Auckland isthmus
The Auckland isthmus, also known as the Tāmaki isthmus, is a narrow stretch of land on the North Island of New Zealand in the Auckland Region, and the location of the central suburbs of the city of Auckland and the central business district. The isthmus is located between two rias : the Waitematā Harbour to the north, which opens to the Hauraki Gulf / Tīkapa Moana and Pacific Ocean, and the Manukau Harbour to the south, which opens to the Tasman Sea. The isthmus is the most southern section of the Northland Peninsula.
The Auckland isthmus is bound on the eastern side by the Tāmaki River and by the Whau River on the west; two tidal estuaries of the Waitematā Harbour. These were used as portages by early Māori migration canoes and Tāmaki Māori to cross the isthmus. Through early European settler history, canals were variously considered at either portage, however by the 1910s these projects were abandoned.
The isthmus was the centre of the Waiohua confederation of iwi in the 17th and early 18th centuries, who centred life around elaborate fortified pā of Maungawhau / Mount Eden and Maungakiekie / One Tree Hill. After the defeat of paramount chief Kiwi Tāmaki circa 1740, the isthmus became the rohe of Ngāti Whātua Ōrākei. In 1840, European settlers established the town of Auckland on the Waitematā Harbour, followed shortly after by the fencible towns of Onehunga, Ōtāhuhu and Panmure. The city developed outwards from the Port of Auckland, and by the mid-20th century the isthmus was almost completely urbanised. Originally organised as a variety of fractured land boards, boroughs and cities, the entire isthmus was amalgamated into a single local authority called Auckland City during the 1989 New Zealand local government reforms, which lasted until the 2010 unification of all local government in the Auckland Region to create the Auckland Council.
Since European colonisation of the region, the isthmus has seen major changes in landscape and infrastructure, including quarrying of scoria cones in the Auckland volcanic field, the draining of swamps and wetlands for farmland and housing and land reclamation on the Auckland waterfront. Large-scale infrastructure projects, including the rail network in the 1870s, the Auckland Motorways from the 1950s, and bridges, have fuelled population growth and suburban sprawl, both on the isthmus and in the greater Auckland Region.
Geological history
The isthmus is formed from sections of Early Miocene Waitemata Group marine sedimentary rock, with Quaternary volcanic rock from geologically recent volcanic eruptions and lava flows. Approximately 23 million years ago, tectonic forces between the Pacific Plate and Australian Plate pushed the Auckland isthmus and surrounding areas to depths of 2,000-3,000 metres under sea-level. This formed a wide sedimentary basin, sheltered by the large Waitākere Volcano to the west. The Waitemata Group sedimentary rocks were formed by eroding deposits from the Northland Peninsula, then an uplifted island. As tectonic forces changed, the begin was uplifted approximately 17 million years ago.The isthmus in its current structure was formed at the end of the Last Glacial Maximum, between 12,000 and 7,000 years ago. As sea levels rose, the river valley to the north, which was carved through the Miocene marine sediments of the Waitemata Group, drowned and became a tidal estuary, the Waitematā Harbour. A similar process occurred on the Manukau Harbour to the south. During the Last Glacial Maximum, the modern isthmus was dominated by podocarp-angiosperm forest such as kahikatea, Prumnopitys taxifolia and tree ferns such as Alsophila smithii. As the area warmed, much of the podocarp forest was displaced by Myrtaceae such as pōhutukawa and Ascarina lucida. Prior to human settlement, much of the isthmus was covered in broadleaf tree forests, predominantly Beilschmiedia tarairi and Vitex lucens trees.
A large section of the Auckland volcanic field is found on the Auckland isthmus, including some of the most prominent basaltic tuff and scoria volcanoes: Maungawhau / Mount Eden, Maungakiekie / One Tree Hill, Ōhinerau / Mount Hobson, Maungarei / Mount Wellington and Ōwairaka / Mount Albert. Most of these volcanoes have erupted in the last 30,000 years, however the oldest identified volcanoes on the isthmus include Albert Park Volcano and Glover Park, which are estimated to have erupted 145,000 and 161,000 years ago respectively). The volcanic activity caused much of the land on the isthmus to be formed from volcanic rock, such as the Te Kōpuke / Mount Saint John eruption, which caused a lava flow crossing the isthmus and forming the Meola Reef in the Waitematā Harbour.
Volcanism has influenced the geography of the isthmus, creating unique forested areas and swamplands. Underneath much of the isthmus are lava caves formed from eruptions such as Maungawhau / Mount Eden. Known as Ngā Ana Wai to Tāmaki Māori, the caves fed fresh water into springs and swamps around Sandringham and Western Springs. The eruption of Maungarei / Mount Wellington blocked existing creeks on the isthmus and led to the formation of Waiatarua, a former lake and current wetland reserve/golf-course in Remuera/Meadowbank. Low-lying swamps were predominantly vegetated with Cordyline australis and Phormium tenax, and also formed behind beach deposits at the mouths of streams
The volcanic eruptions led to the creation of the Epsom rock forest / Almorah rock forest, an ecosystem unique to the isthmus formed of trees such as Meryta sinclairii, Litsea calicaris, Alectryon excelsus, Melicytus ramiflorus, Piper excelsum and Pseudopanax lessonii growing in a primarily in a rock and leaf humus environment, with minimal soil. The largest remaining area of native bush on the isthmus is the Kepa Bush Reserve at the edge of the Purewa Creek in southern Mission Bay, where kohekohe trees dominate the old growth sections of the reserve.
