Devil's Pond

Covasna (Hungarian: Kovászna) is a town in Covasna county, Transylvania, Romania, at an altitude of 550-600 m. First mentioned in a document in 1567 and known as the "town of 1,000 mineral springs," Covasna is famous for its mineral waters. Each spring has a different mixture of minerals, chiefly carbon dioxide, sulfur, and ammonia. Its name is derived from the Slavic word Cvaz, meaning sour, referring to the taste of its mineral waters.

Right in downtown there is a natural monument with a unique value: the so-called "Devil's Pond" - a sort of mud volcano, with permanent eruptions of mud bubbles. Traditionally, in the 1700s, this natural phenomenon was placed further north, but mysteriously moved to the center of the town, leaving in its initial place a brother, "Devil's Little Pond". The bubbles are actually some strong releases of carbon dioxide. Carbonated emanations are related to volcanic processes which took place in the region of Harghita-Călimani in the end of Paleocene and early Quaternary. Gases contain carbon dioxide with a purity of 98%.

The Devil's Pond was open to the public in 1881 and initially used for treatment. The gas accumulated in special places called moffets is an excellent and unique natural factor for the treatment of multiple diseases primarily of cardiovascular diseases.

In the nineteenth century there were some major eruptions: in 1837, 1857, 1864 and 1885, the largest being in 1837. Currently, the volcano is completely harmless, the last major eruption took place in 1984.