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A caldera is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the structural integrity of such a chamber, greatly diminishing its capacity to support its own roof, and any substrate or rock resting above. The ground surface then collapses into the emptied or partially emptied magma chamber, leaving a large depression at the surface. Although sometimes described as a crater, the feature is actually a type of sinkhole, as it is formed through subsidence and collapse rather than an explosion or impact. Compared to the thousands of volcanic eruptions that occur over the course of a century, the formation of a caldera is a rare event, occurring only a few times within a given window of 100 years. Only seven caldera-forming collapses are known to have occurred between 1911 and 2016. More recently, a caldera collapse occurred at Kīlauea, Hawaii in 2018.
Obsidian is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock.
Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock containing 25% to 75% ash is described as tuffaceous. Tuff composed of sandy volcanic material can be referred to as volcanic sandstone.
The Ring of Fire is a tectonic belt of volcanoes and earthquakes.
Rarotonga is the largest and most populous of the Cook Islands. The island is volcanic, with an area of 67.39 km2 (26.02 sq mi), and is home to almost 75% of the country's population, with 10,898 of a total population of 15,040. The Cook Islands' Parliament buildings and international airport are on Rarotonga. Rarotonga is a very popular tourist destination with many resorts, hotels and motels. The chief town, Avarua, on the north coast, is the capital of the Cook Islands.
The Taupō Volcanic Zone (TVZ) is a volcanic area in the North Island of New Zealand that has been active for at least the past two million years and is still highly active. Mount Ruapehu marks its south-western end and the zone runs north-eastward through the Taupō and Rotorua areas and offshore into the Bay of Plenty. It is part of a larger Central Volcanic Region that extends to the Coromandel Peninsula and has been active for four million years. The zone is contained within the tectonic intra-arc continental Taupō Rift and this rift volcanic zone is widening unevenly east–west with the greatest rate of widening at the Bay of Plenty coast, the least at Mount Ruapehu and a rate of about 8 mm (0.31 in) per year at Taupō. The zone is named after Lake Taupō, the flooded caldera of the largest volcano in the zone, the Taupō Volcano and contains a large central volcanic plateau as well as other landforms.
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.
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 Waikato Plains form a large area of low-lying land in the northwest of the North Island of New Zealand. They are the alluvial plains of the Waikato River, the country's longest river with a length of 425 km (264 mi).
Maungatautari is a mountain near Cambridge in the Waikato region in New Zealand's central North Island. The 797 metre high mountain is an extinct stratovolcano. It is a prominent peak and is visible across the Waipa District. The mountain is the site of Sanctuary Mountain Maungatautari a large ecological sanctuary and resoration project.
Hawaiite is an olivine basalt with a composition between alkali basalt and mugearite. It was first used as a name for some lavas found on the island of Hawaii.
This timeline of volcanism on Earth includes a list of major volcanic eruptions of approximately at least magnitude 6 on the Volcanic explosivity index (VEI) or equivalent sulfur dioxide emission during the Quaternary period. Other volcanic eruptions are also listed.
Kakepuku is a volcanic cone which rises from the plain between the Waipā and Puniu rivers, about 3 km (2 mi) NW of Te Kawa and 8 km (5 mi) SW of Te Awamutu in the Waikato region of New Zealand's North Island.
The Taupō Rift is the seismically active rift valley containing the Taupō Volcanic Zone, central North Island of New Zealand.
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.
Omanawa Caldera is inferred by an area of magnetic anomaly that exists to the north-west of the Rotorua Caldera. It is also located to the north west of the present boundary of the modern Taupō Volcanic Zone but its existence would be compatible with activity in the area of intersection of Taupo Rift and Hauraki Rift before 1.9 million years ago. The area of the caldera is covered by Mamaku Ignambrite from the Mamaku eruption of 240,000 years ago that formed the Rotorua Caldera. Eruptions from the Omanawa Caldera would explain formations such as the Waiteariki ignimbrite which covers much of the Bay of Plenty and forms the bulk of the Whakamarama Plateau. This would date the major caldera formation to 2.1 million years ago. However, there are at least eight large eruptions that occurred in the Tauranga Volcanic Centre between 2.4 and 1.9 million years ago and at this time which ones relate to this caldera can not be definite. However to date there is no other obvious closer inferred volcanic structure to assign a super volcanic eruption to, so at least some of these eruptions are likely to be associated with the Omanawa Caldera magnetic anomaly.
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.
References
- 1 2 3 https://dialnet.unirioja.es/descarga/articulo/281059.pdf Archived 2012-02-27 at the Wayback Machine Luis Enrique Ortiz Hernández, An Arc Ankaramite Occurrence in Central Mexico, Revista Mexicana de Ciencias Geológicas, volumen 17, número 1 2000, p. 34-44
- ↑ Pittari, Adrian; Prentice, Marlena L.; McLeod, Oliver E.; Zadeh, Elham Yousef; Kamp, Peter J. J.; Danišík, Martin; Vincent, Kirsty A. (2021). "Inception of the modern North Island (New Zealand) volcanic setting: spatio-temporal patterns of volcanism between 3.0 and 0.9 Ma" (PDF). New Zealand Journal of Geology and Geophysics. 64 (2–3): 250–272. Bibcode:2021NZJGG..64..250P. doi:10.1080/00288306.2021.1915343. S2CID 235736318.
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