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Tsunamis and storms cause considerable coastal flooding, numerous fatalities, destruction of structures, and erosion. The characterization of energy and frequency associated with each wave contribute to the risk assessment in coastal regions. Coastal boulder deposits represent a physical proof of extreme inundation and allow us to study the effects of marine floods further back in time than instrumental and historical records. Age estimation of these deposits is challenging due to lack of materials (such as sand, shells, corals, or organic matter) that retain information about the passage of time. Lichenometry, a simple age estimation method, which is cost-effective, quick to apply, and non-destructive, is here proposed as a solution. A lichen growth model for a calcium-tolerant lichen species was developed and used to estimate the age of a boulder deposit related to extreme marine inundation(s) in Portugal. Estimated ages indicate several very recent events (<700 years) for most of the boulders' stabilization and agree with results obtained with optically stimulated luminescence of marine sands found beneath boulders. Frequent and recent boulder transport implies a storm-origin for this deposit. These conclusions contrast with other works describing identical deposits that are attributed to paleotsunamis. This study presents a methodology using lichenometry as a successful alternative for age estimation in rocky coastal settings. These results offer an alternative explanation for coastal boulder deposits found on the west coast of Portugal. [ABSTRACT FROM AUTHOR]

ABSTRACT Bastos, A.P.; Ponte Lira, C.; Calvão, J.; Catalão, J.; Andrade, C.; Pereira, A.J.; Taborda, R.; Rato, D.; Pinho, P., and Correia, O., 2018. UAV Derived Information Applied to the Morphological Study of Slow-changing Dune Systems. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 226–230. Coconut Creek (Florida), ISSN 0749-0208. São João da Caparica (Portugal) slow-growing dune system was investigated using field-based GPS and UAV surveying methods. Here, vegetation may preclude straightforward extraction of ground surface data from DSM and low sedimentation rates demand high accuracy. The approach used comprised acquisition of UAV-derived DSM and RGB orthomosaics at flight-heights of 30 and 60 m. Results were compared with DTM derived from traditional RTK-GPS ground surveys. Two methods (M1 and M2) where used to convert UAV-derived DSM into a DTM, both departing from supervised classification of land cover. In M1, vegetation areas are removed from the original DSM, which is then re-interpolated. M2 redefines elevation of pixels corresponding to vegetation by subtracting a mean height parameter defined for each vegetation class. It was found that DTM derived from UAV and RTK-GPS data exhibit errors in the same order of magnitude, regardless of the higher resolution of the former. M2 yielded the best compromise when considering deviations in both profile and surface analysis. M2 is strongly dependent on vegetation classification and on parametrization of the vertical correction affecting each vegetation class. UAV methodology presents the best cost-benefit ratio relative to traditional RTK-GPS surveys, providing additional image information (RGB orthomosaic) synchronous of the topographic data. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Integrated Coastal Zone Management / Revista de Gestão Costeira Integrada is the property of Associacao Portuguesa dos Recursos Hidricos and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Lopes, V., Freitas, M.C., Andrade, C., Taborda, R., Ramos, R. and Oliveira, M.A. 2013. A GIS-assisted reconstruction of the Holocene transgressive paleosurface of Pederneira lowland (W Portugal) The Last Glacial Maximum low stand and coeval re-incision of the Portuguese hydrographic network created the space and defined the shape of the main morphological features available to accommodate the inundation resulting from the Holocene transgression and the marine sediments deposited in tune with changing base levels. The reconstruction of the transgressive paleosurface is relevant in paleoenvironmental studies, namely to establish the paleobasin morphology and evaluate accommodation volume. In the case of the study area (Pederneira lowland), the geological data set available to reconstruct that surface consists of borehole logs carried out for geotechnics and groundwater and three cores performed for paleoenvironmental reconstruction. The borehole data scatter non-uniformly across the lowland providing spatially biased information. The surveying of several Transient Electromagnetic Method (TEM) profiles yielded inconclusive results in separating sediment units below and above the transgressive surface due to poor contrast in sediment resistivity and high conductivity of groundwater. This study addresses a method for estimating that paleosurface using the combination of a standard geostatistical interpolation procedure (kriging) with a conceptual geomorphological model. The geomorphological model comprised the sketching of a paleoriver drainage system in which the position of the thalwegs was defined departing from present-day slope morphology and depths estimated by adjusting a mathematical curve describing their longitudinal profile to control points. Final adjustments to the paleodrainage system were constrained by borehole data and expert judgment. This methodology proved to be effective in an area where limited objective geological and geophysical data are available. [ABSTRACT FROM AUTHOR]

