Volcanic eruption conditions
Volcanic eruption is a strong indication of the energy released by magma, that is, when the magma energy in the earth's interior accumulates to a certain extent, it will erupt from the earth's surface along the weak crustal zone under strong pressure, forming a spectacular phenomenon of volcanic eruption. Whether a place can form a volcano mainly depends on it has the following conditions or not.
(1) Formation of Partial Melt, there must be higher geothermal (self-accumulated or generated by external boundary conditions), or uplift decompression processes, or dehydration to reduce the solid line.
(2)The enrichment of magma in the crust or the location of magma chamber formation are related to the depth of the neutral buoyancy surface, while the depth of the neutral buoyancy surface is related to the rheological discontinuity of the crust.
(3)Physicochemical processes in magma chamber, mainly the interaction of crystals, volatiles and fluids, promote or inhibit magma eruption. The existence of magma chamber in the crust plays an important role in intercepting and reforming the magma rising in mantle, and it is also an important condition for the formation of explosive volcanic eruption.
(4) The existence of magma chamber promotes the formation of magma channel, and the tensile stress field generated by tectonic activity is the main reason for the formation of magma channel.
(5) The rise of magma after leaving the magma chamber is driven by pressure gradient and buoyancy.
Summary of volcanic eruption types
The composition, volatile matter content, temperature and viscosity of magma are one of the determinants of eruption types around the world, for example, basaltic magma has low Si02 content, relatively little volatile matter, high temperature and low viscosity, therefore, magma fluidity is large, volcanic eruption is relatively quiet, mostly magma eruption, which can form a large area of lava platform and shield volcano; rhyolitic and andesite magma are rich in Si02 and volatile matter, with low temperature, high viscosity and poor fluidity, therefore, volcanic eruptions are violent and explosive, with a large amount of ash and volcanic bombs erupted, often forming tall pyroclastic cones, accompanied by pyroclastic flow and luminous cloud phenomenon, often causing serious disasters. The second decisive factor is the characteristics of the underground magma rising channel; if the magma in magma chamber reach the surface along a longer fault line, a fissure eruption will be formed; if upwelling along the cylindrical channel formed by the intersection of two sets of faults, under the action of internal pressure of magma, violent central eruption will be produced. The third decisive factor is the tectonic environment of magma ejection, whether it is on land or underwater; is it in the ridge or is it in the plate; is it in the island arc or in the collision zone, etc. Volcanoes are located in different tectonic environments, and the characteristics of volcanic eruption types are also very different.
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