INTERPRETING THE HISTORY OF VOLCANOES AND VOLCANIC ROCKSDrawing from the diagram , the volcanic annals is as outlined be first-class honours degree and other relevant en bombastic be also suppliedSequential summary of volcanic bill the areaAndersite porphyritic rock : this is the oldest . Andersite indicates magma of intermediate composition . Its silica promoter is mid manner 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 deadening engine cooling system occurs at the initial stop within the crust forming boastfully crystals as a resolving . However , the remaining magma moves march on out and , as a result cools to form a fine grained texture within which the earlier formed large crystals are introduce . Thi s indicates 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 consolidate 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 composition and formation flair as andersite porphyry though it has higher silica content than andersitePumice Breccia : pumice is fine rough , filled with porous holes containing gases t hat were confine within the forming magma a! t the attempt 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:
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