There are several factors that control the way a volcano erupts, including the pressure, water content, chemistry, and and temperature of a magma. A hotter magma is less viscous or sticky, while a cooler magma tends to be more explosive due to the accumulation of gas bubbles. The temperature of a magma chamber can be vital information for volcanologists, but there’s no simple way to just stick a thermometer in there to get the necessary data. Instead, scientists use rock compositions to collect the data.
Much like how tree rings can reflect wet or dry years, minerals forming in magma chambers record environmental conditions. Both the changes in temperature and pressure alter the chemical composition of mineral layers, so geochemists use electron microprobe analysis, which bombards rock samples with electrons to measure emitted energy, revealing the mineral’s chemical makeup much like an x-ray.
A chemical comparison between the mineral and the melt, which is often preserved alongside the mineral as volcanic glass, can reveal the temperature history of the magma. Mineral-melt thermometry, as it’s called, can be applied to almost any volcano around the world.
