Geology of Auckland Region
Encyclopedia
The Auckland Region is built on a basement of greywacke
rocks that form many of the islands in the Hauraki Gulf
, the Hunua Ranges
, and land south of Port Waikato
. The Waitakere Ranges
in the west are the remains of a large andesitic volcano, and Great Barrier Island
was formed by the northern end of the Coromandel Volcanic Zone. The main isthmus and North Shore
are composed of Waitemata sandstone and mudstone, and portions of the Northland Allochthon extend as far south as Albany
. Little Barrier Island was formed by a relatively isolated andesitic volcano, active around 1 to 3 million years ago.
The Manukau
and South Kaipara Harbour
s are protected by the recent sand dune deposits of the Awhitu and South Kaipara Peninsulas. Recent basaltic volcanic activity has produced many volcanic cones throughout the Auckland Region, including the iconic Rangitoto Island
.
, the basement rocks of the Auckland Region
are composed of Greywacke
(indurated sandstone, siltstone and mudstone).
Murihiku Terrane Greywacke lies beneath the Auckland Region on the western side, and outcrops south of the Waikato River
. The Murihiku Terrane is considered to be an accretionary wedge of mainly volcanogenic forearc sediments. It was formed in Late Triassic to Late Jurassic times (220-145 Ma).
A line of Maitai Terrane rocks are assumed to pass north-south through the centre of the Auckland Region, separating the Murihiku Terrane and Waipapa Composite Terrane, and produce a detectable Junction Magnetic Anomaly (JMA), but do not outcrop. Some Murihiku rocks occur to the east of the JMA, forming the Taupiri and Hakarimata Ranges, but it is assumed that these rocks have been shifted to their present position.
Hunua Terrane Greywacke lies beneath the Auckland Region on the eastern side, as far south as the Hunua Ranges
, and outcrops in the Hunua Ranges, many islands in the Hauraki Gulf
(Waiheke, Motutapu, Motuihe, Tiritiri Matangi, Kawau, etc.), and Tawharanui Peninsula
. It sometimes includes Chert
and Argillite
. The rocks are generally fine grained and highly deformed. It was formed in Late Triassic to Late Jurassic times (220-145 Ma).
The Morrinsville Terrane Greywacke lies beneath the Auckland Region on the eastern side, south of the Hunua Ranges, and further east to the Coromandel Peninsula
. The rocks are generally coarser grained, with massive sandstones and conglomerate. It was formed in Late Jurassic to Early Cretaceous times (160-120 Ma).
, and King Country
, although they have often been eroded or covered. Rocks containing coal were formed from swampland in Late Eocene times (37-34 Ma). The land sunk and the sea transgressed, and calcareous sandstone, mudstone, and limestone was deposited in Oligocene times (34-24 Ma).
The coal deposits outcrop near Huntly
and Maramarua, where they are mined.
Some amazing scenery, composed of flaggy limestone bluffs, exists in the area south and west of the Waikato River
.
and Albany areas. The rocks came from the northeast, and were emplaced in reverse order, but the right way up. The original rocks are of Cretaceous to Oligocene age (90-25 Ma), and include mudstones, limestone and basalt lava. These rocks outcrop around Silverdale, Warkworth, and Wellsford, reaching as far south as Albany.
The Waitakere volcano has mainly been eroded, but conglomerate
from the volcano formed the Waitakere Ranges
. The Waitakere Ranges also contain many dikes, volcanic plugs, etc., that formed part of this volcano.
These Early Miocene volcanoes, along with the Northland Allochthon, eroded and deposited most of the material that makes up the Waitemata sandstones and mudstones in the Waitemata Basin. The Waitemata sandstones and mudstones form the cliffs around the Waitemata Harbour
and East Coast Bays
, and land further north up to Cape Rodney, with outcrops further south down to Mercer and Miranda. Lahars produced the coarser Parnell Grit, found in many headlands around the East Coast Bays. Greywacke pebble beaches can be seen forming a layer in Waitemata sandstone cliffs on Motutapu Island
.
s and undersea Colville Ridge. The initial activity was andesitic, but later became rhyolytic (12 Ma). In the Kauaeranga Valley, impressive volcanic plug
s remain, as does a lava lake that now forms the top of Table Mountain. Active geothermal systems
, similar to those that now exist near Rotorua
, were present around 6 Ma, and produced the gold
and silver
deposits that were later mine
d in the Coromandel gold rush. Later (5-2 Ma), volcanic activity moved further south to form the Kaimai Ranges.
The Hauraki Plains
and Hauraki Gulf
are believed to represent a rift valley
. The Coromandel Ranges used to be much closer to Auckland, and the rift valley is assumed to have developed about 2 Ma ago, due to the clockwise rotation of the eastern North Island, that stretched the land between Auckland and East Cape. The Waikato River used to flow from Karapiro
, through the Hinuera Gap, and Hauraki Plains, to come out on the east coast in the Hauraki Gulf. The sediment from Oruanui eruption
of Lake Taupo
caused the river to change direction, and come out to the west. Rivers around Auckland, that now flow to the east, such as the rivers around Clevedon, used to flow to the west, and deposited rocks from the Coromandel Ranges in the Manukau Harbour
.
Activity then moved to the Ngatutura Volcanic Field, south of Port Waikato in early Pleistocene times (1.8-1.5 Ma). Little remains of this field.
, is believed to have started around 140,000 years ago, and is still active. It covers the area from Wiri in the south, through the Auckland Isthmus, to Lake Pupuke
and Rangitoto Island
in the north, and contains around 50 vents.
