HIGH-RESOLUTION GEOMORPHOLOGICAL MAPPING OF THE SHALLOW CONTINENTAL SHELF WEST OF THE KAVALA BAY, NORTH AEGEAN

Σημαντικές γεωμορφολογικές δομές του ρηχού τμήματος της υφαλοκρηπίδας δυτικά του Κόλπου της Καβάλας χαρτογραφήθηκαν χρησιμοποιώντας τα δεδομένα από μια υδρογραφική αποτύπωση (τον Ιούνιο 2014) 320 ναυτικών μιλίων, η οποία περιελάμβανε υψηλής διακριτικότητας πολυδεσμική βαθυμετρική καταγραφή και διασκόπηση πυθμένα με σεισμική ανάκλαση. Αναγνωρίστηκε ένα σύστημα ρηγμάτων αποτελούμενο από ένα σετ δυο κυρίων κανονικών ρηγμάτων (καταγεγραμμένο μήκος και μετρημένο κατακόρυφο άλμα αυτών: 12 χλμ, 5 χλμ και > 40 μ, 25 μ, αντίστοιχα,) με έντονη επιφανειακή εκδήλωση στο θαλάσσιο πυθμένα, καθώς και τρία δευτερεύοντα ρήγματα νότια των κύριων ρηγμάτων, τα οποία φανερώνουν συνιζηματογενή τεκτονισμό. Η εντυπωσιακή διαφορά στις υφές των ιζημάτων που καλύπτουν αφενός το υποκείμενο ρηξιτέμαχος του βορειότερου κυρίου ρήγματος και αφετέρου την οροφή του νοτιότερου κυρίου ρήγματος δείχνει τη σημαντική επίδραση του τεκτονισμού στις ιζηματολογκές διεργασίες της περιοχής μελέτης. Όσον αφορά τις υπάρχουσες γεωμορφές, οι περισσότερο ενδιαφέρουσες είναι εκείνες των αμμωδών θινών στο βορειοανατολικό τμήμα της περιοχής μελέτης, ευρισκόμενες σε βάθη από 25 μ μέχρι τουλάχιστον 65 μ. Οι μεγάλες διαστάσεις τους καθώς και ο προσανατολισμός τους ως προς την ακτογραμμή υποδηλώνουν ως μηχανισμό σχηματισμού τους την δράση ισχυρών πυθμιαίων ρευμάτωνProminent geomorphological features of the shallow continental shelf west of the Kavala Bay (Loutra Eleftheron-Nea Peramos) were mapped using the data from a hydrographic survey (June 2014) of 320 nautical miles during which high resolution multibeam bathymetry and seismic-reflection subbottom profiling were carried out simultaneously. A fault zone comprised by a set of two primary sigmoidal gravity faults (recorded lengths and measured offsets: 12 km, 5 km and > 40 m, 25 m, respectively), with distinct expression on the seabed, and three other secondary gravity faults situated southern of the major faults, revealing synsedimentary tectonics, was identified. The striking difference between the texture of the footwall block sediments of the northern major fault and the texture of the sediments occupying the deep hanging wall block of the southern major fault emphasizes the impact of local tectonics on the sedimentary evolution of the study area. Concerning the observed bedforms, the most interesting were the sand dunes occurring at depths from 25 m to 65 m at least and occupying the northeast part of the study area. Their large dimensions and orientation in relation to the coastline position imply as a mechanism for their formation intense bottom-current activity

Sediment transport patterns and beach morphodynamics in the semi-enclosed bay of Platis Gialos, Sifnos Island, Aegean Sea

Pocket beaches are a large part of the Greek coastline, with strong touristic, economic and natural interest. Their morphological characteristics and wave forcing are the main factors influencing their evolution, while the most commonly observed dynamic is beach rotation due to prevailing wave direction. Human activities and climate change call for a better management for these areas, necessitating, therefore, the identification of coastal geomorphodynamic processes. This paper focuses on the geomorphological and sedimentological dynamic processes of Platis Gialos Bay (Sifnos), which have given rise to the present setting. Beach orientation, slope, length, geology, Posidonia Oceanica, degree of embayment, sedimentology and closure are some parameters that must be considered to calculate the morphodynamic and stability indicators that prevail at the beach. Wave exposure forcing conditions, longshore – rip current direction, are also hydrodynamic processes to be determined, as they play a significant role in sediment transport. A number of methodologies took place in order to determine the level of disturbance of this dynamic equilibrium, which included morphological mapping, sedimentary classification, shoreline displacement/evolution monitoring, hydrodynamic and sedimentary modelling. The exposure of the coast to the southern waves, the reduced sediment supply from the local fluvial network, human activities and the construction of the fishing shelter have led the area to a continuous erosion and coastline retreat in its western and central part, in contrast to the eastern part, where there is a continuous deposition reflected by coastal accretion and the formation of a shallow environment. © 2021

Recent evolution of a Mediterranean deltaic coastal zone: Human impacts on the Inner Thermaikos Gulf, New Aegean Sea

The Inner Thermaikos Gulf is located in the northwestern Aegean Sea, receiving water and sediment fluxes from the Axios, Aliakmon, Gallikos and Loudias Rivers. The geomorphological and sedimentological evolution of the system is reconstructed for the last 150 years (1850-2000), on the basis of detailed analysis of historical bathymetric charts. Late Holocene history is considered within the context of changing riverine sediment supply and human activities. Three evolutionary stages are identified. Stage I (1850-1916) corresponds to a natural phase of rapid deltaic progradation and sea-floor deposition, with an average sediment accumulation rate of 6.5 × 106 m3 a-1. During Stage II (1946-1956), human interference (e.g. artificial changes in river delta plains, realignment of channels and land reclamation schemes) to the deltaic system increased sediment delivery to the coastal waters by a factor of three; this, in turn, enhanced the progradation of the active river mouth areas. In contrast, Stage III (1956-2000) is characterized by significant coastline (deltaic) retreat and erosion of the adjacent sea floor (net loss of 2.5 × 106 m3 a-1); this was as a result of extensive river damming, which trapped a significant part of the sediment moving seaward. Furthermore, these human impacts have affected the character of the surficial sea-bed sediments of the Gulf, by reducing the proportion of mud. The response of the deltaic margin of the Inner Thermaikos Gulf to various anthropogenic interventions seems to be analogous to that of other deltas in the Mediterranean region where large drainage projects, the development of irrigation networks and dam construction have taken place within their river basins