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New Zealand Volcanoes and Volcanics

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Location Map, Major New Zealand Volcanoes

New Zealand contains the world's strongest concentration of youthful rhyolitic volcanoes, and voluminous ignimbrite sheets blanket much of North Island. Associated caldera formation places this region at the top of the list, along with Indonesia, of volcanoes with caldera as the primary morphologic feature. A strong emphasis on tephrochronology has documented the Quaternary volcanic history of this active island in unusual detail: No other region has a higher proportion (74 percent) of its large eruptions in the BC age range. ...

The earliest historically-dated eruption was at White Island in 1826. ...

Much of the region north of New Zealand's North Island is made up of seamounts and small islands, including 16 submarine volcanoes. The region has the largest number of eruptions dated by SOFAR technology, or underwater sound. No other region has a higher proportion of eruptions building new islands (21 percent, all in Tonga and the Kermadecs) or producing pyroclastic flows (27 percent, mostly on New Zealand's North Island).

The New Zealand area is characterised by both a high density of active volcanoes and a high frequency of eruptions. Volcanic activity in New Zealand occurs in six areas, five in the North Island and one offshore in the Kermadec Islands.

Volcanoes in New Zealand are not randomly scattered, but are grouped into areas of more intensive and long-lived activity, whose position (and the composition of the lavas erupted) can be related to the large-scale movement of the tectonic plates in the New Zealand region. Most New Zealand volcanism in the last 1.6 million years has occurred in the Taupo Volcanic Zone (TVZ). The zone is an elongate area that extends from White Island to Ruapehu. The Taupo Volcanic Zone is extremely active on a world scale: it includes three frequently active cone volcanoes (Ruapehu, Tongariro/Ngauruhoe, White Island), and two of the most productive calderas in the world (Okataina and Taupo).

here are three major types of volcano in New Zealand.

Volcanic Fields

Volcanic fields such as Auckland and Northland, are where small eruptions occur over a wide geographic area, and are spaced over long periods of time (thousands of years). Each eruption builds a new single new volcano, which does not erupt again. Mount Eden and Rangitoto Island are examples in Auckland.

Cone Volcanoes

Cone volcanoes such as Ruapehu, Egmont and Ngauruhoe are characterised by a succession of small-moderate eruptions from one location. The products from the successive eruptions over thousands of years build the cones.

Caldera Volcanoes

Caldera volcanoes such as Taupo and Okataina (which includes Tarawera) have a history of infrequent but moderate-large eruptions. The caldera forming eruptions create super craters 10-25 kilometers in diameter and deposit cubic kilometres of ash and pumice.

It is thought that Auckland's volcanoes first began to appear between 60 000 and 140 000 years ago, starting with the eruptions of the Domain and Albert Park. The largest and most recent eruption was Rangitoto, about 600 years ago. The Auckland Volcanic Field is expected to have a total life of approximately one million years, so potentially there is a lot of life left in the field yet. ...

The Auckland Volcanic Field is comprised of monogenetic volcanoes which means it is unlikely that Mount Wellington or any of the existing volcanoes will erupt again. The next eruption will probably occur in a new location. ...

Mount Wellington is the most recent site of mainland activity (about 9,000 years ago). Scoria and lava deposits overlie tuff deposits from early eruptions. The 100 metre scoria cone was produced from lava fountaining from 3 vents in the crater. Lava flows streamed from a number of vents to Penrose and then on to the Manukau Harbour forming almost 6-kilometer-long lava flows. ... Mount Wellington is the largest scoria cone (volume of scoria) and the second youngest volcano in the Auckland Volcanic Field. ...

Rangitoto is the largest, most recent and least modified volcano of the Auckland Volcanic Field. It forms a near symmetrical cone at the entrance to the Waitemata Harbour.

Auckland City is built upon an active volcanic field created over the last 150,000 years, with the youngest volcano Rangitoto being formed just 600 years ago. Eruptions from 48 small basalt volcanoes have produced an attractive landscape of cones, craters, and lava flows. Today, these remnants provide us with a unique opportunity to learn about our city's volcanic past and the processes that form volcanoes.

