A City's Slow Descent
Along the northern shore of Turkey's Kekova Island, the ruins of the ancient Lycian city of Dolchiste are partially submerged in the Mediterranean. Stone staircases, once leading from homes to streets, now descend directly into the clear turquoise water. The foundations of buildings and the remnants of a harbor are clearly visible just below the surface. This did not result from a single, catastrophic event, but of a slow, continuous process.
A major earthquake in the 2nd century AD caused significant damage and initiated the city's submergence. The region sits in a geologically active area, between the Hellenic and Cyprus arcs, where tectonic plates interact. This activity causes the land to sink, a process known as tectonic subsidence. While global sea levels have also risen over the centuries—known as eustatic sea-level rise—the submergence at Kekova is too great to be explained by that alone. The ruins, therefore, are a fixed marker, a natural long-term experiment for measuring the rate of the earth's movement.
Calculating Geologic Time
The submerged structures of Dolchiste are a geological yardstick. Geologists and archaeologists can calculate the precise rate of tectonic subsidence by treating the total submergence as a simple equation: Total Submergence = Eustatic Sea-Level Rise + Tectonic Subsidence.
Scientists have established reliable models for the historical rise in Mediterranean sea levels. The other two variables can be measured directly at the site. First, the age of a specific submerged feature, like a Byzantine church floor or a Roman-era quay, is determined through archaeological methods. This provides the time component of the measurement. Next, the exact depth of that dated structure below the current sea level is measured.
By subtracting the known amount of eustatic sea-level rise over that period from the total measured submergence, scientists can isolate the amount of sinking due to local tectonic activity. Repeated measurements on different dated ruins throughout the site average out to a consistent rate of approximately 0.5 millimeters per year for the last two millennia. This is a data point for understanding the long-term behavior of this active plate boundary. Some studies focusing on more recent periods have even suggested a faster contemporary rate of at least 1.6 mm/year over the last 1400 years.