Browsing by Author "Goff, JR"
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- ItemThe 2011 Tohoku-oki tsunami — three years on(Elsevier, 2014-12) Goto, K; Ikehara, K; Goff, JR; Chagué-Goff, C; Jaffe, BEThe 2011 Tohoku-oki tsunami that devastated the Pacific coast of Tohoku, Japan was a turning point for modern research. As a result of this event it was recognized that paleotsunami research is vital to help understand the size and recurrence interval of low-frequency large tsunamis. This paper reviews the progress of geological research on the 2011 Tohoku-oki tsunami and summarizes new questions that are arising out of this work. For example, recent work suggests that the landward extent and thickness of the sandy deposit, as well as the presence or absence of marine microfossils in the sediment are most likely to be mainly controlled by the initial wave properties, sediment source, offshore bathymetry and onshore topography. This in turn implies that there are certain relationships between the characteristics of a tsunami deposit and the wave properties and it may be possible to reconstruct the latter from the deposits. Offshore tsunami deposits related to the 2011 Tohoku-oki tsunami have also been well described. This recent research indicates that sedimentation and erosion in inner bay and open ocean (~ 20 m water depth) locations can be in the order of several meters, suggesting that the tsunami shear force was strong in the nearshore zone. On the other hand, sandy to muddy deposits a few centimeters thick were observed at about 100 to 6000 m water depth. It is likely that the tsunami resulted in resuspension of sea bottom sediments and that suspended material flowed downslope as a turbidity current or suspended flow, although many authors recognize the possibility that strong earthquake groundshaking might have also generated turbidity currents. Studies of the 2011 Tohoku-oki event have led researchers back to two of the fundamental issues of tsunami geology: understanding the linkage between onshore and offshore sedimentation and erosion, and establishing identification criteria for tsunami deposits. Moreover though, beyond the issue of simple tsunami geology, it is important for all researchers to communicate with governments and the general public in order to reduce future casualties by using risk assessments based on our understanding of infrequent large tsunamis.© 2014, Elsevier B.V.
- ItemAnatomy of sand beach ridges: evidence from severe Tropical Cyclone Yasi and its predecessors, northeast Queensland, Australia(American Geophysical Union., 2013-09-01) Nott, J; Chagué-Goff, C; Goff, JR; Sloss, CR; Riggs, NFour well-identified tropical cyclones over the past century have been responsible for depositing distinct units of predominantly quartzose sand and gravel to form the most seaward beach ridge at several locations along the wet tropical coast of northeast Queensland, Australia. These units deposited by tropical cyclones display a key sedimentary signature characterized by a sharp basal erosional contact, a coarser grain size than the underlying facies and a coarse-skewed trend toward the base. Coarse-skewed distributions with minimal change in mean grain size also characterize the upper levels of the high-energy deposited units at locations within the zone of maximum onshore winds during the tropical cyclone. These same coarse skew distributions are not apparent in sediments deposited at locations where predominantly offshore winds occurred during the cyclone, which in the case of northeast Australia is north of the eye-crossing location. These sedimentary signatures, along with the geochemical indicators and the degraded nature of the microfossil assemblages, have proven to be useful proxies to identify storm-deposited units within the study site and can also provide useful proxies in older beach ridges where advanced pedogenesis has obscured visual stratigraphic markers. As a consequence, more detailed long-term histories of storms and tropical cyclones can now be developed.© 2013, American Geophysical Union.
- ItemAnisotropy of anhysteretic remanent magnetization (AARM) reveals cryptic flow fabric of tsunami(American Geophysical Union, 2013-12-09) Kon, S; Nakamura, N; Sugawara, D; Goto, K; Chagué-Goff, C; Goff, JRSandy tsunami deposits may provide valuable information on tsunami inundation as well as hydrodynamics, such as flow speed. However, if the layer does not have sedimentary structures such as cross laminations, it is difficult to infer the flow direction, which is important to interpret the behavior of the tsunami, such as inflow and outflow as well as repetition of waves. Anisotropy of magnetic susceptibility (AMS), in combination with grain size data, can provide information about the hydrodynamic conditions prevailing during the emplacement of tsunami sequences. It might also allow the reconstruction of transport directions because it provides a cryptic alignment of ferromagnetic and paramagnetic minerals, such as coarse-grained magnetite or platy phyllosilicate minerals (e.g. biotite). These minerals behave differently in different hydrodynamic conditions: for example, platy biotite may deposit in a cryptic micro-ripple. This therefore suggests that the usefulness of bulk AMS together with optical observations is limited in the study of flow fabric in tsunami deposits. The anisotropy of anhysteretic remanent magnetization (AARM) on the other hand isolates the fine-grained magnetite subfabric of needle-shaped inclusions exsolved in silicate minerals. Samples (18) from tsunami deposits, believed to have been laid down by the Jogan event (869 AD), were collected from a section on the Sendai Plain, east Japan. The transport direction in these deposits could not be determined by AMS analysis due to large declination and inclination errors. The AARM technique was thus used to determine the cryptic subfabric of magnetite exsolutions along cleavages in biotite and amphibole. Our scanning electron microscopy (SEM) observations confirmed that the maximum AARM orientation is parallel to the needle-shaped magnetite microexsolutions in biotite and amphibole. We therefore infer that the large error of AMS is caused by the alteration of these paramagnetic minerals, and AARM provides a cryptic alignment of fine-grained magnetite microexsolutions. In order to apply this method to ancient historical Tsunami events, we also collected 40 samples from consecutive sand layers of possible tsunami deposits at 7 sites using 2 m long geoslicers in Rikuzen-Takata, northeast Japan. The AARM and SEM confirmed the tendency of same flow direction of sand layers at each site, suggesting a tsunami origin.
