The Mountains immediately behind Göcek are not particularly high. The land around Gökçeovacık is generally around 400 – 600 m above sea level while the median altitude Turkey is 1,128 m. What is more striking are the gradients and the depth of the sea close to land. Final emplacement of the Lycean Nappes was around 10ma. The last mountain building event in Britain was around 300ma.
Weathering breaks down the hard rock and erosion moves loose material downhill. The warmth of the summer together with the high rainfall in the winter provides the conditions for deep (10s of metres below the surface) chemical weathering. The mélange structure of the rock aids weathering. Steep gradients and surface water run off from the intense winter rain are powerful erosion forces.
The products of weathering and erosion will become stable at a slope of around 30 degrees. Where there is sufficient fine material (less than 0.6mm) to fill the spaces between the coarse material and there is good drainage then suction pressures will be generated and near vertical slopes will remain stable for periods of a few months to many years. Surface water will erode these steep slopes, water in the soil will reduce the suction and vibration may trigger a sudden collapse.
Sea level was around 250m higher than present in Cretaceous time (100ma) and 130m below present at the peak of the last ice age (20 ka). During the Eemian interglacial (130-114ka) sea level was 4 – 6m above present.
120 000 years ago Göcek bay probably extended back to the
cliffs behind present day Göcek and the current town centre was shallow water.
As sea level fell so the coast moved away from the cliffs and new regolith formed the sloping ground between the present main
road and the cliffs. Streams cut valleys through the flat ground on their way
to the sea. When sea level rose again, these valleys silted up again but the
steep gradients carried cobble and bolder size material along with the silt.
Such a silted valley exists behind the marsh at the west end of the bay near
Club Marina. See Göcek Gorge