A geologically rapid creation
The Karst en Yesos de Sorbas is a unique landscape in the Almería province, located in Europe's most arid region. The ground here is made of gypsum (hydrated calcium sulfate, CaSO4·2H2O), a soft mineral that is about 100 times more soluble in water than the limestone that forms more typical karst cave systems. This high solubility means the landscape is dissolving at a geologically rapid pace.
The story of this place begins during the Messinian Salinity Crisis, around six million years ago. Tectonic shifts closed the ancient connection to the Atlantic, causing the Mediterranean Sea to nearly dry up. This intense evaporation left behind a layer of gypsum more than 100 meters thick. When the sea eventually returned, these deposits were left exposed. Rainwater, though scarce in this desert environment, began to dissolve the gypsum, carving out a subterranean world of more than 1,000 interconnected caves. This network of passages, the Karst en Yesos de Sorbas Natural Park, is one of the largest gypsum karst systems in the world.
The process happens from below. Groundwater seeps through fractures in the gypsum deposit, slowly widening them. This type of cave formation, occurring entirely below the water table, is called phreatic speleogenesis. Measurements from micro-erosion meters show that passages can grow at an average rate of 0.011 mm per year, with some parts near the ceiling dissolving faster. As these underground labyrinths expand, the surface above becomes unstable, leading to the formation of sinkholes, known as dolines. These surface depressions are the visible evidence of the ongoing dissolution happening underground.
An ecosystem adapted to extremes
The Cueva del Agua is the largest known system in the Sorbas karst, with a length of nearly 8,500 meters, making it the largest gypsum cave in Spain and the second largest in the world. The constant presence of water underground differs from the arid surface. This "oasis effect" supports lush riverine woodlands along the Río Aguas, with species like oleanders and white poplars.
Life has adapted to both the dry surface and the dark, wet caves. The gypsum-rich soil, toxic to most plants, supports a number of endemic species, including the Sorbas daffodil (Narcissus torfilius) and Teucrium turredanum. The area is also a habitat for the spur-thighed tortoise (Testudo graeca), a threatened species whose last populations are found almost exclusively in Almería and Murcia. Inside the caves, bats find a place for hibernation, while a variety of specially adapted invertebrates live in the constant darkness. The surface landscape provides a habitat for mammals like foxes and badgers, and birds of prey such as the Bonelli's eagle. The unique geology and the life it supports led to the area being declared a protected Natural Area in 1989.