Geo-archaeological markers reveal magnitude and rates of Israeli coastal cliff erosion and retreat

摘要

Geo-archaeological studies along the Mediterranean coast of Israel and its seabed have revealed shipwrecks, anchorages, coastal installations and natural features that can act as markers to estimate the formation date and retreat rates of the coastal cliff of central Israel. The Sharon coastal ridge consists of alternating layers of kurkar (local term for aeolian carbonate-cemented, quartz sandstone) and poorly consolidated palaeosol deposits. The ridge was formed during the Late Pleistocene (about 70,000 to 10,000 yr. BP). At about 7,500 yr. BP, sea level reached the western edge of the present coastal ridge, currently located about 8 m below the present sea level, and a coastal cliff developed. Since then the cliff has continuously been eroded and retreated eastward by natural processes, as well as by anthropogenic impact. This article is an interdisciplinary geo-archaeological study of the extent and rates of retreat of the coastal cliff over the last 7,500 years. The findings suggest that overall the cliff has retreated about 730 m in this period, at an average rate of 9.7 cm/yr. However, the study shows that a considerably higher rate of cliff retreat occurred between about 7,500 and 3,900 yr. BP (about 650 m in about 3,600 years, at about 18 cm/yr). Sea level reached its present level at about 4,000 yr. BP (Middle Bronze Age) and has not changed significantly since. Since the Middle Bronze Age, the cliff has retreated about 80 m in 3,900 years (at about 2 cm/yr). Human activity and sea level rise during the last 100 years have significantly accelerated coastal erosion and cliff retreat.