Many of the landforms and soils of Auckland, North Shore and Manukau Cities have been produced by basaltic volcanism in just the last 150,000 years, with the latest eruption, Rangitoto, being witnessed by the Maori 600 years ago. While the older (0.5 to 1.5 million years ago) volcanoes of the Franklin basaltic field around the Pukekohe / Bombay area are extinct, further eruptions from the younger Auckland field are considered likely.

The magma that fed Auckland's volcanoes originated some 100 kilometers below the surface. Periodically, a large buoyant body of molten magma rose up through the overlying rocks to erupt at the surface. Near the surface, the hot gas-charged magma was forced out by the pressure of escaping gases.

Auckland's volcanoes all had short lives and have been once-only eruptions. Each volcano was formed during a single eruption, or sequence of short eruptions, generally lasting no longer than a year or two. It is possible however for a scoria cone or tuff ring to form in a matter of days. Once the magma body was exhausted, eruptions ceased and the subsurface plumbing solidified.

The western 1.500 square kilometers of Taranaki is a volcanic landscape that has been constructed from the products of volcanic eruptions principally derived from Mt Taranaki/Egmont (hereafter referred to as Egmont Volcano). Egmont Volcano last erupted about 200 years ago at the culmination of eight eruptions in the preceding 300 years. Deposits around the base of the Volcano record intermittent volcanic activity at this site for the last 130,000 years. Whilst the eruptions have not occurred at regular intervals there has been a moderate or major sized eruption on average every 340 years with numerous smaller events at more frequent intervals. There is therefore no evidence to suggest Egmont Volcano has finally ceased erupting and has become extinct. Rather it must be regarded as an active volcano in a state of quiescence and is one of a number of volcanoes in New Zealand where future eruptions are to be expected. Egmont Volcano is of the "slumbering" type that could begin renewed activity in the next 100 years. ...

One of the characteristic features in the history of Egmont Volcano has been the irregular occurrence of enormous landslides. On three occasions, twice within a very short period of geological time, former Egmont cones have collapsed to the northeast, southeast and west. In each instance extremely large volumes of material greater than 3.5 cubic kilometers flowed across the landscape to travel over 40 kilometers distance, reaching the present Taranaki coastline. These rapid landslide events are technically referred to as volcanic debris avalanches. They have created the distinctive mounds or hummocks on the lowlands surrounding the Volcano. Near to source these landslides envelope everything in their path, even flowing uphill if there is a barrier in the relief. However beyond distances of about 20 km the landslide debris is guided by any pre-existing dissected relief and flows along channels or valleys. ...

Lava flows from Egmont Volcano have seldom extended beyond 4 kilometers distance for their source crater, and the most distant is the Dawson Falls lava flow, 5 kilometers from its presumed source. Thus all lava flows extruded in the entire history of volcanic activity at Egmont Volcano have never extended beyond the area now delineated as Egmont National Park, an area largely unpopulated. In the past, nearly all of the lava flows have been erupted from the central vents of Egmont crater and Fanthams Peak. These vents are regarded as the likely source-areas for future lava flows in future eruptions of Egmont Volcano.

The Kermadec Islands are the summits of large volcanoes that have been built up on the crest of the Kermadec Ridge, and have emerged above sea level. The ridge stretches for 600 to 700 kilometers north-north-east from about 33^oS 180^ooS 178^oW, and has been upraised by the ongoing collision between the Pacific and Australian plates.

The Kermadec Islands, 750 to 1000 kilometers north-north-east of New Zealand, are mainly of volcanic origin. They are uninhabited, except for a weather station manned by a handful of people on Raoul Island (previously known as Sunday Island), the largest and most northerly island in the group. All the islands are scientific reserves for the protection of fauna and flora. They have a moist subtropical climate, and as a result vegetation normally recovers quickly (in tens of years) after being damaged by volcanic activity. However, a very large eruption could well destroy the seed source, and regrowth of vegetation would then be very slow. The islands are administratively part of New Zealand, and any risks that result from eruptions there are accordingly the Government's responsibility to assess and reduce, if possible.