The field contains many maar
craters, generated by eruptions where the magma encountered water, and a sudden explosive eruption produced a large crater, surrounded by a tuff ring. Examples include Lake Pupuke, Onepoto, Tuff Crater, Orakei Basin, Pukaki Lagoon, etc. Many of the craters have been breached by the sea, and are now filled with mud. The eruption of Lake Pupuke caused the Wairau River, which used to come out around Little Shoal Bay, to change its course to north of Milford.
Other eruptions have produced scoria cones. Examples include North Head, Mount Victoria, Mount Eden, Mount Hobson, Mount St Johns, One Tree Hill, Mount Roskill, Three Kings, Mount Albert, Mount Mangere. Some produced substantial lava flows. For example, a lava flow from Three Kings flows through Sandringham, Morningside, Western Springs, and out to the Waitemata Harbour
, forming Te Tokaroa Reef, which reaches within 500 m of Kauri Point, Birkenhead. Some lava flows contain caves, for example at Wiri, Three Kings, and One Tree Hill.
Rangitoto Island
is the most recent volcano, erupting around 600 years ago. Apart from the summit, it is composed of Pahoehoe (smooth) and ’A’a (broken) lava flows, which are still largely bare of vegetation or soil. It also has lava caves, near the track up to the summit, that are very accessible to visitors.
While the ages of individual volcanoes in the Auckland Volcanic Field are somewhat uncertain, the following ages have been suggested:
The black sand on the west coast beaches is known for its high iron content, and is “mined” north of Waikato Heads, being extracted by electromagnets. The iron comes from the undersea volcanoes, to the west of the coast, and from the Tongariro Volcanic Centre, and Taranaki.
Quartz sand to the north of Auckland, around Tawharanui and Pakiri, appears white, due to its purity.
is exceptionally interesting. Apart from the summit, it is composed of Pahoehoe (smooth) and ’A’a (broken) lava flows. A walk up to the scoria summit passes lava caves. The vegetation is also exceptionally interesting, with pohutukawa forests, astelia growing on the lava, and a grove of kidney ferns.
The coast on Motutapu Island
from Islington Bay to Administration Bay starts with Waitemata sandstone cliffs, and finishes with greywacke and chert near Administration Bay. Ancient greywacke pebble beaches can be seen embedded in the Waitemata sandstone cliffs. It is possible to walk from Rangitoto Island to Motutapu Island via a causeway.
Motuihe Island
has a mixture of Waitemata sandstone, with Parnell Grit in the headlands, greywacke at the south, and even a coastal section with flaggy limestone on the west coast. It is also a bird sanctuary, with kiwi, saddleback, dotteral, oyster catcher, heron, and more common birds such as the fantail, tui, and pukeko.
Tiritiri Matangi Island
is a rugged island composed of greywacke. It also a bird sanctuary, with rare birds, including saddleback, takahē, parakeet, North Island robin, kōkako, whitehead, little spotted kiwi, stitchbird and brown teal.
Waiheke Island
is mostly composed of greywacke. At Stoney Batter, at the western end of the island are the remains of a volcano (7-8 Ma), with the remains of a lava flow in the form of large boulders.
Lake Pupuke
on the North Shore is the crater lake of one of Auckland’s earliest volcanoes. Water flows underground through cracks in the lava from the lake to Thorne Bay, where it is discharged by natural springs. At the northern end of Takapuna
Beach are the remains of a lava flow, that flowed over a forest, preserving casts of the trees before incinerating them. The lava also flowed over mounds, and the material underneath was later eroded, leaving arches. Further north along the coast is a cast of a large Kauri tree.
Onepoto and Tuff Crater beside the North Shore motorway are examples of explosion craters, that have breached and are now open to the sea. Onepoto basin has largely been reclaimed and now forms a park, while Tuff Crater hosts a tidal mangrove swamp.
Volcanic cones, such as Mount Eden, One Tree Hill, Mount Albert, Mount Roskill, Mount Hobson, Mount St John, Auckland Domain, Mount Mangere, North Head, Mount Wellington are well worth a visit, even for the view from the top. Most have large scoria mound and crater. They also often have the remains of a Māori pā
(fortified village). Te Tokaroa Reef is a lava flow that flows 10 km from Three Kings to the Waitemata Harbour, and almost manages to cross the harbour.
Many of the East Coast Bays beaches, such as Long Bay and Campbells Bay are good places to see the Waitemata sandstone and mudstone cliffs, with embedded Parnell Grit. Shakespear Park, at the end of Whangaparaoa Peninsula is also a good place to visit. Large blocks of basalt rock have been moved from the Waitakere Ranges to the coast just beyond Army Bay. Further north is Waiwera, with more Waitemata sandstone cliffs and Parnell Grit, and also commercial hot pools, suitable for children. The next beach over, Wenderholm Regional Park is well worth a visit and a good place for a picnic.
The Waitakere Ranges
are interesting. Streams often flow down narrow gorges surrounded by conglomerate rocks formed from debris from the Waitakere volcano. The Piha Gorge, Pararaha Gorge and Karamatura Valley are good examples.
Maori Bay, just south of Muriwai, has good examples of pillow lavas. It is also the home of a gannet colony.
Te Henga Beach has large sand dunes behind it, and two lakes behind the same dunes. This are has been used to make several TV series, including “Xena: Warrior Princess
”. On the way to the beach, it is worthwhile visiting the Auckland City Walk, to see the native bush, including large kauri trees. The Waitakere River swamp is also interesting.
