'Interpreting The History Of Volcanoes And Volcanic Rocks Essay\r'

'Drawing from the diagram, the volcanic history is as outlined be lowly and other pertinent details ar also supplied.\r\n1.0 back-to-back summary of volcanic history the knowledge base\r\na. Andersite porphyry: this is the oldest. Andersite indicates magma of intermediate composition. Its silicon oxide heart is midway between felsic rocks (having spirited silicon dioxide content) and mafic rocks (having low silica content). Its strivingation is a two-step process where slacken temperature reduction occurs at the initial stage at bottom the crust phase angleing large crystals as a leave alone. However, the remaining magma moves further out and, as a result, cools to form a elegant grained texture at heart which the earlier organise large crystals are embedded. This indicates a slow eruption.\r\nb. Turf grading into braccia: these are pyroclastic rocks form by violent eruption of passing viscous magma. The tuff is first-rater than breccia scarce the two are of the sa me fact of formation. The magma forces its way out shattering the touch plastic rocks into ashes and block fragments. These consolidate to form tuff and breccia respectively and are potential to be felsic since high viscousity indicates a high silica content\r\nc. Dacite porphyry: this is of correspondent composition and formation style as andersite porphyry though it has higher silica content than andersite.\r\nd. rub Breccia: rub is fine textured, filled with porous holes containing gas pedales that were trapped within the forming magma at the trespass of eruption. The gases later escapes to form a light, porous glassy rock. The breccia was probably to have resulted from the shattering of the rocks as the magma erupts out. Pumice is light colured which indicates a felsic composition (felsic rocks are lightly coloured than mafic rocks)\r\ne. Polymictic breccia: this indicates a mixture of breccia of varying silica content which indicates the onset of the formation of an in terrupting basaltic formation which is to preserve after. However, the mode of formation is still violent.\r\nf. Basalt with peckish blacky top: this is a fine grained mafic rock. The coarse top indicates that the forming magma was gently erupted and the viscosity low enough to cause the included gas to just escape leaving the eruct spaces at the top.\r\ng. Andersite: this has been seen as of intermediate silica composition. The absence of porphyritic material may indicate a less compose eruption.\r\nh. Obsidian with pumice streak: the youngest rock; obsidian resembles pumice but without the bubble holes. The presence of pumice streak indicates violent eruption since many of the gases were trapped as a result of the violence. It is felsic.\r\n2.0 Since the last eruption is about 19 years earlier (the age of the youngest layer), the volcano is still active. The earthquakes and the likes are likely pointers to some other volcanic eruption. So evacuation is imminent.\r\n3.0 Th is is an employment of a composite or cinder-cone volcano. The seldom occurrence of pyroclastic materials and rocks of intermediate composition suggests this. These, in addition to the fact that the rocks are from highly viscous magma, also suggests that the volcano is find at a volcanic arc.\r\n'