Browsing by Author "Judd, K"

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    Estimating the inundation limits of small historical tsunamis
    (Geological Society of Australia, 2014-07-10) Judd, K; Chagué-Goff, C; Goff, JR; Zawadzki, A; Gadd, PS; Fierro, D
    There has been considerable progress in tsunami research in recent years, yet most work has been focussed on identifying and understanding the evidence of large events. This talk discusses the evidence for small historical tsunamis in Lyttelton Harbour, New Zealand. The study area has been inundated by numerous relatively small historical tsunamis without depositing any notable sedimentary evidence. However, excavations of shallow soil profiles revealed discontinuous layers of small grey mud clasts, most likely transported from the nearby harbour, at various depths across the study area. The origin of these mud clast layers was investigated using a multi-proxy approach comprising sedimentological, geochemical and diatom analyses complemented by radiometric dating and 179 historical data. Subtle variations consistent with inclusions of marine mud, such as a decrease in organic content and magnetic susceptibility and increases in geochemical markers (e.g. potassium, calcium) were found in the sedimentary profile. Variations in diatom assemblages suggesting marine influence were also recorded at similar depths, aligning with layers of mud clasts. Using 137Cs dating and historical data, these deposits were attributed to the 1960 Chile and possibly 1964 Alaska tsunamis. Sedimentary evidence for the 2010 Chile tsunami was not found at the study site, but geochemical analysis of surface samples revealed marked changes in calcium, chlorine, strontium and titanium concentrations, indicative of a change from terrestrial to marine influence. This was used to identify the landward extent of inundation. Ultimately, this study shows that a broad multi-proxy analysis can distinguish even the subtle signatures of an inconspicuous deposit laid down by a small tsunami.
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    Identifying tsunami deposits in the absence of sand
    (American Geophysical Union, 2015-12-16) Chagué-Goff, C; Judd, K; Goff, JR; Gadd, PS; Fierro, D; Zawadzki, A
    Tsunamis originating in South America are known to have affected Lyttelton Harbour, New Zealand, in the recent past. However, while there was clear evidence of inundation, in particular in 1960 and 2010, there was no report of any sand left behind. Our study aimed to search for evidence of these small historical tsunamis, in the absence of any visible sand layer. Shallow trenches revealed discontinuous layers of small grey mud clasts at various depths across the study area, most likely transported from the nearby harbour. The origin of these mud clast layers was investigated using sedimentological, geochemical and diatom analyses complemented by dating from 137Cs activity profiles and historical data. Subtle variations consistent with inclusions of marine mud such as a decrease in organic content and magnetic susceptibility and increases in geochemical markers (e.g. Ca, K, K/Rb, Si/Rb and Sr/Rb) were found in the sediment profile. Variations in diatom assemblages suggesting a marine influence were also recorded at similar depths, aligning with layers of mud clasts. Based on 137Cs activity profiles and historical data, these deposits were attributed to the 1960 Chile and 1964 Alaska tsunamis, and we also found evidence for an older deposit, possibly associated with the 1868 Arica tsunami. Sedimentary evidence for the 2010 Chile tsunami was not found at the study site, but our study revealed spatial variations in Ca, Cl and Sr concentrations that were inversely related to Ti concentrations. This was used to identify the landward extent of inundation by the 2010 event. We show that a broad multi-proxy analysis can distinguish even the subtle signatures of an inconspicuous deposit laid down by a small tsunami. © 2014 American Geophysical Union.
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    Multi-proxy evidence for small historical tsunamis leaving little or no sedimentary record
    (Elsevier, 2017-01-01) Judd, K; Chagué-Goff, C; Goff, JR; Gadd, PS; Zawadzki, A; Fierro, D
    There has been considerable progress in tsunami research in recent years, yet most work has been focussed on identifying and understanding the evidence of large events. This study aimed to identify the evidence of small historical tsunamis in Lyttelton Harbour, New Zealand. The study area has been inundated by multiple relatively small historical tsunamis that left atypical sedimentary evidence (no sand) or no sediment. Shallow trenches revealed discontinuous layers of small grey mud clasts at various depths across the study area, most likely transported from the nearby tidal flats. The origin of these mud clast layers was investigated using a multi-proxy approach comprising sedimentological, geochemical and diatom analyses complemented by dating from 137Cs activity profiles and historical data. Subtle variations consistent with inclusions of marine mud such as a decrease in organic content and magnetic susceptibility and increases in geochemical markers (e.g. Ca/kcps, K/kcps, K/Rb, Si/Rb and Sr/Rb) were found in the sediment profile. Variations in diatom assemblages suggesting a marine influence were also recorded at similar depths, aligning with layers of mud clasts. Using 137Cs activity profiles and historical data, these deposits were attributed to the 1960 Chile Valdivia and 1964 Alaska tsunamis, as well as a possible earlier event. Sedimentary evidence for the 2010 Chile Maule tsunami was not found at the study site, but geochemical analysis of surface samples revealed marked changes in Ca, Cl, Sr and Ti concentrations, indicative of a change from a terrestrial to marine influence. This was used to identify the landward extent of inundation by the 2010 event. Ultimately, this study shows that a broad multi-proxy analysis can distinguish even the subtle signatures of an inconspicuous deposit laid down by a small tsunami. © 2017, Elsevier B.V.