Explorers in diving suit

The secrets of Malom-lake

Chance frequently can help to experts today as well. It can quite often give perceptible momentum to researches of decades or direct the speleologists' interest into new direction. That happened too, when the managers of Lukács-bad charged the specialists with trying to find out: why the water of the pool became warmer than usual. How can the former conditions be restored? Research divers who examine the springwaters rising in János Molnár-cave, discovered a 2,5 km long new channel at the depth of 62 m. The author of our article - the leader of the diving team - relates about this fact.

The Molnár János Cave
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The spring passages of thermal waters spouting at the feet of the mountains in Buda form one system. The dissolving effect of thermal waters which rush up from the depths and in the spring territory mix with descending karst waters widened the water leading cracks into cave-channels for millions of years. Because of gradual sinking of the tapping-level the water welling up get to surface at lower and lower level so the former water leading channels dry up and became visitable. On the other hand, the development of active cave-channels - which make water leading channels sooner or later - is continuing in the depths. Along the Danube-line, only the cave of springwaters supplying the Lukács-bath is passable to skin-divers.

Marks from Roman age

Malom-lake that can be found on Leó Frankel way a few hundred meters from Margit-bridge, is part of the above-mentioned comprehensive spring system. Its body of water, nourished by natural springs, is separated from the passers-by with a glass-screen.
On a part of the lake which is from the direction of József-mountain, there is a deep crack. That's the place from where people used to get into the heart of the mountain, the present-day János Molnár-cave. This mountain gorge has been known for centuries. Even Roman people had used the water rising from here for bathing and curing. In the gorge, below the present water level we discovered a muddy wall from Roman age. The Romans probably had driven the water flowing away from the spring in the correct direction. The water rushing up operated mills from the XIII. century. The first written entry remained in a charter from the year 1276. In this document, the Pope confirmed the mill possession of the nuns living on the Isle of Rabbits (Margit-Isle). The Malom-lake presumably had existed even then although it was mentioned in written records only in the beginning of the XVI. century because the water had to be swelled for the operation of mills. In these years, many brieves dealt with mills and the water of the lake nourishing them.
We can find reference to the existing of the cave connected with Malom-lake first in the Medical Weekly's 33rd issue in 1858. The first researcher of the cave was the pharmacist János Molnár in the 1860's who surveyed the dry part of the cave opening in the side of the mountain. He supposed the existing of a considerable underwater system in the cave description. Ferenc Papp suggested in his 1942 book about the hot medicinal springwaters in Budapest that the Langyos-cave - which opens 12 meters above the Malom-lake, in the east side of József-mountain - have to be named after its first describer and devoted researcher of curative springwaters in Budapest, János Molnár. The Lake Cave of Lukács-bath was surveyed in 1937 by Ferenc Papp, the later supporter of home cave researches. He published his achievements in 1942.

Revealing streams

The channel-system didn't belong to outstanding large caves with its 480 m length known till the year before last. The cavity evolved at the foot of József-mountain in triassic and eocene carbonate rocks along northwest-southeast and northeast-southwest, as well as east-west and north-south mountain structure lines. The examination of the system wasn't a simple task because its known channels extended to 36 m deep as well.
One most important task of the research was the survey of the known section. It impeded the map drafting that the diver's exhaled air stirred up the dissolving remainder settled down on the walls. This remainder, while getting to the water space worsened visibility and endangered the diver's safe moving. Because of finding the safe return, directing ropes needed to be built in.
As the distance between the entry and the research points increased the underwater time became longer. A diving quite often takes several hours nowadays. Because of long distance and increasing depth, the divers have less and less time for researches. So research divers descending deeper and deeper need to bring more breathing gas with them or place it in the channels in advance, since in these cases they don't use air but special gas-mixes. For longer staying there we work with reduced nitrogen air in shallow water whereas when we descend under 40 m we use Nitrox what consists of helium, nitrogen and oxygen. Using of mixed gases increases safety but makes researches more expensive.

Different temperatures
The János Molnár-cave is a living case of the developing of warm- and cold-watered caves so caves with blended water. On the basis of observations and examinations performed there, Pál Müller published his theory in 1974 about the formation of thermal water caves and spherical niches. In his opinion, the mixing of karst waters with different concentration, temperature and with high yield, created the caves. Since the cave has active water-leading channels nowadays too, it is continuously developing even if we can hardly notice. We can well inquire into the processes of cave formation in its channels.
From the examination of stream- and temperature-conditions in the cave it turned out that the channels are filled up with two different-temperatured water. These enter the system in two well-separable places and their direction of movement is different as well.
The temperature of water filling up the deeper parts (under 12 m) of the cave is 20 degrees in Celsius while in the upper channels there flows a water of 27 degrees in Celsius to the direction of Alagút-spring. The water temperature of the lower channels is constant while water moving in the upper channels has a changing temperature. The temperature of water appearing in the spring depends on the degree of water-mixing. The amount of hot water lifted up from the spring territory in a wider sense, affects the temperature of springwaters making up a geologically common system. This realization established the necessity of researching on the cave and rendered getting acquainted with the internationally unique cave-system possible.

Unusual current

At the latest maintenance, it attracted our interest that water-flowing had began in a section of the cave where we hadn't observed such an incident before. It turned out that the water flows from a narrow gorge which can be widen passable with little effort. After enlarging the constiction, the cave opened out before the curious eyes. The magnitude of the channels amazed all of us. It turned out within few days that we have got to a gigantic crack-system that by far surpasses the known parts of the cave. One chamber of the new section is so large that the previously excavated road sections could be included into it.
The new channels are filled up with waters of three different temperatures. Thermal water rushing up from the depths blend in these gorges with the cold water near the surface so that water temperature depends on the quantity of mixing waters. Water supply in the channels known so far can be estimated at several hundred thousand cubic meters. Because of the irregular cavity-system, it is extremely hard to estimate the real amount of water. We can find 23.500 cubic meters of water in such a gorge which has a length of 80, width of 16-26 m and depth of 5 m at the entry and 24 m at the end.

Sensitive water supply

The channels of the cave developed along cracks so they take up their place like a net and characteristically, their vertical dimensions are larger.
We reached a depth of 62 m during our explorations in János Molnár-cave and we expanded the entire length of the known channels to more than 2,5 km. Considering that the measurement of thermal watered caves forming along fault lines can't be estimated in advance, many work and diving is needed from this time on mapping the passable parts of János Molnár-cave.
The results of researches carried out into one of the largest European thermal watered caves are important in many respects. Thanks to their use - as we hope - the springwater that rushes up to the surface along the thermal line in Buda after travelling 6-7 thousand years, becomes defendable. Over all these, we'll have answer how the usual water temperature of the Lukács-pool can be restored.
The water of the cave lying under block of flats and public utilities is extremely vulnerable. A latent burst of pipe, an oozing sewer is enough to that for this reason sewage got in the depths ruin the water of springs. With our work, we'd like to contribute to the following generations benefitting from the curative effect of clear springwaters for a long time.
SÁNDOR KALINOVITS