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

1997 ◽  
Vol 48 (2) ◽  
pp. 192-204 ◽  
Author(s):  
Boyd E. Benson ◽  
Kurt A. Grimm ◽  
John J. Clague
Keyword(s):  
British Columbia ◽  
Plate Boundary ◽  
Vancouver Island ◽  
Tidal Marshes ◽  
Tsunami Source ◽  
Cascadia Subduction Zone ◽  
Tsunami Deposits ◽  
The North ◽  
Sand Sheet ◽  
Sand Sheets

AbstractTwo 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.

Evidence for a Large Earthquake and Tsunami 100-400 Years Ago on Western Vancouver Island, British Columbia

1994 ◽  
Vol 41 (2) ◽  
pp. 176-184 ◽  
Author(s):  
John J. Clague ◽  
Peter T. Bobrowsky
Keyword(s):  
British Columbia ◽  
Subduction Zone ◽  
Vascular Plant ◽  
Plate Boundary ◽  
Vancouver Island ◽  
Tidal Marshes ◽  
Cascadia Subduction Zone ◽  
Great Earthquake ◽  
Marsh Soil ◽  
Sand Sheet

AbstractA peaty marsh soil is sharply overlain by a sand sheet and intertidal mud at tidal marshes near Tofino and Ucluelet, Vancouver Island, British Columbia. Foraminifera and vascular plant fossils show that the buried soil was submerged suddenly and was covered quickly by sand. Radiocarbon ages place this event between 100 and 400 yr ago. The coastal subsidence suggested by the submergence occurred in an area of net late Holocene emergence, perhaps during the most recent great earthquake on the northern part of the Cascadia subduction zone. The sand sheet overlying the peaty soil records the tsunami triggered by this earthquake. Similar stratigraphic sequences of about the same age have been reported from estuaries along the outer coasts of Washington and northern Oregon, suggesting that hundreds of kilometers of the Cascadia subduction zone may have ruptured during one, or a series of plate-boundary earthquakes less than 400 yr ago.

Optical Dating of Tsunami-Laid Sands

1996 ◽  
Vol 46 (2) ◽  
pp. 127-140 ◽  
Author(s):  
David J. Huntley ◽  
John J. Clague
Keyword(s):  
British Columbia ◽  
Radiocarbon Dating ◽  
Large Earthquake ◽  
Vancouver Island ◽  
Tsunami Source ◽  
Cascadia Subduction Zone ◽  
Stratigraphic Correlation ◽  
Optical Dating ◽  
Tsunami Measurements ◽  
Infrared Excitation

The ages of some tsunami deposits can be determined by optical dating, a key requirement being that the deposits are derived from sediment that was reworked and exposed to daylight by tidal currents, waves, wind, or bioturbation during the last years before the tsunami. Measurements have been made using 1.4 eV (infrared) excitation of K-feldspar grains separated from samples of prehistoric tsunami sand sheets and modern analogs of tsunami source sediments at four sites in Washington state and British Columbia. Source sands gave equivalent doses indicative of recent exposure to daylight. Tsunami sand at Cultus Bay, Washington, yielded an optical age of 1285 ± 95 yr (calendric years before A.D. 1995, ±1σ). At 2σ, this age overlaps the range of from 1030 to 1100 yr determined through a combination of high-precision radiocarbon dating and stratigraphic correlation. Tsunami sands at three sites near Tofino and Port Alberni on Vancouver Island, British Columbia, have optical ages of 260 ± 20, 325 ± 25, and 335 ± 45 yr. Historical records and radiocarbon dating show that the sand at each of the three sites is between 150 and 400 yr old. These optical ages support the hypothesis that the Vancouver Island sands were deposited by a tsunami generated by a large earthquake on the Cascadia subduction zone about 300 yr ago.

The 1946 Mount Colonel Foster rock avalanche and associated displacement wave, Vancouver Island, British Columbia

1989 ◽  
Vol 26 (3) ◽  
pp. 447-452 ◽  
Author(s):  
Stephen G. Evans
Keyword(s):  
British Columbia ◽  
Rock Avalanche ◽  
Vancouver Island ◽  
Wave Crest ◽  
Canadian Cordillera ◽  
Mountainous Terrain ◽  
The North ◽  
Displacement Wave ◽  
Volcaniclastic Rocks ◽  
Landslide Lake

The 1946 Vancouver Island earthquake (M = 7.2) triggered a rock avalanche from the north face of Mount Colonel Foster, central Vancouver Island, British Columbia. Approximately 1.5 × 106 m3 of Triassic volcaniclastic rocks detached from between el. 1965 m and el. 1600 m. Although just over half of this volume was deposited in the upper part of the track above el. 1080 m, approximately 0.7 × 106 m3 descended the lower part of the track and entered the waters of Landslide Lake at el. 890 m. The resultant displacement wave ran up a maximum vertical distance of 51 m on the opposite shore and the wave crest was about 29 m high when it spilled over the lip of the lake. Water displaced during the event destroyed forest in the upper reaches of the Elk River valley up to 3 km from Landslide Lake. The wave at Landslide Lake is comparable to other waves generated by similar magnitude rock avalanches in Peru and Norway and it is the largest recorded in the Canadian Cordillera. The case history illustrates the conditions where substantial damage may be caused by a rock avalanche well beyond the limits of its debris when it produces a landslide-generated wave in the mountainous terrain of the Cordillera. Key words: rock avalanche, earthquake-induced landslides, landslide-generated waves, mountains.

