5 research outputs found
The Santorini-Amorgos Shear Zone: Evidence for Dextral Transtension in the South Aegean Back-Arc Region, Greece
Bathymetric and seismic data provide insights into the geomorphological configuration, seismic stratigraphy, structure, and evolution of the area between Santorini, Amorgos, Astypalea, and Anafi islands. Santorini-Amorgos Shear Zone (SASZ) is a NE-SW striking feature that includes seven basins, two shallow ridges, and hosts the volcanic centers of Santorini and Kolumbo. The SASZ initiated in the Early Pliocene as a single, W-E oriented basin. A major reorganization of the geodynamic regime led to (i) reorientation of the older faults and initiation of NE-SW striking ones, (ii) disruption of the single basin and localized subsidence and uplift, (iii) creation of four basins out of the former single one (Anafi, Amorgos South, Amorgos North, and Kinairos basins), (iv) rifting of the northern and southern margins and creation of Anydros, Astypalea North, and Astypalea South basins, and (v) uplift of the ridges. Dextral shearing and oblique rifting are accommodated by NE-SW striking, dextral oblique to strike-slip faults and by roughly W-E striking, normal, transfer faults. It is suggested here that enhanced shearing in NE-SW direction and oblique rifting may be the dominant deformation mechanism in the South Aegean since Early Quaternary associated with the interaction of North Anatolian Fault with the slab roll-back
Cross-Comparison of the “BathySent” Coastal Bathymetry to Sonar Measurements and Ratio Model Technique: Pilot Sites in the Aegean Sea (Greece)
The proposed novel “BathySent” approach for coastal bathymetric mapping, using the Copernicus Sentinel-2 mission, as well as the assessment and specification of the uncertainties of the derived depth results, are the objectives of this research effort. For this reason, Sentinel-2 bathymetry retrieval results for three different pilot sites in Greece (islands of Kos, Kasos, and Crete) were compared with ground-truth data. These data comprised high-resolution swath bathymetry measurements, single-beam echosounder measurements at very shallow waters (1–10 m), and the EMODnet DTM 2018 release. The synthetic tests showed that the “BathySent” approach could restitute bathymetry in the range of 5–14 m depth, showing a standard deviation of 2 m with respect to the sonar-based bathymetry. In addition, a comparison with the “ratio model” multispectral technique was performed. The absolute differences between conventional Earth Observation-based bathymetry retrieval approaches (i.e., linear ratio model) and the suggested innovative solution, using the Sentinel-2 data, were mainly lower than 2 m. According to the outcome evaluation, both models were considered to provide results that are more reliable within the depth zone of 5–25 m. The “ratio model” technique exhibits a saturation at ~25 m depth and demands ground calibration. Though, the “BathySent” method provides bathymetric data at a lower spatial resolution compared to the “ratio model” technique; however, it does not require in situ calibration and can also perform reliably deeper than 25 m
Assessment of the physical impact of a short-term dredging operation on a semi-enclosed environment: South Euboean Gulf, Greece
The potential influence of short-period (May-June 2012) dredging
activities (for the installation of a submarine gas pipeline) on
physical properties of the marine environment of two shallow-water sites
in the Aliveri and Varnavas areas of South Euboean Gulf (Greece) has
been evaluated. During the dredging operation in Varnavas, the induced
dredge plume traveled up to 750 m from the shoreline, featured by light
attenuation coefficient (c(p)) maxima of 4.01-4.61 m(-1) and suspended
particulate matter (SPM) concentrations up to 6.01 mg L-1. After
dredging the previous parameters reduced to the ambient seawater
condition, 0.45 m(-1) and < 2.8 mg L-1 on average, respectively.
Likewise in Aliveri, the dredging-associated sediment plume drifted
offshore up to 400 m from the shoreline, characterized by c(p) maxima of
2.11-4.86 m(-1) and SPM concentrations up to 13.07 mg L-1. After the
completion of the excavation and trenching activities, the c(p) and SPM
values were restored to the pre-disturbance condition, 0.6 m(-1) and <
2.2 mg L-1 on average, respectively. The migration of the dredge plume
in both dredging sites was accomplished through the formation of
intermediate and benthic nepheloid layers, whose development and
evolution were governed by seawater stratification and flow regime. The
dredging-derived SPM levels appeared to increase within a distance of no
more than 300 m from the shoreline (near-field zone). Based on data from
the literature, this SPM enhancement together with the deposition of a
post-dredging residual mud veneer in the near-field zone could
deteriorate local marine biota, but in a reversible way
Assessment of the Coastal Vulnerability to the Ongoing Sea Level Rise for the Exquisite Rhodes Island (SE Aegean Sea, Greece)
The foreseeable acceleration of global sea level rise could potentially
pose a major threat to the natural charm and functional integrity of the
world-renowned tourist coastal attractions of Rhodes Island, as a result
of the anticipated increasing frequency of flooding and erosion events.
Hence, this study aims to determine the most vulnerable segments (in
terms of physical impact) of the Rhodes coastline through the widely
accepted coastal vulnerability index (CVI), applying a combination of
well-known, broadly used approaches and methods. The frequency
distribution of the current CVI along the island’s coastline suggests a
rather worrying high to very high vulnerability of 40%. In addition, a
CVI projection to the end of the 21st century (based on the
Intergovernmental Panel on Climate Change predictive scenarios)
indicates an enhancement of the total vulnerability by 48%, mainly
focused on the majority of the western coastline. Hence, a considerable
number of popular coastal destinations in the island shall remain under
unignorable threat and, therefore, coastal managers and decision-makers
need to hatch an integrated plan to minimize economic and natural
losses, private property damage and tourism infrastructure deterioration
from flooding and erosion episodes, which will most likely be
intensified in the future
Searching for Neolithic sites in the Bay of Kiladha, Greece
Since the excavations at Franchthi Cave in the 1960s and 1970s, the possibility of finding a submerged Neolithic site in the Bay of Kiladha has been discussed. Initial research, based on marine geophysical survey and core sampling, brought contrasted results. Starting in 2012, new parts of the Bay were investigated, using different techniques and improved methods, such as geological-geophysical survey, further core sampling (including the finding of artefacts and anthropogenic indicators of a given date in the cores), shallow water ERT (with an adapted methodology), and underwater excavation. The combined evidence leads to a reconsideration of previous work, to the discovery of submerged structures directly off the cave, which might well be Neolithic walls, and points to the existence of two new submerged sites, one dating to the Neolithic, in the middle of the Bay, and the other to the Final Neolithic/Early Bronze Age I, at Lambayanna. The implications of these findings are discussed as well