Word: magma
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Dates: during 1940-1949
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Incantations & TNT. Volcanoes, on the other hand, are less mysterious and more dangerous. Though they are worshiped as goddesses and damned as hellholes, bubbling craters are really just safety valves, through which molten rock (magma) under the earth's skin can blow off steam from time to time. Volcanoes can be depended on to act up every so often; since 79 A.D., when Pompeii and Herculaneum were first buried, old Vesuvius has popped off about once every generation...
...geologists know little about the underground conditions responsible for Paricutin. It lies in the "Michoacan volcanic province," dotted with old, dead craters. The whole region may be resting on a "batholith," an enormous mass of "magma" or hot, plastic rock. More likely, Paricutin gets its lava from a smaller "local chamber" of molten basalt which gnawed its way toward the surface until it finally broke through. If the underground lava supply is large enough and active enough, Paricutin may grow as tall as 17,876-ft. Popocatepetl, 200 miles to the east...
...before they separated; but the Pacific shores crumpled the earth's crust ahead of them, like the bows of ships plowing through thin ice. Thus were formed the still growing, earthquaky mountains which ring the Pacific today. When the crumpling broke a hole through the solid crust, hot "magma" burst to the surface, building a volcano...
Most volcanologists think that volcanic and earthquake activity occurs along profound rifts in the earth's subsurface, cracks running down as much as 100 miles or more. At those depths the temperature is high, the pressure strong and steady, and earth material a homogeneous magma of plastic rock. This pressure and material are the source and force of a volcano...
...eruption has released the pressure, the top layer of the molten rock cools and hardens, sealing the volcano temporarily. The cap can contain the pressure for a time-depending on the peculiarities of the individual volcano-when it cracks open again with a rush of burning gas. Molten magma boils up, whipped to a froth by the gases. After the pressure has been relieved, the eruption subsides, the cap forms again and the cycle of eruption is complete...