The isthmus is a part of the Northland temperate kauri forests ecoregion, Locally, the isthmus together with surrounding lowland areas and the North Shore as far north as East Coast Bays form the Department of Conservation's Tāmaki Ecological District. The western side of the isthmus serves as a border between the Western Northland and Hauraki-Auckland bioregions for land snails.
Due to the length of the Northland Peninsula, there are significant tidal differences between the two harbours that border the isthmus. After high tide reaches the Waitematā Harbour, it takes approximately 3.5 hours for high tide to reach the Manukau Harbour.
Human context
Māori history
The Auckland isthmus was an early location visited by many of the Māori migration canoes, including the Matahourua, Aotea, Mātaatua, Tainui, Tākitimu, Tokomaru, Te Wakatūwhenua and Moekākara waka. The area was called Tāmaki Makaurau, meaning "Tāmaki desired by many", in reference to the desirability of its natural resources and geography. Tāmaki Māori found the isthmus to be an important strategic location, due to the fertile soils and rich resources from the two harbours that bound the isthmus.Portages, where waka could be moved across the isthmus at its most narrow points, were important features of the isthmus for Tāmaki Māori. The most important of these was Te Tō Waka, at the modern location of Portage Road, Ōtāhuhu south of Ōtāhuhu / Mount Richmond, where only 200 metres of land separated the Manukau Harbour from the Tāmaki River. Other major portages were Karetu, which was to the south of Mutukaroa / Hamlins Hill Regional Park, and Te Tōanga Waka, which connected the Whau River, Avondale Creek to Karaka, which was the coast on the Manukau Harbour at Green Bay. In addition to portages, trails across the isthmus were created, one of the most notable being Karangahape Road, connecting the central isthmus to Cornwallis / Karangahape in the southern Waitākere Ranges.
Between the 13th and 18th centuries, much of the isthmus was deforested, and devoted to kūmara cultivation. Land underwent periods of shifting cultivation, where once the soil was exhausted, a new field would be tilled, and the former would be colonised by fast-growing native plants. After harvesting, crops would be stored in rua kūmara, a storehouse fitted over a dry pit that is often found on the volcanic cones of the isthmus.
In the 17th century, chief Hua Kaiwaka consolidated tribes on the isthmus as a confederation called Waiohua, a union which lasted for three generations until the early 18th century. Thousands of people lived at fortified pā complexes on Maungawhau / Mount Eden and Maungakiekie / One Tree Hill, and Waiohua settlements were found at Maungarei, Onehunga, Remuera, Ōrākei, Kohimarama, Rarotonga / Mount Smart, Te Tatua-a-Riukiuta, Ōwairaka / Mount Albert, the Waihorotiu Valley, in addition to Māngere to the south of the isthmus. Almost all hills, headlands and mountains on the isthmus have some history of Māori occupancy. The Te Taoū hapū of Ngāti Whātua defeated Kiwi Tāmaki, the paramount chief of Waiohua circa 1741, at a battle at Paruroa in the lower Waitākere Ranges. After Waiohua were defeated in a series of battles, some members of Te Taoū settled at Tāmaki Makaurau and intermarried with Waiohua, later becoming known as Ngāti Whātua Ōrākei. During this period, the isthmus began to be reforested, due to the relatively small population of Ngāti Whātua Ōrākei. In the 1780s, Te Tahuri, a chieftainess of Te Taou gifted land on the Western shore of the Tāmaki River to Ngāti Pāoa at Mokoia, and within a generation Ngāti Pāoa almost outnumbered Ngāti Whātua on the isthmus. While Ngāti Whātua and Ngāti Pāoa peacefully co-exited at first, an incident during a sharking expedition which led to the death of Tarahawaiki began a cycle of revenge attacks between Ngāti Whātua/Waiohua and Ngāti Pāoa. While peacemaking Ngāti Whātua and Ngāti Pāoa began in 1793, Ngāpuhi from the north attacked Ngāti Pāoa, culminating in a battle at the mouth of the Tāmaki River, where Ngāti Pāoa fended off Ngāpuhi. By the time missionaries Samuel Marsden and John Gare Butler visited the isthmus in 1820, there were thousands of inhabitants living along the shores of the Tāmaki River.
In late 1821 during the Musket Wars, a Ngāpuhi taua led by Hongi Hika attacked Mauināina pā and Mokoia village on the banks of the Tāmaki River, causing a great number of deaths. This incident marked the beginning of a period of time when the isthmus was most deserted, when Tāmaki Māori sheltered in regions away from the threat of Te Tai Tokerau Māori raiders that continued on until the early 1830s. Ngāti Pāoa began to return to the Hauraki Gulf region in the 1820s, however primarily focused resettling Waiheke Island, where there were many trade opportunities with whalers. Ngāti Whātua returned to the isthmus by the mid-1830s, resettling in the Māngere Bridge-Onehunga area. By the 1840s, much of the landscape of the Auckland isthmus was covered in bracken fern. The shoreline of the Waitematā Harbour was populated with pōhutukawa trees, however during the 1840s onwards most mature specimens were cut down to use for ship building.