
A caldera is a large
cauldron-like hollow that forms shortly after the emptying of a
magma chamber in a volcanic eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is lost. The ground surface then collapses downward into the emptied or partially emptied magma chamber, leaving a massive depression at the surface (from one to dozens of kilometers in diameter). 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. Only seven caldera-forming collapses are known to have occurred since 1900, most recently at
Bárðarbunga volcano, Iceland in 2014.
Etymology
The term ''caldera'' comes from
Spanish ', and
Latin ', meaning "cooking pot".
In some texts the English term ''cauldron'' is also used,
though in more recent work the term ''cauldron'' refers to a caldera that has been deeply eroded to expose the beds under the caldera floor.
The term ''caldera'' was introduced into the geological vocabulary by the German geologist
Leopold von Buch when he published his memoirs of his 1815 visit to the
Canary Islands, where he first saw the Las Cañadas caldera on
Tenerife, with Mount
Teide dominating the landscape, and then the
Caldera de Taburiente on
La Palma.
Caldera formation

A collapse is triggered by the emptying of the
magma chamber beneath the volcano, sometimes as the result of a large explosive
volcanic eruption (see
Tambora in 1815), but also during effusive eruptions on the flanks of a volcano (see
Piton de la Fournaise in 2007) or in a connected fissure system (see
Bárðarbunga in 2014–2015). If enough
magma is ejected, the emptied chamber is unable to support the weight of the volcanic edifice above it. A roughly circular
fracture, the "ring fault", develops around the edge of the chamber. Ring fractures serve as feeders for fault
intrusions which are also known as
ring dikes.
Secondary volcanic vents may form above the ring fracture. As the magma chamber empties, the center of the volcano within the ring fracture begins to collapse. The collapse may occur as the result of a single cataclysmic eruption, or it may occur in stages as the result of a series of eruptions. The total area that collapses may be hundreds of square kilometers.
Mineralization in calderas

Some calderas are known to host rich
ore deposits. Metal-rich fluids can circulate through the caldera, forming hydrothermal ore deposits of metals such as lead, silver, gold, mercury, lithium and uranium. One of the world's best-preserved
mineralized calderas is the
Sturgeon Lake Caldera in
northwestern Ontario, Canada, which formed during the
Neoarchean era about 2.7 billion years ago. In the
San Juan volcanic field, ore veins were emplaced in fractures associated with several calderas, with the greatest mineralization taking place near the youngest and most silicic intrusions associated with each caldera.
Types of caldera
Explosive caldera eruptions
Explosive caldera eruptions are produced by a magma chamber whose
magma is rich in
silica. Silica-rich magma has a high
viscosity, and therefore does not flow easily like
basalt.
The magma typically also contains a large amount of dissolved gases, up to 7
wt% for the most silica-rich magmas. When the magma approaches the surface of the Earth, the drop in
confining pressure causes the trapped gases to rapidly bubble out of the magma, fragmenting the magma to produce a mixture of
volcanic ash and other
tephra with the very hot gases.
The mixture of ash and volcanic gases initially rises into the atmosphere as an
eruption column. However, as the volume of erupted material increases, the eruption column is unable to
entrain enough air to remain buoyant, and the eruption column collapses into a tephra fountain that falls back to the surface to form
pyroclastic flows. Eruptions of this type can spread ash over vast areas, so that ash flow
tuffs emplaced by silicic caldera eruptions are the only volcanic product with volumes rivaling those of
flood basalts.
For example, when Yellowstone Caldera last erupted some 650,000 years ago, it released about 1,000 km
3 of material (as measured in dense rock equivalent (DRE)), covering a substantial part of
North America in up to two metres of debris.
Eruptions forming even larger calderas are known, such as the
La Garita Caldera in the
San Juan Mountains of
Colorado, where the
Fish Canyon Tuff was blasted out in eruptions about 27.8 million years ago.
The caldera produced by such eruptions is typically filled in with tuff,
rhyolite, and other
igneous rocks.
The caldera is surrounded by an outflow sheet of ash flow tuff.
If magma continues to be injected into the collapsed magma chamber, the center of the caldera may be uplifted in the form of a ''
resurgent dome'' such as is seen at the
Valles Caldera,
Lake Toba, the San Juan volcanic field,
Cerro Galán,
Yellowstone, and many other calderas.
Because a silicic caldera may erupt hundreds or even thousands of cubic kilometers of material in a single event, it can cause catastrophic environmental effects. Even small caldera-forming eruptions, such as
Krakatoa in 1883 or
Mount Pinatubo in 1991, may result in significant local destruction and a noticeable drop in temperature around the world. Large calderas may have even greater effects. The ecological effects of the eruption of a large caldera can be seen in the record of the
Lake Toba eruption in
Indonesia.
