175
A REVIEW OF SOME TSUNAMIS IN CANADA
T.S. MURTY
W.F. Baird & Associates Coastal Engineers Ltd.
1145 Hunt Club Road, Suite 500
Ottawa, Ontario K1V 0Y3, Canada
Abstract
Some past tsunamis in various regions of Canada have been reviewed. These tsunamis have
occurred from a variety of sources: under-ocean earthquakes, sub-marine landslides and
human-made inadvertent large chemical explosions. Resonance amplification of the
tsunami has been identified as important in the Alberni Inlet on the Vancouver Island,
British Columbia and also in the Burin Inlet in Newfoundland. The results of the various
numerical models for tsunami generation, propagation onto the shelf and into the coastal
inlets that formed the scientific basis for the British Columbia tsunami warning system
have been briefly discussed.
1. Introduction
Tsunamis have occurred in Canada due to under ocean earthquakes, submarine landslides
an even from large human made explosions. Geographically these events took place on the
Pacific coast, the Straits of Georgia and Juan de Fuca, the St. Lawrence Estuary, Nova
Scotia and in Newfoundland. In the twentieth century the following is a partial
chronological list of tsunamis in Canada.
1. December 6th , 1917: Large tsunami in Halifax Harbor due to an explosion.
2. November 18th, 1929: Large tsunami in Burin Inlet due to an earthquake off the
coast of Newfoundland.
3. June 23, 1946: Small tsunami in the Strait of Georgia due to an earthquake on the
Vancouver Island.
4. March 28th 1964: Large tsunami on the coast of British Columbia due to an
earthquake in Alaska.
5. April 27, 1975: Large tsunami in Kitimat Inlet due to a submarine landslide.
All these tsunamis have quite different characteristics as can be seen below. During the
First World War, a munitions ship caught fire and exploded in Halifax harbor on December
6th, 1917. In the harbour narrows the amplitude of the tsunami that was generated was
about ten meters in amplitude.
The Grand Banks earthquake of November 18 th, 1929 created a tsunami of at least 12.2
metres in amplitude in the Burin Inlet. Some estimates put the maximum amplitude at
A. C. Yalçıner, E. Pelinovsky, E. Okal, C. E. Synolakis (eds.),
Submarine Landslides and Tsunamis 175-183.
@2003 Kluwer Academic Publishers. Printed in Netherlands
176
about 35 meters, which could be an overestimate. The turbidity currents following the
earthquake caused numerous cable breaks in the Atlantic Ocean. On June 23, 1946, a small
tsunami occurred in the northern part of the Strait of Georgia (between Vancouver Island
and the main land) following an earthquake on Vancouver Island close to the western shore
of the Strait.
The May 1960 Chilean earthquake tsunami was observed at several locations of the
Pacific Coast of Canada.
Following a large earthquake in Alaska on March 28 th, 1964, a major Pacific wide
tsunami was generated. Outside of Alaska, the largest tsunami amplitude anywhere on the
west coast of North America occurred not exactly on the open coast, but inland at Port
Alberni at the head of the Alberni Inlet. This can be explained as due to the amplification of
the tsunami through quarter wave resonance as the tsunami traveled from the mouth to the
head of the inlet.
On April 27th, 1975, following a major submarine landslide, a tsunami was generated in
the Kitimat Inlet in the Douglas Channel system of the northern part of the coast of British
Columbia.
2. The Halifax Harbour Explosion Tsunami
In the midst of World War I, shortly before 9 a.m. on December 6, 1917 the munitions ship
Mont Blanc collided with the relief ship Imo in the Narrows of the Canadian port Halifax.
The Mont Blanc was carrying the equivalent of about 2900 short tons (2000lb/ton) of TNT.
A fire broke out onboard the Mont Blanc and the crew abandoned ship, which drifted into
the Halifax side and grounded near one of the piers. Shortly about 9:00 a.m. the cargo
exploded devastating a large section of the city. Estimates of the casualties are as high as
2000 dead and 9000 injured. Of these, many are thought to have died from the affects of
the tsunami that followed. The documented damage of this, the greatest man made
explosion to that date, would later be used in the Manhattan project to estimate the
devastation of the first nuclear bombs. [1, 2].
There was no operational tide gauge at the time recording the changes in sea level, but
there are several narrative reports of extreme high and low water and useful information
might be obtained from them [3]. The explosion occurred very close to the time of low tide,
about 0.5 m below mean water level.
To hindcast the tsunami, [1] ran a linearized finite element model covering the full area
of Halifax Harbour from the head of the Bedford Basin to the seaward entrance to the
harbour approach. The model was initialized with a setup derived using an empirical
formula for waves resulting from explosions in water. Figures 1 to 2 respectively show the
tsunami travel times and the tsunami amplitudes.
