10:45 〜 12:15
[HDS06-P04] Storegga deposits at Howick Burn and their application to Low Frequency, High Magnitude risk assessment of Offshore Wind
キーワード：Storegga, Tsunami , Fieldwork
Tsunami events are commonly held to be only of relevance to tectonically active or adjacent coastal regions. Such a view has led to protection of commonly held at-risk regions, for instance coastal Japan. However, such preparations are based on 10’s to 100’s of years observations and as such do not often account for tsunami events occurring on longer timescales. Nor have protection considerations been given to coastlines which could be at risk from tsunami events generated not through tectonic action but through instabilities associated with sea level and composition changes brought about through global warming.
Further, given the increasing reliance on seaborne energy infrastructure (Offshore wind) the assessment of such LFHM events on unprepared coastlines (examining both the human cost and energy security risk) has become evermore vital, and using coastline appropriate data sets as a basis for such risk simulations provides an appropriate and accurate starting point.
Presented here are the early stages of fieldwork conducted on a fieldsite at Howick Burn in Northumbria, England. The site has been previously used Boomer et al. (2007) where he located and described a core deposit attributed to the Storegga mega-tsunami event. Our work consists of 5 cores reaching depths of between 4 and 6.5m, with a primary core (core 4/4A) reaching the maximum depth of 6.5m.
The full-length core 4/4A shows a continuous, generally low energy depositional environment to a depth of 6.2m, dominated by muds and clays likely deposited by the river during its final descent into the North Sea. The core has multiple sand-silt rich horizons which can be interpreted either as a significant increase in energy flow of the river itself or as coastal flooding from storms. Below 6.2m there appears to be a repeating set of conglomerates – lignite bed sequences, each presenting erosional bases, sharply fining upper surfaces and a concentration of organic material at the top of each sequence (cf. even dispersal in the other sections of the core).
Nothing similar has been located further up the core sequences. This shows such event to be unique within the time period covered by the cores. Samples from each of the three organic rich upper surfaces have been dispatched for radiocarbon dating. The lack of repeat beds (or similar), the composition of the beds and setting (293m from the modern coastline) would suggest this to be a tsunami deposit. Previous work from Scotland and northern England has shown the Storegga event to be on the only appropriate event to leave deposits of this magnitude. The three repeat sequences align with computer modelling of the Storegga tsunami from other locations, but are much larger than expected when compared to other sites. This is an appropriate extreme event from which to model tsunami impacts upon the UK eastern coastline.
Further, given the increasing reliance on seaborne energy infrastructure (Offshore wind) the assessment of such LFHM events on unprepared coastlines (examining both the human cost and energy security risk) has become evermore vital, and using coastline appropriate data sets as a basis for such risk simulations provides an appropriate and accurate starting point.
Presented here are the early stages of fieldwork conducted on a fieldsite at Howick Burn in Northumbria, England. The site has been previously used Boomer et al. (2007) where he located and described a core deposit attributed to the Storegga mega-tsunami event. Our work consists of 5 cores reaching depths of between 4 and 6.5m, with a primary core (core 4/4A) reaching the maximum depth of 6.5m.
The full-length core 4/4A shows a continuous, generally low energy depositional environment to a depth of 6.2m, dominated by muds and clays likely deposited by the river during its final descent into the North Sea. The core has multiple sand-silt rich horizons which can be interpreted either as a significant increase in energy flow of the river itself or as coastal flooding from storms. Below 6.2m there appears to be a repeating set of conglomerates – lignite bed sequences, each presenting erosional bases, sharply fining upper surfaces and a concentration of organic material at the top of each sequence (cf. even dispersal in the other sections of the core).
Nothing similar has been located further up the core sequences. This shows such event to be unique within the time period covered by the cores. Samples from each of the three organic rich upper surfaces have been dispatched for radiocarbon dating. The lack of repeat beds (or similar), the composition of the beds and setting (293m from the modern coastline) would suggest this to be a tsunami deposit. Previous work from Scotland and northern England has shown the Storegga event to be on the only appropriate event to leave deposits of this magnitude. The three repeat sequences align with computer modelling of the Storegga tsunami from other locations, but are much larger than expected when compared to other sites. This is an appropriate extreme event from which to model tsunami impacts upon the UK eastern coastline.