Formation
They are created when magma reaches the surface but, as there is a large difference in temperature between the lava and the water, the surface of the emergent tongue cools very quickly, forming a skin. The tongue continues to lengthen and inflate with more lava, forming a lobe, until the pressure of the magma becomes sufficient to rupture the skin and start the formation of a new eruption point nearer the vent. This process produces a series of interconnecting lobate shapes that are pillow-like in cross-section. The skin cools a lot faster than the inside of the pillow, so it is very fine grained, with a glassy texture. The magma inside the pillow cools more slowly, so is slightly coarser grained than the skin, but still classified as fine grained.
Read more about this topic: Pillow Lava
Famous quotes containing the word formation:
“The moral virtues, then, are produced in us neither by nature nor against nature. Nature, indeed, prepares in us the ground for their reception, but their complete formation is the product of habit.”
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“That for which Paul lived and died so gloriously; that for which Jesus gave himself to be crucified; the end that animated the thousand martyrs and heroes who have followed his steps, was to redeem us from a formal religion, and teach us to seek our well-being in the formation of the soul.”
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