Regarded as one of the most beautiful cities in Europe, Budapest also features 80 geothermal springs and the world’s largest known thermal water cave system. Since the hills of Buda consist mainly of limestone and dolomite,water seeping through cracks dissolved minerals and created many caves over thousands of years, the most famous ones are Pálvölgyi and Szemlőhegyi. So far, more than 170 caves have been found in Budapest’s underground, and many are still waiting to be explored.
The Molnár János Cave system in the Buda Thermal Karst is home to an underground thermal lake, which was discovered in 2008. Cold and warm waters coexist in the lake. The temperature in the lower part of the lake (deeper than 39 feet/12 meters) is a constant 68 degrees (20 degrees Celsius), while the upper layer has a temperature of 81 degrees (27 degrees Celsius) that is changing with the seasons. The phenomenon is called hydrothermal karst, and it produces a large variety of cave sizes and morphologies.
While the lower layer is more stagnant, the warmer water flows towards the Alagút-spring. The spring of Molnár János empties into Lake Malom, which flows after a few hundred feet/meters into the Danube. Divers have found remains of roman activity at the bottom of Lake Malom.
In 1858, a pharmacist by the name János Molnár explored the dry sections of the cave. After analyzing the water of the spring, he (re)discovered the therapeutic effects that were already known to the Romans and Ottomans centuries ago. The first known efforts to map the cave date back to the 1930s, and divers entered the cave system in the 1950s for the first time.
The Molnár János Cave system is really unique since different tunnels contain water at different temperature levels. When they emerge in one of the huge rooms, the cooler and warmer waters only mix to a certain degree. More than 3.1 miles (5 kilometers) of passageways with a maximum depth of 269 feet (82 meters) have been explored so far, making it the third longest cave in Hungary. But the system is still going and exploration continues.
It is estimated that the water travels 6,000 to 7,000 years along the fault lines before emerging in one of the springs. Drilling in the Buda Mountains has revealed that dozens of unexplored cave systems exists at different levels 492 t0 820 feet (150 to 250 meters) below ground. Nobody really knows if and how they connect.
Scientists believe that Buda Mountains developed 30 to 50 million years ago as the European Alps to the west lifted the area and the Pannonian plain sank eastwards. The ground cracked along the collision line of the mountains and the plain. The Molnár János Cave system sits right in the fault line. Scientists believe that the area was home to an active volcano millions of years ago. While extinct, heated mineral rich acidic water continues to push through the cracks. Gases rising from the lower layers contain hydrogen sulphide, which reacts with the water and becomes sulphuric acid.
Divers are affected by sulphuric acid in the water since it erodes rubber and metals. Seals on diving suites and o-rings in regulators need to be replaced frequently after exploring the cave system. The floor in the deeper parts of the cave is completely covered by silt that has run down from the upper levels. While the hot springs can be clearly seen while diving, there is hardly any noticeable flow.
Since conditions change frequently in the system, it is best to connect to a local guide in Budapest. For example, a chamber previously filled with CO2 (also called CO2 chamber on several maps) is now filled with air after a hole was drilled through the rock ceiling in 2009, allowing the CO2 to vent to the outside.
With a length of 5,335 meters, the Molnár János Cave system is currently number 48 on a list that names the 50 longest known caves on earth. Number one on this list is Sistema Ox Bel Ha in Mexico with a length of 590,676 feet (180,038 meters).
Source: Global Adventures