|MadSci Network: Earth Sciences|
Dear John, The answer is certainly no. The magma beneath or inside a volcano is under tremendous pressure. When that pressure is released the result is an eruption. Depressurization normally occurs when the strength of the overlying rock confining a magma chamber is overcome by the pressure within the magma. Magma contains dissolved water and other volatile gases under pressure, rather like the carbon dioxide dissolved in a fizzy drink. The mechanisms of an explosive eruption are complex, but essentially the release of the confining pressure causes the gases dissolved in the magma to exsolve suddenly. If I can quote the late Peter Francis, a leading authority on volcanoes, “… explosive eruption columns are driven by the thermal energy stored in the magma. Thermal energy is transferred into the kinetic energy of the eruption column through the expansion of the gases diffusing into growing vesicles” in the magma [Peter Francis, “Volcanoes: A Planetary Perspective” (London: Clarendon Press, 1993) p. 167]. Even if we could drill a hole into a magma chamber it would run the risk of depressurising the magma, causing it to erupt. An example of something very like this occurred naturally in the 1980 eruption of Mt. St. Helens. In this case the rise of magma into the volcano caused the north side of the mountain to swell outward until it became unstable. Rising magma triggers earthquakes, and one of these tremors caused the north face of Mt. St. Helens to collapse in a landslide. The landslide removed the confining pressure from the magma chamber inside the volcano, causing it to erupt sideways. The volatile content of magmas varies greatly. Basaltic magmas such as those produced on mid-ocean ridges and hot spots (Iceland and Hawaii are good examples) normally contain less volatile content by volume than magmas at destructive plate boundaries, such as Mt. St. Helens. But even basaltic magmas contain enough volatile content to make eruptions dangerous. The fire fountains associated with eruptions on Hawaii, Iceland and Mt. Etna are driven by the exsolution of dissolved gases. A volcano is merely the surface expression of a complex magma system, which will consist of numerous conduits and chambers fed with magma from great depth, often from the upper mantle from which magma can rise from depths of 60 km or more. The ultimate source of magma is therefore beyond the reach of any conceivable technology. By the time magma has risen to shallow depths beneath a volcano it will be too late to stop any eruption because the magma chamber will explode when the confining pressure is released, however the release occurs. This is not to say that nothing can be done to intervene in eruptions, especially the effusive eruptions of basaltic lavas in which lava flows threaten property. Both on Mt. Etna and in Iceland lava flows have been diverted away from threatened areas, for example by blasting alternative channels in the path of advancing lava. When an explosive eruption is threatening to occur, however, the best thing to do is evacuate the area. I hope this answers your question. Best wishes, David Scarboro
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