Kissomlyo volcano is a Pliocene erosion remnant of an alkaline basaltic tuff ring,
belonging to the Little Hungarian Plain Volcanic Field. Late Miocene shallow subaqueous,
fluvio-lacustrine sand and mud units underlie sub-horizontally bedded lapilli tuff
and tuff beds with an erosional contact. The pyroclastic units, a sequence up to similar
to 20 m thick, constitute a semi-circular mound with gentle (<5 degrees) inward-dipping
beds. Sedimentary features and field relationships indicate that the pyroclastic units
were formed in a terrestrial setting. Phreatomagmatic explosions occurred at a shallow
depth, producing a large amount of juvenile ash and lapilli, which were transported
and deposited predominantly by pyroclastic density currents, subordinate fallout and
reworked by gravity currents. The tuff ring is overlain by a 5 m thick sequence of
cross- and parallel laminated siltstone and mudstone deposited in a take inferred
to have developed in a crater. The textural and structural differences between the
lacustrine units beneath and above the tuff ring sequences suggest that they did not
belong to the same lacustrine environment. The post-tuff ring lacustrine sequence
is invaded by basanite pillow lava. The lava shows a basal peperitic margin partially
destroying the original structure of the lacustrine beds due to fluidisation. The
time gap between the tuff ring formation and the emplacement of the lava flow is estimated
to be in the order of thousands of years. (c) 2005 Elsevier B.V All rights reserved.
