Quarrying & Mining Magazine

Reshaping Auckland's Volcanoes

Auckland's Volcanoes Mt Eden Maungawhau

Auckland’s volcanoes have been forever changed by human occupation – human fortifications and excavations leaving a changed landscape and a few interesting tales. BY MARY SEARLE BELL.

Auckland City Council quarry at Mt Eden, early 1920s
Auckland City Council quarry at Mt Eden, early 1920s

The city of Auckland is nestled amongst some 53 volcanoes – all within 20 kilometres of the CBD. From any high point over the city you can see many of their cones dotted across the landscape – a good number have been set aside as reserves and parks so are surrounded by lush greenery, but others have vanished completely, quarried away for their rock.

Auckland’s volcanoes are powered by a hot spot, some 100 kilometres beneath the surface, where temperatures are high enough so that the rock begins to melt. Every once in a while, a batch of magma breaks off from the hot spot and forces its way up towards a weak place in the Earth’s crust, right under Auckland.

The last eruption in Auckland was Mt Rangitoto, in the Waitemata Harbour, about 600 years ago. Odds are the next volcanic eruption won’t occur in our lifetimes, however, the experts say it is not a case of if a volcano will erupt in Auckland, but when.

The highest of them all is Mt Eden (Maungawhau). At 196 metres it offers spectacular 360 degree views of the city and has a well-preserved crater, some 50 metres deep at the centre of the summit cone.

The main entrance gate to Mt Eden Prison in 1900.
The main entrance gate to Mt Eden Prison in 1900.

The mountain was formed some 15,000 years ago and is actually three overlapping scoria cones. The last eruption created a huge scoria mound with a central crater, forming the Mt Eden we know today. Lava flowed out from the base of the mound, and is up to 60 metres thick in places.

Before European settlers arrived, Maori were well established in the Auckland region, and the Waiohua the dominant tribe. The temperate climate, fertile volcanic soil and access to two harbours made it a preferred place to live, and consequently the area was much fought over. Many volcanic cones were used as fortified villages or pa. Maungawhau (Mt Eden) was large enough to provide refuge for several hundred people.

Terraced gardens and ditches were constructed on the sides of these volcanos, and palisades and stone walls built to provide protection and defend against enemy attack. These earth ramparts and terraces are still distinctive features on a number of mountains.

In the 18th century Maungakiekie (One Tree Hill) was the home of Kiwi Tamaki, paramount chief of the Waiohua. It is one of the largest prehistoric earthworks fortifications known worldwide, and was famed for its 1000 acres of kumara gardens. Mangere mountain, the last of the Waiohua strongholds, dominates the landscape of South Auckland.

During the early 1830s, the musket-armed Nga Puhi raided the Auckland isthmus driving its inhabitants into the Waikato, forcing them to abandon their volcanic pa. Few had returned by the time Auckland was declared the capital of the new colony.

Mt Eden in the late 1800s was a preferred location for wealthy businessmen to build their country residences. A number of these large homes still remain, such as Highwic House.
Mt Eden in the late 1800s was a preferred location for wealthy businessmen to build their country residences. A number of these large homes still remain, such as Highwic House.

At this time the area around the Mt Eden was relatively bare – the Maori had cut down all trees of significant size to build their fortifications. The soil around the volcano is very fertile and free draining and the European settlers soon divided the land into farms. The many rocks that dotted the landscape were cleared and used to build fences – today, these walls are still a feature of the suburb of Mt Eden.

Between 1870 and 1875 much of the farmland was subdivided into large suburban plots and the principal roads were formed.

It’s a little hard to imagine, seeing as it’s only four kilometres from downtown Auckland, but Mt Eden in the late 1800s was a preferred location for wealthy businessmen to build their country residences. A number of these large homes still remain, such as Highwic House, which has a Category 1 listing with Heritage New Zealand and is open to the public.

In 1879 the 27 hectares forming Mt Eden domain was set aside as a public reserve. This was in order to protect the cone from destruction by quarrying, which had begun in earnest soon after the Europeans arrived. One of the earliest quarries belonged to the prison.

A military stockade had been built in Mt Eden in 1856. It became the city’s main prison when the old city jail in the central city was demolished in 1865. The prisoners in the stockade were soon put to work building a prison wall and foundations for a new facility using basalt rocks they quarried on site.

In 1882 they began work constructing the prison buildings, which resemble the gloomy and foreboding Dartmoor Prison in England. The Victorian sentiment was that such facilities should be unpleasant places to be dreaded – and there was certainly plenty of hard labour for inmates.

An extract from the Auckland Weekly News, published on August 3, 1900 describes the new jail:

“The walls are of blue lava, hewn by the prisoners, and the whole work is under the superintendence of Mr Rutherford, foreman of works. One cannot help admiring the quality of the work done by the prison labourers, under Mr Rutherford’s directions, who has constructed similar buildings in the Old Country, and helped to build some of the strongest fortresses in England…

“Many of the men who have been condemned to hard labour have found it very much to their profit, for it has enabled them to learn some useful trade. The masonry of the new building is all done by prison labour. The stones are hewn, and set into place. The mortar work and concrete work follows.”

The prison was finally completed in 1917. Along with building the jail, prisoners provided the labour for the local quarry, breaking the rocks to build roads and houses. They shaped hundreds of thousands of blocks for the city’s kerbstones, some of which are still in place shoring up footpaths.

It is no wonder that in 1915, stone crushing was listed as the principal industry of Mt Eden Prison.

In addition to the prison quarry, W and G Winstone had opened a basalt quarry and scoria pit at the base of the mountain in the 1870s, and others followed. Quarrying continued there until the 1940s, by which time the shape of the mountain had been substantially altered.

Auckland’s cones have in fact been protected since 1915, when a law, the Reserves and Other Lands Disposal and Public Bodies Empowering Act 1915, was passed due to early concern that the distinctive landscape was being eroded, especially by quarrying. However, this law was often ignored until the late 20th century, with devastating effect.

Mt Smart (Rarotonga) is an example of a scoria cone that no longer exists. Its 50-metre cone was quarried out over the course of a century for the city’s roads and railways. In its place we now have Mt Smart Stadium.

Large portions of Mt Albert (Owairaka) and Wiri mountains were taken for railway-line ballast. And several South Auckland cones disappeared in the course of the construction of Mangere airport and sewerage ponds.

Only two of Auckland’s cones have remained untouched – Rangitoto Island and Motukorea (Browns Island), both safely out of reach in the middle of the Waitemata Harbour.

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