A Middle Miocene, ~8 m thick pyroclastic succession, reported from the Bükk Foreland Volcanic Area (BFVA) in
Northern Hungary (Central Europe) specified here as the Jató Member, was produced by silicic
phreatomagmatism (Phreatoplinian sensu lato). Two well-preserved outcrops ~8 km apart and inferred to be
within ~10–50 km from source represent the discontinuously exposed, layered, paleosol-bounded,
phreatomagmatic JatóMember. They show an identical phenocrystal assemblage of feldspar, biotite and amphibole
without weathered zones or signs of erosion, that suggest deposition in one eruption phase lasting hours to
months. The succession contains three subunits: 1) subunit A, 1.8 m thick, a series of well-sorted fine to coarse
ash or lapilli tuff layers with constant thickness; 2) subunit B, 2.1 m thick, a series of normal-graded layers
with an upper fine-grained zone containing abundant ash aggregates with a coarser-grained core and distinctively
finer-grained outer rim; 3) subunit C, 4.5 m thick, a massive, poorly to well-sorted coarse ash with gas escape
structures and ash aggregates at its base. The upward change of these lithofacies implies an initially
sustained dry fallout-dominated deposition of ash and pumice lapilli resulting in subunit A. Subsequently, multiple
wet and dilute Pyroclastic Density Currents (PDCs) dispersed subunits B and C. The general abundance of
PDC-related ash aggregates in the middle-upper part of the succession (particularly in subunit B), and the transformation
of a fall-dominated to a collapsing depositional regime producing wet dilute PDCs, imply the increasing
influence of water during the eruption (Phreatoplinian sensu lato). The presence of water is related to an
epicontinental sea duringMiddle to LateMiocene in the Carpatho-Pannonian region. The transition from an initial
dry magmatic phase generated fallout activity followed by the emplacement of wet PDCs' rich in ash aggregates,
when external water infiltrated from a surrounding lake or sea water entered the vent.