At some points in
geological time, rhyolitic calderas have appeared in distinct clusters. The remnants of such clusters may be found in places such as the
Eocene Rum Complex of Scotland,
the San Juan Mountains of Colorado (formed during the
Oligocene,
Miocene, and
Pliocene epochs) or the
Saint Francois Mountain Range of
Missouri (erupted during the
Proterozoic eon).
Valles
For their 1968 paper
that first introduced the concept of a resurgent caldera to geology,
R.L. Smith and R.A. Bailey chose the Valles caldera as their model. Although the Valles caldera is not unusually large, it is relatively young (1.25 million years old) and unusually well preserved, and it remains one of the best studied examples of a resurgent caldera.
The ash flow tuffs of the Valles caldera, such as the
Bandelier Tuff, were among the first to be thoroughly characterized.
Toba
About 74,000 years ago, this Indonesian volcano released about
dense-rock equivalent of ejecta. This was the largest known eruption during the ongoing
Quaternary period (the last 2.6 million years) and the largest known explosive eruption during the last 25 million years. In the late 1990s,
anthropologist Stanley Ambrose proposed that a
volcanic winter induced by this eruption reduced the human population to about 2,000–20,000 individuals, resulting in a
population bottleneck. More recently,
Lynn Jorde and
Henry Harpending proposed that the human species was reduced to approximately 5,000-10,000 people. There is no direct evidence, however, that either theory is correct, and there is no evidence for any other animal decline or extinction, even in environmentally sensitive species. There is evidence that human habitation continued in
India after the eruption.
Non-explosive calderas
Some volcanoes, such as the large
shield volcanoes
Kīlauea and
Mauna Loa on the island of
Hawaii, form calderas in a different fashion. The magma feeding these volcanoes is
basalt, which is silica poor. As a result, the magma is much less
viscous than the magma of a rhyolitic volcano, and the magma chamber is drained by large lava flows rather than by explosive events. The resulting calderas are also known as subsidence calderas and can form more gradually than explosive calderas. For instance, the caldera atop
Fernandina Island collapsed in 1968 when parts of the caldera floor dropped .
Extraterrestrial calderas
Since the early 1960s, it has been known that volcanism has occurred on other planets and moons in the
Solar System. Through the use of manned and unmanned spacecraft, volcanism has been discovered on
Venus,
Mars, the
Moon, and
Io, a satellite of
Jupiter. None of these worlds have
plate tectonics, which contributes approximately 60% of the Earth's volcanic activity (the other 40% is attributed to
hotspot volcanism).
Caldera structure is similar on all of these planetary bodies, though the size varies considerably. The average caldera diameter on Venus is . The average caldera diameter on Io is close to , and the mode is ;
Tvashtar Paterae is likely the largest caldera with a diameter of . The average caldera diameter on Mars is , smaller than Venus. Calderas on Earth are the smallest of all planetary bodies and vary from as a maximum.
The Moon
The
Moon has an outer shell of low-density crystalline rock that is a few hundred kilometers thick, which formed due to a rapid creation. The craters of the Moon have been well preserved through time and were once thought to have been the result of extreme volcanic activity, but actually were formed by meteorites, nearly all of which took place in the first few hundred million years after the Moon formed. Around 500 million years afterward, the Moon's mantle was able to be extensively melted due to the decay of radioactive elements. Massive basaltic eruptions took place generally at the base of large impact craters. Also, eruptions may have taken place due to a magma reservoir at the base of the crust. This forms a dome, possibly the same morphology of a shield volcano where calderas universally are known to form.
Although caldera-like structures are rare on the Moon, they are not completely absent. The
Compton-Belkovich Volcanic Complex on the
far side of the Moon is thought to be a caldera, possibly an
ash-flow caldera.
Mars
The volcanic activity of
Mars is concentrated in two major provinces:
Tharsis and
Elysium. Each province contains a series of giant shield volcanoes that are similar to what we see on Earth and likely are the result of mantle
hot spots. The surfaces are dominated by lava flows, and all have one or more collapse calderas.
Mars has the largest volcano in the Solar System,
Olympus Mons, which is more than three times the height of Mount Everest, with a diameter of 520 km (323 miles). The summit of the mountain has six nested calderas.
Venus
Because there is no
plate tectonics on
Venus, heat is mainly lost by conduction through the
lithosphere. This causes enormous lava flows, accounting for 80% of Venus' surface area. Many of the mountains are large
shield volcanoes that range in size from in diameter and high. More than 80 of these large shield volcanoes have summit calderas averaging across.
