Pedro J.M. Costa

A tsunami record in the sedimentary archive of the central Algarve coast, Portugal: Characterizing sediment, reconstructing sources and inundation paths

This study describes sedimentation associated with the tsunami generated by the Lisbon earthquake of ad 1755. It is argued here that the tsunami deposited a sand sheet across the Lagoa dos Salgados (central Algarve, Portugal), that is intercalated with late-Holocene estuarine/lagoonal sediments. A wide range of proxies (sedimentological, exoscopic and palaeontological) are used to establish the provenance of the sandy material as well as to constrain the age of the deposit. Stratigraphic criteria are used to distinguish the uniqueness of the event layer. Exoscopic and textural analysis suggest that the source of the event deposit is mainly the dune, beach and underlying layer. Micropalaentological analysis (Foraminifera) indicates a conspicuous increase in diversity and dominance of marine species within the event sediment sheet. The spatial characteristics of the tsunami layer suggests that the barrier prevented widespread overtopping by the incoming tsunami allowing inference of c. 10 m as maximum height at the coast; they also indicate the inlet as the preferential route for both water and sediment transported inland. Dating results (14C, 210Pb and 137Cs) allow extrapolation of an age of deposition compatible with the ad 1755 Lisbon earthquake and tsunami, the most devastating event that affected this coastal area in historical times. Correlations with similar deposits detected in nearby lowlands strengthen the argument that the tsunami sediment layer represents a marker horizon in the coastal stratigraphy along the Portuguese Algarve coast. The stratigraphic uniqueness of this event might have implications in the establishment of millennial scale recurrence intervals for this type of high-energy marine inundation.

Weathering rinds as mirror images of palaeosols: examples from the Western Alps with correlation to Antarctica and Mars

Weathering rinds have been used for decades as relative age indicators to differentiate glacial deposits in long Quaternary sequences, but only recently has it been shown that rinds contain long and extensive palaeoenvironmental records that often extend far beyond mere repositories of chemical weathering on both Earth and Mars. When compared with associated palaeosols in deposits of the same age, rinds often carry a zonal weathering record that can be correlated with palaeosol horizon characteristics, with respect to both abiotic and biotic parameters. As demonstrated with examples from the French and Italian Alps, rinds in coarse clastic sediment contain weathering zones that correlate closely with horizon development in associated palaeosols of presumed Late Glacial age. In addition to weathering histories in both rinds and palaeosols, considerable evidence exists to indicate that the black mat impact (12.8 ka) reached the European Alps, a connection with the Younger Dryas readvance supported by both mineral and chemical composition. Preliminary metagenomic microbial analysis using density gradient gel electrophoresis suggests that the eubacterial microbial population found in at least one Ah palaeosol horizon associated with a rind impact site is different from that in other Late Glacial and Younger Dryas surface palaeosol horizons.

Onshore tsunami sediment transport mechanisms inferred from heavy mineral assemblages

The aim of this study is to discuss and to extend the characterization of (palaeo)tsunami deposits, and their source materials, based upon the detailed study of their heavy mineral assemblages. Results obtained from three distinct locations (Portugal, Scotland and Indonesia), different coastal contexts and chronologies (the tsunami events studied took place at 1500 cal. yr BP, AD 1755 and 2004) are summarized and discussed in order to contribute to the sedimentological study of onshore (palaeo)tsunami deposits. Results indicate that heavy mineral assemblages primarily reflect local specific conditions. For example, in the Portuguese sites, ca. 90% of the heavy mineral population consists of tourmaline+andalusite+staurolite, whereas in the Scottish samples garnet+amphiboles can be dominant in 90% of the assemblage, where at the Indonesian study site amphiboles+andalusite were the most frequent minerals. The application of Principal Component Analysis for each site reveals that the first two components explain at least 55% of the total variance. In the three studied areas, hydraulic sorting by density was observed and a higher presence of the denser heavy minerals of the assemblages was detected. However, it is important to stress that the sediment source plays a key role in the establishment of the heavy mineral assemblages of the (palaeo)tsunami deposits. In this study, relationships between the likely source sediments and the (palaeo)tsunami deposits were described and whenever possible sediment sources were clearly identified. Furthermore, it was also possible to detect the backwash signal using the analysis of the heavy minerals (e.g. higher frequency of denser minerals or variation in the presence of rounded or euhedral zircon). The work presented here, in contributing to the enhancement of sedimentological criteria presently available to recognize and differentiate extreme marine inundation deposits, also highlights new areas for future research.

