The volcanic vein of Eresos, located near the settlement of the same name, is a characteristic volcanic landform created by the latest volcanic activity on Lesbos, which began 17 million years ago.
The volcanic structure was formed through the intrusion of fluid magma, into pre-existing volcanic rocks that were created during the main phase of volcanic activity. Fluid magma moved to the surface through faults (the discontinuities in the crust), where it solidified from the loss of energy, creating the volcanic structure we see today dotting the volcanic landscape.
The rocks that surrounded the volcanic vein were eroded over geological time, while the solidified magma, being more resistant to erosion, created the landform that we observe on the Eresos – Sigri rural road, which looks like a solid stone wall separating two pastures.