ABSTRACT A remarkable accumulation of marine boulders located above the present spring tide level has occurred in two coastal lowlands of the Algarve (Portugal). The size-interval of the particles studied here is seldom reported in the literature in association with extreme events of coastal inundation, thus making this study of relevance to many other coasts worldwide. The spreads of boulders extend several hundred meters inland and well beyond the present landward limit of storm activity. The marine origin of the boulders is demonstrated by well-developed macro-bioerosion sculpturing and in situ skeletal remains of endolithic shallow marine bivalves. The good state preservation of the fossils within the boulders indicates that abrasion during transport and redeposition was not significant. We envisage boulder deposition as having taken place during the Lisbon tsunami of ad 1755 through the simultaneous landward entrainment of coarse particles from nearshore followed by rapid shoreward suspended-dominated transport and non-graded redeposition that excluded significant sorting by weight or boulder dimensions. We use numerical hydrodynamic modeling of tsunami (and storm) waves to test the observational data on boulder dimensions (density, size, distribution) on the most likely processes of sediment deposition. This work demonstrates the effectiveness of the study of boulder deposits in tsunami reconstruction. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Integrated Coastal Zone Management / Revista de Gestão Costeira Integrada is the property of Associacao Portuguesa dos Recursos Hidricos and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Current coastal protection strategy in Portugal defines beach and shoreface nourishment as a valid measure to mitigate coastal erosion in some erosional hot-spots, being considered as an adaptation measure under the present climate change scenario, including the impacts of sea level rise. However, scant objective data on shoreface nourishments are available to evaluate performance of this type of intervention in mitigating beach erosion and managing coast risk. We present the first monitoring results of a ≈2.4 × 106 m3 shoreface nourishment on the Aveiro coast (Costa Nova—Ílhavo), the largest until now in Portugal, focusing on its morphological development, impacts on adjacent beaches due to alongshore spreading and cross-shore redistribution, and contribution to the sediment budget of the nourished sediment cell. The analyses are based on high-resolution coastal monitoring data, provided by the Portuguese COaStal MOnitoring Program (COSMO). A Multiple Monitoring Cell (MMC) approach was used to evaluate local and feeder efficiency of the nourishment, sediment budget exchanges within both the placement and wider survey domains (≈1 km2 and 12 km2, respectively). Results show rapid (ca. 6 months) morphological change over the placement area, with a decrease of about 40% of the initial volume. Fast onshore sediment redistribution explains part of this change, placed sand having merged with the pre-existing bar system increased the volume of the shallower nearshore. Longshore transport is reflected by increasing the robustness of the bar downdrift of the placement area and also explains the negative sediment budget (0.75 × 106 m3) of the survey domain, which corresponds to losses through its southern boundary. Sediment spreading also induced accretion of the subaerial section of Costa Nova beaches in front of the placement area, reversing their long-term erosive trend. In contrast, this trend persisted at downdrift beaches. This suggests that the time lag of the subaerial beach response to this intervention increases with the distance to the placement area, and reversal of the erosive trend will only be noticeable in the following years. This study provides new insights on the time scales of beach response to high-magnitude shoreface interventions in high-energy wave-dominated sandy coasts, which will support decision making regarding similar operations designed to manage erosional hot-spots elsewhere. [ABSTRACT FROM AUTHOR]

