Electron-probe microanalysis (EPMA). These measurements were performed at the Tephrochronological Analytical Unit at the University of Edinburgh using a Cameca SX100 electron microprobe with five vertical wavelength dispersive spectrometers, providing oxide values (wt. %) for 10 major elements (see supplementary information).Beam size: 5Settings:cond1: Na, Al, Si, K†, Ca, Fe, Mgcond2: Mn, P†, Ti