- ItemAssessing tsunami signatures in the geologic record for long-term risk evaluation, Samoan Islands(American Geophysical Union, 2011-12-05) Williams, SP; Goff, JR; Davies, TR; Cheung, KF; Yamazaki, Y; Chagué-Goff, C; Prasetya, G; Wilson, TRecent tsunamis worldwide have prompted significant efforts amongst scientific and disaster management authorities to enhance understanding of these processes, and further mitigate their immediate to long-term impacts. The tsunami of 29 September, 2009, which impacted the Samoan Islands, prompted local demand to improve long-term understanding of the risk these processes have on local communities and environment in general. This research aims to address some of this demand through an inter-disciplinary investigation of tsunami (and cyclone) deposits in the Samoan geologic record. The use of tsunami deposit investigations has become a key component in tsunami hazard assessments globally, as they enable long-term understanding of tsunami risk to communities and property, including loss of life. In the Samoan Islands, historical records of tsunamis are meagre and only date back to 1837 AD. This project enables tsunami records to be extended into Samoan pre-history, thereby forming an information basis for long-term risk mitigation in these islands. It also provides an avenue for establishing a suite of multi-proxy criteria for identifying and distinguishing tsunami and cyclone events specific to Samoa. Further, it provides the opportunity for starting to understand likely source and wave characteristics associated with identified tsunamis. In this paper, we provide a discussion on the applications and implications of results yielded thus far in the project to understanding long-term tsunami risk in the Samoan Islands. Current interpretations of empirical stratigraphies, semi-quantitative X-ray fluorescence spectroscopy analysis, geochronology analysis, and preliminary computational modelling of tsunami resonance are discussed for various investigated sites on Savai'i and Upolu (Independent State of Samoa), and Ta'u (Manu'a Group, American Samoa). We show that a long-term geologic record of tsunamis exist on these islands. Further, we discuss the challenges encountered in detailing this record, as well as the challenges that remain in forming definitive interpretations. Ultimately, results from this project will contribute to enhancing our understanding of tsunami processes and their long-term risk in the Samoan Islands, and will contribute to forming a solid foundation for future studies to build on.
- ItemThe Australian Tsunami Database - a review(Sage Publications Ltd, 2014-04-01) Goff, JR; Chagué-Goff, CThere has been a significant increase in the number of peer-reviewed publications, critical reviews and searchable web-based databases, since the first substantial tsunami database for Australia was published in 2007. This review represents a complete reorganization and restructuring of previous work coupled with the addition of new data that takes the number of events from 57 (including 2 erroneous events) to 145. Several significant errors have been corrected including mistaken run-up heights for the event of 19 August 1977, Sumba Island, Indonesia, that suggested it was the largest tsunami in Australia's history. The largest historical event in the database is now the 17 July 2006, Java, Indonesia, tsunami that had a run-up height of 7.90 m at Steep Point, Western Australia. Although estimated wave heights of 40 ft (approximate to 13 m) were noted for the 8 April 1911 event at Warrnambool, Victoria, no run-up data were provided. One of the more interesting findings has been the occurrence of at least 11 deaths, albeit for events that are generally poorly defined. Data gathered during the construction of this database were rigorously reviewed and as such several previous palaeotsunami entries have been removed and other potentially new ones discarded. The reasons for inclusion or exclusion of data are discussed, and it is acknowledged that while there has been an almost three-fold increase in the number of entries the database is still incomplete. With this in mind the database architecture has been brought in line with others in the region with the ultimate goal of merging them all in order to provide a larger, interrogatable and updatable data set. In essence, the goal is to enhance our understanding of the national and regional tsunami hazard (and risk) and to move towards an open-source database. © 2014, SAGE Publications.