Piha
Beach is Auckland’s most famous surf beach. The area to the south has blowholes, that the sea surges through. Whites Beach, to the north of Piha is also interesting. Further south is Mercer Bay, which has a headland, with an enormous hole corresponding to a volcanic pipe. Still further south are Karekare Beach and Whatipu Beach, backed by steep cliffs. Sand dunes are accumulating along the shore at an amazing rate, and the beach has grown almost two kilometres wider in the last 100 years. Lakes are developing behind the dunes. All the beaches have black iron sand, that can be extracted by using a magnet.
Awhitu Peninsula, south of the Manukau Harbour, is essentially composed of consolidated sand, more than 100 m high. The cliffs are rapidly eroding, and preserved tree stumps and blocks of peat in the cliffs fall down to the beach. It is best to visit places like Hamilton’s Gap at low tide.
The Hunua Ranges
give a good example of greywacke rock. A visit to one of the dams used to supply Auckland with water is worthwhile. Raukura Point, near Kawakawa Bay is a good place to see chert. Regional parks such as Tawhitokino and Tapapakanga are good places to see greywacke boulder beaches. Further south is Miranda Hot Pools, for a relaxing swim.
The route out to Waikato Heads is interesting. It gives good examples of the volcanoes of the South Auckland Volcanic Field, which have eroded sufficiently to make an excellent soil for growing vegetables. Closer to the river mouth, the geology changes to Murihiku greywacke. A walk south from the beach gives good access to the greywacke. Travelling south from Waikato Heads on unsealed roads takes you through country roads, among cliffs composed of Te Kuiti sandstone and limestone, and finally out to the Waikato Plains at Te Kauwhata and state highway 1.
GNS provides a free Map of New Zealand's Geological Foundations.GNS Map of New Zealand's Geological Foundations
The main maps are the 1 : 250 000 QMap series, which will be completed as a series of 21 maps and booklets in 2010. Low resolution versions of these maps (without the associated booklet) can be downloaded from the GNS site for free. The map for the Auckland Area was published in 2002.
There is a 1 : 50 000 map of the Auckland Urban Area, published in 1992, that is worth looking at, and there are also maps of the Waitakere Ranges and Helensville-Whangaparaoa areas published in the 1980s.
Greywacke
Greywacke or Graywacke is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock generally found...
rocks that form many of the islands in the Hauraki Gulf
Hauraki Gulf
The Hauraki Gulf is a coastal feature of the North Island of New Zealand. It has a total area of 4000 km², and lies between the Auckland Region, the Hauraki Plains, the Coromandel Peninsula and Great Barrier Island...
, the Hunua Ranges
Hunua Ranges
The Hunua Ranges form a block of hilly country to the southeast of Auckland in New Zealand's North Island. They cover some 250 square kilometres , containing 178 km² of parkland, and rise to 688 metres at Kohukohunui...
, and land south of Port Waikato
Port Waikato
Port Waikato is on the south bank of the Waikato River at its outflow into the Tasman Sea, in northern New Zealand. Now a small town with a population of under 300, it was an important port during the New Zealand Land Wars of the 19th century...
. The Waitakere Ranges
Waitakere Ranges
The Waitakere Ranges are a chain of hills in the Auckland metropolitan area, generally running approximately 25 km from north to south, 25 km west of central Auckland, New Zealand. The maximum elevation within the ranges is 474 m...
in the west are the remains of a large andesitic volcano, and Great Barrier Island
Great Barrier Island
Great Barrier Island is a large island of New Zealand, situated to the north-east of central Auckland in the outer Hauraki Gulf. With an area of it is the fourth-largest island of New Zealand's main chain of islands, with its highest point, Mount Hobson, rising...
was formed by the northern end of the Coromandel Volcanic Zone. The main isthmus and North Shore
North Shore, New Zealand
North Shore City was the name of a city that existed in the Auckland region of New Zealand from 1989 until 2010. The city had a population of making it the fourth most populous city in New Zealand prior to November 2010...
are composed of Waitemata sandstone and mudstone, and portions of the Northland Allochthon extend as far south as Albany
Albany, New Zealand
Albany is a northern suburb of Auckland, one of the several cities in northern New Zealand. The name derives from Alba and its Latinisation. It is located to the north of the Waitemata Harbour, 15 kilometres northwest of the Auckland city centre. The suburb is in the Albany ward, one of the...
. Little Barrier Island was formed by a relatively isolated andesitic volcano, active around 1 to 3 million years ago.
The Manukau
Manukau Harbour
Manukau Harbour is the second largest natural harbour in New Zealand by area. It is located to the southwest of the Auckland isthmus, and is an arm of the Tasman Sea.-Geography:...
and South Kaipara Harbour
Kaipara Harbour
Kaipara Harbour is a large enclosed harbour estuary complex on the north western side of the North Island of New Zealand. The northern part of the harbour is administered by the Kaipara District and the southern part is administered by the Rodney District...
s are protected by the recent sand dune deposits of the Awhitu and South Kaipara Peninsulas. Recent basaltic volcanic activity has produced many volcanic cones throughout the Auckland Region, including the iconic Rangitoto Island
Rangitoto Island
Rangitoto Island is a volcanic island in the Hauraki Gulf near Auckland, New Zealand. The 5.5 km wide island is an iconic and widely visible landmark of Auckland with its distinctive symmetrical shield volcano cone rising 260 metres high over the Hauraki Gulf...
.
Basement rocks
As with most of New ZealandNew Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, the basement rocks of the Auckland Region
Auckland Region
The Auckland Region was one of the sixteen regions of New Zealand, named for the city of Auckland, the country's largest urban area. With one third of the nation's residents, it was by far the biggest population and economy of any region of New Zealand, but the second-smallest land area.On 1...
are composed of Greywacke
Greywacke
Greywacke or Graywacke is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock generally found...