Io
Io, unusually, is heated by solid flexing due to the
tidal influence of
Jupiter and Io's
orbital resonance with neighboring large moons
Europa and
Ganymede, which keep its orbit slightly
eccentric. Unlike any of the planets mentioned, Io is continuously volcanically active. For example, the NASA ''
Voyager 1'' and ''
Voyager 2'' spacecraft detected nine erupting volcanoes while passing Io in 1979. Io has many calderas with diameters tens of kilometers across.
List of volcanic calderas
*
Africa
**
Ngorongoro Crater (Tanzania)
**
Menengai Crater (Kenya)
**
Mount Elgon (Uganda/Kenya)
**
Mount Fogo (Cape Verde)
**
Mount Longonot (Kenya)
**
Mount Meru (Tanzania)
**
Erta Ale (Ethiopia)
**
Nabro Volcano (Eritrea)
**
Mallahle (Eritrea)
** ''See ''Europe'' for calderas in the Canary Islands
* Americas
**
Argentina
***
Aguas Calientes,
Salta Province
***
Caldera del Atuel,
Mendoza Province
***
Galán,
Catamarca Province
**
United States

***
Mount Aniakchak (
Aniakchak National Monument and Preserve) (
Alaska)
***
Crater Lake on
Mount Mazama (
Crater Lake National Park,
Oregon)
***
Mount Katmai (Alaska)
***
La Garita Caldera (
Colorado)
***
Long Valley (
California)
***
Henry's Fork Caldera (
Idaho)
***
Island Park Caldera (Idaho,
Wyoming)
***
Newberry Volcano (Oregon)
***
McDermitt Caldera (Oregon)
***
Medicine Lake Volcano (California)
***
Mount Okmok (Alaska)
***
Valles Caldera (
New Mexico)
***
Yellowstone Caldera (Wyoming)
**
Canada
***
Silverthrone Caldera (
British Columbia)
***
Mount Edziza (British Columbia)
***
Bennett Lake Volcanic Complex (British Columbia/
Yukon)
***
Mount Pleasant Caldera (
New Brunswick)
***
Sturgeon Lake Caldera (
Ontario)
***
Mount Skukum Volcanic Complex (Yukon)
***
Blake River Megacaldera Complex (
Quebec/Ontario)
****
New Senator Caldera (Quebec)
****
Misema Caldera (Ontario/Quebec)
****
Noranda Caldera (Quebec)
**
Colombia
***
Arenas crater caldera,
Nevado del Ruiz volcano,
Caldas Department
***
Laguna Verde caldera,
Azufral volcano,
Narino Department
**
Mexico
***
La primavera Caldera (
Jalisco)
***
Amealco Caldera (
Querétaro)
***
Las Cumbres Caldera (
Veracruz-
Puebla)
***
Los Azufres Caldera (
Michoacán)
***
Los Humeros Caldera (Veracruz-Puebla)
***
Mazahua Caldera (
Mexico State)
**
Chile
***
Chaitén
***
Cordillera Nevada Caldera
***
Laguna del Maule
***
Pacana Caldera
***
Sollipulli
**
Ecuador
***
Pululahua Geobotanical Reserve
***
Cuicocha
***
Quilotoa
***
Fernandina Island,
Galápagos Islands
***
Sierra Negra (Galápagos)
**
El Salvador 
***
Lake Ilopango
***
Lake Coatepeque
**
Guatemala
***
Lake Amatitlán
***
Lake Atitlán
***
Xela
***
Barahona
** Other
***
Masaya (Nicaragua)
*
Asia
** East Asia
***
Dakantou Caldera (大墈头) (Shanhuyan Village, Taozhu Town,
Linhai, Zhejiang, China)
***
Ma'anshan Caldera (马鞍山) (Shishan Town (石山镇),
Xiuying, Hainan, China)
***
Yiyang Caldera (宜洋) (Shuangxi Town (双溪镇宜洋村),
Pingnan County, Fujian, China)
***
Aira Caldera (
Kagoshima Prefecture,
Japan)
***
Kussharo (
Hokkaido, Japan)
***
Kuttara (Hokkaido, Japan)
***
Mashū (Hokkaido, Japan)
***
Aso Caldera,
Mount Aso (
Kumamoto Prefecture, Japan)
***
Kikai Caldera (Kagoshima Prefecture, Japan)
***
Towada (
Aomori Prefecture, Japan)
***
Tazawa (
Akita Prefecture, Japan)
***
Hakone (
Kanagawa Prefecture, Japan)
***
Mount Halla (
Jeju-do, South Korea)
***
Heaven Lake (
Baekdu Mountain, North Korea)
