure the survival of the best examples of the broad range of physical features and processes found in this country, the New Zealand earth science societies* are compiling a geopreservation inventory of all nationally and regionally important sites. The aim is to identify and protect a full cross-section of the natural landforms, geological features, and soil types which best characterise each part of New Zealand, including the commonplace as well as the unique and spectacular.

Selected features will illustrate the different stages of New Zealand's geological history and the physical processes which have combined to produce its present landscape. Each listed site will be given ratings based on its scientific and educational value and its vulnerability to modification or destruction by human activity. A list will be compiled from these ratings of the most important and most threatened sites which should be given priority for protection. Biological surveys are being carried out under the Department of Conservation's Protected Natural Areas Programme. Combined with the Geopreservation Inventory, they will provide an integrated approach to the future management and protection of New Zealand's valuable natural resources.

*Geological Society, Geographical Society, Geomorphological Group, Soil Science Society, Speleological Society, Institute of Landscape Architects.

Forsyth, P. J. 1985: A beginner's guide to New Zealand Rocks and Minerals. Government Printer.

Soons, J. M. and Selby, M. J. (eds), 1982: Landforms of New Zealand. Longman Paul.

Stevens, G. R. 1974: Rugged Landscape: The geology of central New Zealand. Reed.

Stevens, G. R. 1980: New Zealand Adrift: the theory of continental drift in a New Zealand setting. Reed.

Thornton,J.1985: Field Guide to New Zealand Geology. Reed Methuen.

Geological Society of New Zealand Guidebook Series:

• No 3. Ancient Undersea Volcanoes. (Muriwai, Auckland)
• No 4. Geyserland. (Rotorua)
• No 5. Walks through Auckland's Past. (Rangitoto, Motutapu)
• No 6. Cobb Valley (N.W. Nelson)
• No 7. Extinct Volcanoes (Banks Peninsula)
• No 8. Granite and Marble (Building stones)
• No 9. Queenstown