Danube Bend: Miocene Half-Caldera and Pleistocene Gorge

Abstract

The Danube Bend, a river curvature, called Visegrád Gorge in its deepest and narrowest part, is one of the most picturesque landscapes in Hungary. Its origin and relief evolution has been a long-standing problem in Hungarian earth sciences. A number of geomorphological theories have been put forward in explaining the valley with a U-shaped planform, which is incised in the surrounding Miocene volcanic mountains. In the past fifteen years, thanks to combined volcanological, geomorphological and geochronological studies, the landscape evolution of the river bend of 5 km diameter has been largely clarified. The present-day U-shaped loop is partly inherited from the horseshoe caldera morphology of Keserűs Hill volcano, a 15-Ma-old andesitic lava dome complex with an eroded central depression open to the north. The formation of the Danube Bend was initiated by river incision that started to remove post-volcanic sedimentary cover in middle or rather late Pleistocene times. These processes in turn were triggered by mountain uplift, climate changes, and drop of the remote erosion base level. The present curvature of the river was controlled by the exhumation of the horseshoe caldera as well as the surrounding resistant volcaniclastic rocks (Visegrád Castle Hill) and a hilltop lava dome (Szent Mihály Hill). Moreover, a previous meander may have also inherited. The accelerated Late Quaternary erosion and intense dissection has resulted in a “re-birth” of the volcanic relief that exhibits again steep slopes. At present, exposed spectacular rock formations (e.g. Vadálló-kövek) tower above the gorge that belongs to the Danube-Ipoly National Park in Hungary.