f Geophysical prospecting of Maar-type basaltic craters in Hungary

About 4 million years ago a violent volcanic activity disturbed the calm Pannonian Take system filling up the Carpathian basin. In Hungary the repeated volcanic eruptions not only built up scenic basalt cones (Badacsony, Somló, Sághegy etc.), but-special tuff rings were produced as well. Later on, water filled these maar-type tuff rings and crater lakes came into being. In this closed and silent lakes the nutritive richness, coming from dissolution/decomposition of the volcanic material, yielded an extensive pullulating of algae. Decease and sedimenting of the organic mass produced the alginite, the alga rock. In most places the algaic deposits were covered by basaltic bentonites.