![]() The diagram below shows that heat concentrated in the Earth's upper mantleraises temperatures sufficiently to melt the rock locally by fusing thematerials with the lowest melting temperatures, resulting in small, isolatedblobs of magma. Upon cooling, the liquid magma may precipitate crystalsof various minerals until solidification is complete to form an igneousor magmatic rock. Magmas also contain many other chemical elementsin trace quantities. Originating many tens of miles beneath the ground, the ascendingmagma commonly contains some crystals, fragments of surrounding (unmelted)rocks, and dissolved gases, but it is primarily a liquid composed principallyof oxygen, silicon, aluminum, iron, magnesium, calcium, sodium, potassium,titanium, and manganese. Molten rock below the surface of the Earth that rises in volcanic ventsis known as magma, but after it erupts from a volcano it is called lava. The finest ash particles may be injected milesinto the atmosphere and carried many times around the world by stratosphericwinds before settling out.įountaining lava and volcanic debris during the 1959Kilauea Iki eruption of Kilauea Volcano, Hawaii. Someof the finer ejected materiaIs may be carried by the wind only to fall tothe ground many miles away. If so, an eruptionbegins, and the molten rock may pour from the vent as non-explosive lavaflows, or if may shoot violently into the air as dense clouds of lava fragments.Larger fragments fall back around the vent, and accumulations of fall-backfragments may move downslope as ash flows under the force of gravity. The term volcano also refers to the opening or vent through which the moltenrock and associated gases are expelled.ĭriven by buoyancy and gas pressure the molten rock, which is lighterthan the surrounding solid rock forces its way upward and may ultimatelybreak though zones of weaknesses in the Earth's crust. ![]() ![]() A volcanois most commonly a conical hill or mountain built around a vent that connectswith reservoirs of molten rock below the surface of the Earth. Volcanoes are mountains but they are very different from other mountains they are not formed by folding and crumpling or by uplift and erosion.Instead, volcanoes are built by the accumulation of their own eruptive products - lava,bombs (crusted over ash flows, and tephra (airborne ash and dust).
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