Establishing the Inundation Distance and Overtopping Height of Paleotsunami from the Late-Holocene Geologic Record at Open-Coastal Wetland Sites, Central Cascadia Margin

Schlichting, Robert B.

doi:10.15760/etd.5246

Cited by 13 publications

(18 citation statements)

References 15 publications

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“…For Cascadia, paleotsunami deposits are identified as being anomalous sand layers in low energy marsh or lacustrine environments (Peters et al 2001, Atwater 1987, Clague et al 2000. Additional information that indicates a seaward source of sediments, such as microfossils (Hemphil-Haley 1995) or geochemical signature (Schlichting 2000), are also useful for determining that a deposit was formed by a tsunami. Although at times identification is difficult, deposits believed to be from paleotsunamis have been identified at 53 locations in Cascadia ( Fig.…”

Section: Identification Of Tsunami Depositsmentioning

confidence: 99%

Using Tsunami Deposits to Improve Assessment of Tsunami Risk

Jaffe

Gelfenbaum

2002

Solutions to Coastal Disasters '02

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The maximum depth of sediment biomixing is directly related to the vertical extent of post-depositional environmental alteration in the sediment; consequently, it is important to determine the maximum burrowing depth. This study examined the maximum depth of bio-turbation in a natural marine environment in Funakoshi Bay, northeastern Japan, using observations of bioturbation structures developed in an event layer (tsunami deposits of the 2011 Tohoku-Oki earthquake) and measurements of the radioactive cesium concentrations in this layer. The observations revealed that the depth of bioturbation (i.e., the thickness of the biomixing layer) ranged between 11 and 22 cm, and varied among the sampling sites. In contrast, the radioactive cesium concentrations showed that the processing of radioactive cesium in coastal environments may include other pathways in addition to bioturbation. The data also revealed the nature of the bioturbation by the heart urchin Echinocardium corda-tum (Echinoidea: Loveniidae), which is one of the important ecosystem engineers in sea-floor environments. The maximum burrowing depth of E. cordatum in Funakoshi Bay was 22 cm from the seafloor surface.

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Section: Identification Of Tsunami Depositsmentioning

confidence: 99%

Using Tsunami Deposits to Improve Assessment of Tsunami Risk

Jaffe

Gelfenbaum

2002

Solutions to Coastal Disasters '02

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“…These complications include channel hydrodynamics, coincident tidal stages, and basin seiches (Myers et al 1999). By comparison, paleotsunami sand deposits that are preserved in peat bogs from low-elevation beach plains (Schlichting 2000) provide less complicated evidence of surge inundation distance.…”

Section: Introductionmentioning

confidence: 99%

Mapped Overland Distance of Paleotsunami High‐Velocity Inundation in Back‐Barrier Wetlands of the Central Cascadia Margin, U.S.A.

Schlichting

Peterson²

2006

The Journal of Geology

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Investigations of back-barrier, open-coastal plain settings have been used to establish minimum inundation distances of prehistoric tsunamis produced by great subduction zone earthquakes in the central Cascadia margin. Distinctive sand sheets were characterized at four localities within the central Cascadia margin, a shoreline distance of about 250 km. The sand sheets vary in thickness from 0.2 to 25 cm. They thin in the landward direction and consist of well-sorted beach sand that fines upsection. Many of the sand sheets include capping layers of organic-rich detritus, as well as assimilated mud rip-up clasts and soil litter. Marine diatoms and bromine (i.e., marine tracers) were used to confirm marine surge origins for the anomalous sand sheets. Radiocarbon dating of the sand sheets demonstrates correspondence with reported great Cascadia earthquake events at 0.3, ∼1.1, ∼1.3, ∼1.7, and ∼2.5 Ka. One sand sheet mapped at all four localities is dated at 600-950 calibrated radiocarbon years before present. This interpreted paleotsunami event does not correspond to a central Cascadia rupture, so it is tentatively assigned to a far-field source. Minimum overland inundation distances of the near field (Cascadia tsunami) at the four study localities range from 0.3 to 1.3 km, with a mean inundation for all sand sheets of 0.5 km.

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“…The wreck debris was distributed along the spit and/or the Neahkahnie headland area by seasonally reversing currents for several years or decades. The A.D. 1700 Cascadia earthquake produced a moderate-sized tsunami runup in the Nehalem area (Schlichting, 2000) that swept wreck debris across the Nehalem spit and into Nehalem Bay. Tsunami backwash from Nehalem Bay was directed down the Nehalem channel and over the low-lying sections of the middle spit ( Figure 14).…”

Section: Discussionmentioning

confidence: 99%

Geoarchaeology of the Nehalem spit: Redistribution of beeswax galleon wreck debris by Cascadia earthquake and tsunami (∼A.D. 1700), Oregon, USA

et al. 2011

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A coincidence of the Beeswax galleon shipwreck (ca. A.D. 1650-1700) and the last Cascadia earthquake tsunami and coastal subsidence at ϳA.D. 1700 redistributed and buried wreck artifacts on the Nehalem Bay spit, Oregon, USA. Ground-penetrating radar profiles (ϳ7 km total distance), sand auger probes, trenches, cutbank exposures (29 in number), and surface cobble counts (49 sites) were collected from the Nehalem spit (ϳ5 km 2 area). The field data demonstrate (1) the latest prehistoric integrity of the spit, (2) tsunami spit overtopping, and (3) coseismic beach retreat since the A.D. 1700 great earthquake in the Cascadia subduction zone. Wreck debris was (1) initially scattered along the spit ocean beaches, (2) washed over the spit by nearfield tsunami (6-8 m elevation), and (3) remobilized in beach strandlines by catastrophic beach retreat. Historic recovery of the spit (150 m beach progradation) and modern foredune accretion (Ͼ5 m depth) have buried both the retreat scarp strandlines and associated wreck artifacts. The recent onshore sand transport might re-expose heavy ship remains in the offshore area if the wreck grounded in shallow water (Ͻ20 m water depth of closure).

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Establishing the Inundation Distance and Overtopping Height of Paleotsunami from the Late-Holocene Geologic Record at Open-Coastal Wetland Sites, Central Cascadia Margin

Abstract: are tested by marine diatom and bromine anomalies. These tracers are being used to extend paleotsunami flooding records to include low-velocity inundation distances.

Cited by 13 publications

References 15 publications

Using Tsunami Deposits to Improve Assessment of Tsunami Risk

Using Tsunami Deposits to Improve Assessment of Tsunami Risk

Mapped Overland Distance of Paleotsunami High‐Velocity Inundation in Back‐Barrier Wetlands of the Central Cascadia Margin, U.S.A.

Geoarchaeology of the Nehalem spit: Redistribution of beeswax galleon wreck debris by Cascadia earthquake and tsunami (∼A.D. 1700), Oregon, USA

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