Geophysical Phenomena and the Alexandrian Littoral

N. Evelpidou, C. Repapis, C. Zerefos, H. Tzalas and C. Synolakis Archaeopress Publishing Ltd Summertown Pavilion 18-24 Middle Way Summertown Oxford OX2 7LG www.archaeopress.com

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This book is available direct from Archaeopress or from our website www.archaeopress.com Contents

List of figures and tables ��iii Acknowledgements ��v Preface ��vii 1. Introduction ��1 1.1 Location and physical geography ��1 1.2 Geological characteristics ��5 1.3 Geomorphology ��10 2. Subsidence regime ��14 2.1 Bathymetry ��14 2.2 Submerged ancient structures ��16 3. Evidence of offshore subsidence in Alexandria ��20 4. Palaeogeography ��29 5. Historical maps ��33 Veduta d’Alessandria Codice Urbinate 277 [1472] ��34 View of Alexandria from the Portolano of Piri Reis [1513] ��36 Vray portraict de la Ville d’Alexandrie en Egypte [1547] ��38 Plan M.P.nl-XLIX-43 of Alexandria from the Archivos General de Simancas [1605] ��40 Alexandria, Vetustissimum Aegypti Emporium [1619] ��42 View of Alexandria by Vassili Barkij [1730] ��43 Description de la ville d’Alexandrie, telle qu’elle étoit du terms de Strabon, par M. Bonamy [1731] ��46 Carte et Plan du Port Neuf d’Alexandrie by Capt. Frederick Lewis Norden [1738] and Carte particulière de la Vielle et de la nouvelle Alexandrie et de ses Ports [1738] ��48 Konstantin of Kiev ‘ [1795] ��49 Konstantin of Kiev [1795] ��49 Carte générale des côtes,Θέα του rades, λιμένος ports, της ville Αλεξανδρείας’ et environs d’Alexandrie dressée par M. Gratien le Père [1798] ��‘Χάρτα της Άλεξανδρίας και�� των δύω αυτής λιμένων’ 53 Plan of the city harbours and environs of Alexandria, by Captain Smyth (1825) ��54 Plan d’Alexandrie par Mahmoud Bey el Falaki [1866] ��56 6. Historical references ��62 7. The decline of Alexandria and physical disaster ��66 8. Modelling tsunami vulnerability ��71 8.1 Simulating possible tsunamis in Alexandria ��72 8.2 Scenario megathrust tsunami sources ��73 8.3 Tsunami simulation results ��74 8.4 Tsunami impacts at Alexandria ��75 9. Coastal zone ��78

i 9.1 Silsileh ��78 9.2 Chatby ��78 9.3 Ibrahimia ��82 9.4 Sporting Beach ��83 9.5 Moustafa Kamel ��85 9.6 Gleemenopoulos Beach ��85 9.7 Sidi Bishr ��85 9.8 Miami Island – Gezira Gabal el Khour (Gabr el Khour) ��86 9.9 Montazah ��86 9.10 Maamourah ��87 9.11 Abou Kir ��87 9.12 Nelson’s Island (Abou Kir Island) ��88 10. Fish tanks �� 89 10.1 Fish tanks in Alexandria ��90 10.2 Fish tank findings ��92 10.2.1 Montazah fish tanks ��93 10.2.2 Abou Kir fish tank ��98 10.2.3 Miami Island fish tank ��104 10.3 Main sea level indicators ��112 10.3.1 Protective moles ��112 10.3.2 Upper walkway (upper crepidine) ��113 10.3.3 Lower crepidines ��113 10.3.4 Closing gates (cataractae) ��113 10.3.5 Channels ��114 10.4 Sea level modelling ��115 10.5 Relative sea level changes and Alexandria’s fish tanks ��115 References �� 118