The sedimentological and geochemical study of a core corresponding to sedimentation in the Santo Andrélowland since 14 000 BP allowed the reconstruction of environmental changes of this area and discussion of the relative importance of local versus global forcing factors responsible for its evolution. The pre-Holocene section of the core represents terrestrial sedimentation in a fluviatile environment, contemporaneous of a low sea level and a distal shoreline. Sediment inputs were terrestrial and resulting from intensive weathering and high erosion rate in the adjacent watershed. During the Early Holocene (c. 10 020 to 5380 BP) the sea invaded this lowland and defined an open marine shallow environment corresponding to a wide gulf which has been disturbed by multiple terrestrial inputs that might have been induced by massive episodes of fluvial discharge. The first symptoms of confinement were noticed close to 5400 BP, and c. 5380 BP a major environmental threshold occurred (possibly reflecting the marked deceleration of the sea-level rise rate) corresponding to the establishment of an efficient detrital barrier that completely isolated the bay and changed this lowland into a closed coastal lagoon. After 5380 BP, the lagoonal environment evolved as a function of local forcing factors, among which the frequency and efficiency of exchanges with the ocean predominate: until c. 3570 BP the lagoon was restricted, fed by fresh water and terrestrial sediment inputs; a second episode of lagoonal sedimentation lasts until c. 1620 BP, reflecting brackish conditions and increase in marine influence due to a reduced efficiency of the barrier. The upper section of the core represents the final stages of filling of the lagoonal margin by fluvial activity. Human settling and intervention in the barrier are possible causes of a short-lived return to brackish conditions recorded in the uppermost sediment unit of the core and of the dramatic increase of the sedimentation rates. [ABSTRACT FROM AUTHOR]

The Azores archipelago (Portugal) contains 88 lakes, two located inside caves spread across six of the nine volcanic islands of the archipelago; the formation of the lakes is associated with various types of volcanic structures. Surveys were performed on 45 water bodies corresponding to a representative data set and omitting only small ephemeral ponds to extensively research CO 2 emissions from the volcanic lakes. The modified accumulation chamber method was used to measure the CO 2 flux at the surface of the lakes; 16,119 measurements were performed with flux values ranging from 0 to 20,960 g m−2 d−1. Graphical statistical approaches identified different geochemical populations from the CO 2 flux data. Multiple populations associated with limnological and biogenic processes or volcanic/hydrothermal sources were identified in some cases. The influence of these sources was also confirmed by the determined δ13C content of the lakes. The lakes of the Azores emit approximately ~171 × 103 t yr−1 of CO 2 into the atmosphere; much of this is released by the Furnas and Furna do Enxofre lakes, both showing mantle-derived CO 2 origin. Deep-seated CO 2 accounts for approximately 42% of the total degassing. • Lake stratification influences the amount of CO 2 emitted to the atmosphere. • Higher CO 2 values are associated with lakes having CO 2 of volcanic origin. • Low CO 2 flux and δ13C content on lakes suggest biogenic CO 2 origin. • Total CO 2 degassing from Azores lakes to the atmosphere was estimated at ~171 × 103 t yr−1. • Total deep-seated CO 2 degassing was estimated at ~72 × 103 t yr−1. [ABSTRACT FROM AUTHOR]

