Volcanic cone

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Mayon Volcano in the Philippines has a symmetrical volcanic cone

Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and size of the fragments ejected during the eruption. Types of volcanic cones include stratocones, spatter cones, ash cones, tuff cones, and cinder cones.

Stratocone[edit]

Main article: Stratovolcano
Osorno volcano in Chile is an example of a well-developed stratocone.

Stratocones are large cone-shaped volcanoes made up of lava flows, explosively erupted pyroclastic rocks, and igneous intrusives that are typically centered around a cylindrical vent. Unlike shield volcanoes, they are characterized by a steep profile and periodic, often alternating, explosive eruptions and effusive eruptions. Some have collapsed craters called calderas. The central core of a stratocone is commonly dominated by a central core of intrusive rocks that range from around 500 meters (1,600 ft) to over several kilometers in diameter. This central core is surrounded by multiple generations of lava flows, many of which are brecciated, and a wide range of pyroclastic rocks and reworked volcanic debris. The typical stratocone is an andesitic to dacitic volcanoe that is associated with subduction zones. They are also known as either stratified volcano, composite cone, bedded volcano, cone of mixed type or Vesuvian-type volcano.[1][2]

Spatter cone[edit]

Puʻu ʻŌʻō, a cinder-and-spatter cone on Kīlauea, Hawaiʻi

A spatter cone is a low, steep-sided hill or mound that consists of welded lava fragments, called spatter, which has formed around a lava fountain issuing from a central vent. Typically, spatter cones are about 3–5 meters (9.8–16.4 ft) high. In case of a linear fissure, lava fountaining will create broad embankments of spatter, called spatter ramparts, along both sides of the fissure. Spatter cones are more circular and cone shaped, while spatter ramparts are linear wall-like features.[1][3][4]

Spatter cones and spatter ramparts are typically formed by lava fountaining associated with mafic, highly fluid lavas, such as those erupted in the Hawaiian Islands. As blobs of molten lava, spatter, are erupted into the air by a lava fountain, they can lack the time needed to cool completely before hitting the ground. Consequently, the spatter are not fully solid, like taffy, as they land and they bind to the underlying spatter as both often slowly ooze down the side of the cone. As a result, the spatter builds up a cone that composed of spatter either agglutinated or welded to each other.[1][3][4]

Ash and tuff cones[edit]

Koko Crater is 10,000 year-old tuff cone, youngest in the Honolulu Volcanic Series

An ash cone is composed of particles of silt to sand size. Explosive eruptions from a vent where the magma is interacting with groundwater or the sea (as in an eruption off the coast) produce steam and are called phreatic. The interaction between the magma, expanding steam, and volcanic gases results in the ejection of mostly small particles called ash. Fallen ash has the consistency of flour. The unconsolidated ash forms an ash cone which becomes a tuff cone or tuff ring once the ash consolidates (see also tuff). Flat-floored craters that scientists interpret have formed above diatremes as a result of a violent expansion of magmatic gas or steam; deep erosion of a maar presumably would expose a diatreme.

An example of a tuff cone is Diamond Head at Waikīkī in Hawaiʻi. Their existence was also suggested for several dozens edifices on Mars.[5]

Cinder cone[edit]

Main article: Cinder cone
Cinder cone
Paricutin is a large cinder cone in Mexico.

Cinder cones (scoria mounds) are small, steep-sided volcanic cones built of loose pyroclastic fragments, such as either volcanic clinkers, cinders, volcanic ash, or scoria.[1][6] They consist of loose pyroclastic debris formed by explosive eruptions or lava fountains from a single, typically cylindrical, vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as either cinders, clinkers, or scoria around the vent to form a cone that often is beautifully symmetrical; with slopes between 30-40°; and a nearly circular ground plan. Most cinder cones have a bowl-shaped crater at the summit.[1]

Most cinder cones only erupt once like Paricutin. These cones are called monogenetic volcanic fields. Cinder cones are typically active for very brief periods of time before becoming inactive. Rarely do they erupt either two, three, or more times.[citation needed]

Cinder cones rarely rise more than 300–750 meters (980–2,460 ft) or so above their surroundings, and, being unconsolidated, tend to erode rapidly unless further eruptions occur. Cinder cones are numerous in western North America as well as throughout other volcanic terrains of the world. Parícutin, the Mexican cinder cone which was born in a cornfield on February 20, 1943, and Sunset Crater in Northern Arizona in the US Southwest are classic examples of cinder cones, as are the ancient volcanoes in New Mexico's Petroglyph National Monument. They were also described on Mars; e.g., in caldera of Ulysses Patera,[7] in Ulysses Colles[8] or in Hydraotes Chaos.[9]

Rootless cones[edit]

Main article: Pseudocrater

Rootless cones are named because they have no direct magma supply from the interior of a planet but they are instead fed by a lava flow. Rootless cones can also be formed in lava when it flows over wet sediments. Vapor explosions then open up the crust of the lava flow allowing spatter, tuff or cinder to be ejected.

References[edit]

  1. ^ a b c d e Poldervaart, A (1971). "Volcanicity and forms of extrusive bodies". In Green, J; Short, NM. Volcanic Landforms and Surface Features: A Photographic Atlas and Glossary. New York: Springer-Verlag. p. 519. ISBN 978364265152-6. 
  2. ^ Schmincke, H.-U. (2004). Volcanism. Berlin, Germany: Springer-Verlag. ISBN 3540436502. 
  3. ^ a b "Spatter cone". Volcano Hazard Program, Photo Glossary. U.S. Geological Survey, U.S. Department of the Interior. 2008. 
  4. ^ a b "Spatter rampart". Volcano Hazard Program, Photo Glossary. U.S. Geological Survey, U.S. Department of the Interior. 2008. 
  5. ^ Brož, P.; Hauber, E. (2013). "Hydrovolcanic tuff rings and cones as indicators for phreatomagmatic explosive eruptions on Mars". Journal of Geophysical Research: Planets 118: 1656–1675. Bibcode:2013JGRE..118.1656B. doi:10.1002/jgre.20120. 
  6. ^ "Cinder cone". Volcano Hazards Program, Photo Glossary. U.S. Geological Survey, U.S. Department of the Interior. 2008. 
  7. ^ Plescia, J.B. (1994). "Geology of the small Tharsis volcanoes: Jovis Tholus, Ulysses Patera, Biblis Patera, Mars". Icarus 111: 246–269. Bibcode:1994Icar..111..246P. doi:10.1006/icar.1994.1144. 
  8. ^ Brož, P.; Hauber, E. (2012). "A unique volcanic field in Tharsis, Mars: Pyroclastic cones as evidence for explosive eruptions". Icarus 218 (1): 88–99. Bibcode:2012Icar..218...88B. doi:10.1016/j.icarus.2011.11.030. 
  9. ^ Meresse, Sandrine; Costard, François; Mangold, Nicolas; Masson, Philippe; Neukum, Gerhard; the HRSC Co-I Team (2008). "Formation and evolution of the chaotic terrains by subsidence and magmatism: Hydraotes Chaos, Mars". Icarus 194 (2): 487–500. Bibcode:2008Icar..194..487M. doi:10.1016/j.icarus.2007.10.023.