- ItemCharacterising diagnostic proxies for identifying palaeotsunamis in a tropical climatic regime, Samoan Islands(IEEE, 2011-09-19) Williams, S; Prasetya, G; Chagué-Goff, C; Goff, JR; Cheung, KF; Davis, T; Wilson, TThe September 2009 South Pacific Tsunami (2009 SPT) in the Samoa Islands resulted in local public and national calls to improve understanding of the medium- to long-term risks of tsunamis in these islands in order to further mitigate their impacts. This research addresses some of these calls through an interdisciplinary palaeotsunami investigation. Historical data beginning in 1837 indicate that the Samoan Islands have been impacted by tsunamis from all the major tsunamigenic zones within the Pacific Rim of Fire, making it an ideal location for starting to understand tsunami frequency and distribution within this region. Furthermore, the region has an historical record of extreme tropical cyclones. The overarching concept of this study is that tsunamis, like cyclones, leave a distinct geological deposit within coastal landscapes they impact. The origin of a high-energy geological deposit, be it storm or tsunami, can be determined by using a suite of diagnostic criteria. However, the origin of a deposit can still be ambiguous, because some of the diagnostic criteria (e.g. grain size, microfossil assemblages and characteristics) can be extremely similar for both processes. Moreover, local factors can also influence the characteristics of deposits. This project aims to elucidate this enigma by establishing a suite of diagnostic criteria (e.g., stratigraphy, lithology, macro- and micro-palaeontology, geomorphology, grain size characteristics, geochemistry, anthropology, archaeology, numerical modelling) to distinguish between tsunamis and cyclones in this tropical climatic regime. Preliminary studies show that a geological record of historical /palaeotsunamis and storms/palaeostorms is preserved on the south and south east coast of Upolu, west and northeast coast of Savai'i (Independent State of Samoa), and northwest coast of Ta'u in the Manu'a Group (American Samoa). We present preliminary X-ray fluorescence spectroscopy (XRF) and geochronological results (C-14 radiocarbon dates) conducted on samples (sands and paleosols) collected from various sites on Upolu, Savaii, and Ta'u islands. These serve as a starting point for developing a suite of diagnostic proxies for identifying and distinguishing tsunami from storm deposits in the Samoan Islands, and establishing the geochronology of identified events. Numerical modelling of wave resonance around these islands, as well as identified palaotsunamis will form an additional proxy for interpreting the palaeotsunami data. Further, it forms a basis for starting to understand the likely sources of these events, forming a basis for refining the frequency and (likely) magnitude distributions associated with these events. Planned Pb-210, Cs-137 and C-14 dating will enable a detailed interpretation of the chronology of specific events identified in the geologic record. Furthermore, they will enable a correlation of deposits with known historical events, providing a control on distinguishing recent tsunami from storm deposits (subsequent to 1837 AD), and enabling palaeo-events to be identified. This will form a basis for identifying similar events within the geologic record in similar environmental regimes. Ultimately, this work will significantly improve understanding of the nature and risks of coastal hazards in Samoa, thereby improving local capability to mitigate their medium to long-term impacts. It will also contribute to tsunami hazard mitigation efforts within the broader SW Pacific through a strengthened tsunami database in the region. © Copyright 2020 IEEE
- ItemThe comprehensive Australian Tsunami database – just when you thought it was safe to go back in the water(Geological Society of Australia, 2014-07-07) Goff, JR; Chagué-Goff, CThis new database incorporates peer-reviewed publications, critical reviews and searchable web-based datasets and as such represents a complete re-organisation and restructuring of previous work. These new data take the number of events from 57 (including two “erroneous events”) to 145. Several significant errors have been corrected, not the least of which are mistaken run-up heights for the 19 August 1977 Sumba Island, Indonesia event that suggested it was the largest historical tsunami in Australia’s history. This honour now goes to the 17 July 2006, Java, Indonesia tsunami that had a run-up height of 7.90 m at Steep Point, Western Australia. Although estimated wave heights of 40 feet (~13 m) were noted for the 8 April 1911 event at Warrnambool, Victoria, no run-up data were provided and so its full effects remain uncertain. One of the more interesting findings has been the occurrence of at least 11deaths, albeit for events that are generally poorly defined. Data gathered during the construction of this database were rigorously reviewed and as such several previous paleotsunami entries have been removed and other potentially new ones discarded. The reasons for inclusion or exclusion of data are discussed and it is acknowledged that while there has been an almost three-fold increase in the number of entries, the database is still incomplete. With this in mind the database architecture has been brought in line with others in the region with the ultimate goal of merging them all in order to provide a better understanding of the national and regional tsunami hazard (and risk) and to move towards an open source Australasian database.
