The magma stored beneath a volcano isn’t always liquid, but spends most of its time in a relatively cold, solid state, according to research published this week in the journal Nature. Kari Cooper, a geochemist at the University of California – Davis, says the transition from a crystal-rich magmatic “mush” to a less viscous magma that could erupt is like heating up a jar of peanut butter taken from the fridge. She’s trying to develop a better understanding of the behavior within magma chambers—information that could one day lead to improved monitoring of volcano hazards.