ii List of figures and tables

Figure 1a: Site map of coastal Alexandria. �� 2 Figure 1b: Sites with valuable geomorphological and archaeological features in the Alexandrian coastal zone. �� 4 Figure 2: Long-term average Holocene rates of subsidence along the Nile Delta based on stratigraphic analyses of radiocarbon-dated core data (after Stanley and Warne 1998). Sites: A: East Harbour, B: East Canopus, C: Herakleion, D: NW Burullus lagoon, E: SE Burullus lagoon, F: Tell Tinis and G: Pelusium. �� 7 Figure 3: The major fault zones of the wider Alexandria area (Zaghloul et al. 2001). �� 8 Figure 4: Bathymetric maps of the East Harbour of Alexandria, based on historical maps dating from the end of the 18th to the beginning of the 20th century AD. �� 15 Figure 5: Comparison of bathymetric profiles between Le Diamant–El Hassan, in 1833 and 1920, lead to the suggestion of subsidence in the sea floor of >1.5 m �� 16 Figure 6: Cumulative diagram of earthquakes and tsunamis occurring in Alexandria over the past 2000 years (Goiran 2001; Chalari 2007). �� 19 Figure 7: The map of the Codex Urbinate 277 (1472), depicting the present 12 reefs as protruding features. �� 21 Figure 8: Le Diamant, depicted above sea level (Panchoucke 1821-9). �� 22 Figure 9: Age calibration provided an age of 1735–1806 AD (95.4% probability) for the timber sample dated by the Oxford Radiocarbon Accelerator Unit. �� 24 Figure 10: Age calibration provided an age of 1719–1780 AD (95.4% probability) for the same sample dated using the Klaus-Tschira-Labor für Physikalische Altersbestimmung, Curt-Engelhorn- Zentrum Archaeometrie gGmbH, Mannheim, Germany, in cooperation with the Dimokritos Research Centre, Athens. �� 24 Figure 11: A piece of timber from a wrecked ship found at El Hassan reef at a depth of 10 m. �� 25 Figure 12: Sketch of the ship, impact location, and a detailed design of the ship’s bottom. �� 27 Figure 13: Veduta d’Alessandria, Codice Urbinate 277, 1472 (Jondet, Pl. I). �� 35 Figure 14: Jean-Louis Bacque-Grammont, Michel Turchscherer, Piri Reis – Evliya Celebi, Deux regards ottomans sur Alexandrie, Centre d’Etudes Alexandrines, Alexandria 2013. �� 37 Figure 16: Harry E. Tzalas, The two ports of Alexandria, Plans and maps from the 14th century to the time of Mohamed Ali, Underwater archaeology and coastal management, Focus on Alexandria: 21–22. UNESCO Publishing, Paris, 2000. �� 41 Figure 17: Alexandria, Vetustissimum Aegypti Emporium, 1619. �� 44 Figure 18: The wanderings of Vassili Grigorovich-Barskii to the Holy Places of the East from 1723 to 1747. Published by the Orthodox Palestine Society after a genuine manuscript prepared by Nikolai Barsukov, St Petersburg 1886–1887; see also Τόπος και Εικόνα, χαρακτικά ξένων περιηγητών για την Ελλάδα, 18ος αιώνας, Olkos, Athens, 1979. �� 45 Figure 19: M. de Bonamy, Mémoire, Description de la ville d’Alexandrie, telle qu’elle étoit du tems de Strabon, Paris, 31.8.1731. �� 47 Figure 22: Frederick Lewis Norden, Travels in Egypt and Nubia, London 1757; Jondet, Pl. XII.; Konstantin, Ancient Alexandria, Description of the town during the visit of Archimandrite Konstantin, published in Moscow (1803) ‘at the expense of the well-known Greek Maecenas, the Zosima brothers’. �� 50 Figure 20: Carte et Plan du Port Neuf d’Alexandrie by Capt. Frederick Lewis Norden [1738] and Carte particuliere de la Vielle et de la nouvelle Alexandrie et de ses Ports [1738]. �� 50 Figure 21: Konstantin of Kiev, Θέα του λιμένος της Αλεξανδρείας, 1795. �� 51 Figure 22: Frederick Lewis Norden, Travels in Egypt and Nubia, London 1757; Jondet, Pl. XII.; Konstantin, Ancient Alexandria, Description of the town during the visit of Archimandrite Konstantin, published in Moscow (1803) ‘at the expense of the well-known Greek Maecenas, the Zosima brothers’. �� 52 Figure 23: Jondet, Pl. XVII. There are two other maps of Alexandria and its wider area created by the Bonaparte Expedition: Carte des Cheneaux d’Accès au Port d’Alexandrie, 1798, Jondet Pl. XIX and Carte d’Alexandrie et de ses environs d’Agamy à Aboukir, 1798, Jondet Pl. XVIII. �� 55 Figure 24: Plan of the city harbours and environs of Alexandria, by Captain Smyth (1825). �� 57

iii Figure 25: Mahmoud Bey, Mémoire sur l’Antique Alexandrie ses faubourgs et environs, Copenhague, 1872. �� 58 Figure 26: Alexandrie ancienne par Neroutsos Bey (1888) �� 61 Figure 27: Map of the East Harbour of Alexandria showing archaeological sites (based on Goddio et al. 1998). �� 63 Figure 28: Plots of the wave height in relation to time that would be observed a) in the area of Pharos, and b) off the coast of Alexandria. �� 75 Figure 29: Plots of the wave height in relation to time that would be observed a) in the area of Pharos, and b) off the coast of Alexandria. (Nikos Kalligeris, private communication). For reference, we reproduce here the graph by Shaw et al. (2008) of the wave height against time in the area of Pharos, by the AD 365 earthquake. �� 77 Figure 30: A section of the gateway and tower. �� 80 Figure 31: Traces of the submerged semi-circular and ‘Π’ formation at Chatby from French satellite image, courtesy of the Centre d’ Etudes Alexandrine. �� 81 Figure 32: The Sporting coast and submerged structures (photo: The Greek Mission). �� 83 Figure 33: Underwater ancient remains at Sporting (photos: The Greek Mission). �� 84 Figure 34: The area under study and evidence of possible fish tanks in the littoral region of the east end of the Maamourah Gulf to Abou Kir promontory. �� 90 Figure 35: The Montazah fish tank consists of four main parts, each divided into many smaller tanks linked with each other through channels or arches. �� 94 Figure 36: The cut, outer walls of the Montazah fish tank stand higher than the inner ones to protect the tank from the storms. �� 95 Figure 37: Short channels connect the tanks and distribute the water, ensuring adequate circulation within the fish tank. �� 96 Figure 38: A) Channel C in the Montazah fish tank; B) its sliding grooves (Cs) cut into the stones used for the fitting of sluice gates. �� 97 Figure 39: The western part of the Montazah fish tank is the largest, but with fewer smaller tanks (or possibly the partitions have not survived). �� 97 Figure 40: Submerged tidal notch at -24 cm found at the western part of the Montazah fish tank. �� 98 Figure 41: Τhe eastern part of the Montazah fish tank is the most complex, with many divisions within the main tank. In this part was found a channel for fresh water input from inland to the tank. �� 99 Figure 42: The Abou Kir fish tank, a simple, gamma-shaped construction. ��100 Figure 43: The outer defensive wall of the Abou Kir fish tank. ��101 Figure 44: The lower crepidine in the Abou Kir fish tank, found at -93 cm. ��102 Figure 45: The Abou Kir area, according to Breccia (1926), included several fish tanks (based on Bartocci 1925). ��102 Figure 46: (A) FT2 fish tank (see Figure 30) as seen on Google Earth in a satellite image of 2004, which (B) is described by Jacono (1924) and compared with Castello Del Sangallo in Italy. ��103 Figure 46C: A photograph of the fish tank at Abou Kir as described by Breccia (1926). ��104 Figure 47: The Miami Island fish tank. ��105 Figure 48: The Miami Island fish tank, a complex and sophisticated construction, is carved in the southeastern region of the homonymous island. To the left is a narrow tank dug into the rock (A), which we assume was constructed to provide some shade for the fish during the day. Channels may also be noticed for the renewal of the tank’s water supply from the open sea (B). ��106 Figure 49: The crepidine in the Miami Island fish tank. ��106 Figure 50: The main channel cut around Miami Ιsland. ��107 Figure 51: RSL curves for the site of Montazah, obtained solving sea level equations numerically. GIA models ICE-6G (VM5a) (solid) and ANU (dashed) have been used for the two different time frames. ��115