177
Figure 1
Figure 2
Figure 1. The time of arrival in minutes of the
initial wave taken to be the time the sea level
first exceeded 0.2 m. From Greenberg et al,
(1994)
Figure 2. The maximum elevation (m) achieved during
the model run and locations (estimated) of the anecdotal
observations. The detail of the Narrows is shown in the
lower left. From Greenberg et al, (1994).
The model results when put together with anecdotal reports give a consistent overview
of the tsunami amplitude and progression. The study by [1, 2] indicates that in the Narrows
at the explosion site, the wave was over 10 m high, but that the amplitude diminished
greatly further away. In the Bedford Basin the tsunami would not have been damaging and
in the outer reaches of the harbour, it would have been noticeable only to those looking for
it.
3. The Grand Banks Earthquake Tsunami
The so-called Grand Banks earthquake occurred on Nov. 18, 1929, in the Atlantic Ocean,
southeast of Newfoundland. The epicenter was at 4430’N, 5715’W and the time of
occurrence was 0.432:8 (Newfoundland Standard Time). The turbidity currents following
this earthquake caused numerous cable breaks in the Atlantic Ocean.
This earthquake generated a tsunami with amplitudes of at least 12.2 m [4] in Burin
Inlet on the south coast of Newfoundland and killed 26 people. Gregory [5] gave 30.5 m as
the maximum amplitude in Burin Inlet. McIntosh [6] gave a value of 4.6 m for the tsunami
amplitude at Lamaline. According to Johnstone, no tsunami was observed at Sable Island,
178
Figure 3. Travel-time curves (minutes) for the Grand Banks earthquake tsunami of Nov. 18, 1929.
Probably it’s because of the fact that the island was well protected by sandbanks. Although
the tsunami waves were considerably amplified in a northerly direction (i.e. in the direction
of Newfoundland), they were not significantly amplified in a westerly direction as can be
seen from the water- level records on the Canadian and U.S. east coasts. At Halifax, the
amplitude was only 0.5 m and at Atlantic City the amplitude was 0.3 m. Murty [7]
explained the nonamplification westward as due to the orientation of the fault in an eastwest direction. Murty and Wigen [8] studied this tsunami in detail and showed that
resonance in the V-shaped Burin Inlet accounts for the great amplification of the tsunami in
that inlet. Figure 3 shows the travel-time curves for this tsunami and it can be seen that the
tsunami energy traveled preferentially towards the south coast of Newfoundland.
Although turbidity currents and tsunamis are not directly related, nevertheless both
could be caused by earthquakes such as the 1929 Grand Banks earthquake. Turbidity
currents and tsunamis could also be generated by landslides whether or not an earthquake
occurred.
Most submarine telegraph cables from North America to Europe pass south of
Newfoundland. At about 2032 h GCT, Nov. 18, 1929, an earthquake of magnitude 7.2
occurred on the continental slope southeast of the Cabot Trench. This generated a tsunami
that caused considerable property damage and loss of life along the shores of Placentia
Bay, which was discussed above.
Another important consequence occurred during the 13 h and 17 min following the
earthquake. An orderly sequence of breaks occurred in the telegraph cables of 483 km
south of the epicenter. According to Heezen and Ewing [10], although all cables along the
continental slope and on the floor of the ocean south of the epicenter were broken, none on
the continental shelf were disturbed. The exact times and locations of the cable breaks were
known, respectively, from the telegraph records and resistance measurements.
Bucher [9] hypothesized that erosion in the submarine canyons caused by the tsunami
left the cables unsupported, thus leading to breakage. Heezen and Ewing [10] criticized
Bucher’s explanation on the grounds that the cable breaks were too regular in time and the
cables were of different ages and breaking strengths.
Heezen and Ewing [10] showed rather convincingly that the successive series of breaks
in the telegraph cables following the Grand Banks earthquake of 1929 were caused by the
turbidity current generated.
179
4. Tsunami in Kitimat Inlet Due To a Landslide
A major submarine slide occurred on April 27, 1975 in Kitimat Inlet in the Douglas
Channel system on the West Coast of Canada (Figure 4). Following this slide, at least two
water waves were observed and it was estimated that the range (crest to trough) of the first
wave could have been 8.2 m. Two simple theories have been used by Murty [11] to
estimate the wave height. Considering the uncertainties both in the observed data as well as
in the calculated wave height, there is reasonable agreement.
