The Auckland volcanic field is an area of monogenetic volcanoes covered by much of the metropolitan area of Auckland, New Zealand's largest city, located in the North Island. The approximately 53 volcanoes in the field have produced a diverse array of maars, tuff rings, scoria cones, and lava flows. With the exception of Rangitoto, no volcano has erupted more than once, but the other eruptions lasted for various periods ranging from a few weeks to several years. Rangitoto erupted several times and recently twice; in an eruption that occurred about 600 years ago, followed by a second eruption approximately 50 years later. The field is fuelled entirely by basaltic magma, unlike the explosive subduction-driven volcanism in the central North Island, such as at Mount Ruapehu and Lake Taupō.
The volcanism of New Zealand has been responsible for many of the country's geographical features, especially in the North Island and the country's outlying islands.
The geology of New Zealand is noted for its volcanic activity, earthquakes and geothermal areas because of its position on the boundary of the Australian Plate and Pacific Plates. New Zealand is part of Zealandia, a microcontinent nearly half the size of Australia that broke away from the Gondwanan supercontinent about 83 million years ago. New Zealand's early separation from other landmasses and subsequent evolution have created a unique fossil record and modern ecology.
The Auckland Region of New Zealand 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 Waitākere 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 Auckland 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 Waikato and King Country regions of New Zealand are built upon a basement of greywacke rocks, which form many of the hills. Much of the land to the west of the Waikato River and in the King Country to the south has been covered by limestone and sandstone, forming bluffs and a karst landscape. The volcanic cones of Karioi and Pirongia dominate the landscape near Raglan and Kawhia Harbours. To the east, the land has been covered with ignimbrite deposits from the Taupō Volcanic Zone. Large amounts of pumice from the Taupō Volcanic Zone have been deposited in the Waikato Basin and Hauraki Plains.
The Waitākere volcano, also known as the Manukau volcano, was a Miocene era volcano that formed off the west coast of the modern Auckland Region of New Zealand's North Island. Erupting intermittently between 23 million and 15 million years ago, the volcano was at one point one of the tallest mountains in New Zealand. The volcano alternated between periods as a seamount and as a volcanic island, before tectonic forces raised the volcano up from the seafloor 17 million years ago. Volcanism at the site ceased 15 million years ago and the cone has mostly eroded, however the modern Waitākere Ranges are formed from the remnants of the volcano's eastern slopes. A number of visible volcanic sites associated with the Waitākere volcano remain around Auckland, including Pukematekeo, Karekare and Lion Rock.
The Poutu Fault Zone is a seismically active area of the central North Island of New Zealand.
The Hauraki Rift is an active NeS-to NWeSE-striking rift valley system in the North Island of New Zealand that has produced the Firth of Thames and the Hauraki Plains. It is approximately 25 kilometres (16 mi) wide and 250 kilometres (160 mi) long.
The Taupō Rift is the seismically active rift valley containing the Taupō Volcanic Zone, central North Island of New Zealand.
The Taupō Fault Belt contains many almost parallel active faults, and is located in the Taupō Rift of the central North Island of New Zealand geographically between Lake Taupō and the lakes of Rotorua, Tarawera, Rotomahana and Rerewhakaaitu. The potential active fault density is very high, with only 0.1 to 1 km separating the north-east to south-west orientated normal fault strands on detailed mapping of part of the belt. The Waikato River bisects the western region of the belt.
The Firth of Thames Fault is a postulated minor hinge fault along the western side of the still tectonically active Hauraki Rift which could have a length up to 220 km (140 mi) and fairly likely 150 km (93 mi). The recently identified but yet to be fully characterised 25km long Te Puninga fault is presumably an intra-rift fault within a few kilometres of its line. Up to the discovery of the Te Puninga fault the active displacement of the rift was believed to be accommodated by the active intra-rift Kerepehi Fault.
The Hauraki Fault is a normal fault along the eastern side of the still tectonically active Hauraki Rift which could have a length up to 220 km (140 mi) and fairly likely 150 km (93 mi). The recently identified but yet to be fully characterised 25km long Te Puninga fault is presumably an intra-rift fault which augments the active displacement of the rift accommodated by the active intra-rift Kerepehi Fault. However shallow small earthquakes have been mapped to the presumed location of the Hauraki Fault.
The Wairoa North Fault has a maximum 6.7 potential for normal fault rupture and is the closest known active fault to the city of Auckland being 40 km (25 mi) to the south east.
The South Auckland volcanic field, also known as the Franklin Volcanic Field, is an area of extinct monogenetic volcanoes around Pukekohe, the Franklin area and north-western Waikato, south of the Auckland volcanic field. The field contains at least 82 volcanoes, which erupted between 550,000 and 1,600,000 years ago.
The extinct Ngatutura volcanic field that was active between 1.54 and 1.83 million years ago is one of four volcanic fields in an intraplate back arc relationship with the still active Hauraki Rift and the presently dormant Auckland volcanic field. The other volcanic fields, which are part of the Auckland Volcanic Province, are the oldest, Okete to the south near Raglan in late Pliocene times. and to the north the younger South Auckland volcanic field.
The Alexandra Volcanic Group is a chain of extinct calc-alkalic basaltic stratovolcanoes that were most active between 2.74 and 1.60 million years ago but is now known to have had more recent activity between 1.6 and 0.9 million years ago. They extend inland from Mount Karioi near Raglan with Mount Pirongia being the largest, with Pukehoua on the eastern slopes of Pirongia, Kakepuku, Te Kawa, and Tokanui completing the definitive lineament. The associated, but usually separated geologically basaltic monogenetic Okete volcanic field, lies mainly between Karioi and Pirongia but extends to the east and is quite scattered.
The Coromandel Volcanic Zone (CVZ) is an extinct intraplate volcanic arc stretching from Great Barrier Island in the north, through the Coromandel Peninsula, to the Kaimai Range in the south. The area of transition between it and the newer and still active Taupō Volcanic Zone is now usually separated and is called the Tauranga Volcanic Centre. Its volcanic activity was associated with the formation and most active period of the Hauraki Rift.
Much of the volcanic activity in the northern portions of the North Island of New Zealand is recent in geological terms and has taken place over the last 30 million years. This is primarily due to the North Island's position on the boundary between the Indo-Australian and Pacific Plates, a part of the Pacific Ring of Fire, and particularly the subduction of the Pacific Plate under the Indo-Australian Plate. The activity has included some of the world's largest eruptions in geologically recent times and has resulted in much of the surface formations of the North Island being volcanic as shown in the map.
The 1835 Auckland earthquake was a magnitude 6.5 earthquake that occurred sometime during 1835 in the Auckland region of New Zealand. The earthquake was caused by movement along the Wairoa North Fault, which runs through the area. At the time, the settlement of Auckland was still quite small, and there are limited records of the specific damage caused by the earthquake. However, historical accounts suggest that the earthquake caused significant shaking and rumbling in the area, and it is possible that some buildings or structures may have been damaged or collapsed. Despite this, there are no records of major damage or casualties resulting from the earthquake. The 1835 Auckland earthquake remains an important event in the region's history, particularly as it highlights the seismic activity that can occur in the area due to the presence of faults such as the Wairoa North Fault.
The Whangamata fault zone is part of the seismically active western Taupō rift-bounding normal wall faults and is associated with the major active Whangamata Fault and Haukari/West Whangamata Fault and several unnamed active faults. Obsidian used by the Māori is exposed along these faults.
