Browsing by Author "Chagué, C"

Now showing 1 - 5 of 5
  • No Thumbnail Available
    Item
    A 7300 year record of environmental changes in a coastal wetland (Moawhitu), New Zealand, and evidence for catastrophic overwash (tsunami?)
    (Elsevier, 2020-09) Chagué, C; Cope, J; Kilroy, C; Jacobsen, GE; Zawadzki, A; Wong, HKY
    Three sedimentary sequences from a coastal wetland behind a sand barrier, on the west coast of d'Urville Island, New Zealand, were examined using a multi-proxy approach, including sedimentological, geochemical and microfossil (diatom) analyses, with the chronology established using radiocarbon and 210Pb dating. Data show that a brackish lagoon started developing 7300 year ago after formation of the sand barrier in Moawhitu. This was followed by periods of alternating wetland encroachment and open water, displaying spatial variations, until a peatland was established about 1300 cal. yr BP. The wetland was then partially drained in the early 1900s, leading to compaction of the peat near the surface. A coarse layer containing gravel, sand and shells, with a sharp lower contact, in the northern area of the wetland, is attributed to an overwash about 2500–3000 yr BP, most probably a tsunami generated by the rupture of a local or regional fault. The high-resolution continuous record obtained with XRF core scanning revealed a geochemical signature (Ca and S) for the overwash 600 m inland in the middle area of the wetland, while it was absent from the southern site 1.1 km from the shore. This suggests that, except at the northern end of Moawhitu, the sand dune acted as an effective barrier preventing any sediment from overtopping 2500–3000 yr BP, with only a geochemical evidence marking the extent of seawater inundation. No sedimentological or geochemical evidence could be found in the wetland for the 15th century tsunami that had destroyed almost an entire community in Moawhitu, as recounted in Māori oral tradition (pūrākau), although pebbles at the surface of the dune are likely to be linked to this event. Thus, the sand dune appears to have again acted as an effective barrier for the overwash in the 15th century. However, our study suggests that the area might have been impacted by more than one tsunami in the last 3000 years. It also shows that a high-resolution continuous XRF record can provide the evidence for short-term changes (catastrophic or not) that did not leave any clear sedimentological signature, thus providing a better insight of environmental changes in any depositional environment. © 2020 Elsevier B.V
  • No Thumbnail Available
    Item
    Geological evidence and sediment transport modelling for the 1946 and 1960 tsunamis in Shinmachi, Hilo, Hawaii
    (Elsevier, 2018-02-01) Chagué, C; Sugawara, D; Goto, K; Goff, JR; Dudley, WC; Gadd, PS
    The Japanese community of Shinmachi, established on low-lying land between downtown Hilo and Waiakea, Hawaii, was obliterated by the 1946 Aleutian tsunami but was rebuilt, only to be destroyed again by the 1960 Chilean tsunami. The aim of this study was to find out if any geological evidence of these well documented events had been preserved in the sedimentary record in Wailoa River State Park, which replaced Shinmachi after the 1960 tsunami. This was achieved by collecting cores in the park and performing sedimentological, chronological and geochemical analyses, the latter also processed by principal component analysis. Sediment transport modelling was carried out for both tsunamis, to infer the source of the sediment and areas of deposition on land. The field survey revealed two distinct units within peat and soil, a thin lower unit composed of weathered basalt fragments within mud (Unit 1) and an upper unit dominated by fine volcanic sand within fine silt exhibiting subtle upward fining and coarsening (Unit 2, consisting of Unit 2A and Unit 2B), although these two anomalous units only occur on the western shore of Waiakea Mill Pond. Analysis with an ITRAX core scanner shows that Unit 1 is characterised by high Mn, Fe, Rb, La and Ce counts, combined with elevated magnetic susceptibility. Based on its chemical and sedimentological characteristics, Unit 1 is attributed to a flood event in Wailoa River that occurred around 1520–1660 CE, most probably as a result of a tropical storm. The sharp lower contact of Unit 2 coincides with the appearance of arsenic, contemporaneous with an increase in Ca, Sr, Si, Ti, K, Zr, Mn, Fe, La and Ce. In this study, As is used as a chronological and source material marker, as it is known to have been released into Wailoa River Estuary and Waiakea Mill Pond by the Canec factory between 1932 and 1963. Thus, not only the chemical and sedimentological evidence but also sediment transport modelling, corroborating the historical record, suggest that Unit 2A was deposited by the 1946 tsunami, and the sediment most likely originated from Wailoa River Estuary, beach and nearshore seafloor. The upper part of this unit, Unit 2B, is believed to have been deposited by the 1960 tsunami, as suggested by sediment transport modelling, although limited accommodation space is likely to have resulted in the thin deposit (3 cm thickness) present at that site. Limited accommodation space on the island of Hawaii has led to only rare locations where tsunami deposits are preserved, despite the repeated occurrence of tsunamis affecting the island. © 2017 Elsevier B.V.