Kitimat Inlet on the West Coast of British Columbia has a history of landslides: several
slides occurred during the period 1952 to 1968, and also in 1971. On October 17, 1974,
following a submarine slide, a water wave of 2.8 m amplitude was generated. On April 27,
1975, following a major slide, water waves with ranges up to 8.2 m were generated. In
other parts of British Columbia, also major slides occur – for example, in Howe Sound, in
1995.
Depending on the nature of movement of the sediment, a slide will have two
components: horizontal and vertical. Usually, one component dominates the other. For
theoretical and laboratory studies, it is convenient to distinguish between vertical and
horizontal slides, depending upon which component dominates. Another type of
classification of slides is: (a)
Figure 4. Geography of the Pacific Coast of Canada
land-slides, (b) submarine or under-water slides. Actually, in several instances, there may
be visual manifestations in the surrounding land, even in the case of a submarine slide.
Here, we concern ourselves specifically with the submarine slide of April 27, 1975 in
the Kitimat Inlet. There are visual manifestations of the slide in the Moon Bay area even
now, and it is estimated that about 3 x 10 6m3 of material was involved in this bay alone.
Casagrande [12] estimated the total volume of the material involved in the slide that gave
rise to the water waves to be about 107m3. Based on an examination of the hydrographic
charts prepared before and after the slide, and some rough measurements of shore features,
Murty [11] suggested that an upper limit for the total amount of material involved in the
180
whole slide is about 26 x 106m . Actually, it is not the volume of the material involved in
the slide that directly enters into the calculation of the amplitude of the water waves
generated: various factors associated with the slide together determine the amplitude of the
waves.
At the time of occurrence of the slide of April 27, 1975, there was no major seismic
event reported in that area. Also, there was no meteorological event at that time which
could have caused large water-level oscillations.
Hence, there is no doubt that water waves were generated by the submarine slide. At
least two water waves (and possibly three) were generated, and propagated into the
connecting bays and channels. The largest wave was estimated to be 8.2 m in range (crest
to trough).
Brown [13] mentions that the first wave was observed at 10:05 a.m. (Pacific Daylight
Savings Time) and, at 10:15 a.m., the bottom was visible. The whole water-level
disturbance lasted about an hour. In Bish Creek and Clio Bay, which are about 8 km from
the site of the slide, at least one wave was observed. Some damage occurred in Bish Creek
and the range in Clio Bay was estimated to be about 6.7 m. No wave was noted in Sue Bay,
probably because of the complicated path needed for the wave to travel into that bay.
Although Minette Bay is at the head of the Kitimat Arm, it is an extremely shallow bay
(most of the time there is no water in it) and, further, the bay bottom is very rough because
of vegetation and tree trunks and it is quite conceivable that the wave could not have
penetrated and traveled in Minette Bay.
The Kitimat Submarine Slide of April 27, 1975 occurred approximately 53 minutes
after the occurrence of low tide. There appears to be sufficient observational data to suggest
that submarine slides appear in association with low tide. Murty [11] modeled this
following a technique described in Miloh and Streim [14].
5. Results of Numerical Models for B.C. Tsunami Warning System
Maximum tsunami water levels and currents along the British Columbia outer coast have
been computed for waves originating from Alaska, Chile, the Aleutian Islands (Shumagin
Gap), and Kamchatka [15, 16]. Three computer models have been developed to generate
and propagate a tsunami from each of these source regions in the Pacific Ocean to the
continental shelf off Canada’s west coast, and into twenty separate inlet systems. The
model predictions have been verified against water level measurements made at tide gauges
after the March 28, 1964 Alaska earthquake. Simulated seabed motions giving rise to the
Alaskan and Chilean tsunamis have been based on surveys of the vertical displacements
made after the great earthquakes of 1964 (Alaska) and 1960 (Chile). Hypothetical bottom
motions have been used for the Shumagin Gap and Kamachatka simulation. These
simulations represent the largest tsuanamigenic events to be expected from these areas.
Maximum wave and current amplitudes have been tabulated for each simulated tsunami
at 185 key locations along the British Columbia coast. On the north coast of British
Columbia, the Alaska tsunami generated the largest amplitudes. In all other regions of the
west coast, the largest amplitudes were generated by the Shumagin Gap simulations. Wave
amplitudes in excess of 9 m were predicted at several locations along the coast and current
speeds of 3 to 4 m/s were produced. The most vulnerable regions are the outer coast of
Vancouver Island, the west coast of Graham Island, and the central coast of the mainland.
181
Some areas, such as the north central coast, are sheltered enough to limit expected
maximum water levels to less than 3 m.
