Geological identification of historical tsunamis in the Gulf of Corinth, Central Greece

Geological identification of tsunami deposits is important for tsunami hazard studies, especially in areas where the historical data set is limited or absent. Evidence left by historical tsunamis in the coastal sedimentary record of the Gulf of Corinth was investigated by trenching and coring in Kirra on the north coast and Aliki on the south coast. The Gulf of Corinth has a documented tsunami history dating back to the 4th century BC. Comparison of the historical records and the results of stratigraphical, sedimentological and foraminiferal analyses show that extreme coastal flooding events are detectable in the coastal sequences. The geological record from Kirra shows four sand layers deposited by high-energy marine flooding events. The deposits identified show many similarities with tsunami deposits described elsewhere. The lower sand deposit (layer 4) was radiocarbon dated to 3020–2820 BC. Assuming an average sedimentation rate of 2.6 cm (100 yr)?1, the ages of the other three sand layers were estimated by extrapolation to the time windows 1200–1000 BC, AD 500–600 and AD 1400–1500. There are no historical tsunamis which correlate with layers 2 and 3. However, layer 1 may represent the major AD 1402 tsunami. Sand dykes penetrating from layer 1 into the overlying silts suggest soil liquefaction during an earthquake event, possibly the 1 August 1870 one. At Aliki, no clear stratigraphical evidence of tsunami flooding was found, but results from foraminiferal and dating analyses show that a sand layer was deposited about 180 years ago from a marine flooding event. This layer may be associated with the historical tsunami of 23 August 1817, which caused widespread destruction in the Aegion area. The work presented here supports the idea that geological methods can be used to extend tsunami history far beyond the historical record. Although the tsunami database obtained will be incomplete and biased towards larger events, it will still be useful for extreme event statistical approaches

Mechanical performance of novel cement-based composites prepared with nano-fibres, and hybrid nano- and micro- fibres

Use of hybrid fibre composites that exploit the synergistic effect of nano- and micro-additives can potentially lead to significant improvements in the toughness and mechanical properties of fibre reinforced cementitious materials. In this study, the mechanical properties of two types of novel cementitious composite (Carbon Nano-Fibre (CNF) Composites, and Hybrid-Fibre Composites) at various curing ages have been evaluated, along with their microstructure. Experimental results show a positive impact of nano-fibres on the mechanical performance of the cementitious composites: improvements of 40% in flexural strength, 45% in tensile strength, and 85% in toughness were observed when a low mass % (0.025%) of CNFs was combined with steel fibres. SEM observations revealed that reinforcement at the nanoscale prevented nano-crack development within the composites, with a greater amount of energy required to initiate and propagate cracks and cause material failure

Heavy metal contamination and mixing processes in sediments from the Humber Estuary, Eastern England

The geochemical properties of cores collected from mud flat and salt marsh environments in the Humber Estuary were investigated. A total of 10 cores were collected along a shore-normal transect on the northern bank of the estuary, near Skeffling. Major and trace element concentrations were determined for each core. The vertical distributions of210Pb and137Cs were also examined to provide a measure of the rate of sediment accumulation. Surface intertidal sediments show elevated concentrations of a range of trace and major elements, including Pb, Zn, Cu, Al, Mn and Fe. Concentrations were higher in the upper mud flats and salt marsh where sediment grain size is finer. Dating of salt marsh sediments indicated a local sediment accretion rate of 0·4 cm yr?1. The early-diagenetic remobilization of heavy metals has apparently been limited, and the salt marsh sediments provide a (time-integrated) record of historical pollutant inputs. Heavy metal fluxes have been calculated from the salt marsh sediments and are broadly comparable with other industrialized and semi-industrialized estuaries. Cu, Pb and Zn inputs to the Skeffling area peaked in the mid-20th century, while Ti, Al and Fe, which are discharged into the Humber from two Tioxide-processing facilities, are only slightly enriched in these sediments. On the mud flats, local mixing, resuspension and erosion has resulted in correlatable sedimentary horizons interspersed with mixed sediment layers. Consequently, the vertical distribution of heavy metals in these mud flats is relatively erratic, and the mud flat sediments are unsuitable for studying historical pollution trends

Heavy metal distribution and early-diagenesis in salt marsh sediments from the Medway Estuary, Kent, UK

Salt marsh cores are increasingly being used to study metal pollution chronologies. Salt marshes in macro-tidal estuaries, however, tend to retain a time-integrated or 'smoothed' signal rather than a record of discrete pollutant inputs, due to extensive sediment reworking. More generally, an accurate chronology of metal input to salt marsh sediments can be difficult to assess because of the potential early-diagenetic mobility of both the radionuclides used for dating and the contaminants of interest. A dated salt marsh core from the macro-tidal Medway Estuary, southeast England, was assessed using both total sediment metal data and partitioning data. These data indicate that both Mn and Fe have been significantly remobilised and that these diagenetic processes have slightly modified the vertical distributions of Cu, Pb and Zn. Zinc is the most diagenetically reactive followed by Cu and then Pb. However, general trends in pollutant loading can still be identified with maximum inputs occurring between ca. 1900 and 1950, decreasing towards the present day

High-resolution reconstruction of recent vegetation dynamics in a Mediterranean microtidal wetland: implications for site sensitivity and palaeoenvironmental research

The analysis of recent sediment sequences from coastal wetlands provides an opportunity to examine the response of these sites to environmental change and events, many of which are independently documented. This also permits an evaluation of rates of response to be made that can help in assessing changes identified in longer-term (Holocene) coastal sediment sequences. A short core from the Mulinello estuary, Augusta Bay, south east Sicily, was dated using 210Pb and 137Cs. Samples were analysed for pollen and spore content, and the results are presented here as both percentage and influx data. Temporal resolution of the pollen data is typically 5-15 years for the first 50 years of the record (circa 1895-1945 AD) and 2-5 years for the last 50 years (1945-1995 AD). Two phases of salt marsh expansion in the Bay occurred, up to the 1940s and from the 1960s to the mid 1980s. In the mid 1940s, the salt marsh underwent a significant decline, marked by a sudden fall in influx and percentage data for Chenopodiaceae. This correlates with an inwashing of catchment-derived pollen, particularly of resistant Lactucae grains, indicating more regular fluvial inundation. Climate records show the occurrence of significantly higher precipitation at this time. Since the construction of a port access road in the 1980s a second decline in the local halophyte community occurred. Pollen influx data enable a precise assessment of how quickly local colonisation of surfaces at the sampling site occurred. During both episodes of salt marsh colonisation, the transition from low-moderate to high Chenopodiaceae influx took less than 6 years. The data show that salt marsh communities can expand and decline very rapidly and that these variations can occur independently of significant changes in relative sea level