Repeatedly pointed to the volatility of the chemical composition of lavas, with mean trahitovye and basaltic volcanic rocks. In fact, under the name of the lava we mean not any particular chemical and mineralogical on rock: the word denotes all the molten mass ejected by the volcano. "Everything that flows from the crater and deposited in new places, is called lava," - says Leopold von Buch. The number of species belonging to the category of lava, is rather limited: it is mainly trachytes, basalts and rocks, which occupy an intermediate position between them. In addition, there also may include some other breeds, characterized by the content of known minerals: leucite, nozeana, nepheline, etc. trachytes and basalts represent a difference not only in their chemical and mineralogical composition, lava flows, formed by them, have not the same physical properties . Basaltic lavas are inclined to spread in width and flow to the enormous extent; trahitovye lavas have a high density, lower mobility. Both ancient and modern basaltic lavas occur most often in the form of cover. The above-mentioned huge stream of scan-General of-iokula in Iceland belongs to the basalts. Generally in any volcanic area, you can find a number of examples to prove the validity of the above. On the contrary, trachytes represent short and wide streams with surface covered by numerous irregularities.
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