Principles Of Earth Science

INTERPRETING THE HISTORY OF VOLCANOES AND VOLCANIC ROCKSDrawing from the diagram , the volcanic autobiography is as outlined be mortified and other relevant en bombastic be also suppliedSequential summary of volcanic invoice the areaAndersite porphyritic rock : this is the oldest . Andersite indicates magma of intermediate composition . Its silica content is mid carriage amidst felsic rocks (having high-pitched silica subject area ) and mafic rocks (having low silica content . Its body-buildation is a two-step process where slow engine cooling system occurs at the initial symbolise within the crust forming boastfully crystals as a solution . However , the remaining magma moves march on out and , as a result cools to form a fine grained metric grain within which the earlier formed large crystals are embed . This indi cates a slow eruptionTurf grading into braccia : these are pyroclastic rocks formed by violent eruption of highly gummy magma . The tuff is fine than breccia but the two are of the aforesaid(prenominal) occurrence of formation .

The magma forces its way out shattering the meet plastic rocks into ashes and block fragments . These unite to form tuff and breccia separately and are potential to be felsic since high viscousity indicates a high silica contentDacite porphyry : this is of akin(predicate) composition and formation flair as andersite porphyry though it has higher silica content than andersitePumice Breccia : pumice is fine unsmooth , filled with holey holes containing gases that were confine within the forming magma! at the incursion of eruption . The gases later escapes to form a light , porous glassy rock . The breccia was likely to...If you want to get a full essay, order it on our website: OrderEssay.net

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