Mélida Schliz-Antequera , Claus Siebe, Sergio Salinas, Geoffrey A Lerner 

The formation of phreatomagmatic volcanoes (PVs) usually involves small volumes of magma but also very violent eruptive activity. Along the Trans-Mexican Volcanic Belt (TMVB) the basic conditions that favor water-magma interaction are provided by the presence of frequent small-volume monogenetic volcanism and several inter-montane lacustrine basins. The TMVB is a Plio-Quaternary continental volcanic arc dominated by >3000 monogenetic volcanic structures with only ~3% being the result of phreatomagmatic eruptions. Around 70% of these are clustered in three specific areas within volcanic fields in Valle de Santiago, Serdán-Oriental, and Los Tuxtlas. Here we investigate the low frequency of PVs and their selective locations and whether local environmental conditions play an important role in their formation. An inventory of 103 PVs within the TMVB has been compiled, including tuff cones, tuff rings, and maar-diatremes. The inventory contains morphometric parameters for each structure along with data regarding geological (internal) and environmental (external) parameters of the areas where the PVs are built. The magmatic flux is the first-degree influence in the formation of PVs. Different combinations of environmental parameters have a secondary-degree influence which varies spatially and temporally related to paleoclimate, hydrology, and hydrogeology. A couple of environmental parameter sets are met more often, reflected in the areas with clustered PVs, but less frequent sets of parameters are also detected, reflected in the scattered PVs. Morphometric correlations allow for a clear differentiation between the group of tuff cones and the group of maar-diatremes and tuff rings. In both groups elongated and compound shapes are more frequent. Very often, human settlements are built around or inside PVs. However, their shapes and relatively small size can be misguiding regarding the hazard that this type of volcanism represents, especially in the absence of knowledge about the conditions that result in these type of eruptions. This inventory allows for the study of the many different conditions and places in which a phreatomagmatic eruption could occur, providing a better base of information to prepare for future eruptions.