Table 1: Fish tanks identified and discussed in the text, with their geographical coordinates �� 91 Table 2: Measurements from on the fish tanks studied and architectural characteristics ��106

iv Acknowledgements

For the last seventeen years, the Hellenic Institute of Ancient and Medieval Alexandrian Studies (HIAMAS), under the leadership of the historian H. Tzalas, and in collaboration with the Department of Underwater Antiquities of the Supreme Council of Antiquities of Egypt in Alexandria and the Mariolopoulos-Kanaginis Foundation for the Environmental Sciences, have conducted twenty-nine campaigns of underwater archaeological and geophysical surveys along the Alexandrine littoral. Countless teams of divers, historians, archaeologists and geologists were involved in these missions, and the findings are presented in a series of HIAMAS reports (1–29). The present authors also wish to thank Professor Phillip England for his constructive comments related to the submergence of the El Hassan reef.

v vi Preface

The study of Alexandria’s historical geomorphological changes that occurred on its littoral coasts is a fairly new subject of investigation and research. Over its long history Alexandria has been subjected to recurrent natural forces of destruction, such as earthquakes and tsunamis. These forces were responsible for the disappearance of its great monuments of antiquity and the eclipse of its great civilization.

While such natural phenomena have left their mark, such as the soil subslides of the city’s littoral coasts, they continue to bring changes with rising sea levels and the erosion of its coasts. Hence comes the importance of such studies in tracing back the past implications of such natural phenomena on the city, while also trying to access and guide the future safeguarding and conservation of its littoral environment.

Historically, man looked helplessly at the natural forces of destruction with fatalism, investing them with some superpower or interpreting them as the acts of some obscure god, reverting to mystic legend and religious revelation to safeguard and protect him from whatever threatened his existence and welfare.

Maat in ancient Egyptian polytheistic religion represented balance in the cosmic order. Isfat represented the exact opposite, imbalance and disorder. Egyptians feared the drought of the Nile and its disastrous inundations, and so they conducted sacrifices at the Nile festivities (Wafa’a El Nil).

Similarly, Zeus the thunder god was worshipped in Greek mythology. Nature deities were therefore symbolically in charge of its forces in our ancient civilizations.

Ancient philosophical thought and reason brought other legendary approaches, attempting to deal with the issue of natural destructive phenomena. The most symbolic legend comes in Plato’s Timaeus in 335 BC as Atlantis, the lost continent. Atlantis was

vii believed to be a scientifically advanced and marvelous city; it was destroyed, buried and sank in the deep sea. Plato’s student Aristotle remarked that Plato was trying to make a point, but Aristotle’s writings on the subject did not clarify the mystery. Aristotle’s connection with Alexander the Great is well known. Did the tutor bring the legend to the attention of his student? Was the destiny of Alexandria in any way connected to the legend of Atlantis?

Atlantis is believed to have existed on the marshes of Dona Island in Spain when a number of earthquakes and tsunamis swept the area, destroying the city of Tartessos. Another location for Atlantis was suggested to have been closer to Plato’s homeland Crete in Greece, referring to its great Minoan civilization 1500 BC, which was abruptly destroyed by the Santorinas volcano eruption, earthquake and tsunami. Their effects and consequences were felt on the shores of the Mediterranean including Egypt’s.

Plato’s calculations on the location of Atlantis and its time is suggested by Galanopoulos to have had an error of translation, adding an extra zero to his figures, (900 instead of 9000 and 250 instead of 2500 miles), implying a more likely proximity and connection between Crete and the Egyptian littoral coast.1 Heracleon, east of Abu Kir on the Egyptian Mediterranean littoral, also destroyed by an earthquake and sunken by a tsunami, echoes the same destiny of Atlantis.

Alexandria’s ancient history since its foundation is full of mystical revelations. The prophecy that the city will be repetitively destroyed and rebuilt again is taken from Alexander’s dreams and is accounted for in Plutarch’s Parallel Lives2 (46-120 AD) and Arrian’s (92-175 AD) narratives in his Anabasis of Alexander.3 Arab medieval historians and travelers such as Aboul Hassan Ali Al Masudi (895-956), described as the Herodotus of the Arabs, recounts in his encyclopedic century book Meadows of Gold and Mines of Gems that Alexander had prepared for setting the signal for the beginning of the works to lay the foundations of the city, through a system of strings and bells. During his sleep, a crow rested on the strings and rang the bells. This being an involuntary act disturbed Alexander himself, considering it to be a bad omen. The myth continues when during the night monsters repeatedly surged out of the deep seas every night, and successively destroyed what was being built during the day. A collection of drawings of those monsters with human bodies and animal heads was prepared and put on the surface of the stones, so that when the monsters surged again and saw their own faces on the blocks, they went back to the sea and never returned again. At a later date the Alexandrian myth is brought again in the inscribed