Sete Cidades Lake (São Miguel Island, Portugal) is subdivided into two interconnected branches: the Green Lake and Blue Lake. The lake has an area and maximum depth of 4.39 km2 and 29.5 m (Blue Lake), respectively, with evidence of eutrophication, particularly in the northern area of the Green Lake. In this study, we conducted a sampling survey during January 2017 to measure CO 2 fluxes from the lake using a floating accumulation chamber. We also produced two hydrogeochemical profiles for each of the lake's branches. A total of 1760 CO 2 flux measurements were taken along the lake's surface. The lake water was relatively cold (14.0 °C on average) and weakly mineralised (average electrical conductivity of 116 μS cm−1) with a neutral pH (7.7 on average). The relative composition of major ions occurred in the following decreasing order: Na+ > Mg2+ > Ca2+ > K+ for cations and Cl− > HCO 3 − > SO 4 2− for anions. The lake water was mainly the Na–Cl type due to sea salt input from seawater spraying. CO 2 fluxes ranged from 0.3 to 17.2 g m−2 d−1 and from 2.1 to 17.9 g m−2 d−1 for the Blue and Green Lakes, respectively. Highest CO 2 degassing occurred in areas dominated by macrophytes and algal blooms. The measured values suggest that the CO 2 was predominantly biogenically sourced, which was further supported by the δ13C isotopic data. The estimated total CO 2 emissions varied between 5.8 t d−1 (Green Lake; area = 0.81 km2) and 24.9 t d−1 (Blue Lake; area = 3.58 km2). This study further elucidates the lake's trophic and chemical pollution status and has major implications for lacustrine CO 2 emissions to the atmosphere. Our study also provides a reference for understanding potential future variations in volcanic activity. Image 1 • Water in Sete Cidades Lake is mostly Na–Cl water type. • Higher CO 2 values are associated with areas with dense macrophyte masses. • The low CO 2 fluxes and the δ13C content suggests a biogenic origin of CO 2. • The total CO 2 emitted to the atmosphere was estimated in the 30.7 t d−1. [ABSTRACT FROM AUTHOR]

Recent work on the central Algarve (south Portugal) has revealed a complex coastal stratigraphic sequence on the Almargem lowland. This sector of the coast is characterized by strong coastline recession, previous studies suggesting that it has retreated over 200 meters over the last 3 centuries. A group of six trenches, making two N-S cross shore profiles, were excavated with 25 m distance between them in the lowland. The trenches were app. 5 m long, 2 m wide and 1.5 m deep. The aim was to identify signature of extreme wave events in the sedimentary infill, using a multidisciplinary analytical approach, including lithostratigraphic descriptions, x-rays imaging, digital photography grain-size, magnetic susceptibility and morphoscopic analysis of sediment. OSL samples were collected and are being processed to establish a chronological framework.Macroscopic analysis revealed that the topmost section of the Holocene sediments is marked by the presence of one macroscopically massive peculiar bioclastic medium sand layer, app. 10 cm below the present-day surface, which decreases in thickness inland and wedges out on the landward-most trenches. By opposition, the seaward-most trench presented multiple heavy mineral laminae at lower depths, likely resulting from successive washovers by storm events. In all trenches the basal section consists of greenish silt that increases in thickness inland.This setting (presence of multiple storm deposits and one likely tsunami event in a receding coastline) makes this a challenging study site. In terms of tsunami deposition, the site preserves to the extreme, most inland depositional imprint of a tsunami event. Despite its massive character, the multidisciplinary approach followed herein allowed to clearly identify and differentiate three inundation phases within the tsunami layer probably associated to the 1755 tsunami event. Inundation phases were established based in variations of magnetic minerals, bioclastic composition and grain-size variations. Results seem to match historical records of the AD 1755 that commonly refer to 3 major waves having affected the coast of the Algarve.The opportunity to establish trends of storm frequency or magnitude is also challenging, in particular within this coastal setting. Within a receding coast, the record is biased to the more recent storm events. Nevertheless, besides the peculiar tsunami layer, ongoing OSL work will allow to narrow the time-window of observation and will provide a unique and chronologically controlled record of storm events affecting this coastal sector, allowing future discussions on storm impacts during the last couple of millennia in the Portuguese south coast. AcknowledgementsWork supported by FCT- project UID/GEO/50019/2019 - Instituto Dom Luiz and by Project OnOff - PTDC/CTA- GEO/28941/2017 – financed by FCT. [ABSTRACT FROM AUTHOR]