- ItemCrossing thresholds – human responses to tsunami forcing in the Pacific(American Geophysical Union, Fall Meeting., 2014-12-15) Goff, JR; Chagué-Goff, CThe 11 March 2011 Tohoku-oki tsunami caused widespread devastation to coastal communities in Japan. This event however was merely the latest in a long line of similar occurrences throughout the Pacific over time. All the recent large tsunamis have had their predecessors, and a growing database of palaeotsunamis in the Pacific suggests that several past events have been either similar in magnitude or greater than their historical counterparts. Not only are we gathering data concerning Pacific palaeotsunamis but we are also identifying contemporaneous punctuated histories of changing human settlement patterns across the Pacific. In particular, the almost two millennia 'long pause' in eastward Polynesian migration and the abandonment of long distance sea-voyaging in the 15th century. It is suggested that large palaeotsunamis and their generating mechanisms forced major societal responses. Given the unquestioned impacts of recent tsunamis on human societies, it is reasonable to suggest that past societal responses can be used as proxies for contemporaneous environmental forcing in those parts of the world where independent evidence of the effects of these events is still being gathered. In the Pacific there are a range of responses that extend well beyond the abandonment of long distance sea-voyaging such as the outbreak of region-wide conflict and the associated abandonment of settlements in exposed (coastal) locations. The contemporaneity of these effects across a vast region requires a driver that is external to particular island groups. Given that this must have impacted coastal resources severely and enduringly, the only possibility is that this driver was of oceanic origin. This hypothesis is compelling when considered alongside the growing database of more conventional lines of evidence. The question therefore is how well are similar threshold responses recognised throughout the World? Are there similar region-wide responses that have been pigeonholed under the more prosaic interpretations of archaeological dogma?
- ItemDeposits, flow characteristics, and landscape change resulting from the September 2009 South Pacific Tsunami in the Samoan Islands(Elsevier Science, 2011-07-01) Richmond, B; Buckley, M; Etienne, S; Chagué-Goff, C; Clark, K; Goff, JR; Dominey-Howes, D; Strotz, LThe September 29th 2009 tsunami caused widespread coastal modification within the islands of Samoa and northern Tonga in the South Pacific. Preliminary measurements indicate maximum runup values of around 17 m (Okal et al., 2010) and shore-normal inundation distances of up to similar to 620 m (Jaffe et al., 2010). Geological field reconnaissance studies were conducted as part of an UNESCO-IOC International Tsunami Survey Team survey within three weeks of the event in order to document the erosion, transport, and deposition of sediment by the tsunami. Data collected included: a) general morphology and geological characteristics of the coast, b) evidence of tsunami flow (inundation, flow depth and direction, wave height and runup), c) surficial and subsurface sediment samples including deposit thickness and extent, d) topographic mapping, and e) boulder size and location measurements. Four main types of sedimentary deposits were identified: a) gravel fields consisting mostly of isolated cobbles and boulders, b) sand sheets from a few to similar to 25 cm thick, c) piles of organic (mostly vegetation) and man-made material forming debris ramparts, and d) surface mud deposits that settled from suspension from standing water in the tsunami aftermath. Tsunami deposits within the reef system were not widespread, however, surficial changes to the reefs were observed. Published by Elsevier B.V.
