Was Alexandria (Egypt) Destroyed in A.D. 365? A Famous Historical Tsunami Revisited

Ammianus Marcellinus, a fourth-century writer, reported that after an earthquake, on 21 July 365, the sea retreated and then flooded numerous coasts, among them Alexandria (Egypt) and Methoni (southwest Greece). Several other ancient authors seem to mention this event as a “universal earthquake.” The inferred tsunami is usually assigned to reactivation of a fault in the Hellenic (Aegean) Arc, derived from an up to 9 m seismic uplift of Crete. Modeling of this uplift revealed an 8.5+ magnitude earthquake and a tsunami that affected most of the Eastern Mediterranean. For Alexandria, a flooding wave arrival is predicted, and marginal impacts are not excluded because of the topography of the ancient town. On the other hand, ancient sources lead to contradictory results, from no damage to devastation, but new historical evidence indicates that many of the historical reports of the critical period are biased by religious and political ideas, and the Ammianus description was questioned. Hence, for Alexandria there exist three scenarios: major destruction, marginal damage, and no damage by the 365 tsunami. To shed light to this debate (1) ancient sources were analyzed in view of new evidence for their significance, (2) possible impacts of a tsunami in the town’s infrastructure were discussed, and (3) possible impacts of a major destruction were investigated in the framework of the well-known ecclesiastical and civil history of Alexandria. The main conclusions of this study are that (1) no significant tsunami destruction is likely for Alexandria, in agreement with sedimentary evidence, and no major tsunami runup for Methoni; (2) a major earthquake in 365 is likely offshore Crete; and (3) it is inferred that Ammianus brings together two tsunamis, a local slump offshore that produced water retreat and then flooding and local denudation in the eastern Nile Delta, and a second tsunami generated by a fault offshore Crete or in the Ionian and the Adriatic Sea.

Chemical Evolution of Calc-alkaline Magmas during the Ascent through Continental Crust: Constraints from Methana, Aegean Arc

Quaternary calc-alkaline andesitic to dacitic lavas effusively erupted on top of about 30 km thick accreted continental crust at Methana peninsula in the western Aegean arc. We present new data of major and trace element concentrations as well as of Sr–Nd–Pb isotope ratios along with mineral compositions of Methana lavas and their mafic enclaves. The enclaves imply a parental basaltic magma and fractional crystallization processes with relatively little crustal assimilation in the deep part of the Methana magma system. The composition of amphibole in some mafic enclaves and lavas indicates deeper crystallization at ∼25 km depth close to the Moho compared with the evolved lavas that formed at <15 km depth. The presence of amphibole and low Ca contents in olivine suggest high water contents of ∼4 wt% in the primitive magmas at Methana. The compositions of andesitic and dacitic lavas reflect fractional crystallization, assimilation of sedimentary material, and magma mixing in the upper 15 km of the crust. The Methana magmas have fO2 of FMQ + 1 to FMQ + 2 (where FMQ is the fayalite–magnetite–quartz buffer) at temperatures of 1200 to 750 °C and the fO2 does not vary systematically from mafic to felsic compositions, suggesting that the mantle wedge was oxidized by sediment subduction. Amphibole is an important fractionating phase in the more evolved Methana magmas and causes significant changes in incompatible element ratios. Although xenocrysts and mineral compositions indicate magma mixing, the major and trace element variation implies only limited mixing between dacitic and basaltic melts.

The Kos–Nisyros–Yali Volcanic Field

The Kos–Nisyros–Yali volcanic field has produced a range of volcanic products over the last 3 million years. Volumetrically, silicic magma dominates, and activity includes one of the largest known explosive eruptions of the Aegean arc, the >60 km3 (dense-rock equivalent), 161 ka rhyolitic Kos Plateau Tuff. The Kos–Nisyros–Yali volcanic field is situated within an area of active crustal extension, which has greatly influenced magmatic processes and landscape development in the region. Recent seismic unrest, surface deformation and intense geothermal activity indicate that the system remains active, particularly around the Nisyros and Yali edifices. These signs of magmatic activity, together with the fact that the most recent eruptions have become increasingly silicic, would justify detailed monitoring of the area.

MAGMA INTRUSION IN 'PROTO-CALDERA CALDERA' SYSTEMS: EXAMPLE FROM THE NISYROS VOLCANO

The interdependence of volcanism and tectonism has been focused upon in the last decade as a result of previously accumulated evidence, as well as, due to the application of remote sensing techniques in both these fields. Volcanoes depend on tectonic features such as faults for their positioning and operation and on petrotectonic environment for the chemistry of their magmas. Faults provide the plumbing system for magma ascent and therefore volcano localisation and distribution in space greatly depends on the tectonic pattern of an area. On the other hand, volcanoes locally imprint their volcanotectonic features such as radial and ring faults which result from cycles of magma replenishment (inflation) and evacuation (deflation) of magmatic reservoirs (magma chambers). Under this light, the area in the easternmost extremity of the Aegean Arc is being reconsidered. Our main preliminary findings of ongoing research in the area, using field and remote sensing methods indicate localization of volcanic activity on Kos and on the Datca Peninsula of Asian Minor since Miocene due to the northbounding faults of the Datca Graben. Localisation of volcanic vents and calderas in the Kos-Nisyros area follows intersection of a major tectonic line of northnorthwesterly trending faults the 'Kos-Nisyros-Tilos Line' with N50°E, N30°E and N20°W trending faults. On the well-preserved volcano ofNisyros the architecture of the volcanic edifice has significantly been affected by 'trap-door' volcanotectonics of a major volcanic infrastructure in the area namely the Kos-Caldera