ENGINEERING GEOLOGICAL SURVEY OF RÓZSADOMB AREA, BUDAPEST, HUNGARY

Abstract

Late Triassic platform and extensional basinal sediments and Eocene shallow self carbonates are mainly covered by Oligocene clays, Pleistocene-Holocene slope sediments in the Rózsadomb area. Eocene carbonates are the host rocks of the extended (25 km) cave system, which passages are primarily tectonically controlled. The fractures and joints of the three major tectonic phases vvere enlarged by ascending thermal waters in the Plio-Pleistocene period. The presence of near surface cave passages raises special problems: hazards of cave collapse, especially when the cover beds are fractured Eocene marls; pollution of karst and related thermal water system from failure of sewer system or cesspits via fissures and cave passages. Damages in built environment are mainly related to landslides of the soaked clayey slope sediments, since in the deeper zones the 'solid' carbonate rocks are stable. The major trigger mechanism of the landslides is the precipitation combined with slope instability (human activity). To reduce the risk of landslides, damages and contaminations the reconstruction and extension of sewer system; the stricter regulations of human impact (control of townplanning regulations); the extension of protection zones and the exploration of the unknown cave system would be necessary.