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Geomorphology – a history

by  Rebecca Priestley

When James Cook and his crew first saw New Zealand, in 1769, they probably believed the land had been shaped by the biblical Great Flood. But why was this dramatic landscape so different from England? A century later, science had begun to find the answers – in particular, it had become clear that the land was constantly changing.


Early ideas

A dynamic landscape

When James Cook first arrived in New Zealand, in 1769, the ship’s naturalist, Joseph Banks, described the country as ‘in general mountainous, especially inland, where probably runs a chain of very high hills’. 1 It would fall to future explorers and surveyors to map the country’s interior, but it was already clear that New Zealand, with its high mountains and fast-flowing rivers, was very different to England, which had rolling hills and sluggish rivers. What made New Zealand’s landscape so dynamic?

Pre-scientific ideas

At the time of Cook’s visit, most Europeans believed in the biblical creation story, which said that God had made the world in seven days (estimated to be 4004 BC), and that catastrophic events like the Great Flood shaped the land.

Māori had their own traditions. After the legendary hero Māui fished up the North Island with his magic hook, the landscape was formed by fire-brandishing tohunga and powerful ancestors. Lakes were hollowed out with digging sticks, and volcanoes showed where fires were lit. Waka (canoes), the ancestors who sailed in them, and the cargo they carried became manifest as the mountains, hills and rocks.

Uniformitarianism: ongoing processes

Scientists who studied the landscape had other explanations. By the mid- to late 19th century, the study of how landforms were created (later called geomorphology) was dominated by the theory of uniformitarianism. This suggested that landscapes were formed by continuous or ‘uniform’ natural processes. The present was the key to the past, and the earth’s shaping forces were still active. For example, erosion by rain, rivers and the sea shaped the land’s surface, and earthquakes and volcanoes caused uplift.

First descriptions

The first European geologists to systematically describe New Zealand’s landforms were Ferdinand Hochstetter and Julius Haast. In late 1858 and during 1859 Hochstetter and Haast travelled to Auckland, Waikato, the central North Island and Nelson. Haast later surveyed west Nelson and Canterbury. Hochstetter wrote widely about New Zealand over the next decade, in German and English, and incorporated many of Haast’s ideas about the South Island. Hochstetter’s influential book New Zealand: its physical geography, geology and natural history (1867) was the first to use uniformitarianism to interpret the New Zealand landscape.

Hochstetter was very perceptive. For example, he suggested that the lake basins of the ‘volcanic Taupo Zone’ formed in depressions (calderas) created after major volcanic eruptions. He also recognised Lake Taupō as a major source of the pumice found throughout the North Island.

Footnotes
  1. Joseph Banks, Journal of the Rt Hon Sir Joseph Banks. London: Macmillan, 1896, p. 222. › Back

The extent of glaciers

A ‘Great New Zealand Ice Period’?

In the mid-19th century a Swiss scientist, Louis Jean Agassiz, promoted the idea that northern Europe’s glaciers were the remnants of an ancient and more widespread glaciation. He pointed out striated rock surfaces and moraines (gravel deposits) that could only have been created by glaciers. Geologist Ferdinand Hochstetter noticed that Nelson’s Lake Rotoiti resembled the moraine-dammed lakes he had seen in Italy, and saw it as possible evidence of a similar glacial period in New Zealand.

Lyrical landscapes

Julius Haast loved the outdoors, and delighted in the scenery while he studied the landscape. In 1861, describing the headwaters of the Rangitātā River, he wrote lyrically of ‘beautiful waterfalls’, mountains ‘towering to the blue heaven’, and glaciers ‘shining like molten silver’.

Julius Haast extended Hochstetter’s work. He found evidence – including lakes and fiords made by glacial erosion, and other landforms shaped by glacial deposits – to support what he called the ‘Great New Zealand Ice Period’. Haast mapped numerous moraines in the Southern Alps that marked the extent of glaciers at different periods.

