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 cone 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 cylindrical structures built up around a main tubular volcanic vent by more than one eruption. Stratocones can form large mountains and possess a distinctive layering of lava flows and tephra.

Spatter cone[edit]

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

A spatter cone is formed of molten lava ejected from a vent, with a viscosity somewhat like taffy. Expanding gases in the lava fountains tear the liquid rock into irregular blobs that fall back to earth, forming a heap around the vent. The still partly liquid rock which splashes down and over the sides of the developing mound is called spatter. Because spatter is not fully solid when it lands, the individual deposits are very irregular in shape and weld together as they cool, and in this way particularly differ from cinder and ash. Spatter cones are typical of volcanoes with highly fluid magma, such as those found in the Hawaiian Islands. The spatter that builds up the cone can either be agglutinated or welded, the former meaning that the individual spatters pose one above each other with a lesser degree of welding occurring, while welded spatter is almost fluid when it lands and therefore welds easily.

Ash and tuff cones[edit]

Koko Crater is a very old tuff cone. It was formed by the group of eruptions called Honolulu Volcanic Series. This series of violent eruptions ejected lava and ash. Eruptions continued until 10,000 years ago when the Ko'olau Range became extinct or dormant. Koko Crater is one of the youngest of the tuff cones and Diamond Head is one of the oldest.

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.[1]

Cinder cone[edit]

Main article: Cinder cone
Cinder cone
Paricutin is a large cinder cone in Mexico. People think that Paricutin will never erupt again because cinder cones usually erupt only once.

A cinder cone or scoria cone is a volcanic cone built almost entirely of loose volcanic fragments called cinders (pumice, pyroclastics, or tephra). They are built from particles and bits of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit.

Most cinder cones only erupt once like Paricutin. They call these cones Monogenetic Volcanic Field. Some have enough magma to erupt twice or three times which is very unlikely. Even though cinder cones are volcanoes, they become extinct quickly.

Cinder cones rarely rise more than 300 to 750 m 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,[2] in Ulysses Colles[3] or in Hydraotes Chaos.[4]

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. ^ Brož, P.; Hauber, E. "Hydrovolcanic tuff rings and cones as indicators for phreatomagmatic explosive eruptions on Mars". Journal of Geophysical Research: Planets: 1656–1675. doi:10.1002/jgre.20120. 
  2. ^ Plescia, J.B., 1994. Geology of the small Tharsis volcanoes: Jovis Tholus, Ulysses Patera, Biblis Patera, Mars. Icarus 111, 246–269.
  3. ^ Brož, P.; Hauber, E. "A unique volcanic field in Tharsis, Mars: Pyroclastic cones as evidence for explosive eruptions". Icarus 218 (1): 88–99. doi:10.1016/j.icarus.2011.11.030. 
  4. ^ Meresse, Sandrine; Costard, François; Mangold, Nicolas; Masson, Philippe; Neukum, Gerhard. "Formation and evolution of the chaotic terrains by subsidence and magmatism: Hydraotes Chaos, Mars". Icarus 194 (2): 487–500. doi:10.1016/j.icarus.2007.10.023.