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Tsunami Deposits Beneath Tidal Marshes on Northwestern Vancouver Island, British Columbia

Published online by Cambridge University Press:  20 January 2017

Boyd E. Benson ,
Kurt A. Grimm  and
John J. Clague
Boyd E. Benson
Affiliation:
Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia, V6T 1Z4, Canada
Kurt A. Grimm
Affiliation:
Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia, V6T 1Z4, Canada
John J. Clague
Affiliation:
Geological Survey of Canada, 101-605 Robson Street, Vancouver, British Columbia, V6B 5J3, Canada
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Abstract

Two sand sheets underlying tidal marshes at Fair Harbour, Neroutsos Inlet, and Koprino Harbour on the northwestern coast of Vancouver Island, British Columbia, were probably deposited by tsunamis. The sand sheets become thinner and finer-grained landward, drape former land surfaces, contain marine microfossils, are locally graded or internally stratified, and can be correlated with earthquakes that generated tsunamis in the region. 137Cs dating and historical accounts indicate that the upper sand sheet was deposited by the tsunami from the great Alaska earthquake in 1964. Radiocarbon ages on plant fossils within and on top of the lower sand sheet show that it was deposited sometime after about A.D. 1660. We attribute the lower sand sheet to a tsunami from the most recent plate-boundary earthquake on the Cascadia subduction zone about 300 yr ago, extending the documented effects of this earthquake north of the Nootka fault zone. The 1964 tsunami deposits differ little in thickness and continuity among the three marshes. In contrast, the lower sand sheet becomes thinner and less continuous to the north, implying a tsunami source south of the study area.

Type
Research Article
Information
Quaternary Research , Volume 48 , Issue 2 , September 1997 , pp. 192 - 204
Copyright
University of Washington

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