Submerged Bronze Age caves. Stalactite U-series dating shows they formed when sea level was 30m lower during the last ice age, then flooded 12,000 years ago, preserving ancient formations.
A landscape shaped by ice and water
The marine caves near Cabo de Palos are a direct record of massive climate shifts. These are karst formations, created when freshwater dissolved soluble limestone bedrock. Their story begins during the Last Glacial Maximum, around 20,000 years ago, when Earth's climate was significantly colder. Huge quantities of water were locked up in continental ice sheets, causing the global sea level to drop by as much as 120-125 meters. What is now the seafloor was then dry land, and these caves formed high above the ancient coastline.
Rainwater, made slightly acidic by atmospheric carbon dioxide, seeped through the limestone. Over thousands of years, this water dissolved the rock, carving out passages and chambers. Inside these dry caves, calcite-rich water dripped from the ceilings, slowly building stalactites and other cave formations known as speleothems. The caves existed in this state for millennia, open to the air while the Mediterranean Sea was dozens of meters below its current level. The entire system records of speleogenesis—the origin and development of caves—that is now only accessible to scuba divers.
A record written in stone
The end of the ice age triggered a global warming period. As glaciers and ice sheets melted, the sea began to rise. Around 12,000 years ago, the advancing Mediterranean waters reached the mouths of these caves and began to flood them. This marine transgression halted the growth of the stalactites and stalagmites, effectively sealing them in a moment of geological time. The submergence preserved the delicate calcite structures, which would have otherwise been subject to weathering and erosion on land.
Scientists use Uranium-series dating to determine the age of these formations with high precision. This radiometric technique measures the decay of uranium isotopes (238U and 234U) into thorium (230Th) within the calcite of a speleothem. Uranium is water-soluble and is incorporated into the stalactite as it grows, but thorium is not. By measuring the ratio of uranium to the accumulated thorium, researchers can calculate the time since the speleothem formed, dating samples up to 500,000 years old. This method provides a clear timeline for the caves' formation on dry land before the sea claimed them. While the caves themselves are from the Pleistocene, their entrances may have been accessible to humans during the Bronze Age, when sea levels were still rising toward their present-day position.
Today, these caves are part of the protected Cabo de Palos and Islas Hormigas Marine Reserve, established in 1995. The volcanic origins of the seabed have created a complex underwater terrain of cliffs, canyons, and pinnacles that are now home to a rich marine ecosystem.
💡Fun Facts
The Cueva del Agua, a well-known cave in the region, is one of Europe's only geothermally warmed underwater cave systems, with water temperatures around 29°C year-round.
Global sea levels during the last ice age were so low that land bridges connected many areas that are now separated by water.
The Islas Hormigas Marine Reserve is considered one of the best diving destinations in the Mediterranean, partly due to the confluence of currents from the Atlantic and the Mediterranean.
Some underwater rock formations in the reserve, called "bajos," rise from a depth of 50 meters to just 3 meters below the surface.
The caves are natural formations within a marine reserve and are accessible only through certified local dive centers. Hours vary by operator and season.
Admission
Prices for guided dives vary, typically starting around €40-€50 per dive, with equipment rental costing extra.
Accessibility
Access is restricted to certified scuba divers. Many caves feature narrow passages and require advanced training, such as cave diving certifications, for safe exploration.