All these volcanoes lie along the zone of collision of two of the major structural plates of which the Earth's crust is composed, the Pacific plate to the east, and the Australian plate to the west. The line of collision is marked by the succession of deep ocean trenches which characterise this part of the south-west pacific, the Tonga Trench in the north, the Kermadec Trench in the centre, and the Hikurangi Trench in the south, off the coast of the North Island of New Zealand. Along this line, the Pacific plate is being forced beneath the overriding Australian plate as a result of the relentless pressure of convergence of these two huge regions of the Earth's surface. The rate at which this process is taking place is relatively high, about 7 centimeters per year on average (although it is not yet known whether the process is continuous, or whether it proceeds as a series of sudden jumps, perhaps associated with large earthquakes). Earthquakes occur on the upper surface of the Pacific plate down to depths of more than 600 kilometers, as it is forced down at a steep angle below the overriding Australian plate, which is itself buckled upwards by the pressure of collision forming structural highs, two of which are the Tonga and Kermadec Ridges. The line of volcanoes formed when rock melted by the heat of collision, over a range of depths at which the increasing temperature outweighed the effect of increased pressure (which tends to prevent melting), then rose under its own buoyancy through denser overlying rock to intrude the upper crust. The primary melting process, shown by earthquakes taking place in the roots of the volcanoes, occurs at depths of about 100 kilometers below the surface.

Raoul Island

The northernmost known volcanic centre in the Kermadecs is Raoul Island, which is the summit of a large submerged massif about 35 kilometers by 20 kilometers, with its long axis aligned north-east, slightly inclined to the overall trend of the Kermadec Ridge. It is possible, however, and indeed likely, that there are submarine volcanoes, as yet undiscovered, further north along the ridge, which rises in several places to within 500 metres of the surface. Raoul Island itself, the largest of the Kermadec Islands, is an anvil-shaped island, about 30 km2 in area, with a maximum length of about 10 kilometers in an east-west direction along the north coast, and about 6 kilometers from north to south. The island has undergone many changes as a result of eruptions during the past few thousand years, and as a result of earlier eruptions. It now contains a large central depression, a little over 3 kilometers east-west by about 2 kilometers north-south, formed largely by subsidence immediately after large eruptions. This type of structure, resembling a very large volcanic crater, is known as a caldera. Just west of Raoul Caldera, and almost touching it at one point, is Denham Bay, a second caldera (also a little over 3 kilomters long, but in a north-south direction, by rather less than 3 kilometers wide), which has been flooded by the sea.

Haroharo Caldera and Okataina Volcanic Center lie in the northern half of the Taupo Volcanic Zone (TVZ), a region of intense volcanic and geothermal activity. The TVZ is about 250 kilometers long and up to 50 kilometers wide; more than 16,000 cubic kilometers of lavas and pyroclastics have been erupted from the TVZ since volcanism commenced in the late Pliocene. Phyolites were erupted from the central part of the TVZ, a deep volcano-tectonic depression in which eruptions were associated with ring structures, cauldron subsidence, and calderas. A complex system of normal faults runs through the TVZ, and andesite volcanoes are found near its ends (Healy, 1962, 1964; Rogan, 1982).

Haroharo Caldera and Okataina Volcanic Center have been the sites of repeated large silicic eruptions during the past 300,000 years or more (Cole, 1970, 1979; Wilson and others, 1984). At least 20 additional explosive eruptions have occurred within the past 50,000 years (Froggatt, 1982), those in the past 20,000 years along fissures (Wilson and others, 1984). ... Recent eruptions have been from Tarawera, located on the southern margin of the caldera, and from thermal areas within and adjacent to the caldera. A major prehistoric eruption of Tarawera, the Kaharoa eruption of ca. A.D. 1250, produced thick pyroclastic deposits and four rhyolite domes at the summit of Tarawera that are now exposed in cross section along the 1886 rift (Cole, 1970).

Rotorua Caldera lies near the western margin of the Taupo Volcanic Zone, west of Okataina Volcanic Center.

Rotorua Caldera formed as a result of eruption of the 200 cubic kilometer (dense-rock equivalent) Mamaku ignimbrite. Subsequent lava domes in the calder, from 1 to 10 cubic kilometers in volume, have not been dated. No eruptions (other than hydrothermal explosions) are known within the past 10,000 years, but the Rotorua-Whakarawarewa area is known for numerous hot springs, geysers, and other geothermal features that support a significant tourist industry.