Glaciers and the Canterbury plains

Haast compared small gravel fans in the Southern Alps with the immense fans that made up the Canterbury Plains and could be traced up the valleys to glacial moraines. If little streams could form small fans, he surmised, then the Canterbury Plains ‘were formed by the deposits of huge rivers issuing from the frontal end of gigantic glaciers’. 1 Some contemporary scientists, including Otago provincial geologist Frederick Hutton, refused to believe that glaciers could create landforms, claiming instead that the gravel plains were uplifted sea-bed deposits. But Haast’s view was soon widely accepted.

The extent of glaciers

New Zealand, like Europe, had undergone a major glaciation, but there was debate over its extent. In 1910 James Park, professor of mining at Otago University, suggested that glaciers had once covered much of New Zealand, and were part of a vast ice sheet originating in Antarctica. This theory was disputed by Patrick Marshall, professor of geology at the university, and there was a vigorous public debate. The issue was settled in Marshall’s favour when Leslie Adkin, a young amateur geologist, showed that only the highest peaks of the North Island’s Tararua Range had been affected by glaciers.

Multiple glaciations

In the first decade of the 20th century the Austrian earth scientists Eduard Bruckner and Albrecht Penck identified four distinct European ice advances or glacial periods, separated by interglacial periods. It was not known if these were local or global, but a search began to correlate the European ice advances with those in New Zealand and elsewhere. By the 1920s, Robert Speight and other geologists had found evidence for multiple glacial periods in New Zealand.

Today, it is agreed that in the last 2.5 million years there have been about 30 global periods of glaciation, alternating with warm periods (interglacials), when the climate was similar to that of today. Almost all the glacial deposits now seen in the South Island are from the last two or three glacial periods. The deposits from earlier ice ages have been largely obliterated by erosion.

Footnotes
  1. Julius von Haast, Geology of the provinces of Canterbury and Westland, New Zealand: a report comprising the results of official explorations. Christchurch: Times Office, 1879, p. 396. › Back

Key theories: 1880s–1940s

Darwin and landscape evolution

Charles Darwin’s theory of biological evolution, introduced in his 1859 book Origin of species, influenced earth scientists. It contributed to the idea that landscapes gradually evolved from one form to another.

William Morris Davis’s cycle of erosion

In 1884 an American geomorphologist, William Morris Davis, proposed a ‘cycle of erosion’ – all landscapes were formed when blocks of land were rapidly uplifted and then eroded, in a sequence of stages: youth, maturity and old age. Normal erosion was the work of rain and rivers, but in other places wind and sea could be the main agents. Volcanoes and glaciers also had an impact. It took millions of years of tectonic and climatic stability for a cycle of erosion to pass through all its stages. In old age, the landscape had worn down to a peneplain – almost flat, with an elevation near sea level.

Charles Cotton

Davis came to New Zealand in 1914, and his ideas influenced a number of earth scientists. In particular Charles Cotton, geology lecturer at Victoria University College in Wellington, found Davis’s cycle of erosion useful for interpreting the development of the New Zealand landscape. Like Davis, Cotton used diagrams to show a progression of the land from youth, through maturity to old age.

Cotton’s ideas came together in his first and most influential book, The geomorphology of New Zealand (1922), which was revised and reprinted many times in the 50 years following its publication. He wrote several more books, including Volcanoes and landscape forms (1944).

Cotton and McCahon

Charles Cotton’s carefully illustrated books influenced many earth scientists, and a few artists too. In 2000 the Adam Art Gallery in Wellington held an exhibition, ‘An artist and a scientist’, bringing together the work of Charles Cotton and landscape artist Colin McCahon, New Zealand’s most acclaimed 20th-century painter. The exhibition celebrated the role Cotton’s illustrations had played in McCahon’s painting.

Because of their clear illustrations, Cotton’s books were widely used as geography textbooks. Several generations of students used his methods of observation and learnt to draw simple diagrams in his distinctive style.

