Hidrológiai Közlöny 1948 (28. évfolyam)

ÉRTEKEZÉSEK - JAKUCS LÁSZLÓ: A hévforrásos barlangkeletkezés földtani és fizikai tényezői

é2 HIDROLÓGIAI KÖZLÖNY XXVIII. évf. l!>/,8. 1—i. szám. formes calcaires et dolomitiques; plus tard avec la surreotion des plates-formes karstiques disloquées, le niveau de eette nappe s'est abaissé. Quant aiix études détaillées, on peut citer Celles se rapportant ä l'évolution orographique des massifs du Nagykevély, Hosszúhegy et du groupe Pilis. Le développement de la surface karstique du groupe Nagykevély s'explique comme suit: vers le milieu du Tertiaire, la pénéplaine ancienne occupant l'emplacement de la chaíne se disloqua et les lambeaux séparés s'élevérent les uns au-dessus des autres en gradins. Avec la surrection lente, le niveau de la nappe karstique s'abaissa. Ces phénoménes se manifestent bien dans la grotte Mackó et celle d'Ezüsthegy. Le groupe de Hosszúhegy, jeune chaine aussi, émergea en pente et se disloqua. Avec cela, la nappe karstique s'abaissa et les sources des grottes Ziribári, Hosszúhegy, Pilisszántó et Szurdokvölgy cessérent de jaillir ainsi que les plus petits résurgences d'eau au niveau de la nappe karstique. Le groupe de Pilis s'éleva le plus haut au-dessus de la nappe karstique actuelle. Un degré de la surrection est démontré par la grotte de Pilisszántó, ainsi que par les grottes Leány et Legény. Les études sur place seront continuées. GEOLOGICAL, AND PHYSICAL FACTORS OF CAVE FORMATION BY THE ACTION OF HOT SPRINGS. By L. Jakucs. (Hungarian text with figs, on p. 53.) I). ('. 551.142:553.78(139.11) Sátorkőpuszta Caves of the borderland of the Great Hungarian Plain and especially those of the Buda Mountains are due without exception to the action of hot springs. It is therefore necessary to examine the process of such cave formation and to fit it into the framework of general geological knowledgeThe Sátorkőpuszta Cave discovered in 1946 by the Author may be regarded as the purest type of cave thus formed, so that these general examinations can be carried through on basis of this example. (Fig. 1.) The Author sums up his results in the following: 1. Caves of this kind were formed by hot wells breaking up from deeper strata of the earth's crust. 2. As hot wells characterise mostly mountains of faulted structure, such caves also are formed in broken blocklands. 3. Caves due hot spring action are always formed along some important fault line or at the crossing of two faults. 4. Caves due to hot springs as well as Karstic caves are generally formed in limestone, rarely in dolomite. 5. Hot springs form caves partly by solution, partly by pulverization of the rock. 6. The aptitude of hot wells to produce caves by solution and pulverization exerts itself only at the level of live Karstic water flowing along in horizontal directions. In consequence of this caves due to hot spring action, though they cannot be regarded as Karst phenomena, are formed at the base or above the level of the live Karst. (Fig. 4.) 7. Important and general characteristics of such caves are: a

) Cave channels are producced in contrast to Karst caves not horizontally but radiating upward from a deepest centre. The vertical development and its connection with the deepest base point give valuable data for the genesis of the cave. b) Channels, chimneys trending upward do not thin out gradually but finish abruptly in a sperical or cupola surface. Only one chimney reaches the surface through which the hot well spouted out, but even this is clogged by lime sinter when the spring has ceased. c) Characteristic features of caves due to hot springs are spherical holes which are not found in Karstic caves. These are almost entirely closed holes, of the shape of a regular sphere or a double sphere, of 1—3 m. diameter. Their formation is due to the pulverizing action of the well on the limestone. (Sec. 8.) d) Caves produced by hot wells, which are in the first stage of subsequent gradation and which possess spherical spaces are characterized by loose, pulverulent rock surfaces. The thickness of this pulverulent layer is variable, and it is thicker where the temperature of the hot spring producing the cave was higher. e) The following minerals are primarily found only in caves produced by hot springs: cristalline or amorphous aragonite, cristalline gypsum originating from anhydrite by hydratation, baryte, fluorite, lublinite, etc. 8. A main factor of cave formation by thermal action is the above mentioned pulverization of the rock, which consists of the following: In capillary fissures of the karstificated rock heated above 30° C. by hot water, aragonite is deposited from circulating Karst waters. This mineral entirely fills up the network of capillary fissures of the rock. When the hot spring has discontinued and the rock has cooled down, the aragonite changes into calcite involving an increase of volume of 8.35% wich loosens the texture of rock along the fissures and disintegrates it. Where the jet of hot water knocks against the rock surface, (Fig. 2.) more heat is transmitted to the latter than where the stream flows along surfaces. The isothermal surface of 30' C. bulges in here to a spherical form (Fig. 3.) and subsequent disintegration also produces spherical shapes. After repeated hot spring action in 3 4 phases, the bulge assumes spherical shape. Aragonite crystals are still to be traced in the pulverized rock. 9. In the same way may be explained the well known pulverization of dolomites and limestones which is a general local feature especially of Triassic rocks in Hungary. 10. As caves produced by hpt springs are developed at the base of the live Karst, which had varying elevations in different geol(%ical times, the altitude of the cave base helps to determine its age. 11. As the natural or artificial entrance to the cave always lies above the bottom denoting the previous Karst Water level, whereas the natural apertures of Karstic caves with flowing streams is at Karst Water level, the following principle may be formulated: Of two caves of the same age one of which is due to Karstification the other to the action of hot springs, the natural entrance to the former always lies lower than that of the latter. 12. The Formation of sphercial holes is only a feature of homogeneous Karstic rocks which are free from previously developed crevices or tectonic cleats. A condition of the formation of spherical holes is namely water feowing under high pressure and and with high velocity, becausfe it is only thus capable of differential heat transfer to surfaces of collision and to such parallel to its direction of flow. It is evident that where the hot spring spouted up secondarily through a previously formed fault crevice or Karstic cave, no. spherical spaces were formed, because the stream of water was' slowed down in the wide spaces of flow.