A Hévízi-tó forráskrátere

The source crater of Hévíz Lake (A Hévízi-tó forráskrátere) is the geological heart of Europe's largest biologically active natural thermal lake, a 38-metre-deep volcanic crater in Zala county, Hungary, from which sulphurous spring water at 33-38°C erupts at a rate of 80 million litres daily to create and sustain the 4.4-hectare thermal lake of Hévíz. This natural spring crater, formed by volcanic activity in the Tertiary period and continuously active ever since, produces the thermal flow that has made Hévíz one of the most extraordinary natural bathing sites in the world, with a lake temperature that permits year-round open-air bathing even in snowfall. The geological phenomenon of this upwelling source crater — rare in the world for its scale and biological productivity — represents one of Europe's most remarkable natural geothermal features.