May 28, 2012
Credits: NASA/JPL/University of Arizona - Credits for the additional JP2 process.: Dr Gianluigi Barca/Lunar Explorer Italia/IPF
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Today's APOD is an extreme EDM (---> Extra Detail Magnification) of a NASA - Mars Reconnaissance Orbiter Frame (obtained by additionally processing the original one in JP2 format) showing a very interesting - and somehow peculiar - Surface Feature located on the Flank of the Giant Martian Volcano Arsia Mons. Such a Surface Feature is, in our opinion (as IPF), a small, and (as you can notice very simply) remarkably recent, Secondary Volcanic Vent (or, better yet, a Fissure) that - apparently - has not been noticed neither by the people of NASA, nor by the Researchers of the University of Arizona, when they published the Main (or Contextual) NASA - Mars Reconnaissance Orbiter Frame PSP_002922_1725 on their "HI-Rise Image Catalog" (as a matter of fact, the Context Frame where this EDM was taken from had been entitled "Glacier-Like Flow on Arsia Mons Flank" and the short comment about it that was made by Dr Kelly Kolb did not mention at all this Surface Feature - actually, and always, of course, in our humble opinion, the only really interesting Surface Feature clearly visible in the whole picture...). Anyway, what we call "Volcanic Vents", of even "Fissures", are simple Openings in the Crust of any given Celestial Body, where Molten Lava and/or Volcanic Gases escape from and, respectyively, spread onto the Surface, and disperse into the Atmosphere. Most Volcanoes have a Circular Central Vent near their Summit Craters (---> Calderae) that serves as a Conduit for ongoing Volcanic Construction: think about, for instance and in relation to the creation of large-scale Volcanic Features, to Basaltic Lavas - that, once they cool, may end up forming Oceanic Crust and/or Oceanic Plateaux - as well as to Continental Flood Basalts, which erupt from large, elongate, Planar Vents - or "Fissures". On Earth, new Oceanic Crust is created at the Axial Fissures which are positioned along the Globe-encircling Ocean Ridge System. On the other hand, and in order to create small-scale Volcanic Features (like Gaseous Fumaroles, Hot Springs, Geysers, and Rootless Splatter Cones - also known as "Hornitos"), small Cracks and Ducts positioned in Volcanic and Hydrothermal Provinces may serve as Vents for escaping Lava, Gas, and even Water and Water Vapor. Each of the 3 (three) main types of Volcanoes (such as Cone-shaped, Shield, and Composite) form by Eruption of Lava, Volcanic Ashes and Gases from a Central Vent: a Cinder Cone Volcano, like Volcan Parícutin in Mexico, begins with an eruption from a Vent located in the Land Surface and then grows into a steep-sloped, Circular Mountain, as Cinders from successive Eruptions form a Cone around the Vent. Shield Volcanoes, like the ones in the Hawaiian Islands on Earth, and in the Tharsis Volcanic District on Mars, are composed of low-viscosity Basaltic Lava that flows easily and rapidly from a Central Vent. Though sometimes very large, Shield Volcanoes have a simple structure of stacked, low-angle Lava Flows around the Central Vent. Composite Volcanoes (also known as "Stratovolcanoes"), are very large Volcanic Edifices composed of alternating Layers of Volcanic Ash, Volcanic Ejecta and Lava Flows. Mt. Rainier in the American State of Washington, Cotopaxi in Ecuador, Mt. Etna in Italy, and Mt. Fuji in Japan are all Stratovolcanoes. Extremely large, Pyroclastic Eruptions of Gas-charged, Viscous Lava issue from a Central Vent (or even a group of Vents), located in the Summit Crater of the Composite Volcano; however, since the Andesitic (such as formed by molten Andesite) and Rhyolitic (meaning formed by molten Rhyolite) Lava that composes a Stratovolcano is extremely viscous, the Central Vent System often gets "plugged-up" for the time in between large Eruptions. The Molten Lava fills the Fissures located on the Flanks of the Mountain, so creating Radial Dikes. Gases and Fluids also may escape from Secondary Vents, creating Fumaroles and Hot Springs on the Slopes of a Stratovolcano. When a Composite Volcano becomes Dormant, erosion (due to the combined action of Winds and Water) can wear away the Outer Edifice that the Volcano was made of, thus leaving visible the Vertical Column that cooled off in the so-called "Feeder Duct", existing beneath the Volcanic Vent. Shiprock in the American State of New Mexico and the VERY famous Devil's Tower in Wyoming are extremely good examples of "Volcanic Necks" that formed this way. Mars Local Time: 15:49 (Middle Afternoon)
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