- ItemDetermining flow patterns and emplacement dynamics from tsunami deposits with no visible sedimentary structure(John Wiley and Sons, 2016-09-16) Kain, CL; Wassmer, P; Goff, JR; Chagué-Goff, C; Gomez, C; Hart, DE; Fierro, D; Jacobsen, GE; Zawadzki, AIn the absence of eyewitness reports or clear sedimentary structures, it can be difficult to interpret tsunami deposits or reconstruct tsunami inundation patterns. The emplacement dynamics of two historical tsunami deposits were investigated at seven transects in Okains Bay, New Zealand, using a combined geospatial, geomagnetic and sedimentological approach. The tsunami deposits are present as layers of sand and silt intercalated between soils and become finer and thinner with distance inland. The deposits are attributed to the 1960 and possibly the 1868 tsunamis, based on radiometric dating and correlation with historical records. Measurements of Magnetic Fabric (MF: Anisotropy of Magnetic Susceptibility) and particle size were used to reconstruct the evolution of flow dynamics laterally and vertically. A combination of statistical methods, including spatial autocorrelation testing, Spearman's rank order correlation, Principal Component Analysis (PCA) and K-means cluster analysis, was applied to examine relationships between MF parameters and sediment texture, and infer depositional hydrodynamics. Flow patterns deduced from MF show the estuary channel acted as a conduit for inundation, with flow commonly aligned sub-perpendicular to the estuary bed. MF and sediment data suggest deposition occurred from settling during laminar flow. Evidence of both uprush and backwash deposition, as well as wave reflection from infrastructure, was found. Statistical analysis of data showed significant relationships between grain size parameters and MF parameters associated with flow speed and magnetic fabric type. PCA and cluster analysis differentiated samples into two primary hydrodynamic groups: (1) samples deposited from laminar flow; and (2) samples deposited close to the limit of inundation, which includes samples deposited further inland, those affected by flow convergence, and those in the upper part of tsunami deposits. This approach has potential as a tool for reconstructing hydrodynamic conditions for palaeotsunamis and by combining spatial and statistical analyses, large-scale investigations can be more easily performed. Copyright © 2016 John Wiley & Sons, Ltd.
- ItemEnvironmental impact assessment of the 2011 Tohoku-oki tsunami on the Sendai Plain(Elsevier B.V., 2012-12-30) Chagué-Goff, C; Niedzielski, P; Wong, HKY; Szczuciński, W; Sugawara, D; Goff, JRLarge areas of farmland in the Sendai Plain, Japan, were inundated by the 11 March 2011 Tohoku-oki tsunami and covered by a discontinuous 30–0.2 cm thick sediment layer consisting of sand and/or mud and generally thinning and fining inland. Two months after the tsunami, numerous rice paddy fields and depressions remained ponded with brackish or saline water. A series of field surveys in May, August and October 2011 were carried out north of Sendai airport, in order to assess the environmental impact of the tsunami. While evaporation had resulted in elevated conductivity in ponded water in May (up to 68.2 mS cm− 1), rainfall over the next five months led to dilution, although brackish water was still recorded in depressions and on paddy fields. Tsunami sediments, underlying soil and soil beyond the tsunami inundation limit were collected at 43 sites along and near a transect extending over 5 km inland, and analysed for grain size, organic content, water leachable ions, acid leachable metals and exchangeable metalloids. Water leachable anion and cation concentrations were elevated in sandy and muddy tsunami deposits and soils particularly in areas, where seawater had stagnated for a longer period of time after the tsunami, with up to 10.5% Cl, 6.6% Na, 2.8% SO4, 440 mg kg− 1 Br measured in surface sediments (< 0.5 cm depth). Vertical variations were also recorded, with higher concentrations often measured in the surface samples. A similar trend could be observed for some of the metalloids (As) and metals (Zn, Cu and Ni), although in general, maximum concentrations of metals and metalloids were not much higher than in soils not inundated by the tsunami and were within background levels for uncontaminated Japanese soils. The impact of saltwater inundation was documented in the chemistry of soils underlying tsunami sediments, which were affected by salt contamination down to ~ 15 cm depth, and soils not covered by tsunami deposits. The latter implies that the extent of tsunami inundation may successfully be determined using geochemical markers in absence of any sedimentological evidence. Water leachable ions mostly decreased over time, however, they remained high enough to impact on rice farming, which was completely halted in 2011. Although further work is required to assess the longer term impact of tsunami inundation, flushing of salt with freshwater, as well as the possible removal of sandy/muddy sediments and underlying soil are recommended to allow crop production to resume. © 2020 Elsevier B.V.