The analysis of particle size, shape, size, and their spatial arrangement (i.e. fabric) in a sedimentary deposit plays a significant role in their interpretation in terms of transport mechanism, flow conditions, and sediment source. The present work focuses on the use of X-ray computed tomography (X-CT) to analyze tsunami deposits (core samples), as examples of complex sedimentary assemblages. A workflow of image processing is proposed to measure 3D parameters of particle size, shape, and orientation using two different software packages (Fiji-ImageJ, and IPSDK) and two different methods of image segmentation. The semi-automated method provides better segmentation quality of the tsunami deposit, as compared with the poor performance of fully-automated image segmentation. We also provide some clues to reduce the computational time. This workflow is applied to two examples of tsunami deposits on the coasts of the Algarve (1755 Lisbon tsunami, southern Portugal). Optimized processing of X-CT images gives access to detailed vertical variations of grain size, grain shape, and componentry (clayey matrix, silicates, and carbonates, including marine bioclasts), as well as information on flow directions inferred from the sedimentary fabric in 3D. High-resolution analysis of the bedforms and vertical grain size grading allows determining the flow conditions during the inundation phase of the tsunami. • X-ray tomography is a revolutionary tool for conducting structural and textural analysis of tsunami deposits. • Image processing is challenging because particle of different type, size, and shape, are mixed in a muddy matrix. • The optimized semi-automated segmentation method developed here applies to all types of complex geological samples. [ABSTRACT FROM AUTHOR]

The well-known 1755 CE Lisbon tsunami caused widespread destruction along the Iberian and northern Moroccan coastlines. Being affected by the powerful 1755 CE Lisbon tsunami, the southwestern Algarve shelf provides environments for detecting offshore tsunami imprints. Our multidisciplinary investigations (hydroacoustics, sedimentology, geochemistry, radiocarbon dating) of the Holocene sediments have revealed tsunami deposits linked to this tsunami and a ca. 3600 cal yr BP event. The latter event is until now unidentified in Portugal. Both event deposits contrast with the background shelf sedimentation by their coarser grain size, element composition, internal structure, and erosive base, making them discernible in the sub-bottom data and cores. Especially the ca. 3600 cal yr BP deposit is exceptionally well-preserved at one of the coring sites. The clear differentiation into several sections enables further insights into offshore tsunami transport and depositional processes. This study demonstrates that the record and preservation of tsunami deposits were possible on the Algarve shelf in specific locations sheltered from possible alterations. Our findings extend the tsunami catalogs of Portugal with a previously unknown tsunami dated to ca. 3600 cal yr BP. • Offshore tsunami deposits of the 1755 CE Lisbon and a previously unknown tsunami • The ca. 3600 cal yr BP tsunami extends the Portuguese tsunami catalog. • Characteristics of offshore tsunami deposits are strongly site-specific. • Tsunami backwash can transport sediments as grain or debris flows. [ABSTRACT FROM AUTHOR]

Coastal overwash is one of the most important hazards affecting the coastal zone and therefore has been the focus of several studies related to the establishment of setback lines. However, studies of extreme overwash (EO) events along urban beaches backed by a seawall or structure are scarce, and reveal the difficulties associated with its assessment, measurement and validation. The Nazaré coastal urban area (located on the west coast of Portugal) is developed adjacent to an embayed reflective beach and is subject to frequent and localized inundation due to EO events capable of overtopping the protection seawall. The current work develops a methodological approach to simulate total water levels (TWL) and seawall overtopping occurrences in time and space, with the ultimate goal of identifying the factors that govern the extreme overwash regime. The method uses multi-decadal time series of site-specific wave and tide, and high-resolution topo-bathymetric data, and recreates the TWL time series for a 36-year period. The model is successfully validated against video imagery and maximum swash line data that provide information on the reach of the water levels measured during modal and extreme TWL conditions along the studied beach. This study establishes the importance of the interaction of the modal and extreme hydrodynamic processes with the beach and backshore morphology. The Nazaré embayment is in equilibrium with the alongshore-varying modal wave conditions, resulting in higher vulnerability of the most sheltered sector during extreme events. [ABSTRACT FROM AUTHOR]

