Geochemical mapping of tsunami inundation : beyond the sand
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Date
2013-11-17
Journal Title
Journal ISSN
Volume Title
Publisher
The Association of Applied Geochemists
Abstract
Tsunami 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.
Description
Keywords
Tsunamis, Erosion, Japan, Chile, Preservation, Mitigation
Citation
Chagué-Goff, C., Wong, H., Goff, J., Szczuciński, W., Gadd, P., & Cohen, D. (2013). Geochemical mapping of tsunami inundation : beyond the sand. Paper presented at the 26th International Applied Geochemistry Symposium, 17-21 November 2013, Rotorua, New Zealand.