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Abstract:The maar-diatreme volcanic structure in the vicinity of the village of Lomnice near the town of Bruntál (North Moravia, Czech Republic) has been investigated using a set of geophysical methods including ground magnetometry, gravimetry and electrical resistivity tomography. The structure was detected by an aerial magnetic survey in the second half of the 20 th century. Since its discovery only limited information about this buried structure has been available. The coherence of the magnetic anomaly of 190 nT and Bouguer anomaly of -4.7 mGal indicates a volcanic origin of the structure. The funnel-shaped maar-diatreme structure is filled with lacustrine clay and colluvium of Carboniferous greywacke, which forms the country rock. The surface diameter of the structure is about 600 m, the depth is more than 400 m. The spatial association with other volcanic centers in the surroundings of the town of Bruntál infers the relative dating of the Lomnice maar. The phreatic eruption and maar-diatreme formation could be an indirect consequence of effusive activity of the nearby Velký Roudný volcano. The Lomnice structure is the first Plio-Pleistocene maar-diatreme ever described in North Moravia and Silesia.

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Th e dyke on the Pohoř hill represents the most southeastern occurrence of Cenozoic volcanic rock in the Bohemian Massif. It has been studied since the second half of the 19 th century, when it was discovered during a construction of railroad. Since that time the dyke has been considered to be hidden and there was no actual data about the site. We have carried out a ground magnetic survey to revise the location and shape of the volcanic body. Several boulders of the volcanic rock have been sampled. According to new petrographical and geochemical analyses we have classifi ed the rock from Pohoř as an olivine melilitite.

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