Extreme sea level events in the coastal waters of western Estonia

Extraordinarily low and high sea level events are analysed on the basis of historical data and their mechanisms of occurrence are studied with the 1 km grid size 2D hydrodynamic model in the two almost tideless semi-enclosed sub-basins of the Baltic Sea, the Gulf of Riga and the Väinameri. The sea level is modelled with realistic meteorological forcing and comparison data from 1999 and 2001. Resonance properties of the sub-basins are studied and their possible role in the formation of extraordinary sea level events is discussed. While the extremely low levels (−1.23 m below the mean sea level) in the Estonian coastal waters do not generally originate locally, the high levels (up to 2.53 m above the mean as measured in the Pärnu Bay) are short-term and local. They occur in combination with several forcing and morphometrical factors and are localised in the shallow and narrow bays exposed to the direction of the strongest possible storm winds, SW and W. Model simulations show that extremely high and low sea levels in some small bays of western Estonia can exceed the corresponding values in the Pärnu Bay.     

Decadal-scale variation in dune erosion and accretion rates: An investigation of the significance of changing storm tide frequency and magnitude on the Sefton coast, UK

Monitoring of frontal dune erosion and accretion on the Sefton coast in northwest England over the past 50 years has revealed significant spatial and temporal variations. Previous work has shown that the spatial variations primarily reflect longshore differences in beach and nearshore morphology, energy regime and sediment budget, but the causes of temporal variations have not previously been studied in detail. This paper presents the results of work carried out to test the hypothesis that a major cause of temporal variation is changes in the frequency and magnitude of storms, surges and resulting high tides. Dune toe erosion/accretion records dating from 1958 have been compared with tide gauge records at Liverpool and Heysham. Relatively high dune erosion rates at Formby Point 1958–1968 were associated with a relatively large number of storm tides. Slower erosion at Formby, and relatively rapid accretion in areas to the north and south, occurred during the 1970's and 1980's when there were relatively few major storm tides. After 1990 rates of dune erosion at Formby increased again, and dunes to the north and south experienced slower accretion. During this period high storm tides have been more frequent, and the annual number of hours with water levels above the critical level for dune erosion has increased significantly. An increase in the rate of mean sea-level rise at both Liverpool and Heysham is evident since 1990, but we conclude that this factor is of less importance than the occurrence of extreme high tides and wave action associated with storms. The incidence of extreme high tides shows an identifiable relationship with the lunar nodal tidal cycle, but the evidence indicates that meteorological forcing has also had a significant effect. Storms and surges in the eastern Irish Sea are associated with Atlantic depressions whose direction and rate of movement have a strong influence on wind speeds, wave energy and the height of surge tides. However, preliminary analysis has indicated only a modest relationship between dune erosion/accretion rates and the North Atlantic Oscillation index.     

The ∼ 1245 yr BP Asososca maar: New advances on recent volcanic stratigraphy of Managua (Nicaragua) and hazard implications

Asososca maar is located at the western outskirts of Managua, Nicaragua, in the central part of the active, N–S trending and right-lateral Nejapa–Miraflores fault that marks an offset of the Middle America Volcanic Arc. It constitutes one of the ∼ 21 vents aligned along the fault, between the Chiltepe Volcanic Complex to the North and Ticomo vents to the South.     

DYNAMIC CHARACTERISTICS OF SEA CURRENTS AND SEDIMENT DISPERSION IN THE YELLOW RIVER ESTUARY

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渤海湾西岸风暴潮:叠加地质因素的新探讨

通过对渤海湾西岸1895年以来11次风暴潮高水位的厘定,证实并确定了50年、100年、200年直至10000年一遇的风暴潮高水位值。定量评估了风增水与波浪对风暴潮高水位的贡献。进一步从地学角度讨论了21世纪10年间隔的海面上升量、地面下沉与围海造陆共同作用、海面上升引发的净增水效应及河口增水效应。根据上述各类参数,预测了至2050年的10年间隔、50~10000年不同重现期的极端水位,并讨论了地面下沉对风暴潮测量准确性的影响。认为当前的防潮堤(海垱)高度可抵御50~100年一遇的风暴潮的侵袭,但据所讨论的综合因素的影响,建议2020年防潮堤的高度应达到+4.8m,2030年达到+5.1m(85高程)。     

Evidence of early Flandrian tidal surges in Lower Strathearn,Scotland

Detailed stratigraphic, palaeobotanical (diatom and pollen) and radiometric evidence from a sequence of buried estuarine deposits, buried peat and overlying estuarine ‘carse’ deposits at Wester Rhynd, in Lower Strathearn, suggests the occurrence of two brief marine incursions between the abandonment by the sea of a buried estuarine flat, probably the Low Buried Beach, at about 8765 ± 75 BP, and c. 8500 BP. The first incursion, shortly after 8565 ± 85 BP, caused bottom-living marine diatoms to be thrown without clastic material onto the rapidly accumulating terrestrial peat. The second, bracketed by dates of 8485 ± 80 and 8510 ± 85 BP, deposited an extremely thin (1 mm) layer of fine sand that interrupts an otherwise unbroken buried peat succession covering the period 8765 ± 75 to 7710 ± 70 BP. The marine diatom, lithostratigraphic and ¹⁴C evidence together are consistent with a storm, storm-surge or tsunami origin for these events, which are recognised principally from the diatom evidence, having left no mark in the pollen record.     

Physical Modelling and Human Survival in Pyroclastic Flows

Volcanic eruptions increasingly present catastrophic natural risks with hundreds of millions of people now living in areas of active volcanism and major conurbations around active eruptive centres. Interdisciplinary studies in disaster reduction have an important role in volcanic emergency management through advancing our understanding of the physical impacts of eruptive phenomena and the causes of death and injury in explosive eruptions. Numerical modelling of pyroclastic flows, amongst the most destructive of eruptive phenomena, provides new opportunities to improve the evaluation of the potential destructiveness of volcanic events and their human impacts in densely populated areas. In this work, the results of numerical modelling of pyroclastic flow propagation at Vesuvius have been analysed in terms of the physical parameters (temperature, ash in air concentration, and dynamic pressure) that are most critical for human survival. Our numerical simulations of eruptions of Vesuvius indicate that a large area exists where total destruction may not be inevitable in small to medium scale events, a finding that has prompted us to explore further the implications for human survival as part of an interdisciplinary approach to disaster reduction. The lessons of modelling at Vesuvius should be integrated into civil protection plans for other urban centres threatened by volcanoes.     

非均匀风场作用下太湖风成流风涌水的数值模拟及验证

本文采用浅水波方程数值模式，考察太湖局地风场的影响，模拟了太湖风成流，风涌水的变化情况，模拟结果与实测值符合较好，另外，将实测风场资料代入模式计算，结果表明，模拟对风涌水有较好的预报能力，流向流速的计算值与实测值在态势上较为一致。