- ItemErosion, deposition and landscape change on the Sendai coastal plain, Japan, resulting from the March 11, 2011 Tohoku-oki tsunami(Elsevier B.V., 2020-12-12) Richmond, B; Szczuciński, W; Chagué-Goff, C; Goto, K; Sugawara, D; Witter, R; Tappin, DR; Jaffe, BE; Fujino, S; Nishimura, Y; Goff, JRCase studies of recent tsunami impacts have proven to be extremely useful in understanding the geologic processes involved during inundation and return flow, and refining the criteria used to identify paleotsunami deposits in the geologic record. Here, we report on erosion, deposition and associated landscape change resulting from the March 11, 2011 Tohoku-oki tsunami along a nearly 4.5 km shore-normal transect on the coastal plain near Sendai, Japan. The study area on the broad, low-relief prograding coastal Sendai plain comprised a sand beach backed by ~ 3 m high sand dunes and a forest, a wetland, the Teizan canal, agricultural rice fields, buildings and roads. Field observations focused on measurements of tsunami flow characteristics (height and direction), mapping of erosion features and assessing sediment deposition based on shallow trenches at 50–100 m spacing. Recorded tsunami inundation heights reached up to about 11 m above mean sea level within the first 500 m from the shoreline and then ranged between 3 and 5 m for the next 2 km, gradually decreasing to about 3 m close to the inundation limit. The tsunami deposit generally thinned landward from an average maximum ~ 30 cm thick sand deposit in the coastal forest to a thin mud drape several mm thick near the inundation limit. A discontinuous sand-dominated sheet was prevalent to about 2800 m from the shoreline where mud content then gradually increased further landward eventually resulting in a mud-dominated deposit ranging from 3.5 cm to a few mm thickness. The overall thinning and fining of the deposit was often interrupted by localized features that led to complex sedimentological relationships over short distances. Satellite imagery taken on 14 March 2011, 3 days after the Tohoku-oki Tsunami shows prominent foreshore incisions with 100 s + meters spacing alongshore, a foredune ridge that underwent severe erosion and development of a prominent shore-parallel elongated scour depression. Our field survey in early May 2011 revealed that the foreshore recovered quickly with rapid post-tsunami sediment deposition from incident waves, whereas the dune–ridge complex had undergone only minor re-working from eolian processes. © 2020 Elsevier B.V
- ItemEstimating 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, DThere 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.
- ItemExpanding the proxy toolkit to help identify past events: Lessons from the 2004 Indian Ocean Tsunami and the 2009 South Pacific Tsunami(Elsevier, 2011-07-01) Chagué-Goff, C; Schneider, JL; Goff, JR; Dominey-Howes, D; Strotz, LSome of the proxies used to identify palaeotsunamis are reviewed in light of new findings following the 2004 Indian Ocean Tsunami and the 2009 South Pacific Tsunami, and a revised toolkit provided. The new application of anisotropy of magnetic susceptibility (AMS) to the study of tsunami deposits and its usefulness to determine the hydrodynamic conditions during the emplacement of tsunami sequences, together with data from grain size analysis, are presented. The value of chemical proxies as indicators of saltwater inundation, associated marine shell and/or coral, high-energy depositional environment, and possible contamination, is demonstrated and issues of preservation addressed. We also provide new findings from detailed studies of heavy minerals. New information gathered during the UNESCO - International Oceanographic Commission (IOC) International Tsunami Survey of fine onshore sediments following the 2009 South Pacific Tsunami is presented, and includes grain size, chemical, diatom and foraminifera data. The tsunami deposit varied, ranging from fining-upward sand layers to thin sand layers overlain by a thick layer of organic debris and/or a mud cap. Grain size characteristics, chemical data and microfossil assemblages provide evidence for marine inundation from near shore, and changes in flow dynamics during the tsunami. (C) 2011 Elsevier B.V.
- ItemExtreme wave deposits on the Pacific Coast of Mexico: tsunamis or storms? - A multi-proxy approach(American Geophysical Union, 2011-12-05) Ramirez-Herrera, MT; Lagos, M; Hutchinson, I; Chagué-Goff, C; Kostoglodov, V; Goff, JR; Ruiz-Fernandez, A; Machain-Castillo, ML; Caballero, M; Goguitchaichrili, A; Aguilar, B; Urquijo, PHistorical and instrumental data show that the Pacific coast of Mexico has been exposed to destructive tsunamis over at least the past 500 years. This coast is also affected by hurricanes generated in the eastern Pacific. The great 1985 Mexico earthquake and its aftershock generated tsunamis that affected the Ixtapa-Zihuatanejo and Michoacán coast. The purpose of our study was two-fold, a) to determine whether we could distinguish storm from tsunami deposits, and b) whether tsunami deposits from historical events are preserved in the tropical environments of the Ixtapa-Zihuatanejo coast. Two anomalous sand units in the Ixtapa estuary are interpreted as the result of high-energy marine inundation events that occurred in the last century. Several lines of evidence using a multi-proxy approach (historical studies, interviews with local witnesses, geomorphological and geological surveys, coring and trenching, and laboratory analyses including grain size, micropaleontology, geochemistry, magnetic susceptibility and radiometric dating) indicate the occurrence of two tsunamis that we link to local events: the 1985 Mexico and possibly the 1979 Petatlan earthquakes. We thereby provide the first onshore geological evidence of historical tsunamis on the Pacific coast of Mexico. © American Geophysical Union