(indurated sandstone, siltstone and mudstone).
Murihiku Terrane Greywacke lies beneath the Auckland Region on the western side, and outcrops south of the Waikato River
Waikato River
The Waikato River is the longest river in New Zealand. In the North Island, it runs for 425 kilometres from the eastern slopes of Mount Ruapehu, joining the Tongariro River system and emptying into Lake Taupo, New Zealand's largest lake. It drains Taupo at the lake's northeastern edge, creates the...
. The Murihiku Terrane is considered to be an accretionary wedge of mainly volcanogenic forearc sediments. It was formed in Late Triassic to Late Jurassic times (220-145 Ma).
A line of Maitai Terrane rocks are assumed to pass north-south through the centre of the Auckland Region, separating the Murihiku Terrane and Waipapa Composite Terrane, and produce a detectable Junction Magnetic Anomaly (JMA), but do not outcrop. Some Murihiku rocks occur to the east of the JMA, forming the Taupiri and Hakarimata Ranges, but it is assumed that these rocks have been shifted to their present position.
Hunua Terrane Greywacke lies beneath the Auckland Region on the eastern side, as far south as the Hunua Ranges
Hunua Ranges
The Hunua Ranges form a block of hilly country to the southeast of Auckland in New Zealand's North Island. They cover some 250 square kilometres , containing 178 km² of parkland, and rise to 688 metres at Kohukohunui...
, and outcrops in the Hunua Ranges, many islands in the Hauraki Gulf
Hauraki Gulf
The Hauraki Gulf is a coastal feature of the North Island of New Zealand. It has a total area of 4000 km², and lies between the Auckland Region, the Hauraki Plains, the Coromandel Peninsula and Great Barrier Island...
(Waiheke, Motutapu, Motuihe, Tiritiri Matangi, Kawau, etc.), and Tawharanui Peninsula
Tawharanui Peninsula
Tawharanui Peninsula is a finger of land projecting into the Hauraki Gulf from the east coast of the much larger North Auckland Peninsula of New Zealand. It separates Omaha Bay to the north from Kawau Bay and Kawau Island to the south...
. It sometimes includes Chert
Chert
Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...
and Argillite
Argillite
An argillite is a fine-grained sedimentary rock composed predominantly of indurated clay particles. Argillaceous rocks are basically lithified muds and oozes. They contain variable amounts of silt-sized particles. The argillites grade into shale when the fissile layering typical of shale is...
. The rocks are generally fine grained and highly deformed. It was formed in Late Triassic to Late Jurassic times (220-145 Ma).
The Morrinsville Terrane Greywacke lies beneath the Auckland Region on the eastern side, south of the Hunua Ranges, and further east to the Coromandel Peninsula
Coromandel Peninsula
The Coromandel Peninsula lies in the North Island of New Zealand. It is part of the Waikato Region and Thames-Coromandel District and extends 85 kilometres north from the western end of the Bay of Plenty, forming a natural barrier to protect the Hauraki Gulf and the Firth of Thames in the west...
. The rocks are generally coarser grained, with massive sandstones and conglomerate. It was formed in Late Jurassic to Early Cretaceous times (160-120 Ma).
Te Kuiti group coal and limestone
The Te Kuiti Group Rocks overlie the basement rocks, and are present in Northland, Auckland, the WaikatoWaikato
The Waikato Region is a local government region of the upper North Island of New Zealand. It covers the Waikato, Hauraki, Coromandel Peninsula, the northern King Country, much of the Taupo District, and parts of Rotorua District...
, and King Country
King Country
The King Country is a region of the western North Island of New Zealand. It extends approximately from the Kawhia Harbour and the town of Otorohanga in the north to the upper reaches of the Whanganui River in the south, and from the Hauhungaroa and Rangitoto Ranges in the east to near the Tasman...
, although they have often been eroded or covered. Rocks containing coal were formed from swampland in Late Eocene times (37-34 Ma). The land sunk and the sea transgressed, and calcareous sandstone, mudstone, and limestone was deposited in Oligocene times (34-24 Ma).
The coal deposits outcrop near Huntly
Huntly, New Zealand
Huntly is a town in the Waikato region of the North Island of New Zealand. It is on State Highway 1, 93 kilometres south of Auckland and 35 kilometres north of Hamilton. It is situated on the North Island Main Trunk Railway and straddles the Waikato River.Huntly was called Rahui Pokeka when...
and Maramarua, where they are mined.
Some amazing scenery, composed of flaggy limestone bluffs, exists in the area south and west of the Waikato River
Waikato River
The Waikato River is the longest river in New Zealand. In the North Island, it runs for 425 kilometres from the eastern slopes of Mount Ruapehu, joining the Tongariro River system and emptying into Lake Taupo, New Zealand's largest lake. It drains Taupo at the lake's northeastern edge, creates the...
.
The Northland Allochthon
In Early Miocene times (24-21 Ma), a series of thrust sheets was emplaced over Northland, extending as far south as the Kaipara HarbourKaipara Harbour
Kaipara Harbour is a large enclosed harbour estuary complex on the north western side of the North Island of New Zealand. The northern part of the harbour is administered by the Kaipara District and the southern part is administered by the Rodney District...
and Albany areas. The rocks came from the northeast, and were emplaced in reverse order, but the right way up. The original rocks are of Cretaceous to Oligocene age (90-25 Ma), and include mudstones, limestone and basalt lava. These rocks outcrop around Silverdale, Warkworth, and Wellsford, reaching as far south as Albany.