1 Krystek, Lee. ‘The Lost Continent: Atlantis’. Series of Articles [1997-2006]. 2 Plutarch. Parallel Lives. 1919. 3 Arrian, F. Anabasis of Alexander. Arrian’s History of the Expedition of Alexander the Great and Conquest of Persia. Translated by Mr. Rooke. London. 1813.

viii figurations of zoomorphites and a favourable horoscope set on the foundations of the famous Cleopatra’s needles in front of the Caesarium on the shores of the eastern harbour, in an act to protect the city from the curse of the monstrous sea.4 The later Arab historian Al Makrizi5 (1375) in his famous Khitat mentions the city taken by the swollen sea, referring to the earthquake that hit the city in 1341, causing the collapse of the Pharos.

But since the time of Plutarch, Arrian, Al Masudi and Al Makrizi, our knowledge of such natural phenomena, their causes and effects have been rationally explored and scientifically determined. However, their consequences still persist, threatening our safety and existence, which require a priority concern and a coordinated effort to deal with the complexity of its issues.

This study is both chronological and synchronic in its approach. It deals with the aftermaths and the historical effects of natural phenomena, and their implications on the Alexandrian coastal shores. But it also involves a multidisciplinary team of research experts, contributors, and sponsors, and may be considered a step forward in the right direction to reveal the city’s past history, and, more importantly, to contribute to guarding and protecting its environment from future threats. Moreover, it has brought back to the city its renewed spirit of multiculturalism, symbolically demonstrated in the contribution and the cooperation of a Graeco-Egyptian symbiosis, and in the much valued attachment and affinity of its Egyptiotis6 to their second homeland and patritha.

Mohamed Awad

4 Al Masudi. Meadows of Gold and Mines of Gems.Translated by P. Lunde, C. Stone, and A. Sprenger. UK 1989. 5 Al Makrizi. Mawa’iz wa Itibar Al Khitat wal Athar. 2 vols. Bowlak. 1854. 6 Referring to the Greeks of Egypt in Diaspora.

ix x 1. Introduction

The submergence of ancient coastal sites, such as harbours, has been mainly attributed to progressive sea level rise and/or land subsidence, or both (relative sea level rise). Studies have also highlighted the significant role of impulsive natural events, such as earthquakes (Clark 1995; Reinhardt and Raban 1999), tsunamis (Boyce et al. 2004) and river floods (Stanley et al. 2004a). Nevertheless, the anthropogenic stresses on coastal regions and harbours which resulted in their submergence are not fully understood.

1.1 Location and physical geography

Alexandria is located on the Mediterranean coast of Egypt and is bordered by Egypt’s Western Desert and the Mareotis Lagoon, a large shallow wetland, to the south, and by the fertile Nile Delta to the east (Rowe 1954) (Figure 1a, b). The city of Alexandria was constructed on a long ENE/WSW-trending coast-parallel ridge of Pleistocene age that extends from southwestern Alexandria to Canopus, the modern town of Abou Kir east of Alexandria. This ridge, called Abu Sir, reaches a height of 35 m in its western part and 6 m in Abu Kir, and it was formed by poorly to moderately cemented sandy carbonate, known as kurkar formation (Butzer 1960; Stanley and Hamza 1992; Hassouba 1995). The sediment age ranges from 90,000 to 110,000 BP (Shukri et al. 1956; El-Asmar and Wood 2000). This ridge separates the shallow, brackish Mariotis lagoon, now called Maryut (Loizeau and Stanley 1994), to the south from the ports that lie to the north. The area of both ports (East and West Harbours) was formed between two carbonate sandstone kurkars. Seawater flooded the basin in between during the transgression, about 8000 years BP, and wind and wave driven currents deposited clastic sediments at an average rate of 1–3 mm/year. The Holocene sediments that were trapped in this significant harbour formed marine calcareous sand, muddy sand and mud. The association of distinct biological components, failed slump-like sediment strata and important hiatuses in the Holocene sediments have recorded the episodic influence of impulsive natural events, such as storm surges, seismic shocks and tsunamis (Stanley

1 Geophysical Phenomena and the Alexandrian Littoral Figure 1a: Site map of coastal Alexandria. Figure

2 1. Introduction

Figure 1b: Sites with valuable geomorphological and archaeological features in the Alexandrian coastal zone.

and Bernasconi 2006). Furthermore, high-relief carbonate features occur seawards and include Pharos Island to the NW, the harbour margin to the NE, as well as several small islets offshore (Butzer 1960; Jondet 1916; Stanley and Hamza 1992; Wali et al. 1994). Two large and submerged carbonates, reef-like features, have been mapped in the east-central sector of the East Harbour (Goddio et al. 1998).

3 Geophysical Phenomena and the Alexandrian Littoral

In Alexandria and its environs, total annual rainfall reaches an average of 200 mm. More specifically, the precipitation is concentrated from November to February, with almost no rainfall from May to early October. The mean annual air temperature is 20.4 °C, ranging from a monthly mean of 14 °C in January to 26 °C in August.

Alexandria’s tidal regime is characterized as micro-tidal, with a range of up to about 30 cm, and, also, the sea-surface temperatures range from temperate to warm, i.e. between 16.7 °C and 26 °C. The salinity of the surface has an average rate of 38.8‰. Water masses are driven by coastal currents towards the east, having a mean velocity of 143 cm/s. In the coastal region of Alexandria, during summer, winds that derive from NW and W predominate and during winter they originate from SW. During winter, also, on the inner shelf of the wider coastal region of Alexandria, heights of waves north of the East and West Harbours reach 1.5 to 2 m; when entering the two ports the height decreases, reaching 0.5 to 1 m. This wave activity leads to abrasion of the sediments of the harbour floor, especially at shallow depths. The swell in the littoral is 40–75 cm according to Manohar (1981) and Naffa (1995).

