Submergence of Ancient Greek Cities Off Egyptʼs Nile Delta—A Cautionary Tale

Abstract

This geoarchaeological analysis illustrates the extreme consequences that occur when protection measures related to coastal sites and associated environmental conditions are overlooked. Two ancient Greek cities, Herakleion and Eastern Canopus, originally occupied low-lying delta coastal areas along the Canopic channel of the Nile. Both were unprotected against flooding, earthquake, tsunami, and consequent subsidence. These sites, recently discovered in Abu Qir Bay on the northwestern margin of Egypt's Nile delta, were lowered a total of 8 m during the past 2500 yr, and now lie at water depths of 5-7 m. The two cities were located along the delta coast at river mouths that flooded annually, and man-made structures were built directly on underconsolidated sediment prone to geohazards. Processes leading to their submergence are interpreted on the basis of integrated archaeological, physiographic, geological (including cores), and geophysical (side-scan sonar, nuclear resonance magnetometer, high-resolution seismic) information. Gradual subsidence due to relative sealevel rise (eustatic rise, land lowering by sediment compaction) accounted for 4-5 m of submergence. Episodic failure during floods and earthquakes by loading and sediment remobilization of the water-saturated substrate upon which the cities were situated likely caused the additional 3-4 m of subsidence. Without foundations, pilings, dikes, or other protection measures, it is not surprising that the sites, over the long term, were damaged and subsided completely into the bay. Ancient cities discussed here cause us to reflect on present-day site selection and construction practices in modern deltaic and associated wetland settings, and potential challenges related to substrate failure and other coastal hazards.

Tracing Holocene channels and landforms of the Nile Delta through integration of early elevation, geophysical, and sediment core data

“…The morphology of these deltaic systems has undergone large-scale changes owing to both natural and anthropogenic processes (Gupta, 2008). The Nile Delta of Egypt (Figure 1), the study area, provides opportunities to examine the interplay of these processes by examining the lateral and spatial variations of its sedimentary record (Frihy et al, 1991) and paleochannel distribution (Frihy et al, 1991; Stanley et al, 2004). It is believed that the regional tectonic activities during the oligo-Miocene were responsible for the opening of the Red Sea and the canyon occupied by ancestors of the Nile (Abd-Allah et al, 2012), and that the delta is located on a passive continental margin that developed in response to the separation of the Afro-Arabian plate from the Eurasian plate (Sarhan, 2015).…”

Seafloor geological studies above active gas chimneys off Egypt (Central Nile Deep Sea Fan)

“…Moreover, sedimentary instability induced by high sedimentary fluid content or gas emissions, in some cases introduced together through dissociation of gas hydrates (Bouriak et al, 2000), can cause slope failures and mass flows that can pose potentially serious hazards to society. Such events might have contributed to the destruction of the coastal city of Alexandria and the close surroundings in ancient times (Stanley et al, 2004;Stanley et al, 2001). This paper focuses on four wide mud volcanoes located above gas chimneys in the upper slope domain of the Central Nile Deep Sea Fan.…”

Estuarine Habitat Assessment for Construction of a Submarine Transmission Line

“…The main sources of pollution are: Abu-Qir Drain, Lake Edku and Rosetta Branch. Moreover the sediment characteristics of this area varied from sand, muddy sand to mud (Frihy et al 1996;El Raey et al 1997;Abdel-Moati 2001;Aboul-Naga et al 2002;Nasr et al 2004;Stanley et al 2004;AbdelFatah 2006;EL-Nemr et al 2007;Fahmy and Abo Elkhair 2007;Abd-Allah 2007;Zakaria 2007). …”