West Coast volcanism
A volcanic arc became active to the west of the current land in Northland in Miocene times (23 Ma), and gradually moved south down to Taranaki. It produced mainly andesitic strato-volcanoes. Volcanoes were produced in what is now sea to the west of the Auckland Region, near the Kaipara Harbour and Waitakere Ranges (22-16 Ma), and Waikato Heads (14-8 Ma).The Waitakere volcano has mainly been eroded, but conglomerate
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
from the volcano formed the Waitakere Ranges
Waitakere Ranges
The Waitakere Ranges are a chain of hills in the Auckland metropolitan area, generally running approximately 25 km from north to south, 25 km west of central Auckland, New Zealand. The maximum elevation within the ranges is 474 m...
. The Waitakere Ranges also contain many dikes, volcanic plugs, etc., that formed part of this volcano.
Waitemata sandstone
While the volcanic activity occurred to the west, a rapidly deepening basin developed further to the east, in the Auckland area.These Early Miocene volcanoes, along with the Northland Allochthon, eroded and deposited most of the material that makes up the Waitemata sandstones and mudstones in the Waitemata Basin. The Waitemata sandstones and mudstones form the cliffs around the Waitemata Harbour
Waitemata Harbour
The quite famous Waitemata Harbour is the main access by sea to Auckland, New Zealand. For this reason it is often referred to as Auckland Harbour, despite the fact that it is only one of two harbours surrounding the city, and is crossed by the Auckland Harbour Bridge. The Waitemata forms the north...
and East Coast Bays
East Coast Bays
East Coast Bays is the collective name for a series of small suburbs of North Shore City, in the Auckland metropolitan area of New Zealand, which line the northeast coast of the city along the shore of the Hauraki Gulf and Rangitoto Channel...
, and land further north up to Cape Rodney, with outcrops further south down to Mercer and Miranda. Lahars produced the coarser Parnell Grit, found in many headlands around the East Coast Bays. Greywacke pebble beaches can be seen forming a layer in Waitemata sandstone cliffs on Motutapu Island
Motutapu Island
Motutapu Island is a island in the Hauraki Gulf to the northeast of the city of Auckland, New Zealand. The island is part of the Hauraki Gulf Maritime Park....
.
Coromandel volcanism
Shortly after (18 Ma), a volcanic arc developed further east to create the Coromandel RangeCoromandel Range
right|thumb|250px|A true-colour image showing Auckland city , the Hauraki Gulf and the Coromandel Peninsula . The scene was acquired by NASA's Terra satellite, on October 23, 2002.The Coromandel Range is a ridge of rugged hills running the length of the Coromandel Peninsula in the North Island of...
s and undersea Colville Ridge. The initial activity was andesitic, but later became rhyolytic (12 Ma). In the Kauaeranga Valley, impressive volcanic plug
Volcanic plug
A volcanic plug, also called a volcanic neck or lava neck, is a volcanic landform created when magma hardens within a vent on an active volcano. When forming, a plug can cause an extreme build-up of pressure if volatile-charged magma is trapped beneath it, and this can sometimes lead to an...
s remain, as does a lava lake that now forms the top of Table Mountain. Active geothermal systems
Geothermal Systems
A geothermal heat pump, ground source heat pump , or ground heat pump is a central heating and/or cooling system that pumps heat to or from the ground.It uses the earth as a heat source or a heat sink...
, similar to those that now exist near Rotorua
Rotorua
Rotorua is a city on the southern shores of the lake of the same name, in the Bay of Plenty region of the North Island of New Zealand. The city is the seat of the Rotorua District, a territorial authority encompassing the city and several other nearby towns...
, were present around 6 Ma, and produced the gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
and silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
deposits that were later mine
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...
d in the Coromandel gold rush. Later (5-2 Ma), volcanic activity moved further south to form the Kaimai Ranges.
The Hauraki Plains
Hauraki Plains
The Hauraki Plains are a geographical feature and non-administrative area located in the northern North Island of New Zealand, at the lower end of the Thames Valley...
and Hauraki Gulf
Hauraki Gulf
The Hauraki Gulf is a coastal feature of the North Island of New Zealand. It has a total area of 4000 km², and lies between the Auckland Region, the Hauraki Plains, the Coromandel Peninsula and Great Barrier Island...
are believed to represent a rift valley
Rift valley
A rift valley is a linear-shaped lowland between highlands or mountain ranges created by the action of a geologic rift or fault. This action is manifest as crustal extension, a spreading apart of the surface which is subsequently further deepened by the forces of erosion...
. The Coromandel Ranges used to be much closer to Auckland, and the rift valley is assumed to have developed about 2 Ma ago, due to the clockwise rotation of the eastern North Island, that stretched the land between Auckland and East Cape. The Waikato River used to flow from Karapiro
Lake Karapiro
Lake Karapiro is an artificial reservoir lake on the Waikato River in the North Island of New Zealand. The lake, near Cambridge and some south-east of the city of Hamilton, was created in 1947 to store water for the Karapiro Power Station, the last of the eight hydroelectric power stations on the...
, through the Hinuera Gap, and Hauraki Plains, to come out on the east coast in the Hauraki Gulf. The sediment from Oruanui eruption
Oruanui eruption
The Oruanui eruption of New Zealand's Taupo Volcano was the world's largest known eruption in the past 70,000 years, with a Volcanic Explosivity Index of 8...
of Lake Taupo
Lake Taupo
Lake Taupo is a lake situated in the North Island of New Zealand. With a surface area of , it is the largest lake by surface area in New Zealand, and the second largest freshwater lake by surface area in geopolitical Oceania after Lake Murray ....
caused the river to change direction, and come out to the west. Rivers around Auckland, that now flow to the east, such as the rivers around Clevedon, used to flow to the west, and deposited rocks from the Coromandel Ranges in the Manukau Harbour
Manukau Harbour
Manukau Harbour is the second largest natural harbour in New Zealand by area. It is located to the southwest of the Auckland isthmus, and is an arm of the Tasman Sea.-Geography:...
