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

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.

The first geological record of a palaeotsunami on the southern coast of the Baltic Sea, Poland

“…In addi tion, a tsu nami does not ex plain the gen e sis of the hemi spheri cal hol lows at Rowy by it self. Around the world, tsu nami events along flat coastal low lands have been re corded as thin lay ers of sand up to 0.5 m thick that ex tended be tween several hun dred metres and sev eral kilo metres in land (Hindson et al, 1996;Benson et al, 1997;Clague et al, 2000;Dawson and Shi, 2000;Goff et al, 2000Goff et al, , 2010Smoot et al, 2000;Bryant and Nott, 2001;Scheffers and Kelletat, 2003;Jaffe and Gelfenbaum, 2007;Mor ton et al, 2007;Abrantes et al, 2008;Choowong et al, 2008;Pe ter son et al, 2008;Fujino et al, 2008;Peter son and Cruikshank, 2011;Pe ter son et al, 2013). The sand came from the ero sion of a rel a tively nar row near shore and beach zone (Dawson, 1994;Jaffe and Gelfenbaum, 2007;Morton et al, 2007) and cov ered the man tle re lief, which showed no signs of ero sional un con formity at its base (Dominey-Howes et al, 2006;Dominey-Howes, 2007;Choowong et al, 2008;Szczuciński, 2008;Piotrowski et al, 2013).…”

“…The thick ness of the TD var ies from 0.23 m to 3.05 m and av er ages 1.09 m, which is sig nif i cantly greater than the thick nesses of tsu nami lay ers re ported from along low-en ergy coasts around the world. Data from such coasts show that tsu nami lay ers are usu ally 1-50 cm thick and are of ten <5 cm thick (Hindson et al, 1996;Benson et al, 1997;Clague et al, 2000;Dawson and Shi, 2000;Goff et al, 2000;Smoot et al, 2000;Bryant and Nott, 2001;Scheffers and Kelletat, 2003;Jaffe and Gelfenbaum, 2007;Mor ton et al, 2007;Abrantes et al, 2008;Choowong et al, 2008;Pe ter son et al, 2008;Fujino et al, 2008;Goff et al, 2010;Pe terson and Cruikshank, 2011;Pe ter son et al, 2013). The rel a tively large thick ness of the TD at Rowy is prob a bly caused by the subsurface palaeorelief.…”

“…Tsu nami de pos its found at dif fer ent sites around the world con tain var i ous biogenic rem nants, such as ma rine, brack ish and fresh wa ter shells pre served in their en tirety or in the form of de bris (Moore and Moore, 1988;Hindson et al, 1996;Benson et al, 1997;Witter, 1999;Clague et al, 2000;Fujiwara et al, 2000;Goff et al, 2000Goff et al, , 2001Goff et al, , 2006Goff et al, , 2010Hutchison et al, 2000;Bryant and Nott, 2001;Dominey-Howes et al, 2006;Dominey-Howes, 2007;Pe ters et al, 2007;Mamo et al, 2009;Engel and Brückner, 2011; Pe ter son and Cruikshank, 2011), valves of ma rine and brack ish di a toms and other microfossils (Clague et al, 1994aHemphill-Haley, 1996;Witter, 1999;Dawson and Shi, 2000 Clague and Bobrowsky, 1994a, b;Clague et al, 1994;Witter, 1999;Domniney-Howes et al, 2006;Pe ters et al, 2007;Goff et al, 2010). The tsu nami de pos its found at Rowy are also rich in a diverse and quan ti ta tively large ad mix ture of biogenic in con tent de rived from ma rine, brack ish and fresh wa ter en vi ron ments as well as from the ter res trial en vi ron ment.…”

Historical and paleo-tsunami deposits on Kamchatka, Russia: long-term chronologies and long-distance correlations

“…Evidence of strong modern and pre-historic earthquakes and tsunamis has been found and studied in Japan, North America, and a number of other localities (e.g. Minoura et al, 1994;Benson et al, 1997;and others). On Kamchatka, studies of tsunami deposits began in about 1990 (e.g.…”

地層中に存在する古津波堆積物の調査

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