Tsunamis are amongst the most catastrophic natural hazards affecting worldwide coastal areas. Their impacts are recorded in the geological archives and its study provides crucial insights into the dynamics and intensity of these events. The accurate establishment of return periods can also be derived using sedimentological data. Onshore tsunami deposits have been extensively described over recent years through the application of a wide range of sedimentological proxies, including micropalaeontological analysis. In this work, the identification of palaeotsunami evidence, in both the onshore and offshore sedimentary record of south Portugal, was performed, relying mostly on the study of Foraminifera assemblages. Three onshore trenches and one offshore core were analyzed and imprints of the AD 1755 tsunami were observed based in the identification of allochthonous foraminiferal species, increase in the number of broken/abraded tests and its correlation with coarser mean grain size. This was possible after micropalaeontological environmental characterization of both low-energy onshore and offshore present-day sedimentation regimes. In the onshore record, three distinct sediment transport phases were differentiated within the tsunamigenic unit. The basal phase portraying the initial inundation represented by the dominance of marine Foraminifera species in a highly diverse assemblage. The higher energetic character of this phase was also reflected in the identification of the highest number of broken/abraded tests. The intermediate phase reflects an unspecified number of inundation and backwash pulses that were recognized based in the well-balanced presence of estuarine (brackish) and marine species, the sharp decrease in the diversity index and in the number of broken/abraded tests. The final phase recorded in the tsunamigenic unit registers the imprint of the last relevant backwash which was identified based on the dominance of estuarine (brackish) fauna. The overlying unit is dominated by tidal marsh species, demonstrating the start of the coastal system recovery phase. In the offshore record, it was possible to identify 2 distinct historical tsunami events (AD 1755 and AD 1969). This was achieved through the identification of significant increases in coastal Foraminifera species coupled with the presence of coarser layers. This interpretation was sustained by indirect age-estimation methods (radiocarbon and 210 Pb) that ascribed compatible ages to the historical tsunami events. The results obtained in this study stress the relevance and innovative character of this onshore and offshore multiproxy approach in the recognition and understanding of tsunami events. [ABSTRACT FROM AUTHOR]

The study of coastal boulder accumulations generated by extreme marine events, and of the energy and frequency involved in boulder transport, is of paramount importance in understanding the risk associated with extreme marine inundations. One of the frequently asked questions is whether the deposits are storm or tsunami-related, both events being characterized by different return periods. Boulder transport by storms was monitored on the west coast of Portugal. Significant changes were detected in boulders' position as a result of extreme inundation by the 2013/2014 winter storms. Results presented in this work indicate that the wave power associated with the "Christina" and "Nadja" storms occur once every three years. However, this interval is not supported by field observations of boulder displacement, which suggests that wave power over-predicts boulder movement in the study area. Furthermore, wave parameters from the "Christina" and "Nadja" storms were very similar, but have generated different impacts in the boulder accumulation described herein. Differences include the magnitude and direction of boulder movement, and are most likely associated with distinct tidal levels during the events. Higher tide levels generated an increase in the sea surface level and thus in the reach of waves, which generated displacement of larger boulders and consequent cross-shore contribution in boulder transport. Regardless, the combination of monitoring campaigns, wave data, and statistical modelling of extreme values indicate that boulder transport by storms is more frequent than initially expected. Based on recorded boulder movements, we present a conceptual model for boulder ridge formation and development and identify significant control of incoming flow by local geomorphological/topographical features. Storm events, not less frequent tsunamis, are identified as the events responsible for modulating this rocky coastline. These results question a direct attribution of coastal boulder deposits to tsunamis in coastal regions with a high risk of tsunami inundation. • Significant boulder movement by storms was detected in 2013–14. • Source-sink relationships show boulder paths during different storms. • Boulder ridges are dynamically stable features. • Local geomorphology partly controls water flow in rocky coastlines. • Tidal level maximizes the reach of waves and boulder transport by the swash. [ABSTRACT FROM AUTHOR]

