Magma degassing and fragmentation control hazardous tephra production in glaciovolcanic eruptions, and strongly influence the generation of meltwater. Characterisation of volatile species in eruptive products allows reconstruction of degassing systematics, and magmatic textures provide insight into fragmentation mechanisms and interactions with external water. In this session we will describe the methods used to quantify volatile species concentrations and magmatic textures, and use Icelandic case studies to examine how results can be used to constrain eruptive controls, quenching pressures, and interactions with meltwater.