.
Recent basaltic volcanism
Intra-plate basaltic volcanism in the Auckland region started in the south, at Okete, near Raglan in late Pliocene times (2.7-1.8 Ma), and has moved north since then. Lava flows from the Okete Volcanic Field generated the Bridal Veil Falls. Scoria cones and tuff rings were also generated.Activity then moved to the Ngatutura Volcanic Field, south of Port Waikato in early Pleistocene times (1.8-1.5 Ma). Little remains of this field.
South Auckland Volcanic Field
Activity then moved to the South Auckland Volcanic Field, in the area from Pukekawa north to Waiuku and Papakura, in mid Pleistocene times (1.5-0.5 Ma), producing over 100 eruptions. This field includes the lava flows at Hunua Falls, scoria cones that form the Bombay Hills, Pukekohe and Pukekawa, and tuff rings at Pukekohe and Onewhero. These volcanoes have weathered to produce excellent soils that are used for market gardening.Auckland Volcanic Field
The Auckland Volcanic FieldAuckland Volcanic Field
The Auckland volcanic field is a monogenetic volcanic field in the North Island of New Zealand. Basaltic in nature, it underlies much of the metropolitan area of Auckland....
, is believed to have started around 140,000 years ago, and is still active. It covers the area from Wiri in the south, through the Auckland Isthmus, to Lake Pupuke
Lake Pupuke
Lake Pupuke is a heart-shaped freshwater lake occupying a volcanic explosion crater between the suburbs of Takapuna and Milford on the North Shore of Auckland, New Zealand. The heart shape is a result of its formation by the linking of two circular craters - a larger one forming most of the lake...
and Rangitoto Island
Rangitoto Island
Rangitoto Island is a volcanic island in the Hauraki Gulf near Auckland, New Zealand. The 5.5 km wide island is an iconic and widely visible landmark of Auckland with its distinctive symmetrical shield volcano cone rising 260 metres high over the Hauraki Gulf...
in the north, and contains around 50 vents.
The field contains many maar
Maar
A maar is a broad, low-relief volcanic crater that is caused by a phreatomagmatic eruption, an explosion caused by groundwater coming into contact with hot lava or magma. A maar characteristically fills with water to form a relatively shallow crater lake. The name comes from the local Moselle...
craters, generated by eruptions where the magma encountered water, and a sudden explosive eruption produced a large crater, surrounded by a tuff ring. Examples include Lake Pupuke, Onepoto, Tuff Crater, Orakei Basin, Pukaki Lagoon, etc. Many of the craters have been breached by the sea, and are now filled with mud. The eruption of Lake Pupuke caused the Wairau River, which used to come out around Little Shoal Bay, to change its course to north of Milford.
Other eruptions have produced scoria cones. Examples include North Head, Mount Victoria, Mount Eden, Mount Hobson, Mount St Johns, One Tree Hill, Mount Roskill, Three Kings, Mount Albert, Mount Mangere. Some produced substantial lava flows. For example, a lava flow from Three Kings flows through Sandringham, Morningside, Western Springs, and out to the Waitemata Harbour
Waitemata Harbour
The quite famous Waitemata Harbour is the main access by sea to Auckland, New Zealand. For this reason it is often referred to as Auckland Harbour, despite the fact that it is only one of two harbours surrounding the city, and is crossed by the Auckland Harbour Bridge. The Waitemata forms the north...
, forming Te Tokaroa Reef, which reaches within 500 m of Kauri Point, Birkenhead. Some lava flows contain caves, for example at Wiri, Three Kings, and One Tree Hill.
Rangitoto Island
Rangitoto Island
Rangitoto Island is a volcanic island in the Hauraki Gulf near Auckland, New Zealand. The 5.5 km wide island is an iconic and widely visible landmark of Auckland with its distinctive symmetrical shield volcano cone rising 260 metres high over the Hauraki Gulf...
is the most recent volcano, erupting around 600 years ago. Apart from the summit, it is composed of Pahoehoe (smooth) and ’A’a (broken) lava flows, which are still largely bare of vegetation or soil. It also has lava caves, near the track up to the summit, that are very accessible to visitors.
While the ages of individual volcanoes in the Auckland Volcanic Field are somewhat uncertain, the following ages have been suggested:
- Auckland Domain: 140,000 years ago.
- Pupuke: 100,000 years ago.
- Maungataketake: 50,000 years ago.
- North Head, Onepoto, Tuff Crater: 30,000-40,000 years ago.
- Crater Hill, Panmure Basin, Mount Richmond, Wiri: 25,000-30,000 years ago.
- Puketutu, Mangere, One Tree Hill, Three Kings: 20,000-25,000 years ago.
- Mount Hobson, Mount Eden: 15,000-20,000 years ago.
- Motukorea, Mount Wellington: 10,000 years ago.
- Rangitoto Island: 600 years ago.
