Jump to content

Caldera: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
Line 1: Line 1:
''debfzdbvbasdvbjbdfbIn 1815, the German geologist [[Leopold von Buch]] visited the Las Cañadas Caldera [[Teide]], [[Tenerife]] and the [[Caldera de Taburiente]], [[La Palma]], both in the [[Canary Islands]]. When he published his memoirs he introduced the term "caldera" into the geological vocabulary.
''debfzdbvbasdvbjbdfbIn 1815, the German geologist [[Leopold von Buch]] visited the Las Cañadas Caldera [[Teide]], [[Tenerife]] and the [[Caldera de Taburiente]], [[La Palma]], both in the [[Canary Islands]]. When he published his memoirs he introduced the term "caldera" into the geological vocabulary.
pitote
==Caldera formation==
A collapse is triggered by the emptying of the [[magma chamber]] beneath the volcano, usually as the result of a large [[volcano|volcanic eruption]]. If enough magma is erupted, the emptied chamber will not be able to support the weight of the ''volcanic edifice'' above it. A roughly circular fracture - the "Ring Fault" develops around the edge of the chamber. These ''ring fractures'' serve as feeders for fault intrusions which are also known as ring dykes. 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 or thousands of square kilometers.

[[Image:Toba zoom.jpg|thumb|300px|right|[[Landsat]] image of [[Lake Toba]], on the island of [[Sumatra]], [[Indonesia]]. A [[resurgent dome]] formed the island of [[Samosir]].]]''===Explosive calderas===
If the [[magma]] is rich in [[silica]], the caldera is often filled in with [[ignimbrite]], [[tuff]], [[rhyolite]], and other [[igneous rock]]s. Silica-rich magma does not flow like [[basalt]] due to having a high [[viscosity]]. As a result, gases tend to become trapped at high pressure within the magma. When the magma approaches the surface of the Earth, the gases decompress rapidly, causing explosive destruction of the magma and spreading [[volcanic ash]] over wide areas. Further [[lava]] flows may be erupted.

If volcanic activity continues the centre of the caldera may be uplifted in the form of a ''[[resurgent dome]]'' such as is seen seen at [[Galán|Cerro Galán]], [[Lake Toba]], [[Yellowstone]] etc; by subsequent intrusion of magma. A ''silicic'' or ''rhyolitic caldera'' may erupt hundreds or even thousands of [[cubic kilometer]]s of material in a single event. 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.

When [[Yellowstone Caldera]] last erupted some 640,000 years ago, it released about 1,000 km<sup>3</sup> of dense rock equivalent (DRE) material, covering a substantial part of [[North America]] in up to two metres of debris. By comparison, when [[Mount St. Helens]] erupted in 1980, it released ~1.2 km<sup>3</sup> (DRE) of ejecta. The ecological effects of the eruption of a large caldera can be seen in the record of the [[Lake Toba]] eruption in [[Indonesia]].

===Toba===

About 75,000 years ago, this Indonesian volcano released about 2,800 </sup> km<sup>3</sup> DRE of ejecta, the largest known eruption within the [[Quaternary]] Period (last 1.8 million years) and probably the largest explosive eruption withtin the last 25 million years. In the late 1990s, [[anthropologist]] Stanley Ambrose<ref>[http://www.anthro.uiuc.edu/faculty/ambrose/ Stanley Ambrose<!-- Bot generated title -->]</ref> 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]] (''see'' [[Toba catastrophe theory]]). More recently several geneticists, including Lynn Jorde and [[Henry Harpending]] have proposed that the human race was reduced to approximately five to ten thousand people.<ref>[http://www.bbc.co.uk/science/horizon/1999/supervolcanoes_script.shtml BBC - Science & Nature - Horizon - Supervolcanoes<!-- Bot generated title -->]</ref> Whichever figure is right, the fact remains that the human race seemingly came close to extinction about 75,000 years ago.

Eruptions forming even larger calderas are known, especially [[La Garita Caldera]] in the [[San Juan Mountains]] of [[Colorado]], where the 5,000 km<sup>3</sup> Fish Canyon Tuff was blasted out in a major single eruption about 27.8 million years ago.

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 [[San Juan Mountains]] of [[Colorado]] (erupted during the [[Tertiary Period]]) or the [[Saint Francois Mountain Range]] of [[Missouri]] (erupted during the [[Proterozoic]]).

[[Image:La Cumbre - ISS.JPG|thumb|300px|right|Satellite photograph of the summit caldera on [[Fernandina Island]] in the [[Galapagos]] archipelago.]]

===Non-explosive calderas===
Some volcanoes, such as [[Kīlauea]] on the island of [[Hawaii (island)|Hawaii]], form calderas in a different fashion. In the case of Kilauea, the magma feeding the volcano 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]] underwent a collapse in 1968, when parts of the caldera floor dropped 350 meters.<ref>[http://www.volcano.si.edu/world/volcano.cfm?vnum=1503-01=&VErupt=Y&VSources=Y&VRep=Y&VWeekly=Y&volpage=photos&photo=062078 Global Volcanism Program | Fernandina | Photo<!-- Bot generated title -->]</ref> [[Kilauea]] Caldera has an inner crater known as Halema‘uma‘u, which has often been filled by a lava lake. At the summit of largest volcano on Earth, [[Mauna Loa]] is a subsidence caldera called Moku‘āweoweo Caldera.

It is very frequent for a caldera to become emptied by drainage of melted lava throughout a breach on the caldera's rim. The [[Caldera de Taburiente]] and the Caldereta, both in the island of [[La Palma]] ([[Canary Islands]]) are '''calderas''' emptied by a river of lava some 500.000 years ago.


==Mineralization==
==Mineralization==

Revision as of 22:07, 17 November 2008

debfzdbvbasdvbjbdfbIn 1815, the German geologist Leopold von Buch visited the Las Cañadas Caldera Teide, Tenerife and the Caldera de Taburiente, La Palma, both in the Canary Islands. When he published his memoirs he introduced the term "caldera" into the geological vocabulary.

pitote

Mineralization

Some calderas are known to support rich mineralogy. One of the world's best preserved mineralized calderas is the Neoarchean Sturgeon Lake Caldera in northeastern Ontario, Canada.[1]

Notable calderas

See also Category:Volcanic calderas

Crater Lake, Oregon, formed around 5,680 BC
File:Silverthrone Caldera.jpg
Silverthrone Caldera, southwestern British Columbia, Canada
Satellite photo of Lake Taupo

See also

Wikimedia Commons has media related to Caldera.

Notes

  1. ^ UMD: Precambrian Research Center

References

  • Clough, C. T; Maufe, H. B. & Bailey, E. B; 1909. The cauldron subsidence of Glen Coe, and the Associated Igneous Phenomena. Quart. Journ. Geol. Soc. 65, 611-678.
  • Kokelaar, B. P; and Moore, I. D; 2006. Glencoe caldera volcano, Scotland. ISBN. 0852725252. 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. ISBN 0-12-643140-X
  • Williams, H; 1941. Calderas and their origin. California University Publ. Geol. Sci. 25, 239-346.
Retrieved from "https://wiki.riteme.site/w/index.php?title=Caldera&oldid=252448437"