Numerical models of tsunami inundation and sedimentation can provide useful insights to better understand the dynamics of paleotsunamis. We applied a coupled field data and numerical modeling approach for the AD 1755's tsunami at Salgados, a lowland on the south coast of Portugal where tsunami deposits from AD1755 mostly consist of massive or normally-graded, landward thinning layers of shell-rich sand with an erosive base within the mud-dominated lowlands. Landward of the foredune, the AD1755's deposit is roughly 10 cm thick and thins in the landward and alongshore directions. It is possible to ascribe the source of this deposit to the dune and/or beach based on mineralogical and grain-size comparisons with modern surface samples. From the combination of spatial distribution of the deposit thickness and GPR data, which shows an erosional surface at approximately 6m above MSL, we infer that the maximum tsunami water level at the coast was between 6 and 10m. Regional tsunami historical records, however, suggest higher heights, up to 12m above MSL at the coast.This work used geological signatures (both depositional and erosional) of the AD 1755's tsunami to validate tsunami hydrodynamic and sediment transport models from 7 different proposed fault ruptures. These epicentral areas have been previously proposed in literature and include Marquês de Pombal Fault, Gorringe Bank, Cadiz Accretionary Wedge, Horseshoe Fault and 3 different scenarios combining some of these structure with deeper (30-60 km) ones. A classification of more likely scenarios was established based on physical and validated numerical parameters (tsunami travel time, run-up, erosion depth, volume of sediment and post-event coastal profile). Model results suggest that the Cadiz Accretionary Wedge source largely exceeds the field and historical data. By contrast, Gorringe Bank, two combined scenarios display modeled results that are insufficient to reflect the real damage and imprints in the geological record. Moreover, the Horsheshoe Fault presents a partial correspondence between hydrodynamic and sediment transport models and its field data. Finally, the best correlation between field and modeled data is presented by the Marquês de Pombal Fault and by one combined scenario. These present extremely good compatibility in travel time, depth of erosion, sediment volume and also presents a good correlation with the observed run-up and the best matches between modeled and field coastal profile after the AD 1755.This modeling exercise results puts in evidence the shortcomings related with the discussion surrounding the AD 1755's source: no known structure seems to have enough dimension to cause an AD 1755-tsunami like event or the available models do not respond well to far distance sources. Either way, the methodological approach followed here stresses the importance of further modeling developments and the need to address this topic from a combined perspective.AcknowledgementsWork supported by FCT- project UID/GEO/50019/2019 - Instituto Dom Luiz and by Project OnOff - PTDC/CTA-GEO/28941/2017 – financed by FCT. [ABSTRACT FROM AUTHOR]

Sete Cidades Lake (São Miguel Island, Portugal) is subdivided into two interconnected branches: the Green Lake and Blue Lake. The lake has an area and maximum depth of 4.39 km 2 and 29.5 m (Blue Lake), respectively, with evidence of eutrophication, particularly in the northern area of the Green Lake. In this study, we conducted a sampling survey during January 2017 to measure CO 2 fluxes from the lake using a floating accumulation chamber. We also produced two hydrogeochemical profiles for each of the lake's branches. A total of 1760 CO 2 flux measurements were taken along the lake's surface. The lake water was relatively cold (14.0 °C on average) and weakly mineralised (average electrical conductivity of 116 μS cm -1 ) with a neutral pH (7.7 on average). The relative composition of major ions occurred in the following decreasing order: Na +  > Mg 2+  > Ca 2+  > K + for cations and Cl -  > HCO 3 -  > SO 4 2- for anions. The lake water was mainly the Na-Cl type due to sea salt input from seawater spraying. CO 2 fluxes ranged from 0.3 to 17.2 g m -2 d -1 and from 2.1 to 17.9 g m -2 d -1 for the Blue and Green Lakes, respectively. Highest CO 2 degassing occurred in areas dominated by macrophytes and algal blooms. The measured values suggest that the CO 2 was predominantly biogenically sourced, which was further supported by the δ 13 C isotopic data. The estimated total CO 2 emissions varied between 5.8 t d -1 (Green Lake; area = 0.81 km 2 ) and 24.9 t d -1 (Blue Lake; area = 3.58 km 2 ). This study further elucidates the lake's trophic and chemical pollution status and has major implications for lacustrine CO 2 emissions to the atmosphere. Our study also provides a reference for understanding potential future variations in volcanic activity., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)