Long-term retreat rates of Israel's Mediterranean sea cliffs inferred from reconstruction of eroded archaeological sites

Erosion and inland retreat of coastal cliffs present one of the most dynamic earth-surface processes presently challenging coastlines. The rate of cliff retreat is central to coastal planning and protection of shoreline infrastructure. Until now, the majority of retreat rate estimates have been based on aerial photos from the past century, and therefore do not provide multicentury estimates of retreat rates. Here, we studied Bronze Age to Crusader archeological sites (∼3700 years) located on Israel's coastal cliff and used their spatial relation to the cliff to estimate the long-term centurial-millennial retreat rates of the cliff. To accomplish this, original layouts of partially eroded archaeological structures were reconstructed and compared to the modern coastal cliff line. The eroded parts of the studied structures and their original age constrained the maximum timing of the retreat. The resulting retreat rates are significantly lower than those previously calculated using observations of around 100 years. The archeological data also record the episodicity of the cliff failure events. The research highlights both the issue of the loss of valuable archaeological cultural resources, and simultaneously the usefulness of eroding coastal archaeological features to resolve questions of modern significance.