Analysis of hourly tide-gauge observations over ten years (1996–2005) in Alexandria showed that the short term variations in sea level is a combination of only ± 20 cm elevation due to astronomical tide, and up to 1 m elevation under the effect of meteorological factors, such as air temperature, wind regime, atmospheric pressure and steric effect (Eid 1990; Saad et al. 2011; El-Geziry and Radwan 2012; El-Geziry 2013). The mean sea level between the daily readings of high and low water level during the period 1898–1906 has been set as the mean sea level (m.s.l.) datum at Alexandria Harbour and this was found 33.8 cm above the zero of the installed tidal gauge (Dawod 2001). The m.s.l. for the period 1944–1989 was calculated at 40.0 cm (Frihy 1992), for the period 1956–1966 it was at 44.1 cm (Sharaf El-Din 1975), for the period 1974–2006 at 47.9 cm (Said et al. 2012), and for the period 1996-2005 at 50.67 cm, above the zero of the installed tide gauge (El-Geziry and Radwan 2012).

Particularly over the last 100 years, climate change has contributed to the increase of the relative sea level. It is known that the average sea level worldwide is rising at a rate of about 1 mm/year, a rate that approximately applies to the Eastern Mediterranean (El-Sayed 1996; Serageldin 2014). Nevertheless, Evelpidou et al. (2018) in a recent study of the fish tanks in Alexandria concluded that the relative sea level has risen 70 cm since Greek-Roman times (see Chapter 10).

The study of tide-gauge data over the last 60 years in Alexandria’s West Harbour reveals that the relative sea level in the area is rising. El Fishawi and Fanos (1989), Sharaf El Din et al. (1989) and Frihy (1992) have calculated that the rate of relative sea level change in the coastal zone of Alexandria ranges from +2–2.9 mm/year, while Frihy (2003)

4 1. Introduction estimated that the relative sea level change in the port of Alexandria is +1.6 mm/year. On the other hand, Emery et al. (1988), based on short-term measurements, calculated that the rate of the relative sea level change is -0.7 mm/year (i.e. sea level falls due to tectonic movement of the land). East of Alexandria, from Abu Qir to Port Said, the rate of relative sea level change increases. El Fishawi and Fanos (1989) estimate a rise rate of 2.4 mm/year, Emery et al. (1988) a rate of +4.8 mm/year, and Frihy (2003) a rise ranging from +1.0 mm/year on Lake Burullus, and up to +2.3 mm/year in Port Said.

The prevailing winds in Alexandria are of NW direction, as it was in ancient times (Stanley and Bernasconi 2006). The same authors mention that the mean wave height is about 2 m, while large waves reach 4 m. According to Chalari (2007), the maximum height during winter is 5.5 m, in spring 4 m, and 3.3 m in summer. Waves of 4 m height have a return period of 1 year, while 8 m waves have return periods of 100 years according to Aelbrecht et al. (2000). In contrast, storm waves of 7.6 m in height were calculated to occur with a return period of 50 years, while waves over 8 m occur with a returning period of 100 years (Iskander 2013); Shah-Hosseini et al. (2016) mention that storm waves higher than 9 m occur every 100 years.

According to Frihy (1992), the subsidence rate in Alexandria during the last 60 years is 2 mm/year, while Frihy et al. (2010) consider Alexandria as relatively stable over the long term, providing subsidence rates of 0–0.5 mm/year. The rate of the relative long- term mean sea level rise for the period 1944–1999 has been estimated by Dawod (2001) to be 1.7 mm/year, while other researchers provide values in the range of 1.6–2.9 mm/year for various periods of observation (Chalari et al. 2009). For the East Harbour, covering the 2300 years from the foundation of Alexandria, the rate of the long-term relative mean sea level rise is calculated from archaeological evidence at 2.9 mm/year (Stanley and Bernasconi 2006). Subsidence rates, based on core stratigraphy, range from 0.9–4.3 mm/year, varying irregularly from west to east along the northern Delta coast and averaging ~2.5 mm/year (Stanley and Toscano 2009).

1.2 Geological characteristics

The study area is located on the relatively tectonically stable margin of northeast Africa. The recorded periodic instability that affects this region results from readjustment to down warping (sediment compaction faulting, isostatic lowering) of the thick underlying sedimentary sequence (locally exceeding 4000 m). The thin Holocene cover of unconsolidated deposits overlies Quaternary and Tertiary sequences of Nile Delta origin that, in turn, are superposed on Mesozoic sedimentary units (Said 1981; Schlumberger 1984). This sector, directly west of the Nile Delta, has been periodically affected by quite strong seismic tremors (Kebeasy 1990), growth faulting (Stanley 2005) and destructive tsunamis (Guidoboni et al. 1994). Generally, the low-lying region of the

5 Geophysical Phenomena and the Alexandrian Littoral

Nile Delta is subjected to significant differential subsidence (Figure 2). Τhe analysis of several core samples conducted in the East and West Harbours, as well as the description of surficial sediments from the coast and the shelf of Alexandria, have shown that Holocene deposits have accumulated directly upon the Pleistocene kurkar limestone. In addition, in the aforesaid area bioclastic and muddy carbonate sand strata can be found, interbedded with finer-grained sandy silt, silty mud and dark organic-rich layers (Jorstad and Stanley 2006; Stanley and Bernasconi 2006; Stanley and Landau 2010) and minor amounts of wind-blown quartz silt (Yaalon and Ganor 1979).