Evaluation Criteria for Cloud Services

Cloud Computing is revolutionizing the Information Technology (IT) industry by enabling organizations to have flexible costs by buying a service instead of owning their assets. Nevertheless, decision makers (DM) in IT organizations have difficulties in evaluating Cloud services because there are no guidelines or any structured form to decide what Cloud services they should use. In this paper, we propose a model based on a set of criteria to evaluate Cloud services that consists in six groups of thirty measurement criteria. In order to evaluate our proposal we have made demonstrations with Google Apps and Microsoft Office 365. We have also made twelve interviews with clients, suppliers, and experts of Cloud services. The results showed that the model was globally accepted and can help the decision-making about Cloud services.

Stratigraphy of the Gorges moraine system, Mount Kenya: palaeosol and palaeoclimate record

Moraines marking an Early Pleistocene glaciation on Mt. Kenya are known from several valleys along the eastern and southeastern flanks of the mountain. The most prominent group of end moraines delimiting the lowermost extent of the Early Pleistocene Gorges Glaciation (2900 m above sea level) overlie either older till or weathered bedrock, the latter composed of thin pedostratigraphic remnants covered with locally derived aeolian sediments truncated by the ingress of ice. The loess, tills and interbedded palaeosols of the Gorges Glaciation crop out adjacent to the Nithi River, which drains the Gorges Valley, and abut the upper timberline of montane forest. The lowermost palaeosols at these sites were formed either in till predating the Gorges Glaciation or in weathered bedrock of trachytic textured lavas, similar to the lithology forming the base of the Mt. Kenya volcanic series of Miocene or Pliocene age. Palaeomagnetism and weathering characteristics are here used to refine the age of sediments assigned to the Gorges Glaciation. These normally magnetized deposits carry a persistent reversed overprint, suggesting that they were deposited during one of the normal subchrons within the Matuyama Reversed Chron. They are underlain either by a reversely magnetized till, or by weathered bedrock and lower palaeosol, the latter exhibiting normal magnetization (Gauss?) with reversed overprint (Matuyama?). The sediments of the Gorges Glaciation are overlain at all three sites by normally magnetized loesses and palaeosols, presumably of Brunhes age but carrying a high percentage of well-weathered recycled grains. The normal magnetization and reversed overprint recorded in sediments of the Gorges Glaciation most probably span a considerable portion of the Olduvai subchron (1.78–1.950 Ma), which persisted for sufficient time to accommodate an extensive montane glaciation followed by a prolonged period of weathering and soil formation. The importance of these sediments in global palaeoclimate reconstruction and insolation changes is discussed. The stratigraphic evidence contradicts the cosmogenic exposure ages presented by previous workers attempting to obtain true ages of deposits using exhumed coarse clastic sediment without analysis of complex pedostratigraphic complexes. Supplementary materials: Tables 1S–5S are available at www.geolsoc.org.uk/SUP18592.

The application of microtextural and heavy mineral analysis to discriminate between storm and tsunami deposits

Abstract Recent work has applied microtextural and heavy mineral analyses to sandy storm and tsunami deposits from Portugal, Scotland, Indonesia and the USA. We looked at the interpretation of microtextural imagery (scanning electron microscopy) of quartz grains and heavy mineral compositions. We consider inundation events of different chronologies and sources (the AD 1755 Lisbon and 2004 Indian Ocean tsunamis, the Great Storm of 11 January 2005 in Scotland, and Hurricane Sandy in 2012) that affected contrasting coastal and hinterland settings with different regional oceanographic conditions. Storm and tsunami deposits were examined along with potential source sediments (alluvial, beach, dune and nearshore sediments) to determine provenance. Results suggest that tsunami deposits typically exhibit a significant spatial variation in grain sizes, microtextures and heavy minerals. Storm deposits show less variability, especially in vertical profiles. Tsunami and storm quartz grains had more percussion marks and fresh surfaces compared to potential source material. Moreover, in the studied cases, tsunami samples had fewer fresh surfaces than storm deposits. Heavy mineral assemblages are typically site-specific. The concentration of heavy minerals decreases upwards in tsunamigenic units, whereas storm sediments show cyclic concentrations of heavy minerals, reflected in the laminations observed macroscopically in the deposits.