Ruapehu, (2,779 meters), one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes. The 110 cubic kilometer volcanic massif is elongated in a NNE-SSW direction and is surrounded by another 100 cubic kilometer ring plain of volcaniclastic debris, including the Murimotodebris-avalanche deposit on the NW flank. A single historically active vent, Crater Lake, is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.

Ruapehu volcano is the southernmost of the large active volcanoes of the North Island. Rising to 2,797 meters (9,175 feet), Mount Ruapehu is the highest mountain in the North Island and the most recent of the North Island volcanoes to have erupted. Ruapehu is located at the southern end of the Taupo Volcanic Zone (TVZ), a spreading segment of the Earth's crust and the source of spectacularly explosive eruptions over the last 2 million years. Subsidence in the central axis of the TVZ has led to prominent active faults developing to the east and west of Ruapehu volcano, which are downthrown towards the mountain. These faults mark the boundary of the TVZ in this region, which terminates 20 kilometers south of Ruapehu's summit.

Ruapehu is largely comprised of the volcanic rock andesite. Accumulations of andesite lava flows interbedded with fragmental rubble radiate from the summit region forming a stratovolcano that rises 2,000 meters from the surrounding lowlands. As stratovolcanoes build up they become steep and have a propensity to collapse generating debris avalanches and lahars that spread outwards onto the surrounding lowlands. These lowlands form a roughly circular apron of fragmented rocks (volcaniclastics) termed the ring plain, mainly derived from debris avalanches and lahars, but also including some river (fluvial) and glacial deposits. Mantling the lowlands are various thicknesses of volcanic ash forming the parent material of most of the soils in the region. Due to the dominantly westerly wind direction, ash thickness for a given distance from the summit is always considerably greater to the east than to the west.

Dominating the summit area is a crater lake which, when full to overflowing contains 8-10 million cubic meters of acid waters. During historical eruptions (in 1945 and 1995) the lake water has been ejected out of the crater and onto surrounding glaciers, and/or propelled across the outlet and into the Whangaehu catchment. Displacement of lake water during these eruptions was followed by dome extrusion and/or dry ash eruptions. When water again accumulates in the summit crater, phreatomagmatic (or wet) eruptions occur with accompanying water expulsion creating lateral surges and lahars. Lahars generated in such a way are one of the devastating and hazardous of volcanic events. Throughout history, lahars have been responsible for much loss of life in the countries of the Pacific margin, including New Zealand.

Tauhara Volcano is a complex of five dacite domes of Late Pleistocene age (Lewis, 1968). Tauhara lies 2-3 kilometers outside the northeast rim of Taupo Caldera, along a postulated deep-seated northeast-trending fracture that bounds the east side of the caldera (Wilson and others, 1984). The exact age of Tauhara is not known; its minimum age is 9,000 years (Lewis, 1968).

Taupo Caldera is a poorly defined caldera within the central graben of the southern Taupo Volcanic Zone. Ring fractures are partly hidden by Lake Taupo (Northey, 1982; Wilson and others, 1984). Gravity data suggest that the caldera is deepest near the northernmost point of Lake Taupo, but this is poorly constrained because the lake makes gravity measurements difficult (Rogan, 1982). Rhyolite domes occur within and around the caldera ...

Lake Taupo occupies the center of an approximately 40-kilometer-diameter basin that has been the site of many rhyolite eruptions during the past 10,000 years (Wilson and others, 1984; Wilson and Walker, 1985; Houghton and Wilson, 1986; Nairn and Wood, 1986). At least three major ignimbrites were produced between 330,000 years B.P. and 230,000 years B.P. No major pyroclastic eruptions are recognized between 230,000 years B.P. and 50,000 years B.P., but at least five rhyolite eruptions occurred between 50,000 years B.P. and 20,000 years B.P.. A 10,000-year hiatus followed the last of those eruptions, before the present sequence of eruptive activity began about 10,000 years ago. A series of ten plinian or subplinian pyroclastic eruptions climaxed with the exceptionally violent Taupo Pumice eruptions about 1,800 years ago (90+ cubic kilometers bulk volume) (Healy and others, 1964; Wilson and others, 1980; Froggatt, 1981b, c; Wilson and Walker, 1985; Wilson, 1985). Those eruptions are thought to have been from vents near the Horomatangi Reefs (Walker, 1980); the deepest point in the lake (164 meters) is just south of the reefs.