Tectonic landforms

Cotton expanded the ideas of geologist Alexander McKay. In 1886 McKay had suggested that uplift of mountains along fault lines during earthquakes influenced landscape evolution. Cotton realised that the South Island’s Kaikōura ranges had been formed by the splitting and uplifting of blocks of the earth’s crust. From this, he argued that the whole of New Zealand was ‘a concourse of earth blocks’. At the time, the idea that movement along a fault could produce uplifted blocks and mountain ranges was revolutionary. Cotton wrote several papers on the identification of faults in the landscape, describing features such as fault traces, abruptly blocked valleys, and shutter ridges.

In 1941, two young geologists, Harold Wellman and Dick Willett, identified the huge Alpine Fault that bisects the South Island. Wellman was one of Cotton’s students, and both he and Willett were influenced by Cotton’s ideas.


Mid- to late 20th century ideas

Geography as an academic subject

Geography is the study of the land (including geomorphology), and how people live on it. Although widely taught in New Zealand schools, geography was not regarded as a respectable university subject until the mid-20th century. In 1937 George Jobberns was appointed to be the first geography lecturer at Canterbury University College, and by 1950 all the universities were teaching geography.

As taught by Charles Cotton and his contemporaries, geomorphology was the description and classification of landforms. From the 1960s, a younger generation of earth scientists became interested in the processes responsible for landscape evolution, and used new tools to measure rates of change.

Plate tectonics

Emerging in the 1960s was the concept that the earth's crust is made up of about a dozen huge plates of rock. This explained the relationship between many of the earth’s features. New Zealand was found to lie at the junction of the Australian and Pacific plates. Their collision beneath the South Island is now known to have caused the uplift of the Southern Alps and to control the formation of New Zealand’s distinctive landscapes. In the North Island the Pacific Plate is sliding beneath the Australian Plate, producing volcanic activity.

Rainfall and erosion

New Zealand’s rainfall had been recorded for many years, but almost always from low altitudes, where people lived. In the 1970s, measurements taken on the western side of the Southern Alps revealed a 10-kilometre-wide zone of exceptionally heavy rainfall, averaging 11.2 metres per year (equal to the height of a four-storey building).

In this high rainfall zone, the rate of erosion reaches 12 millimetres per year – about the same as the rate of uplift. It is now known that there is a close relationship between plate tectonics, rainfall and erosion. The rapidly uplifting mountains cause the prevailing moist westerly winds to rise and drop much of their moisture on the western side of the main divide. Although the mountains are rising rapidly, they are not getting any higher because the uplift is balanced by erosion.

Giant landslide

The Green Lake landslide, covering more than 45 square kilometres in Fiordland, was discovered by scientist Roger McPherson when scanning aerial photographs. Many of his colleagues were sceptical because no landslide of that size had previously been identified in New Zealand.

Neocatastrophism

In the 1970s the neocatastrophic model of landscape evolution was developed. It stated that, in New Zealand’s dynamic physical environment, infrequent but powerful events such as landslides, floods, volcanoes and earthquakes had as much – if not more – of an impact on landscape evolution as slow, ongoing processes such as uplift and erosion.

Mountain uplift

In 1979 geologist Harold Wellman and his colleagues used a range of evidence, including tilted lake shorelines and uplifted terraces, to estimate the rates at which mountains were rising. The maximum uplift rate of more than 10 millimetres per year was found to occur along the western edge of the Southern Alps. It is one of the fastest rates of mountain uplift in the world.

Technological advances

Until the mid-20th century the land was viewed at ground level, with a panorama only possible from a mountainside. The cloud-free aerial photographs of the 1950s revealed previously unknown landforms, and were used to prepare topographic maps. Satellite imagery became available in the 1980s, and is now a key tool for monitoring changes in the landscape and the way land is being used.

Isotope dating techniques have allowed landscape features to be dated with increasing accuracy. Carbon-14 dating, mainly used for dating fragments of wood and charcoal, was the first to be used. A variety of other dating techniques are now available, allowing detailed chronologies of landscape evolution to be developed.


External links and sources

More suggestions and sources


How to cite this page: Rebecca Priestley, 'Geomorphology – a history', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/geomorphology-a-history/print (accessed 17 July 2018)

Story by Rebecca Priestley, published 24 Sep 2007