Recent Developments in the Analysis of the Black Mat Layer and Cosmic Impact at 12.8 ka

Abstract Recent analyses of sediment samples from “black mat” sites in outh merica and urope support previous interpretations of an impact event that reversed the Late Glacial demise of ice during the Bølling Allerød warming, resulting in a resurgence of ice termed the Younger Dryas (YD) cooling episode. The breakup or impact of a cosmic vehicle at the boundary coincides with the onset of a 1‐kyr long interval of glacial resurgence, one of the most studied events of the Late Pleistocene. New analytical databases reveal a corpus of data indicating that the cosmic impact was a real event, most possibly a cosmic airburst from Earths encounter with the Taurid Complex comet or unknown asteroid, an event that led to cosmic fragments exploding interhemispherically over widely dispersed areas, including the northern ndes of enezuela and the Alps on the Italian/French frontier. While the databases in the two areas differ somewhat, the overall interpretation is that microtextural evidence in weathering rinds and in sands of associated paleosols and glaciofluvial deposits carry undeniable attributes of melted glassy carbon and e spherules, planar deformation features, shock‐melted and contorted quartz, occasional transition and platinum metals, and brecciated and impacted minerals of diverse lithologies. In concert with other black mat localities in the Western , the etherlands, coastal rance, yria, entral sia, eru, rgentina and exico, it appears that a widespread cosmic impact by an asteroid or comet is responsible for deposition of the black mat at the onset of the glacial event. Whether or not the impact caused a 1‐kyr interval of glacial climate depends upon whether or not the Earth had multiple centuries‐long episodic encounters with the Taurid Complex or asteroid remnants; impact‐related changes in microclimates sustained climatic forcing sufficient to maintain positive mass balances in the reformed ice; and/or inertia in the Atlantic thermohaline circulation system persisted for 1-kyr.

Imprints of the AD 1755 Tsunami in Algarve (South Portugal) Lowlands and Post-impact Recovery

The AD 1755 tsunami was the most devastating tsunami that affected Atlantic Europe in historical times. In this work we summarize its sedimentological signatures in lowlands (Martinhal, Barranco, Furnas, Boca do Rio, Salgados-Alcantarilha) of the Algarve coast that contrast in geologic and geomorphological settings and sediment abundance. We found remarkable similarities between tsunami deposits and the materials available for transport at the coast prior to the tsunami. A number of 2–4 m high and 30–70 m wide scarps (i.e. steep slopes in dunes resulting from erosion) are the only erosive geomorphic signature preserved in the study areas (Boca do Rio and Salgados-Alcantarilha). Recovery of the coastal system to pre-event conditions, inferred from the documentary records, is evaluated and analyzed in terms of sediment availability and supply, climate, hydrodynamic regime and geomorphic setting. Sediment-starved pocket beaches bypassed landward most of the sediment previously accumulated in the coastal system, failing to recover the pre-event morphology. Moreover, and solely in Martinhal, the abrupt morphological changes translated in increased and lasting permeability of the barrier and adjacent wetland to storms. The Alcantarilha-Salgados beach-dune system, in moderate sand supply, was extensively scarped but not fully overtopped. Here, recovery was partly achieved by destabilization of the remnant dune, formation and (limited) advance of parabolic dunes following the 1755 event. A schematic conceptual model is presented summarizing: the pre-event conditions; the depositional and geomorphological features directly related with the tsunami impact; and the post-event geomorphological adaptation. In the studied cases post-event recovery seems to be reduced mainly due to a conjugation of pre-event geomorphological setting and low sediment input.

Geological Recognition of Onshore Tsunami Deposits

The study and understanding of coastal hazards is a fundamental aspect for most modern societies. The consequences of extreme events such as tsunamis are being regarded as major threats for coastal regions. The sedimentological record provides a database useful to characterize and evaluate recurrence of tsunamis, which contributes to assessing the vulnerability of any coastal area to this natural hazard. Thus, the enhancement of our ability to recognize (palaeo) tsunami specific signatures in coastal sediments, through the application of diverse sedimentological techniques, is of unquestionable interest.

Evaluating Cloud Services Using a Multiple Criteria Decision Analysis Approach

The potential of Cloud services for cost reduction and other benefits has been capturing the attention of organizations. However, a difficult decision arises when an IT manager has to select a Cloud services provider because there are no established guidelines to help make that decision. In order to address this problem, we propose a multi-criteria model to evaluate Cloud services using the MACBETH method. The proposed method was demonstrated in a City Council in Portugal to evaluate and compare two Cloud services: Google Apps and Microsoft Office 365.