North Island surface volcanic deposits | |
---|---|
Stratigraphic range: Miocene, ~ | |
Type | Igneous |
Overlies | Murihiku Terrane, Caples Terrane and Waipapa Composite Terrane Greywacke, some Haast Schist near Rotoroa |
Lithology | |
Primary | Basalt, andesite and rhyolite |
Location | |
Coordinates | 37°S175°E / 37°S 175°E |
Region | North Island |
Country | New Zealand |
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 active or dormant volcanoes extend from Northland through the "City of Volcanoes", Auckland to Taranaki on the west coast and Bay of Plenty on the East with the North Island Volcanic Plateau hosting multiple active volcanoes. There has been activity within the last 5000 years in all these areas, with most activity on North Island Volcanic Plateau where the Taupō Rift is widening by as much as 19 mm (0.75 in)/year, [1] much faster than other continental intraarc rifts. [2] The Taupō volcanoes most recent major eruption, the Taupō or Hatepe eruption, took place around 232 CE, and ejected some 120 cubic kilometres (29 cu mi) of material (rating 7 on the VEI scale) [3] [4] This included pyroclastic deposits and ash that impacted much of the North Island which was not settled by man at the time.
The large ignimbrite sheets of the North Island Volcanic Plateau extend, under later sedimentary and volcanic deposits, from Hawkes Bay all the way to Auckland. This is as the Kidnappers eruption of a million years ago (1 Ma) produced 1,200 km3 (287.9 cu mi) of ignimbrite deposits, the most widespread on Earth, being over 45,000 km2 (17,000 sq mi) in area. [5] This eruption had an estimated VEI of 8 and has been assigned a total eruption volume (not just tephra) of 2,760 km3 (662.2 cu mi). [5] The basaltic volcanism of the far north is tens of millions of years older than this but towards the south by the Bay of Islands we have basaltic volcanoes that erupted only shortly before human colonisation, being Te Puke at between 1300 and 1800 years ago. [6] Also associated with the 20 million year old Kaikohe-Bay of Islands volcanic field are andesitic and rhyolitic centres. The slightly older 8 million to 250,000 year ago mix of basaltic and dacitic Whangārei volcanic field volcanoes [7] is adjacent to the andestic and dacitic remnants of 22 to 18 million years ago activity of a large stratovolcano off Whangārei Heads Further south is the basaltic Rangitoto Island off Auckland which last erupted about 600 years ago [8] It is part of the a line of monogenetic volcanic fields extending southward as they get older along the west coast from the dormant Auckland volcanic field to the South Auckland volcanic field, then Ngatutura volcanic field and finally the Okete volcanic field. This last is situated on the slopes of the calc-alkalic basaltic stratovolcanoes of the Alexandra Volcanic Group. While considering stratovolcanoes, by Auckland on its west coast is the Waitākere Ranges, which are the andesitic conglomerate remnants of the 23 to 15 million year old Waitākere volcano. [9] Much further south on the west coast is the potentially active andesitic Taranaki group of stratovolcanoes that have a history of collapse events. To the east of Auckland is the dacite stratovolcano of Little Barrier Island that is between 3 and 1.2 million years old and older Great Barrier Island at 18.5 to 12.3 million years. Great Barrier Island leads on to the Coromandel Volcanic Zone which towards its south last erupted about 5 million years ago but has similar timings to Great Barrier to the north. The Coromandel Volcanic Zone contains andesitic and rhyolitic eruptives mainly. Mayor Island just off the Coromandel east coast is a rhyolitic caldera that last erupted only about 6,340 years ago. [10] The Tauranga Volcanic Centre on the east coast was active with andesitic and rhyolitic events between 2.95 and 1.9 million years ago. [11] Inland from the Coromandel and Tauranga are a line of andesitic volcanoes such as Maungatautari that are located on the far side of the Hauraki Rift and have ages of about 1.8 million years. [12] The Hauraki Rift intercepts the Taupō Rift creating the most active area of silicic volcanism on Earth in the Taupō Volcanic Zone. Its northeastern and southeastern portions are active andestic volcanoes while the central calderas erupt rhyolitic ignimbrite with later basaltic eruptions.