  • No Thumbnail Available
    Item
    Late Holocene environmental changes and anthropogenic impact in Dee Why Lagoon, New South Wales
    (Taylor & Francis, 2019-02-02) Chagué, C; Edwards, D; Ruszczyk, J; Gadd, PS; Zawadzki, A; Jacobsen, GE; Fierro, D; Goralewski, J; Clement, L; Albani, A
    Late Holocene environmental changes were examined in Dee Why Lagoon, New South Wales, based on the sedimentological, geochemical and geochronological analysis of six cores collected from the fluvial delta and lagoon basin. The lagoon formed about 7300–7200 cal yr BP, following the post-glacial marine transgression and establishment of a sand barrier. Infilling of the lagoon occurred at a rate of 0.09–0.15 mm/yr until about 3300–3200 cal yr BP, when the barrier closed, resulting in mostly freshwater conditions, as evidenced by a change from pyrite-rich units to sediment containing little sulfur and a lack of foraminifera. Sedimentation rates increased to 0.23 then 0.43 mm/yr until about 100 years ago. Post-European land clearance led to an increase in sedimentation rates to 1.0–1.3 mm/yr on the fluvial delta, which are lower than those from other wave-dominated estuaries in New South Wales as well as those estimated by previous studies in Dee Why Lagoon. Our study shows that the fluvial delta started forming much earlier than originally thought, based on results of radiometric dating, and confirmed using sedimentological and geochemical data, as well as a critical examination of historic aerial photographs. Human impact has resulted in an increase in heavy metal (Cu, Pb, Zn) and metalloid (As) concentrations in the recent sediment, most likely attributed to stormwater discharge. Pb and As concentrations are above the ANZECC high sediment quality guideline values at the site closest to the stormwater outlet, with As-based pesticides one of the possible sources. Using the mean enrichment quotient, which is based on normalised Cu, Pb and Zn concentrations over their normalised background concentrations, we show that the surface sediments in Dee Why Lagoon are severely enriched, reflecting the recent anthropogenic impact that has also led to an increase in sedimentation rates. Copyright © 2019 Informa UK Limited
  • No Thumbnail Available
    Item
    New Zealand's most easterly palaeotsunami deposit confirms evidence for major trans-Pacific event
    (Elsevier, 2018-11-01) Goff, JR; Goto, K; Chagué, C; Watanabe, M; Gadd, PS; King, DN
    Sedimentary, geochemical, geomorphological, radiocarbon and numerical modelling data were used to examine the nature, extent and age of a boulder scatter at Okawa Point, Chatham Island, New Zealand. Boulders up to 98 t were traced around 800 m inland and comprised both a landward and seaward grouping on either side of a mid-Holocene high-stand storm ridge dated to around 4840–4810 cal BP. The landward boulder scatter was linked with an enigmatic coarse sand/gravel layer that extends up to 1100 m inland and has been dated to around 3500–4500 cal BP. Numerical modelling indicated that while the seaward boulders that mainly rest upon the Chatham Island Schist shore platform could have been emplaced by either storm or tsunami waves, those landward of the mid-Holocene storm ridge were most probably transported by a tsunami. There are several near-contemporaneous palaeotsunami deposits reported from mainland New Zealand, Australia, SW Pacific and the wider Pacific region. If some or all of these are associated with the same basin-wide palaeotsunami then it appears likely to have been one of the largest Holocene Pacific palaeotsunamis. An analysis of historical and numerically modelled data suggests that the most likely candidate is from within the northern Chile seismic gap, with early evidence suggesting that a large palaeoseismic and palaeotsunami event may have occurred around 4000 yr BP. If correct, this has important implications for assessing the largest possible magnitude earthquakes in the northern Chile seismic gap and the size of the tsunamis they generate. © 2018 Elsevier B.V.
  • No Thumbnail Available
    Item
    The Waikari River tsunami: New Zealand's largest historical tsunami event
    (Elsevier, 2019-02-16) Donaldson, G; Goff, JR; Chagué, C; Gadd, PS; Fierro, D
    The Waikari River tsunami was caused by a landslide triggered by the 1931 Hawke's Bay earthquake, New Zealand's deadliest natural disaster to date. Although it was reported in newspapers and personal diaries at the time, this is the first study to examine the tsunami using a multi-proxy approach aimed at investigating the physical evidence of this event. Sedimentological, geochemical, chronological and microfossil analyses were carried out on an anomalous gravel layer within the sedimentary sequence of Waikari Station located in a meander bend close to the river mouth. The chronology was established by extrapolation from 137Cs data coupled with historical artefacts found within the gravel layer. Diatoms within the deposit were brackish, and most probably sourced from the adjacent tidally-influenced Waikari River. Principal component analysis performed on geochemical data showed that the anomalous gravel layer at all sites is associated with a cluster of elements not related to detrital input nor organic matter, but indicative of an estuarine source. A second, older, gravel layer was also identified. It is considered to have been deposited by an earlier tsunami, quite likely caused by a landslide generated by the 1863 Hawke's Bay earthquake. The deposit has similar sedimentological, geochemical and microfossil characteristics to the gravel layer deposited by the 1931 event. This study adds valuable insights into the poorly understood topic of landslide generated tsunamis by investigating the largest historical event of its kind to occur in New Zealand. © 2019 Elsevier B.V.