The coastal zone is often affected by earthquakes of large magnitude, making Alexandria a hazardous place, even though it is characterized as an area of small to medium seismic activity. In general terms, these large earthquakes occur on tectonic plate margins such as the Hellenic Trench, Red Sea and Aqaba Bay (Maamoun et al. 1984; Kebeasy 1990; Ambraseys et al. 1994). These seismic zones lie at a distance of 300–600 km from Alexandria, thus their tectonic activity generates the fault zones, some of which bound the Nile Delta; therefore, the Delta shape is tectonically controlled (Zaghloul et al. 2001). These major fault zones are (Figure 3): a) the Qattara- Eratosthenes zone, forming the western limit of the Nile cone and trending NE–SW (Neev 1977; Frihy 2003); b) the Temsah fault zone (Abdel Aal et al. 1994), which is the eastern boundary of the cone and trending NW–SE; c) the Suez-Cairo-Alexandria zone (NW–SE), comprising the western limit of the Nile Delta (Ben-Avraham et al. 1987; Frihy 2003); and d) the Pelusium zone (NE–SW), comprising its eastern limit (Neev 1977). Additionally, Alexandria is also influenced by smaller faults, such as the Abu Qir and Rosetta faults, located some km east of Alexandria (Zaghloul et al. 2001).

The city of Alexandria has suffered from 25 destructive earthquakes in the period between AD 320 and 2000, nine of which had their epicentres on its coastal zone (Maamoun et al. 1984; Ambraseys et al. 1994; El-Sayed et al. 2000). The other 14 tremors had their epicentres in the Eastern Mediterranean region (i.e. Hellenic Arc). The earthquakes in the marine area north of Alexandria are characterized by small to medium magnitudes (Ms = 6.7), while those produced in the East Mediterranean present relatively large magnitudes (Ms = 7.8) (El-Sayed et al. 2004). The former ones, despite their moderate magnitudes, were felt with intensities reaching IX on the Medvedev–Sponheuer-Karnik scale (MSK), which is a macroseismic intensity scale used to evaluate the severity of ground shaking on the basis of observed effects in the area of earthquake occurrence (Ambraseys et al. 1994). The 1955 event (MS = 6.7) was the latest locally damaging earthquake. During this earthquake a few people were injured and a considerable number of adobe houses were destroyed, as well as damage to a few concrete constructions (Maamoun et al. 1984; Ambraseys et al. 1994). Generally, the duration of shaking in the city of Alexandria from those earthquakes in its coastal zone did not exceed a couple of seconds (Ambraseys et al. 1994). The

6 1. Introduction

Figure 2: Long-term average Holocene rates of subsidence along the Nile Delta based on stratigraphic analyses of radiocarbon-dated core data (after Stanley and Warne 1998). Sites: A: East Harbour, B: East Canopus, C: Herakleion, D: NW Burullus lagoon, E: SE Burullus lagoon, F: Tell Tinis and G: Pelusium.

latter ones (MS = 7.8) were felt with intensities reaching MSK VI. These earthquakes, being more remote than the first ones, were generally felt in Alexandria for around 3 minutes or more, according to Ambraseys et al. (1994). The most severe damage in Alexandria was related to events located in the Eastern Mediterranean (Ambraseys et al. 1994; El-Sayed et al. 2004).

Apart from these recorded earthquakes, modern and historical, there were clearly unrecorded events that caused disasters. For example, in Abou Kir, part of the city of Alexandria, the cities of East Canopos, Menouthis and Herakleion, positioned at the mouth of the Canopic branch of the Nile, were completely destroyed and submerged in the gulf of Abou Kir, under 6–8 m of water, and probably a destructive earthquake played a role in this. On the other hand, Stanley et al. (2001) concluded that the west branch of the Nile Delta, the so-called Canopic branch during ancient times, migrated almost 30 km east of Cape Abou Kir, developing finally the Rosetta Branch in the second millennium AD. The source and date of destruction of these cities are not exactly known and no details are available; however, the disasters (land subsidence or earthquakes) most likely took place during the 7th or 8th century, as indicated by the coins and jewelry excavated (Geotimes 2000; Stanford Report 2000; El-Sayed et al. 2004). Stanley et al. (2001) attribute the Canopic river bank sediment failure triggered by exceptional flooding of the Nile to the end of the first millennium AD.

7 Geophysical Phenomena and the Alexandrian Littoral

Figure 3: The major fault zones of the wider Alexandria area (Zaghloul et al. 2001).

The coastal zone of Alexandria is also vulnerable to tsunamis. Although tsunamis are rather rare in the Eastern Mediterranean, highly destructive ones were recorded at several locations in the Mediterranean, but only few events are known to have affected Alexandria on the north coast of Egypt (Eckert et al. 2012). One of the largest tsunamis resulted from the earthquake of 8 August, AD 1303, which struck many localities in the Mediterranean basin and reached the Egyptian coast (Maamoun et al. 1984; Kebeasy 1990; Ambraseys et al. 1994; Goiran et al. 2005; Zerefos et al. 2008). In Alexandria, preceded by heavy thunder and lightning, the stability of the whole region was threatened. Soyuti (after Ambraseys 1961) states that the advance of the sea caused by that earthquake submerged half of the town of Alexandria and overwhelmed and killed many thousands of people. The rapid whirlpools created by the retreating waters destroyed many ships, leaving them wrecked, while others were hurled by the waves onto roof tops; some were