Tongariro is a large andesitic volcanic massif, located immediately northeast of Ruapehu volcano, that is composed of more than a dozen composite cones constructed over a period of 275,000 years. Vents along a northeast-trending zone extending from Saddle Cone (below Ruapehu volcano) to Te Mari crater (including vents at the present-day location of Ngauruhoe) were active during a several hundred year long period around 10,000 years ago, producing the largest known eruptions at the Tongarioro complex during the Holocene. North Crater stratovolcano, one of the largest features of the massif, is truncated by a broad, shallow crater filled by a solidified lava lake that is cut on the northwest side by a small explosion crater. The youngest cone of the complex, Ngauruhoe, has grown to become the highest peak of the massif since its birth about 2,500 years ago. The symmetrical, steep-sided Ngauruhoe, along with its neighbor Ruapehu to the south, have been New Zealand's most active volcanoes during historical time.

The uninhabited 2 x 2.4 kilometer White Island (321 meters) is the emergent summit of a 16 x 18 kilometer submarine volcano. The island consists of two overlapping stratovolcanoes; the summit crater appears to be breached to the SE because the shoreline corresponds to the level of several notches in the SE crater wall. Intermittent steam and tephra eruptions have occurred throughout the short historical period, but its activity also forms a prominent part of Maori legends.

White Island is the northernmost active volcano in the Taupo Volcanic Zone - a 250-kilometer-long zone of intense volcanism that marks the boundary of the Australian and Pacific tectonic plates. Scientists from the Institute of Geological & Nuclear Sciences Limited are regular visitors to the privately-owned island, which attracts an ever-increasing number of tourists. Sitting 48 kilometers offshore, the island has been built up by continuous volcanic activity over the past 150,000 years. About 70 percent of the volcano is under the sea, making this massive volcanic structure the largest in New Zealand.

The island has a history of long periods of continuous hydrothermal activity and steam release, punctuated by small-to-medium eruptions. Between 1976 and 1993 White Island was more active than at any time in the past few hundred years, and ash from its 1998 eruptions was recorded as far inland as Rotorua. The volcano's activity is often visible to people in Bay of Plenty with gas and ash plumes rising as high as 10 kilometers on clear, still days. Craters and fumaroles on the island continually emit gases at rates of several hundred to several thousand tonnes per day. The gases are mostly steam, carbon dioxide and sulphur dioxide, with small quantities of chlorine and fluorine. Acid gases combine with water in the steam to form acid droplets that can sting the eyes and skin, and can affect breathing. The acid can also damage cameras, electronic equipment and clothes. In spite of its hostile environment, the island is host to a number of bird species including a gannet colony.

The upper slopes of the island, which rises to a height of 321 meters, are steep and deeply eroded. A sulphur mining venture on the island stopped abruptly in 1914 when part of the crater wall collapsed and a landslide destroyed the sulphur mine and miners' village. Twelve lives were lost. Mining resumed again in the 1920s and the remains of buildings from that era are a tourist attraction. The sulphur was used to make fertiliser, for export as sulphur ore, and for the manufacture of sulphuric acid. ...

White Island is the summit of a large (16 by 18 kilometers) submarine volcano which has grown up from the sea floor at 300 meters to 400 meters depths. Only half the height and a very small proportion of the volume of this volcano are above sea level. The main crater was formed in prehistoric times, apparently by the collapse of three overlapping roughly circular subcraters. The eastern subcrater was formed first, and now contains only minor hot spring activity. The central subcrater contains the Donald Mount fumaroles (vents emitting steam and hot gases), and the Noisy Nellie and Donald Duck craters and fumaroles. The western subcrater contains most of the eruption sites that have formed since 1960 and has been the main focus of activity during the island's recorded history. Deep pits mark the sites of recently active vents. Most of the present main crater floor lies less than 30 meters above sea level, and has an irregular surface covered by mounts of avalanche debris from the 1914 disaster.

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