Reconnaissance of historic (post-AD 1000) high-energy deposits along the Atlantic coasts of southwest Britain, Ireland and Brittany, France

Abstract

Sand and gravel deposits from the Atlantic coasts of southwest Britain, Brittany and western Ireland are identified as potential indicators of historic (post-AD 1000) ocean-sourced high-energy events, such as storm surges and tsunami. This is an important historic period as it includes the climatic perturbations of the Medieval Warm Period and the Little Ice Age, and also seismogenic events, such as the Lisbon tsunami of 1755. Ten new sites are identified from various coastal settings and dated using eight new radiocarbon dates alongside previously published data. Generally, sites do not appear to record multiple high-energy events, suggesting that either only the most extreme and/or recent events are registered. A number of radiocarbon dates from marine shell yield modern ages when corrected for the marine reservoir effect. Rather than necessarily indicating recent deposition, this may reflect a poor understanding of terrestrial carbon input into coastal and estuarine waters, and the practice of applying broad regional ΔR values at the local scale. Two groupings of radiocarbon dates are recognised; a Medieval Group and a Post-Medieval Group, which might reflect events within known climatic perturbations and/or tsunami occurrences. These events may include the Lucia Flood of 1287, the All Saint's Day Flood of 1570, the 1607 Flood, the Great Storm of 1703, and the Lisbon tsunami. Some older (pre-AD 1000) deposits indicate the potential to construct frequency/ magnitude records of high-energy events throughout the Holocene. Data presented here support the view that salt marshes within the Bristol Channel and Severn Estuary were completely eroded away early in the 17th century. AbstractSand and gravel deposits from the Atlantic coasts of southwest Britain, Brittany and western Ireland are identified as potential indicators of historic (post-AD 1000) ocean-sourced high-energy events, such as storm surges and tsunami. This is an important historic period as it includes the climatic perturbations of the Medieval Warm Period and the Little Ice Age, and also seismogenic events, such as the Lisbon tsunami of 1755. Ten new sites are identified from various coastal settings and dated using eight new radiocarbon dates alongside previously published data. Generally, sites do not appear to record multiple high-energy events, suggesting that either only the most extreme and/or recent events are registered. A number of radiocarbon dates from marine shell yield modern ages when corrected for the marine reservoir effect. Rather than necessarily indicating recent deposition, this may reflect a poor understanding of terrestrial carbon input into coastal and estuarine waters, and the practice of applying broad regional ǻR values at the local scale. Two groupings of radiocarbon dates are recognised; a Medieval Group and a Post-Medieval Group, which might reflect events within known climatic perturbations and/or tsunami occurrences. These events may include the Lucia Flood of 1287, the All Saint's Day Flood of 1570, the 1607...

Historic tsunami in Britain since AD 1000: a review

“…6 m OD (Ordnance Datum Newlyn). We undertook field visits to these named sites in October 2007. Sediment coring at Big Pool confirmed the presence of a substantial sand layer as recorded by Foster et al (1991Foster et al ( , 1993, although based on the error bars of their dating the 1755 event is not the only candidate for its deposition (Haslett and Bryant, 2007a). Stonehouse Creek was found to have been infilled during the 19 century with several meters of rubble for the development of recreational and sports fields (e.g.…”

Mental models of sea-level change: A mixed methods analysis on the Severn Estuary, UK

“…The global trend is exacerbated here by isostatic subsidence in response to the last glacial, which is causing the shoreline to subside at a rate of around 0.76 mm/year (Shennan and Horton, 2002). With regards to shorter term SLC, the Estuary is particularly vulnerable to storms because of its low-lying topography, funnelshaped coastal configuration, orientation with respect to prevailing winds, and tidal setting, which together enhance surge heights from storms tracking east and north-eastward (Horsburgh and Horritt, 2006;Haslett and Bryant, 2007). Historically, these factors have contributed to a number of severe coastal flooding events, including a catastrophic event in 1607 that flooded more than 500 km 2 and killed more than 2000 people .…”

Evolution of a Coastal Beach/Barrier/Marsh System in Response to Sea Level Rise, Storm Events and Human Impacts: A Case Study of Trunvel Marsh, Western Brittany

“…The first concerns the possible impact of high magnitude events such as tsunamis. Haslett and Bryant (2007) reveal clear evidence of the 1755 Lisbon Tsunami at nearby Baie des Trépassés. At Ushant island, Regnauld et al (2010) demonstrate, on the other hand, that it is very difficult to resolve the relative importance of tsunamis as a factor in coastal morphodynamics because subsequent storm events may rework the tsunami deposits.…”

“…Trunvel marsh is located in a part of Brittany known as the Pays Bigouden and was chosen because morpho-dynamic evidence already exists to the north, at Baie des Trépassés, Pointe du Raz (Haslett and Bryant 2007) and to the south, at Penmarc'h (Van Vliet et al 2014). Additional research has also been conducted on another marsh nearby, Nérizelec (Regnauld 1999).…”