Pumice deposits
Over the last few million years, rhyolitic pumice deposits from the centre of the North Island have been washed down into the Auckland area, and form substantial deposits around the Hauraki Plains and Manukau Harbour, Western Waitemata Harbour, and even up into the Kaipara Harbour.Coastal dunes
The Awhitu Peninsula (the west coast from Waikato Heads up to Manukau Heads), and the coastal barriers north and south of the entry to the Kaipara Harbour, are essentially consolidated sand dunes, built up over the last few million years.The black sand on the west coast beaches is known for its high iron content, and is “mined” north of Waikato Heads, being extracted by electromagnets. The iron comes from the undersea volcanoes, to the west of the coast, and from the Tongariro Volcanic Centre, and Taranaki.
Quartz sand to the north of Auckland, around Tawharanui and Pakiri, appears white, due to its purity.
Geological sites of interest
As a very recent volcano, Rangitoto IslandRangitoto Island
Rangitoto Island is a volcanic island in the Hauraki Gulf near Auckland, New Zealand. The 5.5 km wide island is an iconic and widely visible landmark of Auckland with its distinctive symmetrical shield volcano cone rising 260 metres high over the Hauraki Gulf...
is exceptionally interesting. Apart from the summit, it is composed of Pahoehoe (smooth) and ’A’a (broken) lava flows. A walk up to the scoria summit passes lava caves. The vegetation is also exceptionally interesting, with pohutukawa forests, astelia growing on the lava, and a grove of kidney ferns.
The coast on Motutapu Island
Motutapu Island
Motutapu Island is a island in the Hauraki Gulf to the northeast of the city of Auckland, New Zealand. The island is part of the Hauraki Gulf Maritime Park....
from Islington Bay to Administration Bay starts with Waitemata sandstone cliffs, and finishes with greywacke and chert near Administration Bay. Ancient greywacke pebble beaches can be seen embedded in the Waitemata sandstone cliffs. It is possible to walk from Rangitoto Island to Motutapu Island via a causeway.
Motuihe Island
Motuihe Island
Motuihe Island lies between Motutapu and Waiheke islands in the Hauraki Gulf of New Zealand, near Auckland. The island measures about , of which around are remnants of coastal forest. The island is a recreation reserve controlled by the Department of Conservation and administered by the Motuihe...
has a mixture of Waitemata sandstone, with Parnell Grit in the headlands, greywacke at the south, and even a coastal section with flaggy limestone on the west coast. It is also a bird sanctuary, with kiwi, saddleback, dotteral, oyster catcher, heron, and more common birds such as the fantail, tui, and pukeko.
Tiritiri Matangi Island
Tiritiri Matangi Island
Tiritiri Matangi Island lies in the Hauraki Gulf of New Zealand, east of the Whangaparaoa Peninsula in the North Island and north east of Auckland. The island is an open nature reserve managed under the supervision of the Department of Conservation and is noted for its bird life, including kiwi...
is a rugged island composed of greywacke. It also a bird sanctuary, with rare birds, including saddleback, takahē, parakeet, North Island robin, kōkako, whitehead, little spotted kiwi, stitchbird and brown teal.
Waiheke Island
Waiheke Island
Waiheke Island is an island in the Hauraki Gulf of New Zealand, located about from Auckland.The island is the second-largest in the Hauraki Gulf after Great Barrier Island. It is the most populated, with nearly 8,000 permanent residents plus another estimated 3,400 who have second or holiday homes...
is mostly composed of greywacke. At Stoney Batter, at the western end of the island are the remains of a volcano (7-8 Ma), with the remains of a lava flow in the form of large boulders.
Lake Pupuke
Lake Pupuke
Lake Pupuke is a heart-shaped freshwater lake occupying a volcanic explosion crater between the suburbs of Takapuna and Milford on the North Shore of Auckland, New Zealand. The heart shape is a result of its formation by the linking of two circular craters - a larger one forming most of the lake...
on the North Shore is the crater lake of one of Auckland’s earliest volcanoes. Water flows underground through cracks in the lava from the lake to Thorne Bay, where it is discharged by natural springs. At the northern end of Takapuna
Takapuna
Takapuna is a central, coastal suburb of North Shore City, located in the northern North Island of New Zealand, at the beginning of a south-east-facing peninsula forming the northern side of the Waitemata Harbour...
Beach are the remains of a lava flow, that flowed over a forest, preserving casts of the trees before incinerating them. The lava also flowed over mounds, and the material underneath was later eroded, leaving arches. Further north along the coast is a cast of a large Kauri tree.
Onepoto and Tuff Crater beside the North Shore motorway are examples of explosion craters, that have breached and are now open to the sea. Onepoto basin has largely been reclaimed and now forms a park, while Tuff Crater hosts a tidal mangrove swamp.
Volcanic cones, such as Mount Eden, One Tree Hill, Mount Albert, Mount Roskill, Mount Hobson, Mount St John, Auckland Domain, Mount Mangere, North Head, Mount Wellington are well worth a visit, even for the view from the top. Most have large scoria mound and crater. They also often have the remains of a Māori pā
Pa
-Places:* Pâ, a town in Burkina Faso* Pâ Department, a department in Burkina Faso* PA postcode area, in Scotland* Province of Palermo, Italy* Palo Alto, California* Panama, ISO country code** .pa, the country code top level domain for Panama...
(fortified village). Te Tokaroa Reef is a lava flow that flows 10 km from Three Kings to the Waitemata Harbour, and almost manages to cross the harbour.
Many of the East Coast Bays beaches, such as Long Bay and Campbells Bay are good places to see the Waitemata sandstone and mudstone cliffs, with embedded Parnell Grit. Shakespear Park, at the end of Whangaparaoa Peninsula is also a good place to visit. Large blocks of basalt rock have been moved from the Waitakere Ranges to the coast just beyond Army Bay. Further north is Waiwera, with more Waitemata sandstone cliffs and Parnell Grit, and also commercial hot pools, suitable for children. The next beach over, Wenderholm Regional Park is well worth a visit and a good place for a picnic.
