Hévíz Springcave

The Hévíz spring cave is one of the caves in Hungary that are under heightened protection. The cave and the namesake of Hévíz are the well‑known healing spring. It is the only cave under heightened protection in the Zala Hills.

Description

It opens on the side of a spring crater hidden at the bottom of Lake Hévíz, 38 metres deep beneath the lake floor. It consists of a spherical chamber of about 70 × 90 m², 14 metres high and 17 metres in diameter. Through the cave entrance a spring of 38 °C flows out with a yield of 30–40 thousand litres per minute. The water rises from the upper Triassic main dolomite and the spring reaches the lake at the boundary of the karst rock and the overlying Pannonian clay and sandstone. The spring vent probably formed as thermal water rising along fault lines gradually dissolved, collapsed and cut through the clayey, sandy layers to create the spring channel.

The healing water of 38.8 °C that replenishes the lake water was formed by the mixing of two waters of different temperatures exiting through the spring opening. On the K‑side of the cave mud wall, at depths of 43 m and 40 m, water of 17.7 °C emerges, while on the Ny‑side, at a depth of 46 m, water of 41.5 °C emerges. Around the emergence point of the warm water, yellowish, metallic‑shining marcasite crystals and marcasite blocks weighing up to 5–6 kg appear, whose surfaces have often been polished bright by the moving sand of the spring.

There, at the strongest water flow, the walls are covered with a 3 cm thick light‑brown, velvety coating composed of heat‑loving radiobacter species and other bacteria. Long white threads, probably also bacteria, hang from the cave ceiling, while on the steep crater wall, where the warm water flows to the surface, thread‑like blue mats are found in a width of about 3–4 m. Divers have discovered freshwater sponges covering an area of 2 m² in the 26–30 °C water at several places on the crater wall.

It occurs in the literature under the names Amphora-spring cave (Eszterhás 1984), Anphora-spring chamber (Eszterhás 1984), Hévíz-spring cave (Eszterhás 1984), Hévíz lake spring crater (Eszterhás 1984), Hévíz Spring Cave (Takácsné, Eszterhás, Juhász, Kraus 1989), Hévíz-spring-cave (Fleck, Vid 1982), Hévíz lake spring (Kordos 1984), Hévíz lake spring cave (Kovács 2003), Hévíz lake spring crater (Kordos 1984), Hévíz lake spring mouth (Kovács 2003), Hévíz lake cave (Kordos 1984), Hévíz lake spring cave (Kordos 1984) and Plózer István-cave (Kordos 1984).

Research history

The first map of the lake was made in 1769, but its present shape cannot be recognized on it. Later, between 1864 and 1869 (during the construction of the lake spa buildings), Antal Hencz, an architect from Keszthely, surveyed it in detail and found it to be 43 m deep. In 1907 Károly Jordán took samples from the lake bottom and already suspected the spring cave. In January 1908, at the request of Lajos Lóczy, a diver of the Hungarian Royal Naval Authority in Fiume could dive only to a depth of 22 m, but on the side of the vertical crater wall he found several cracks and cavities from which, according to his observation, water was flowing out. In the same year three divers from Fiume arrived, who took water samples from depths of 12 m and 8 m. In Hungary these two dives were the first speleological dives, because the divers indicated several narrow cave passages on the north side of the lake.

In 1953 and then in 1958 later diving expeditions established that warm and cold water emerge from the spring crater at different points. Based on the dives conducted since 1958 it became increasingly clear that the main spring group is at the base of the vertical rock wall at a depth of 38 m.

In 1972, György Kovács and István Plózer, on behalf of the OVH Flood and Groundwater Protection Central Organization, began removing the large amount of debris that blocked the spring entrance. On March 16, after diving down, they found that new debris had slid down together with the underlying silt into the place where the wood debris had been removed. The water breakthrough was clearly visible on the left side opposite the spring. The divers, helping each other, forced their way through the debris into the widened spring opening and were surprised to find that the water emerged from a horizontal cave passage. The debris‑filled opening was about 2–3 m wide and 0.6–0.8 m high. The corridor was visible for about 10–15 m, the walls narrowed to 1.5–2 m, but the ceiling of the passage rose and the end of the corridor disappeared into the darkness.

The exploration of the Hévíz Lake cave was continued in 1975, under the commission of VITUKI, by five researchers of the Amphora Diver Club led by István Plózer: Sándor Ember, György Kovács, Károly Szilágyi, János Nagy and Béla Köves. They entered the extremely narrow and dangerous opening at the spring side, where they also had to overcome the flow of a spring at 38.8 °C with a discharge of 30–40 thousand liters per minute. After the narrow entrance came a spacious hall 14 m high and 17 m in diameter, which was named the Amphora Hall. In the middle, at a depth of 40–41 m, a mud ridge divided it, forming a smaller depression on the K side and a larger one on the Ny side. Finally, the centuries‑old mystery was clearly resolved for the researchers, confirming not only a doubtful hypothesis but a tangible reality: the water of Hévíz Lake has a dual origin: warm and cold karst water.

On behalf of VITUKI water samples were taken from the cold and warm water, whose absolute chronological analysis determined that they are 8 and 12 thousand years old. That much time has passed since, at the end of the Pleistocene, precipitation formed from the meltwater of ice caps due to warming fell on the Bakony area, seeped into the depths, became enriched in mineral components, and then emerged as thermal water at the surface. It is no coincidence that, for the preservation of the therapeutic effect of Lake Hévíz, underwater research continued in the following years, during which, with about 300 hours of total diving time, the source crater caves were precisely mapped. It was clarified that, besides the large cave, there are tube‑like caves on the north wall of the crater, whose floor is covered by a 15–20 cm thick layer of silt. Already in 1972 they were able to swim 25 m into the first cavity, 17 m into the second, and 15 m into the third. No branches were found anywhere and the passages continued narrowed.