Thoughts on the criteria to determine the origin of volcanic unrest as magmatic or non-magmatic.As our ability to detect volcanic unrest improves, we are increasingly confronted with the question of whether the unrest has a magmatic origin (magma on the move) or a non-magmatic origin from a change in the hydrothermal system (fluids that are not magma on the move) or tectonic processes.  These include measurements of gas fluxes and compositions and the isotopic signature of some components (e.g. H2, He, C, SO2, H2 O, CH4 and CO2), the spatial and temporal characteristics of ground deformation, thermal output, seismicity, changes in gravity, and whether there is topographic uplift or subsidence spanning hundreds to thousands of years. 
THERM