Tsunamis and tectonic deformation at the northern Cascadia margin: a 3000-year record from Deserted Lake, Vancouver Island, British Columbia, Canada

Abstract

Three layers of sand occur within a sequence of muddy gyttja in a 3 m core recovered from Deserted Lake, which lies at the head of a fjord on the central west coast of Vancouver Island, British Columbia, Canada. The sedimentology and microfossil assemblages of these layers are consistent with deposition by tsunamis. Radiocarbon ages suggest that the tsunamis were generated by plate-boundary earthquakes at the Cascadia subduction zone about 2600, 1600 and 300 years ago. Diatom and protozoan contents of the gyttja layers indicate that relative sea level fell in the periods between tsunamis. The sea-level changes are probably a product of interseismic uplift of the North America plate margin. Post-tsunami diatom and protozoan assemblages are generally more marine than their pre-tsunami counterparts, suggesting that the study site subsided during earthquakes. Estimates of interseismic and coseismic deformation during one earthquake cycle indicate that less than half of the interseismic uplift was recovered during the earthquake, leading to cumulative, or permanent, uplift of the area.

Towards a record of Holocene tsunami and storms for northern Hawke's Bay, New Zealand

“…However, in many cases, the context in which the deposit is found may be the most reliable way of attributing a causal event to the deposit (Gelfenbaum et al 2002). Coincidence of tsunami deposits with evidence for vertical deformation caused by earthquakes in the sedimentary record is widely reported in international literature, especially at subduction zone boundaries (e.g., Atwater 1987;Hutchinson et al 2000;Pinegina & Bourgeois 2001;Nanayama et al 2003). In most cases the earthquake is assumed to be the triggering mechanism for the tsunami.…”

The Role of Holocene Relative Sea-Level Change in Preserving Records of Subduction Zone Earthquakes

“…As a result, widespread stratigraphic evidence of coseismic subsidence is limited to the AD 1700 great earthquake [70][71][72]. One of the few longer records (∼2500 years) of coseismic subsidence comes not from a coastal wetland, but from a study by Hutchinson et al [73] that identified three tsunami deposits in a lake coincident with changes in lake salinity. Salinity changes were inferred to be the result of coseismic subsidence lowering the bedrock sill of the lake sufficiently for it to be breached by tidal waters in the decades to centuries following the earthquakes (Figs.…”

“…Gray shaded area beginning at ∼1 ka highlights the period of continuous marsh formation and preservation. c Age ranges for three instances of coseismic subsidence preserved at Deserted Lake, western Vancouver Island [73] …”

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

“…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.…”