** Southeast Asia

***
Apolaki Caldera (
Benham Rise, Philippines)
***
Corregidor Caldera (Manila Bay, Philippines)
***
Mount Pinatubo (
Luzon, Philippines)
***
Taal Volcano (Luzon, Philippines)
***
Laguna Caldera (Luzon, Philippines)
***
Irosin Caldera (Luzon, Philippines)
***
Batur (
Bali, Indonesia)
***
Krakatoa (
Sunda Strait, Indonesia)
***
Lake Maninjau (
Sumatra, Indonesia)
***
Lake Toba (Sumatra, Indonesia)
***
Mount Rinjani (
Lombok, Indonesia)
***
Mount Tondano (
Sulawesi, Indonesia)
***
Mount Tambora (
Sumbawa, Indonesia)
***
Tengger Caldera (
Java, Indonesia)
** Southwest Asia
***
Derik (
Mardin, Turkey)
***
Nemrut (volcano) (Turkey)
**
Russia 
***
Akademia Nauk (
Kamchatka Peninsula)
***
Golovnin (
Kuril Islands)
***
Karymsky Caldera (
Kamchatka Peninsula)
***
Khangar (
Kamchatka Peninsula)
***
Ksudach (
Kamchatka Peninsula)
***
Kurile Lake (
Kamchatka Peninsula)
***
Lvinaya Past (
Kuril Islands)
***
Tao-Rusyr Caldera (
Kuril Islands)
***
Uzon (
Kamchatka Peninsula)
***
Zavaritski Caldera (
Kuril Islands)
***
Yankicha/Ushishir (
Kuril Islands)
***
Chegem Caldera (
Kabardino-Balkarian Republic,
Northern Caucasus Region)
*
Europe

**
Banská Štiavnica (Slovakia)
**
Bakuriani/Didveli Caldera (Georgia)
**
Samsari (Georgia)
**
Santorini (Greece)
**
Nisyros (Greece)
**
Askja (Iceland)
**
Grímsvötn (Iceland)
**
Bárðarbunga (Iceland)
**
Katla (Iceland)
**
Krafla (Iceland)
**
Phlegraean Fields (Italy)
**
Lake Bracciano (Italy)
**
Lake Bolsena (Italy)
**
Mount Somma which contains
Mount Vesuvius (Italy)
**
Las Cañadas (
Tenerife, Spain)
**
Glen Coe (Scotland)
**
Scafell Caldera (
Lake District, England)
**
Laacher See (Germany)
**
Lagoa das Sete Cidades &
Furnas (
São Miguel,
the Azores, Portugal)
*
Oceania 
**
Cerberean caldera (Australia)
**
Dakataua (Papua New Guinea)
** Kapenga (New Zealand)
**
Kilauea (
Hawaii, US)
**
Lake Ohakuri (New Zealand)
**
Lake Okataina (New Zealand)
**
Lake Rotorua (New Zealand)
**
Lake Taupo (New Zealand)
** Maroa (New Zealand)
**
Moku‘āweoweo Caldera on
Mauna Loa (Hawaii, US)
**
Mount Warning (Australia)
**
Prospect Hill (Australia)
**
Rano Kau (
Easter Island, Chile)
**
Reporoa caldera (New Zealand)
*
Antarctica
**
Deception Island
*
Indian Ocean
**
Cirque de Mafate,
Cirque de Salazie,
Enclos Fouqué, and
Cirque de Cilaos on
Réunion
Extraterrestrial volcanic calderas
*
Mars
**
Olympus Mons caldera
*
Venus
**
Maat Mons caldera
Erosion calderas
* Americas
**
Guaichane-Mamuta (Chile)
**
Mount Tehama (
California, US)
* Europe
**
Caldera de Taburiente (Spain)
* Oceania
**
Tweed Valley (
New South Wales,
Queensland, Australia)
* Asia
**
Chegem Caldera (
Kabardino-Balkarian Republic,
Northern Caucasus Region, Russia)
**
Taal volcano (Philippines)
Batangas Province
See also
*
*
*
*
Explanatory notes
References
Further reading
*
*
* Kokelaar, B. P; and Moore, I. D; 2006. ''Glencoe caldera volcano, Scotland''. . Pub. British Geological Survey, Keyworth, Nottinghamshire. There is an associated 1:25000 solid geology map.
* Lipman, P; 1999. "Caldera". In Haraldur Sigurdsson, ed. ''Encyclopedia of Volcanoes''.
Academic Press.
*
External links
USGS page on calderasList of Caldera VolcanoesCollection of references on collapse calderas(43 pages)
*
ttp://www.bbc.co.uk/science/horizon/1999/supervolcanoes_script.shtml Supervolcanoes
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