scholarly journals New Study on the 1941 Gloria Fault Earthquake and Tsunami

2016 ◽  
Author(s):  
Maria Ana Baptista ◽  
Jorge Miguel Miranda ◽  
Josep Batlló ◽  
Filipe Lisboa ◽  
Joaquim Luis ◽  
...  
Keyword(s):  
Waveform Inversion ◽  
Plate Boundary ◽  
Surface Displacement ◽  
Tsunami Source ◽  
Ne Atlantic ◽  
Atlantic Basin ◽  
North East ◽  
The North ◽  
Seismological Data ◽  
Tsunami Waveforms

Abstract. The M~8.3–8.4 25th November 1941 was one of the largest submarine strike-slip earthquakes ever recorded in the North East (NE) Atlantic basin. This event occurred along the Eurasia-Nubia plate boundary between the Azores and the Strait of Gibraltar. After the earthquake, the tide stations in the NE Atlantic recorded a small tsunami with maximum amplitudes of 40 cm peak to throw in Azores and Madeira islands. In this study, we present a re-evaluation of the earthquake epicentre location using seismological data not included in previous studies. We invert the tsunami travel times to obtain a preliminary tsunami source location using a backward ray tracing (BRT) technique. We invert the tsunami waveforms to infer the initial sea surface displacement using Empirical Green Functions without prior assumptions on the geometry of the source. The results of the BRT simulation locate the tsunami source quite close to the new epicentre. This fact suggests that the co-seismic deformation of the earthquake induced the tsunami. The waveform inversion of tsunami data favours the conclusion that the earthquake ruptured approximately 160 km segment of the plate boundary, in the eastern section of the Gloria Fault between −20.249°E and −18.630°E. The results presented here contribute to the evaluation of tsunami hazard in the North East Atlantic basin.

Intersecting intracontinental Tertiary transform fault systems in the North American Cordillera

1993 ◽  
Vol 30 (6) ◽  
pp. 1262-1274 ◽  
Author(s):  
Lambertus C. Struik
Keyword(s):  
British Columbia ◽  
North American ◽  
Plate Boundary ◽  
Late Eocene ◽  
Strike Slip ◽  
Plate Motion ◽  
Crustal Extension ◽  
North American Cordillera ◽  
The North ◽  
Dextral Strike Slip

In central British Columbia, north-trending dextral strike-slip faults that cut Late Eocene granite also truncate northwest-trending dextral strike-slip faults. The northwest-trending strike-slip faults bound the Wolverine Metamorphic Complex (Wolverine Complex), which has been uplifted primarily by northwest–southeast Eocene crustal extension and somewhat by Late Eocene northerly extension. The crustal extension is indicated by shallow-dipping extensions faults, dyke complexes, and stretching lineations. The Wolverine Complex and its bounding faults define a crustal pull-apart in an en echelon dextral transform. The northwest- and north-trending dextral strike-slip faults in central British Columbia are the continuations of faults that transect the interior of the North American Cordillera, and they represent at least two distinct plate boundaries intermittently active during the Early to Middle Eocene, and the Late Eocene to Early Oligocene. Each of these systems consists of en echelon strike-slip faults linked by extensional pull-aparts, locally represented by metamorphic core complexes. These two plate-boundary systems represent two distinct plate-motion configurations between the North American and Kula–Pacific plates. The older plate boundary is truncated and disrupted by the younger one. These two systems may in turn be disrupted by a younger and different plate-motion configuration represented by the transverse Basin and Range extension complex and its northern and southern transform boundary faults.

VII.—Sketch of the Geology of British Columbia

1881 ◽  
Vol 8 (5) ◽  
pp. 214-227
Author(s):  
George M. Dawson
Keyword(s):  
British Columbia ◽  
Vancouver Island ◽  
Fossil Plants ◽  
North East ◽  
The North ◽  
Time Spread

Cretaceous.—Lying everywhere quite unconformably below the Tertiary beds are the Cretaceous rocks, which constitute on the coast the true Coal-bearing horizon of British Columbia. These rocks probably at one time spread much more widely along the coast than they now do, but have since been folded and disturbed during the continuation of the process of mountain elevation, and have been much reduced by denudation. Their most important area, including the coal-rnining regions of Nanaimo and Comox, may be described as forming a narrow trough along the north-east border of Vancouver Island, 130 miles in length. The rocks are sandstones, conglomerates, and shales. They hold abundance of fossil plants and marine shells in some places, and in appearance and degree of induration much resemble the true Carboniferous rocks of some parts of Eastern America.

The plainfin midshipman’s soundscape at two sites around Vancouver Island, British Columbia

2018 ◽  
Vol 603 ◽  
pp. 189-200 ◽  
Author(s):  
WD Halliday ◽  
MK Pine ◽  
APH Bose ◽  
S Balshine ◽  
F Juanes
Keyword(s):  
British Columbia ◽  
Vancouver Island
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