8 1. Introduction even washed up several miles from the shore (Papazachos 1990; Ambraseys et al. 1994; Riad et al. 2003; Hamouda 2006). This tsunami also damaged the great lighthouse, and much of the city wall was destroyed (El-Sayed et al. 2000; Papadopoulos et al. 2010; 2014; Shah-Hosseini et al. 2016). Historic records indicate that, in Alexandria, more than 5000 people lost their lives and more than 50,000 homes were destroyed after the earthquake of AD 365 that destroyed much of Crete and caused a tsunami that struck Alexandria (Ambraseys et al. 1994). According to radiocarbon dating, as well as land observations, this was the only earthquake of large magnitude in this area over the last 1650 years (Shaw et al. 2008). The tidal wave of AD 365 reached the coast of Alexandria from a SW direction and therefore the Island of Pharos could provide no protection for the city, and consequently the Heptastadion flooded (Chalari 2007; Shaw et al. 2008). In addition, this tsunami destroyed coastal regions as far as western Egypt and eastern Sicily. Nowadays, evidence of impacts from tsunamis has been traced in sediment core records (Goiran et al. 2000). Goiran et al. (2000) analyzed sediment cores near the East Harbour and identified a layer, dated around the 6th–7th c. AD (Late Roman period), which may correspond to one or more tsunamis and/or high energy storms.

Apart from earthquakes and tsunamis, Alexandria has also been affected since ancient times by sedimentation, which constitutes an important and dominant geological process in this area. The function in the past of many small channels that diverged from the Rosetta Nile branch resulted in Alexandria’s sedimentation. The provoked mass loading, isostatic depression, tectonic readjustment by fault, the slumping and compaction of the unconsolidated sediments, as well as debris accumulation by the various natural catastrophes and by anthropogenic activity over the last 2500 years, has resulted in the 5–7 m higher relief, compared to ground level in antiquity, according to archaeological excavations.

Finally, there is another phenomenon that affects Alexandria and magnifies the submersion of the northern coast of the Nile Delta, and more specifically the east coast of Alexandria: the relative sea level rise. Sea level variations around Alexandria have been the focus of many researches (e.g. Eid 1990; Mosetti and Purga 1990; Jorda et al. 2012; El-Geziry 2013).

To this effect, according to long-term observations (over the past 2300 years), the relative sea level change in the Nile Delta is upward. This ascertainment results from the presence of submerged port facilities of ancient cities in the coastal zone of the Delta. More specifically, in Alexandria’s West Harbour ancient breakwaters were found, whose construction age has not been completely verified, at depths of 5 m and 8 m below sea level (Jondet 1916). In the East Harbour, ancient moles of the Hellenistic period were found to a depth of 5.5–6.5 m (Goddio 1998; Stanley and Bernasconi 2006). The fact that the antiquities in the East Harbour were at least 1 m above sea level at

9 Geophysical Phenomena and the Alexandrian Littoral the time of their construction leads to the conclusion that the total relative sea level change ranges approximately between 6.5 m and 7.5 m. Therefore, the average rate of relative sea level rise over the last 2300 years in the coastal zone of Alexandria ranges from about +2.8 to +3.4 mm/year. The same upward trend in sea level is also observed during Holocene (8000–6500 BP). Stanley (1988; 1990), Stanley and Warne (1993), and Warne and Stanley (1993) calculated that the rate of the relative sea level change is 3mm/year in the region of Alexandria (Chalari 2007).

1.3 Geomorphology

According to the geomorphological setting, the Egyptian margin, west of the Nile Delta, is defined by a straight SW–NE coastline that presents a length of more than 100 km. In this area, and particularly between the Arabian Gulf to the west and the Nile Delta east of Alexandria, the only suitable sites for the construction of protected ports were the two bay-like re-entries adjacent to Pharos Island.

The West Harbour has a rectangular shape with an area of about 26 km2 and a length of nearly 10.7 km, between the SW margin (El Agami) and the Heptastadion coast to the east. The West Harbour has mostly depths exceeding 10 m. Its floor is asymmetric, deepening gently from the outer kurkar islet margin towards the SE, while towards Alexandria’s shoreline it becomes rapidly shallower, from 20 to 15 m. The port can be subdivided into three coast-parallel bands according to the depth (NIMA 1999). More specifically, it can be subdivided into a wide northern (seaward) one, with shallow to intermediate depths from 1 to 10 m, a deep middle sector with depths ranging from 10 to >20 m, and a very narrow, steeply-inclined southern band along the coast with intermediate depths, generally <10 m. The deepest depression (25 m) lies in the port’s western sector. Three major ship paths to and within the port, having depths of almost 20 m (El-Dikheilah Pass, Great Pass, El-Bogaz Pass), and other actively used navigational sectors, are maintained by dredging.

The East Harbour, known as the Port of the Ptolemies, or Portus Magnus, during early Hellenistic history, is positioned north of Alexandria’s city centre and about 20 km west of the Nile Delta’s NW coastal margin. It is shallower and much smaller, with an area of about 2.8 km2. It is a partially enclosed elliptical basin, with a maximum distance of 2.5 km measured between its eastern and western edges, whereas the distance between its southern coastline and northern outlet is 1.5 km. The southern margin of the harbour is noticeably arcuate, as the result, in part, of considerable anthropogenic modification of the coastline of the city over many years. The port has depths of 5 m or less over half its area, while the north-central part, at the El-Boughaz outlet, along the western margin of the El-Silsila breakwater, reaches a maximum

10 1. Introduction depth of 11 m (El-Geziry et al. 2007). An irregular distribution of small shallow kurkar islets form the northern margin of the East Harbour and several larger (to >500 m wide) submerged kurkar highs are distributed in the east-central sector of the port (Goddio et al. 1998), probably submerged parts of the kurkar ridge I. The harbour is now almost completely enclosed artificially by protection structures, which are emplaced along its northern margin. During the early Hellenistic period, under Greek rule, several important port facilities were constructed in the eastern and western sectors of the East Harbour (Goddio et al. 1998; Bernard and Goddio 2002). By Roman times, the coastline bordering the East Harbour had been moderately reshaped by large warehouse and dock structures, built in order to absorb trade that had been previously directed to Athens and other Eastern Mediterranean cities.