- ItemField observations of erosion, deposition, and tsunami flow characteristics on the Sendai Coastal Plain after the March 2011, Tohoku-oki Tsunami, Japan(American Geophysical Union, 2011-11-05) Richmond, BM; Goto, K; Fujino, S; Nishimura, Y; Sugawara, D; Tappin, DR; Witter, RC; Jaffe, BE; Chagué-Goff, C; Szczuciński, W; Yulianto, E; Goff, JRHistorical and instrumental data show that the Pacific coast of Mexico has been exposed to destructive tsunamis over at least the past 500 years. This coast is also affected by hurricanes generated in the eastern Pacific. The great 1985 Mexico earthquake and its aftershock generated tsunamis that affected the Ixtapa-Zihuatanejo and Michoacán coast. The purpose of our study was two-fold, a) to determine whether we could distinguish storm from tsunami deposits, and b) whether tsunami deposits from historical events are preserved in the tropical environments of the Ixtapa-Zihuatanejo coast. Two anomalous sand units in the Ixtapa estuary are interpreted as the result of high-energy marine inundation events that occurred in the last century. Several lines of evidence using a multi-proxy approach (historical studies, interviews with local witnesses, geomorphological and geological surveys, coring and trenching, and laboratory analyses including grain size, micropaleontology, geochemistry, magnetic susceptibility and radiometric dating) indicate the occurrence of two tsunamis that we link to local events: the 1985 Mexico and possibly the 1979 Petatlan earthquakes. We thereby provide the first onshore geological evidence of historical tsunamis on the Pacific coast of Mexico. © American Geophysical Union
- ItemThe future of tsunami research following the 2011 Tohoku-oki event(Elsevier B.V., 2012-12-20) Goto, K; Chagué-Goff, C; Goff, JR; Jaffe, BEIn this paper we summarize the regional setting, our previous understanding of historical and pre-historical tsunamis on the Pacific coast of Tohoku, Japan, prior to the 2011 Tohoku-oki tsunami, and our current understanding of the sedimentological, geochemical and paleontological features of the onshore and offshore deposits of the event. Post-tsunami surveys revealed many new insights, such as; (1) the maximum extent of the sand deposit is sometimes only 60% of the inundation distance, (2) the inundation limit can be estimated by geochemical analysis even a few months after the event, (3) a minor amount of marine sediment was transported inland by the tsunami on the Sendai and adjacent plains with the major sediment sources being from beach and dune erosion or vented sediments from liquefaction, although nearshore and offshore surveys revealed that there was a significant amount of sediment transport on the seafloor, (4) coarse gravel deposits (~ 1 m in thickness) were usually thicker than the sand ones (~ 30 cm in thickness), and (5) beach erosion was minimal in some places while severe in others. Another important aspect of this event is that it was a large, infrequent, tsunami that took place where possible predecessors (e.g., AD869 Jōgan) were already known to have occurred based on historical and geological evidence. The AD869 Jōgan tsunami deposits are noticeably similar to the 2011 Tohoku-oki sands, therefore suggesting that the Jōgan and its source mechanism may have been larger than previously thought. While we have learned many lessons from the 2011 Tohoku-oki event, more research is needed to provide reliable tsunami risk assessments around the world. © 2020 Elsevier B.V.
- ItemGeochemical indicators and diatoms as true markers of the inundation limit of the 2010 Maule Tsunami(American Geophysical Union, 2013-01-12) Chagué-Goff, C; Goff, JR; Wong, HKY; Cisternas, MIt has long been known that tsunamis inundate further than the limit of the sand deposit they leave behind, and that relying on the extent of the sandy sedimentary evidence is likely to result in an under-estimation of event magnitude and risk. However, the question remains about how to identify the real limit of tsunami inundation, particularly several months or more after the event. Here we report on a study carried out at a site on the Pacific coast of Chile south of Constitución in August 2010, nearly 6 months after the Mw 8.8 Maule tsunami. Eight pits were dug along a 480 m long shore-perpendicular transect, incorporating the area covered by tsunami sediment, a zone covered by a discontinuous and decomposing debris scatter up to the point of maximum inundation, and an area further landward from this point. The tsunami sand deposit extended from ~160 to 260 m inland and ranged in thickness from 22 to less than 1 cm at the limit of sediment deposition. It consisted of dark, generally well-sorted, coarse to medium sand. Logs, pumice and various organic debris were found up to a limit of tsunami inundation (380 m inland - confirmed by a local eye witness). New grass growth also covered the tsunami deposit and the field further inland. While the chemical composition of the tsunami deposit differed to that of the underlying soil, indicators of saltwater inundation were low in the sandy units, reflecting downward leaching and dilution by rainfall in the porous material in the 6 months since the tsunami. Concentrations of saltwater indicators (e.g. chloride, sulphate, bromide) were however elevated in the area covered by scattered debris up to the limit of tsunami inundation, suggesting preferential retention in organic-rich material. Marine and brackish-marine diatoms were found both in the sandy units and beyond, at the surface of the grass field, and occurred in higher concentrations than in the underlying soil. Both diatom assemblages and geochemical marine proxies are indicative of tsunami inundation well beyond the sediment limit. While sea spray and associated wind cannot be totally excluded as the source of soluble salts and wind-blown diatoms, chloride concentrations do not decrease landward within the area of tsunami inundation. A decrease in chloride would have been expected if it was solely due to sea spray. While further research is required to allow us to distinguish the effects of marine inundation from sea spray, the use of geochemical proxies and diatoms provides a means to identify the limit of tsunami inundation beyond the limit of sand deposition, and as previous studies have shown, even after debris marking it have decayed. This is of importance for tsunami risk assessment and mitigation.
