Maahunui volcanic field | |
|---|---|
Volcanic field | |
 Approximate extent of Maahunui volcanic field | |
| Coordinates: 44°00′32″S172°33′54″E / 44.008986°S 172.564949°E | |
| Offshore water bodies | Pacific Ocean |
| Age | |
| Area | |
| • Total | 1,520 km2 (590 sq mi) [2] |
| Last eruption | 11.5 Ma |
The Maahunui volcanic field is an extinct basaltic submarine Miocene monogenetic volcanic field [2] off the east coast of the South Island of New Zealand to the south of the more recent Banks Peninsula Volcano. [3]
Over 30 volcanic features including craters and cones have been described in the Maahunui Volcanic Field, [2] even although most are buried in up to 1 km (0.62 mi) thickness of ocean sediment. [1] These are intraplate small-volume single event volcanoes. [4] A feature of the field is that it was always underwater, but some of the cones formed islands in the historic sea and then have been eroded with characteristic flattened tops. It has been thought that explosive eruptions are rare in volcanoes whose vents are more than 100 m (330 ft) deep under water, but such must have occurred for some of the located craters that must have been formed at about 1 km (0.62 mi) deep. [2] The eruptions occurred between 15.9 to 11 million years ago, mostly in the last 2 million years of this period. [1] The resulting seamounts were finally all buried about the time that Banks Peninsula was formed in the late Miocene. The area of the field is about 1,520 km2 (590 sq mi) and the presence of the volcanoes is relevant to mineral and other potential exploitation of the Canterbury submarine basin. [2] The detailed understanding of the field results from bore hole and seismic data accumulated over many years of geological mapping.
The name Maahunui relates to the canoe of Maui which (according to Māori legend) became the South Island of New Zealand. It is the term Māori use for the coast south of Banks Peninsula. It was so named after appropriate consultation in 2019. [3]
The Ring of Fire is a tectonic belt of volcanoes and earthquakes.
Rangitoto Island is a volcanic island in the Hauraki Gulf near Auckland, New Zealand. The 5.5 km (3.4 mi) wide island is a symmetrical shield volcano cone capped by central scoria cones, reaching a height of 260 m (850 ft). Rangitoto is the youngest and largest of the approximately 50 volcanoes of the Auckland volcanic field, having erupted in two phases about 1450 CE and 1500 CE and covering an area of 2,311 ha. It is separated from the mainland of Auckland's North Shore by the Rangitoto Channel. Since World War II, it has been linked by a causeway to the much older, non-volcanic Motutapu Island.
Whakaari / White Island, also known as White Island or Whakaari, is an active andesite stratovolcano situated 48 km (30 mi) from the east coast of the North Island of New Zealand, in the Bay of Plenty. The island covers an area of approximately 325 ha, which is just the peak of a much larger submarine volcano.
A monogenetic volcanic field is a type of volcanic field consisting of a group of small monogenetic volcanoes, each of which erupts only once, as opposed to polygenetic volcanoes, which erupt repeatedly over a period of time. The small monogenetic volcanoes of these fields are the most common subaerial volcanic landform.
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.
A volcanic field or crater row is an area of Earth's crust that is prone to localized volcanic activity. The type and number of volcanoes required to be called a "field" is not well-defined. Volcanic fields usually consist of clusters of up to 100 volcanoes such as cinder cones. Lava flows may also occur. They may occur as a monogenetic volcanic field or a polygenetic volcanic field.
A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption. A maar characteristically fills with water to form a relatively shallow crater lake, which may also be called a maar.
The Panmure Basin, also sometimes known as the Panmure Lagoon, is a tidal estuary within a volcanic crater or maar in New Zealand's Auckland volcanic field. It is located to the south of Panmure town centre.
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 Banks Peninsula Volcano is an extinct volcanic complex to the east of Christchurch on New Zealand's South Island. While the volcano is highly eroded it still forms the majority of Banks Peninsula with a highest point of 919 m (3,015 ft). It is a composite of two main eruptive centres one originating at Lyttelton Harbour, the other at Akaroa Harbour. The eruptions were predominantly basaltic, with associated andesite and trachytes, with minor rhyolite. The volcanic activity occurred in the Late Miocene and possibly extended into the Early Pliocene. There are four volcanic groups, all of which are within the Māui Supergroup. The Christchurch earthquakes led to rumors of a possible eruption, however, there is no known magma chamber beneath the volcano and there has not been any sign of volcanic activity in the last 5 million years.
Lunar Crater volcanic field is a volcanic field in Nye County, Nevada. It lies along the Reveille and Pancake Ranges and consists of over 200 vents, mostly small volcanic cones with associated lava flows but also several maars, including one maar named Lunar Crater. Some vents have been eroded so heavily that the structures underneath the volcanoes have been exposed. Lunar Crater itself has been used as a testing ground for Mars rovers and as training ground for astronauts.
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 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.
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 volcanic activity in the South Island of New Zealand terminated 5 million years ago as the more northern parts of the North Island became extremely volcanically active. The South Islands surface geology reflects the uplift of the Pacific Plate as it collides with the Indo-Australian Plate along the Alpine Fault over the last 12 million years and the termination of subduction, about 100 to 105 million years ago. There is a very small chance of reactivation of volcanism in the Dunedin Volcano. This chance is made slightly higher by the observation that Southland's Solander Islands / Hautere just off the coast of the South Island were active as recently as 50,000 years old, and on a larger scale 150,000 years old.
The Dunedin volcanic group is a volcanic group that covers over 7,800 km2 (3,000 sq mi) of Otago in the South Island of New Zealand. It is a recent reclassification of the group previously known as the Waiareka-Deborah volcanic field due to common magma melt ancestries of the Dunedin Volcano with the overlapping alkali basaltic monogenetic volcanic field. Excluded from the group are a group of volcanics of different composition and older age near Oamaru, which have been given the name previously used for the Dunedin group. The older Waiareka-Deborah volcanic field overlaps the new Dunedin volcanic group geographically; though Dunedin Volcano has been well studied from the 1880s since New Zealand's first school of geology was established at the University of Otago, detailed studies of north-central volcanoes such as the Crater near Middlemarch were done much later, and high-quality composition studies still need to be done to properly classify many volcanics near Oamaru.