The area of the East Harbour was once a sub-aerially exposed topographic depression that was formed between a series of carbonate kurkar high-relief features. During the early Holocene, land subsidence, sea level rise, and consequent landward coastal retreat, resulted in flooding by marine water and thus the East Harbour was formed. There are several sediment sources to the harbour. At first, substantial soil runoff, as well as sediment, much of it carbonate, eroded from the bordering emergent land and the areas is defined by the accumulation of considerable terrigenous sediment on the basin floor. Clay sediment was also transported landwards in the harbour through coastal erosion, storm surges and bottom currents. Organic and detrital material was deposited into the harbour, because of transport on the seabed and suspension in the water column (Stanley and Bernasconi 2006). Significant amounts of carbonate particles, including shell fragments, accumulated in the harbour from coastal areas west of Alexandria and the Nile shelf offshore. Meanwhile, quartz was largely transported from the mouths of Nile branches, delta margins and the Nile shelf to the ENE (El-Wakeel and El-Sayed 1978; Hassouba 1995; Shukri et al. 1956; Summerhayes et al. 1978; Warne and Stanley 1993). In addition, wind transport was a significant sediment source for the harbour. The wind-released material includes coarse sands originated from contiguous desert sectors (Stanley and Bernasconi 2006), as well as silt and dust from more distal desert terrains in Egypt, Libya, Sudan, and Chad to the S and W (El-asmar 2000; Guerzoni and Chester 1996; Yaalon and Ganor 1979). Generally, the outer northern margins of both harbours are formed by linear, discontinuous series of emergent to shallow submerged islets and ridges formed of kurkar.

The Maryût Lagoon is located on the western margin of the Nile Delta. It is a vast coastal plain, located beneath the Delta (Hume and Hughes 1921; Warne and Stanley 1993; Goodfriend and Stanley 1996; Flaux et al. 2011). It is located below sea level and is separated from it via a coast, which contains Pleistocene sediments (El-asmar and Wood 2000). Since antiquity, the Maryût Lagoon was a basin containing slightly brackish water in communication with the Nile, through several canals, and with the

11 Geophysical Phenomena and the Alexandrian Littoral sea as well, with secondary channels, as described by Strabo: ‘[Alexandria] is bathed by two seas, to the north by the Egyptian sea, as it is called, and to the south by the lake of Mareia, also called Maréôtis’ (Strabo XVII, 7, in Yoyotte et al. 1997). This is how the Canopic branch works, which serves the entire system of the Mareotis Lake (Toussoun 1922), and was also the main source of natural fresh water for both Alexandria and the Maryût Basin. The decline in water flow, in this branch, began in the Roman period, while there was a gradual increase to the east, and more specifically to the Rosetta branch (Guest 1912; Toussoun 1922; 1926; Chen et al. 1992; Stanley et al. 2004a; Ducène 2004; Stanley and Jorstad 2006). It is therefore probable that the drying of the Canopic branch may be the result of the diversion of its increasing flow into the irrigation system of the Delta’s western margin, which has contributed significantly to the development of Alexandria (Bernard 1970). The decrease of water flow is caused by two main factors – the deposition of sediment load and the decrease of the slope. The two phases of the Maryût Basin show a slow desiccation process of the Nile’s western boundaries, most likely with a subsequent reduction in the Canopic branch, 2000 years ago. The progressive blockade of the Canopic branch is placed between the 10th and 14th centuries AD, and is a process that took place gradually (Hairy and Sennoune 2006).

The expansion of the Maryût Basin appears to have fluctuated some 2000 years ago. The city of Alexandria experienced major political changes from the 7th century AD. At the beginning of this century an armed conflict between the Byzantine emperors Phokas and Heraklion took place in Maryût (Rodziewicz, 1998). One of the generals was ordered to fill the basin supply channels to reduce the water level. This rapid reaction, if any, shows the dependence and viability of the lagoon by preserving the channels connecting the Nile. All areas associated both with economy and exports were quickly abandoned. At the same time, the construction in Alexandria of the newly fortified city completely dissociates the city from the lagoon (Haas 2001). Between 930 and 1070, the Roda Nilometer in Cairo records successive phases of Nile levels, including floods and water shortages. This last phase may have favoured the creation of a deficit in the Maryût Basin, which was less likely to communicate with the Nile. At the end of the 12th century AD, the commentator Ambul Hassan al-Makhzoumi describes the irrigation process during the Nile overflow in the Behera area (Toussoun 1926), the western Rosetta branch. Toussoun (1926) also mentions the reconstruction of an important Behera channel between 1263 and 1265 AD, during the reign of Mamluk Sultan al-Zaire Baybars. These testimonies reflect the resumption of agricultural activities in the Behera area, and this could be interpreted as stopping the operation of the Maryût evaporites Basin, through irrigation in the area. The region is affected by a major demographic crisis due to the plague, which also occurs in Europe during the same period. The second drainage of Maryût, from the 12th century AD, affecting

12 1. Introduction all irrigation channels, resulted in the general decline of Behera. The northwestern Delta was then linked to the Nile again by large-scale irrigation projects that began at the same time as the economic development of Alexandria, during the reign of Méhémet Ali, in the early 19th century.