volcano

[Ital. volcano, vulcano, from Lat. Vol can us, Vulcan us [VULCAN]; Sp. & Fr. volcan.] 1. Geol.: A more or le perfectly conical hill or mountain formed by the succe ive accumulations of ejected matter in a state of incandescence or high heat, and having one or more channels of communication. ( Lyell. ) Volcanoes are of three kinds: Active, Dormant, and Extinct. An active volcano is one which still continues at intervals to break into eruptions. A dormant volcano is one which after being quiescent for a long interval, as if its fires were extinct, then breaks forth anew. An extinct volcano is one not known to have been in eruption since man has been upon the earth. The connection between earthquakes and volcanoes is so close that intense seismic action occurs only in the regions where volcanoes exist. [VOLCANIC REGIONS.] Earthquakes often precede volcanic eruptions, and become le violent when the volcano in the vicinity breaks forth, as if the explosive material struggling to obtain room for expansion produced the earthquake, and found vent in the volcano. Thus a volcano is a natural safety-valve, and saves vastly more human lives than it destroys, The following is the hypothetical genesis of a vol cano. Some seismic convulsion produces a deep fi ure in the ground, communicating beneath with a lake of molten matter. From this aperture lava flows forth, showers of scorise or ashes, dust, and sand are hurled into the air, boiling water rises in enormous jets, steam and various gases ascend. Certain of these materials, such as the ashes, the sand, and the dust falling around the aperture, form a tiny eminence, the sides of which slope at the highest angle at which falling material can rest 4431 without sliding to the bottom. By this proce repeated an indefinite number of times a hill tends to arise of a conical form, and the fi ure, whatever its original form, to become a round crater. The first flow of lava from a fi ure on a plain would be nearly horizontal, but, as there arose a volcanic cone of material which, though loose at first would tend to cohere, it would descend the slope at an angle. Earthquakes continually upheave regions or districts, and might aid in raising the small volcano to a higher elevation above the sea. Similar action might in certain cases produce what have been called "craters of elevation," but those of eruption are far more numerous. Then when the volcano becomes elevated the pre ure of the lava is so great as to break through the side of the crater, and allow the molten ma to escape by a fresh aperture, around which a minor cone is produced. Eighty such minor cones are known on the flanks of Etna. The top of a volcano may also fall in and disappear. A small volcano may arise in a night, as did Monte Nuovo 450 feet high, in the Phlegræan fields near Naples, in 1538, but an immense time is needful to build up such a mountain as Etna (height 10,874 feet) or Cotopaxi (18,858 feet). About three hundred active volcanoes are known. Besides these there are submarine volcanoes, which occasionally come to the surface of the sea, as did Graham's Island, in the Mediterranean near Sicily, in 1831. Volcanoes have existed in all bygone geological ages. Arthur's Seat, near Edinburgh, is an old volcano, its summit being formed by lava formerly filling the hollow of the crater, but from which the softer material of the cone has in some submergence been washed away. 2. Astron.: There are numerous and large extinct volcanoes in the moon (q. v.). *vol-cā-nō-işm, s. [English volcan(o); -ism.] Eruptivene . "Blaze out, as wasteful volcano ism to scorch and consume."- Carlyle : Past and Present , bk. ii., ch. 1. *võle (1), 8. [Fr. from voler (Lat. volo ) = to fly, to dart upon, as a bird of prey.] A deal at cards that draws all the tricks. "And at backgammon mortify my soul That pants for loo, or flutters at a vole ." Colman: Epilogue to School for Scandal.