The impressive Pournias coastal erosion formations are visible in the thick layered sandstone and conglomerate rocks of northern Lemnos, west of Cape Pournia.

The area is covered with sedimentary geological formations from Upper Eocene-Lower Oligocene deposited in underwater channels 27-33 million years ago.

Honeycomb and spheroidal types of weathering have been observed in the area. This is the result of the differential erosion of the sandstone rocks, caused by the structure of the rock which creates weak areas on its surface which are affected by sea waves and salt deposited by sea spray. This process results in impressive and complicated formations in the rocks.