Volcanoes are strange things. Like earthquakes, they follow scientific principles to a sufficient extent to be generally understood, but their behaviour remains unpredictable. To this end, volcanologists continue to gather information which might give them an understanding of the processes which lead to an eruption – and a new study from the University of Bristol, in the UK, hopes to make just such a contribution.
Understanding a Volcanic Eruption Through Geology: How Magma Chambers Work
Understanding the workings of a volcano is, at its simplest level, schoolboy stuff – rock melts and rises, collecting in a magma chamber and, eventually, forces its way to the surface where it appears as lava, the product of a volcanic eruption. For most people, that’s all you need to know.
Inevitably, of course, the processes are much more complicated. Over the lifetime of a volcano, the composition of a magma chamber (and of the lava which eventually erupts) changes as the magma goes through eruptive cycles, with new pulses of magma arriving in the chamber itself from the melted rock below.
Fractional Crystallisation of Magma
Magma is made up of different minerals, which melt and solidify at different temperatures. As a result, during the cooling process, the minerals which solidify at the highest temperature crystallise first, and settle out from the liquid – therefore changing the composition of both the remaining magma in the chamber, and, in consequence, the lava which is erupted (which may be further altered by the addition of a fresh influx of molten rock).
Such crystals often form over a considerable period of time, during which the chemical composition of the liquid magma around them may change several times. The outer layer of the crystal reflects the composition of the magma chamber at the period of formation and as the crystal grows the composition successive outer layers may change, leading to a feature known as zonation.
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