Local Structures around Si, Al and Na in Hydrated Silicate Glasses

XANES spectra were collected at the Si‐, Al‐, and Na K‐edge in hydrous silicate glasses to understand the effect of water on the local structure around these cations. Around network forming Si and Al, no drastic changes are observed. Around Na, the dissolution of water creates more ordered environments in Al‐bearing glasses and less ordered environment in Al‐free glasses. Ab‐initio XANES calculations were undertaken to understand the structural origins for these features. Based on these results, a bond valence model was refined that considers not only the present XANES experiments and models but also NMR information. The double percolation model refined explains, among others, the explosive properties of water‐bearing hydrous melts, at the origin of a number of cataclysmic eruptions in subduction zones.