A History of the Water
The water that fills the thermal baths of Murcia began its cycle a millennium ago. Around the time the Vikings were exploring North America, this water fell as rain over southeastern Spain. It seeped into the earth, beginning a slow percolation downward through the subterranean geology of the Betic Cordillera, a complex mountain system shaped by the collision of the African and Eurasian tectonic plates.
This rainwater travels to a depth of approximately 2 kilometers. At this depth, the Earth's geothermal gradient—the rate at which temperature increases with depth—heats the water to around 80°C. Chemical analysis of the water at the surface provides the data for these calculations. Geothermometry uses the concentrations of specific minerals, like silica, that dissolve into the water at temperature-dependent rates. The mineral signature of the emerging water acts as a subsurface thermometer, revealing the extreme temperatures it reached deep within the crust. After reaching its maximum depth and temperature, the now mineral-rich water rises relatively quickly along geological fault lines. This rapid ascent allows it to retain much of its heat, emerging at springs like those at the Balneario de Archena at a surface temperature of 52.5°C. The entire cycle, from rainfall to resurfacing, takes an estimated 1,000 years to complete.