Basalt Volcanoes under the Lake Balaton

The oldest volcano in the Bakony – Balaton-highland Volcanic Field is the Tihany Volcano (7,99-7,93 Ma). Due to its phreatomagmatic origin there was no lava flow onto the surface, one can find only tuffs and pyroclasts. In these pyroclasts there are volcanic bombs at multiple levels, derived from the ripped up basement clasts of the Balaton-highland. Reconstructed trajectories of these clasts suggest the existence of a volcanic center towards the East of the peninsula. According to the interpretation of seismic sections, recorded in the eastern part of the Lake Balaton, basalt intrusions can be present at a few places bellow the lake. In September 2010 we carried out magnetic survey in this area to confirm the seismic interpretation. We have acquired 14 north-south directed sections of the total magnetic field, with a complete length of 140 km. Correction of temporal variation of the field strength was performed on the basis of the continuous record in the Tihany geomagnetic observatory. After spatial correction based on the relevant normal formula, we arrived at a magnetic anomaly map. Although the resulting amplitude of the anomaly (30-40 nT) is lower than expected, it occurred exactly where the seismic interpretation indicated basaltic intrusions.