The Waitakere Ranges
Waitakere Ranges
The Waitakere Ranges are a chain of hills in the Auckland metropolitan area, generally running approximately 25 km from north to south, 25 km west of central Auckland, New Zealand. The maximum elevation within the ranges is 474 m...
are interesting. Streams often flow down narrow gorges surrounded by conglomerate rocks formed from debris from the Waitakere volcano. The Piha Gorge, Pararaha Gorge and Karamatura Valley are good examples.
Maori Bay, just south of Muriwai, has good examples of pillow lavas. It is also the home of a gannet colony.
Te Henga Beach has large sand dunes behind it, and two lakes behind the same dunes. This are has been used to make several TV series, including “Xena: Warrior Princess
Xena: Warrior Princess
Xena: Warrior Princess is an American–New Zealand supernatural fantasy adventure series that aired in syndication from September 4, 1995 until June 18, 2001....
”. On the way to the beach, it is worthwhile visiting the Auckland City Walk, to see the native bush, including large kauri trees. The Waitakere River swamp is also interesting.
Piha
Piha
Piha is a northern New Zealand coastal settlement with a population of about 600. It is one of the most popular beaches in the area and a major day-trip destination for Aucklanders throughout the year, although especially so in summer.-Location:...
Beach is Auckland’s most famous surf beach. The area to the south has blowholes, that the sea surges through. Whites Beach, to the north of Piha is also interesting. Further south is Mercer Bay, which has a headland, with an enormous hole corresponding to a volcanic pipe. Still further south are Karekare Beach and Whatipu Beach, backed by steep cliffs. Sand dunes are accumulating along the shore at an amazing rate, and the beach has grown almost two kilometres wider in the last 100 years. Lakes are developing behind the dunes. All the beaches have black iron sand, that can be extracted by using a magnet.
Awhitu Peninsula, south of the Manukau Harbour, is essentially composed of consolidated sand, more than 100 m high. The cliffs are rapidly eroding, and preserved tree stumps and blocks of peat in the cliffs fall down to the beach. It is best to visit places like Hamilton’s Gap at low tide.
The Hunua Ranges
Hunua Ranges
The Hunua Ranges form a block of hilly country to the southeast of Auckland in New Zealand's North Island. They cover some 250 square kilometres , containing 178 km² of parkland, and rise to 688 metres at Kohukohunui...
give a good example of greywacke rock. A visit to one of the dams used to supply Auckland with water is worthwhile. Raukura Point, near Kawakawa Bay is a good place to see chert. Regional parks such as Tawhitokino and Tapapakanga are good places to see greywacke boulder beaches. Further south is Miranda Hot Pools, for a relaxing swim.
The route out to Waikato Heads is interesting. It gives good examples of the volcanoes of the South Auckland Volcanic Field, which have eroded sufficiently to make an excellent soil for growing vegetables. Closer to the river mouth, the geology changes to Murihiku greywacke. A walk south from the beach gives good access to the greywacke. Travelling south from Waikato Heads on unsealed roads takes you through country roads, among cliffs composed of Te Kuiti sandstone and limestone, and finally out to the Waikato Plains at Te Kauwhata and state highway 1.
Maps
Geological maps of New Zealand can be obtained from the New Zealand Institute of Geological and Nuclear Science (GNS Science), a New Zealand Government Research Institute.GNS provides a free Map of New Zealand's Geological Foundations.GNS Map of New Zealand's Geological Foundations
The main maps are the 1 : 250 000 QMap series, which will be completed as a series of 21 maps and booklets in 2010. Low resolution versions of these maps (without the associated booklet) can be downloaded from the GNS site for free. The map for the Auckland Area was published in 2002.
There is a 1 : 50 000 map of the Auckland Urban Area, published in 1992, that is worth looking at, and there are also maps of the Waitakere Ranges and Helensville-Whangaparaoa areas published in the 1980s.
Further reading
- Graham, Ian J. et al.;A continent on the move : New Zealand geoscience into the 21st century - The Geological Society of New Zealand in association with GNS Science, 2008. ISBN 9781877480003
- Lava and Strata: A guide to the volcanoes and rock formations of Auckland - Homer, Lloyd; Moore, Phil & Kermode, Les; Landscape Publications and the Institute of Geological and Nuclear Sciences, 2000. ISBN 0-908800-02-9.
- Vanishing volcanoes : a guide to the landforms and rock formations of Coromandel Peninsula - Homer, Lloyd; Moore, Phil; Landscape Publications and the Institute of Geological and Nuclear Sciences, 1992. ISBN 0908800010.
- City of volcanoes : a geology of Auckland, E.J. Searle, R.D. Mayhill, Longman Paul, 1981. ISBN 0582717841.
- Walks through Auckland's geological past : a guide to the geological formations of Rangitoto, Motutapu and Motuihe Islands, Peter F. Ballance and Ian E.M. Smith, Geological Society of New Zealand guidebook, no. 5.
- GNS Information on New Zealand Volcanoes, including the Auckland Volcanic Field
- Auckland Museum Information on New Zealand Volcanoes, including the Auckland Volcanic Field
- Auckland Regional Council Information on the Auckland Volcanic Field
- The age of volcanoes of the Auckland Volcanic Field, by Graham Leonard, Andy Calvert, Phil Shane, Jan Lindsay, Paul Augustinus, Ian Smith, Michael Rosenberg