Adamkó Péter - Dénes György - Leél-Őssy Szabolcs: The Caves of Buda - Our Budapest (Budapest, 1992)
The origin of the caves Most of Budapest’s caves, including all of the major ones, fall into the type of caves formed by hydrothermal processes, that is, by hot water. The formation of caves was linked to suitable rocks, mainly limestones. It was controlled by faults and associated fissures widespread in the Buda Hills. These joints and fissures originated from tectonic activity and conducted the thermal waters ascending from great depth as well as waters descending from the surface. Thus caves were formed along the preexisting tectonic fractures. The fissures were widened as the water dissolved their walls. Larger chambers were formed at the intersection of several fissures. Looking at a map of any major Buda cave, it can immediately be seen that the cave system consists of more or less parallel sets of branches supplemented by transversal ones. This is due to the more or less parallel nature of the tectonic fissures formed within a particular stress field. However, in different geological periods the rocks were affected by stresses of different orientation which is recorded in the fissure systems. Underground waters of different origin are solutions with different properties and ion concentrations. They can dissolve rocks until reaching a saturation level. Should a mixing of waters occur, the previously saturated waters may resume dissolving capability. This process is called mixing corrosion. If mixing is sustained at a particular site through a long period of time, large chambers may develop. In the Buda Hills the mixing zone always occurred where the ascending thermal waters met the descending rain-waters of completely different composition and ion concentration. Within bodies of limestone and other carbonate rocks, where interconnected fissures create a system enabling the flow of water according to the law of communicating vessels, a constant water level develops. It is known as the karst water table. This is controlled by the level of springs which drain the system at the foot of mountains. In Budapest it has corresponded to the level of Danube as the thermal springs (such as those supplying the Lukács, Gellért, and Rudas spas) have risen roughly at this level. This was true even in prehistoric time, in the latest geological periods. As the Buda Hills have been 7