The Northland region contains two recently active volcanic fields, one centred around Whangarei, [13] and the other is the Kaikohe-Bay of Islands volcanic field. [14] The latest activity in the Kaikohe-Bay of Islands field, around 1300 to 1800 years ago, created four scoria cones at Te Puke (near Paihia). [14]
Earlier, during the Miocene, a mainly andesitic volcanic arc ran through Northland and neighbouring regions (including the Three Kings Ridge and northern Coromandel Peninsula), with western and eastern belts active between 25—15 million years ago and 23–11 million years ago respectively. [16] Although this produced substantial volcanic edifices, including New Zealand's largest known stratovolcano, the Waitakere volcano, [17] most of these have been eroded away, buried, or submerged, especially in the west, where a series of volcanoes buried offshore stretches south almost to New Plymouth. This is called the Northland-Mohakatino Volcanic Belt. [18] Remnants of these two ancient volcano belts are still exposed in many places, including Whangarei Heads, the Hen and Chickens Islands, around Whangaroa Harbour, Waipoua forest, and the Waitākere Ranges.
The basaltic Auckland volcanic field is a monogenetic volcanic field underlying much of the Auckland metropolitan area. The field's many vents have produced a diverse array of explosion craters, scoria cones, and lava flows. The largest and most recent is Rangitoto in the Hauraki Gulf, which last erupted 600–700 years ago. Currently dormant, the field is likely to erupt again within the next "hundreds to thousands of years" (based on past events), a short timeframe in geologic terms. [19] Auckland's residents, however, face more danger from volcanoes farther south. [19]
Auckland's volcanoes are believed to be the latest product of an unusual magma source related to local tectonics which is not a classic hot spot, as the earlier volcanic fields are to the south, the opposite expected from movement of the Australian Plate over a stationary mantle plume source. [20]
Three volcanic fields erupted between 2.7 and 0.5 million years ago, migrating northwards from Mount Pirongia to the Bombay Hills. The earliest of these fields formed the Alexandra Volcanics [21] which is distinguished by large arc volcano tholeiitic cones but did have associated Okete Volcanics which were traditionally more akaline and oxidised and were in the monogenetic volcanic field pattern seen in the later fields. The distinction between the Alexandra and Okete volcanics is not necessarily clear cut and is still being studied. Alexandra Volcanic Group rocks (mostly basalt) cover about 450 km2 amounting to 55 km3 from at least 40 vents. Mount Pirongia and Mount Karioi are part of the main lineament in the group. [22] The later fields are the smallest Ngatutura Volcanics which comprises about 16 volcanoes south of Port Waikato on the west coast and the South Auckland volcanic field with over 80 volcanoes. [23] The magma body that created the Auckland volcanic field is considered to have been related to these outpourings also. Unlike typical hot spots such as the one underlying Hawaii, it does not seem to have stayed still, but instead is migrating northward at a faster pace than the surrounding Indo-Australian plate. Its motion has been explained as the tip of a propagating crack produced by the twisting of the North Island's crust. [24] [20]
The extinct Coromandel Volcanic Zone (CVZ) was a volcanic arc stretching from Great Barrier Island in the north, through the Coromandel Peninsula, to Tauranga and the southern Kaimai Ranges in the south. Activity began in the north around 18 million years ago, and was primarily andesitic until around 9–10 million years ago, when it changed to a bimodal basaltic/rhyolitic pattern. Eruptive centres gradually migrated southward, [26] where they transitioned into early activity in the Taupō Volcanic Zone. Later activity in the CVZ and its interface with the Taupō Volcanic Zone is obscured by subsequent events and is not fully understood, but continued in the south until perhaps 1.5 million years ago in the Tauranga Volcanic Centre. [27] Together with the extinct undersea Colville Ridge, the CVZ formed a precursor to the modern Taupō Volcanic Zone and Kermadec Ridge. [28]
Mayor Island / Tūhua is a peralkaline shield volcano with a caldera partly formed in a large eruption some 7000 years ago. It has exhibited many eruptive styles, and its last eruption may have occurred only 500–1000 years ago. [29] The island's Maori name, Tuhua, refers to the obsidian they found on the island and prized for its sharp cutting edge.