- ItemGeochemical mapping of tsunami inundation : beyond the sand(The Association of Applied Geochemists, 2013-11-17) Chagué-Goff, C; Wong, HKY; Goff, JR; Szczuciński, W; Gadd, PS; Cohen, DDTsunami deposits range from mud to boulders, depending upon the material available for transport by these devastating waves. As sandy beaches are most often eroded, many of the reported tsunami deposits are dominated by sand, and are identified in the geological record as an anomalous sand layer within a soil or peat profile, a bit like a layer cake. However, recent posttsunami surveys have shown that the sand layer may extend up to only 60‐70% of the tsunami inundation limit, and is thus not representative of the magnitude of the event. This invariably leads to underestimates of the size of the tsunami and the generating event. As shown by the 2011 Tohoku‐oki tsunami in Japan, this can have devastating outcomes. While the inundation limit can be mapped immediately after the event using the extent of debris, salt‐burned vegetation and water marks, this evidence is often lost over time and is therefore absent in the geological record. Here we report on two studies, where the tsunami inundation limit was mapped using geochemical methods. Six months after the 2010 Maulem Tsunami in Chile, the limit of inundation was identified based on chemical and microfossil data. In Japan, geochemical markers allowed the precise limit of inundation to be identified in the absence of any sedimentological evidence. Follow‐up studies also revealed that the marine geochemical signature was preferentially preserved in the mud component of the tsunami deposit which is found inland beyond the limit of sand deposition. As no marine microfossils were recovered in this area of Japan, geochemical mapping is proving to be the only means by which tsunami inundation maps can be redrawn allowing tsunami mitigation measures to be re‐assessed.
- ItemGeochemical signatures and source material of marine incursion deposits(Elsevier, 2016-01-01) Chagué-Goff, C; Andrew, AS; Szczuciński, W; Goff, JR; Nishimura, YThe geochemical signature of the Tohoku-oki tsunami deposit and underlying soil was assessed two months, five months and seven months after the 11 March 2011 tsunami inundated the Sendai Plain. The extent of the recognisable sand deposit was traced up to 2.9 km inland while a mud deposit was found up to 4.65 km inland, representing 60% and nearly 95% of the maximum tsunami inundation, respectively. The limit of tsunami inundation was identified 4.85 km from the shore using geochemical marine markers (S and Cl) two months after the tsunami, in the absence of any sedimentological evidence. Concentrations of other geochemical markers (K, Ca, Sr) indicative of the marine incursion and associated minerals were found to decrease landward. δ13C and δ15N and C/N ratios suggested a mixture of terrestrial and marine organic sources in the sediment, while δ34S of sulphate reflected the marine source of water soluble salts. The chemical composition of the 869 AD Jogan tsunami sand deposit was characterised by high Sr and Rb concentrations and was comparable to that of the Tohoku-oki tsunami deposit, suggesting that the sources of sediment may be similar. Marked decreases in S and Cl with time indicated that rainfall resulted in the leaching of salts from the sandy sediments. However, both S and Cl markers as well as Sr were still well preserved in the muddy sediments and underlying soil beyond the limit of the recognisable sand deposit seven months after the tsunami. This suggests that geochemical indicators may well be useful in identifying the extent of historical and palaeotsunamis by determining the marine origin of fine grained sediments beyond the limit of recognisable sand deposition, in particular when marine microfossils are sparse or lacking as is the case on the Sendai Plain. This would allow researchers to redraw palaeotsunami inundation maps and re-assess the magnitude of events such as the Jogan tsunami and other palaeotsunamis, not only on the Sendai Plain but also elsewhere around the world. This has important implications for tsunami risk assessment, hazard mitigation and preparedness.© 2012 Elsevier B.V.