Con vulcanic
De la Wikipedia, enciclopedia liberă
Con vulcanic este denumirea uzuală dată uneia dintre cele mai simple formaţii vulcanice care apare în întreaga lume unde există fisuri ale plăcilor tetonice. Conul este format din magma topită care se solidifică în timp, având un rol de liant pentru celelalte materiale ejectate de erupţiile vulcanice.
Datorită atracţiei gravitaţionale, forţei erupţiei şi sedimentării, materialele solide şi lichide ejectate se depun treptat în jurul gurii de evacuare a vulcanului, formând în timp o structură care se înalţă treptat şi care se conturează în timp sub forma unui con care creşte atât volumic, masic şi, uneori, ca grad de înclinare al pantei.
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[modifică] Spatter cone
A spatter cone is formed of molten lava ejected from a vent somewhat like taffy. Expanding gases in the lava fountains tear the liquid rock into irregular gobs that fall back to earth, forming a heap around the vent. The still partly liquid rock splashed 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.
[modifică] Ash cone
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).
An example of a tuff cone is Diamond Head at Waikīkī in Hawaiʻi.
[modifică] Cinder cone
A cinder cone is a volcanic cone built almost entirely of loose volcanic fragments called cinders (pumice, pyroclastics, or tephra). They are built from particles and blobs 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.
Cinder cones rarely rise more than 500-750 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.