About 350 kilometres long by 50 kilometres wide, the Taupō Volcanic Zone (TVZ) is the world's most productive area of recent silicic volcanic activity, [30] with the highest concentration of young rhyolitic volcanoes. [31] Mount Ruapehu marks its southwestern end, and it continues up through Ngauruhoe, Tongariro, Lake Taupō, the Whakamaru, Mangakino, Maroa, Reporoa, and Rotorua calderas, the Okataina Volcanic Complex (including Mount Tarawera) and 85 kilometres beyond Whakaari / White Island to the submarine Whakatāne Seamount. The TVZ also contains numerous smaller volcanoes, along with geysers and geothermal areas. Volcanic eruptions began here around two million years ago, with silicic eruptions starting around 1.55 million years ago, as activity shifted southeast from the Coromandel Volcanic Zone. [27]
Volcanism in the Taranaki region has migrated southeastward during the last two million years. Beginning in the Sugar Loaf Islands, near New Plymouth, activity then shifted to Kaitake (580,000 years ago) and Pouakai (230,000 years ago) before creating the large stratovolcano called Mount Taranaki, (former name Mount Egmont), which last erupted in 1854, and its satellite vent, Fanthams Peak. [32] This southeastward migration is the continuation of the 25 million year activity of the Northland-Mohakatino Volcanic Belt that extends mainly under the present Tasman Sea from the west of Northland down to Mount Taranaki. [18]
Copied content from Volcanism of New Zealand on pages creation date; see Volcanism of New Zealand: Revision history for attribution.
The Taupō Volcanic Zone (TVZ) is a volcanic area in the North Island of New Zealand. It has been active for at least the past two million years and is still highly active.
Mount Tarawera is a volcano on the North Island of New Zealand within the older but volcanically productive Ōkataina Caldera. Located 24 kilometres southeast of Rotorua, it consists of a series of rhyolitic lava domes that were fissured down the middle by an explosive basaltic eruption in 1886. While the 1886 eruption was basaltic, study has shown there was only a small basalt component to the previous recent rhyolitic predominant eruptions. This eruption was one of New Zealand's largest historical eruptions, and killed an estimated 120 people. The fissures run for about 17 kilometres (11 mi) northeast–southwest.
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.
Lake Taupō, in the centre of New Zealand's North Island, fills the caldera of the Taupō Volcano, a large rhyolitic supervolcano. This huge volcano has produced two of the world's most powerful eruptions in geologically recent times.
The Mangakino caldera complex is the westernmost and one of oldest extinct rhyolitic caldera volcanoes in the Taupō Volcanic Zone of New Zealand's North Island. It produced about a million years ago in the Kidnappers eruption of 1,200 km3 (287.9 cu mi), the most widespread ignimbrite deposits on Earth being over 45,000 km2 (17,000 sq mi) and was closely followed in time by the smaller 200 km3 (48.0 cu mi) Rocky Hill eruption. The Kidnappers eruption had a estimated VEI of 8 and has been assigned a total eruption volume of 2,760 km3 (662.2 cu mi).
Ōkataina Caldera is a volcanic caldera and its associated volcanoes located in Taupō Volcanic Zone of New Zealand's North Island. It has several actual or postulated sub calderas. The Ōkataina Caldera is just east of the smaller separate Rotorua Caldera and southwest of the much smaller Rotomā Embayment which is usually regarded as an associated volcano. It shows high rates of explosive rhyolitic volcanism although its last eruption was basaltic. The postulated Haroharo Caldera contained within it has sometimes been described in almost interchangeable terms with the Ōkataina Caldera or volcanic complex or centre and by other authors as a separate complex defined by gravitational and magnetic features.. Since 2010 other terms such as the Haroharo vent alignment, Utu Caldera, Matahina Caldera, Rotoiti Caldera and a postulated Kawerau Caldera are often used, rather than a Haroharo Caldera classification.
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 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 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 Tauranga Volcanic Centre is a geologic region in New Zealand's Bay of Plenty. It extends from the southern end of Waihi Beach and from the old volcanoes of the Coromandel Peninsula that make up the northern part of the Kaimai Range, towards the Taupō Volcanic Zone.
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.
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 Rotoiti Caldera is a postulated, mainly infilled sub caldera of the Ōkataina Caldera based upon gravitational and magnetic evidence. While bathymetry of Lake Rotoiti is consistent with volcanic vents being present, they could be in an area of collapse subsidence outside the north western margins of the Rotoiti Caldera itself.