INTERPRETING THE HISTORY OF VOLCANOES AND VOLCANIC ROCKSDrawing from the diagram , the volcanic recital is as outlined below and other relevant flesh out be also suppliedSequential summary of volcanic history the areaAndersite porphyry : this is the oldest . Andersite indicates magma of intermediate composition . Its silica national is midway between felsic rocks (having advanced silica sate ) and mafic rocks (having low silica content . Its giveation is a two-step process where slow temperature reduction occurs at the initial stage within the crust forming big crystals as a result . However , the remaining magma moves farther out and , as a result cools to form a fine grained texture within which the earlier formed pear-shaped crystals are embedded . This indicates a slow eruptionTurf grading into braccia : these are pyroclastic rocks formed by violent eruption of highly gummy magma . The tuff is finer than breccia but the two are of the very(prenominal) occurrence of formation .
The magma forces its way out shattering the environ plastic rocks into ashes and block fragments . These consolidate to form tuff and breccia one by one and are probably to be felsic since high viscousity indicates a high silica contentDacite porphyry : this is of similar composition and formation modality as andersite porphyry though it has higher silica content than andersitePumice Breccia : pumice is fine textured , filled with porous holes containing gases that were pin down within the forming magma at the onset 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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