We note that the effects of dry land flooding have not been included owing to the large
amount of additional topographic data that is required and the special demands created for
high-resolution, local-area models in many locations. This does not pose serious problems
inmost areas. However, near the heads of inlets (where these is often an extensive area of
flatlands associated with a river mouth) modeled wave heights may be appreciably
overestimated. The four source areas shown in Figure 5 have been identified as likely sites
for generation of tsunamis that could threaten Canada’s coastline. This is based on the
occurrence of previous tsunamigenic earthquakes and on estimates of the likelihood of
future great earthquakes in each area.
Figure 5. Epicenters of earthquakes used in tsunami simulations. The bold line is the boundary of the deep
ocean model (DOM). (1: Alaska, 2: Chile, 3: Shumagin Gap, 4: Kamchatka). [16]
Tsunamis arriving at British Columbia’s outer coast propagate into all exposed inlet
systems. Twenty of the more exposed systems have been identified and incorporated into
this study. Each has a corresponding numerical model that uses time-varying water
elevations at one or more connections to the continental shelf to calculate the water surface
response and currents within the system. Construction of each model required detailed
extraction of bathymetry and dimensional data (cross-sectional and surface areas) and
calibration.
Seismic activity in the Pacific Ocean is confined primarily to zones adjacent to the
continental margins where subduction of the oceanic plates under the continental
landmasses episodically releases bursts of energy in the form of an earthquake. Other areas,
such as the Hawaiian Islands, are also sites of large earthquakes but these do not pose a
threat of producing a destructive tsunami in British Columbia waters.
If an earthquake results in vertical (dip-slip) motion of the oceanic crust, then it is
tsunamigenic, that is, it will result in the deformation of the water surface and subsequent
propagation of the disturbance outward form the source as a seismic sea wave (tsunami).
182
Tsunamis from even moderately small earthquakes may result in significant damage within
a short distance of the source. If the earthquake is sufficiently large (with a Richter scale
magnitude greater than 7.5 to 8.0), however, then a large tsunami may be generated and
damage will result at great distances from the source. This latter situation is most relevant
to the west coast of Canada.
Three distinct numerical models were used to simulate tsunami generation and
propagation to the inlets of British Columbia. A deep ocean model (DOM) with 0.5
resolution (Figure 5) has been used to simulate bottom motions that give rise to tsunamis
and to propagate the resulting waves to the continental shelf (Figure 6) off Canada’s west
coast. There, a 5-km
Figure 6. Shelf model grid outline (A) and outline of
region used for field plots of northern British
Columbia (B). From Dunbar et al, 1989.
Figure 7. Map showing water level and current
locations in some inlets. From Dunbar et al,
1989
resolution model (C2D) covering the shelf propagates the waves to the entrances of the
inlets. Finally, 2-km resolution models (FJORDID) determine water levels and current
velocities in the inlet (Figure 7). The shelf and inlet models were run simultaneously as a
coupled system. Wave amplitudes on the edge of the shelf were specified from a preceding
run of the deep ocean model reported in [16].
After confirming the correctness of all model components using historical tsunami data,
the three models were run for a set of simulated tsunamigenic earthquakes. These included
simulations for measured bottom displacements at the source regions of the 1960 Chilean
and 1964 Alaskan tsuanmigenic earthquakes, and hypothetical earthquakes at the Shumagin
Gap and Kamchatka Peninsula sites. In addition, the Alaskan simulation was repeated for a
case where bottom motions were amplified by 25%. The simulations provided wave
amplitudes and currents.
183
References
1. Greenberg, D.A., Murty, T.S. and Ruffman, A. (1993). A Numerical Model for the Tsunami in Halifax Harbour
due to the Explosion in December 1971. Marine odesy, 16:153-167.
2. Greenberg, D.A., Murty, T.S. and Ruffman, A. (1994). Modeling the Tsunami From the 1917 Halifax Harbor
Explosion, Science of Tsunami Hazards, Vol. 11, No. 2, 67-80.
3. Ruffman, A, Greenberg, D.A. and Murty, T.S. (1995). The Tsunami from the Explosion in Halifax Harbour,
Ground Zero, pp. 327-344, Edited by A. Ruffman And C.D. Howell, Nimbus Publishing Ltd. Halifax.
4. Johnstone, J.H. L. 1930. The Acadian-Newfoundland earthquake of November 18, 1929. Proc. Trans. N.S. Inst.
Sci. Halifax, N.S. 17:223-237.
5. Gregory, J.W. 1929. The earthquake south of Newfoundland and submarine canyons. Nature 124: 945-946.
6. McIntosh, D.S. 1930. The Acadian-Newfoundland earthquake. Proc. Trans. N.S. Inst. Sci. 17:213:222.
7. Murty, T.S. (1977). Seismic Sea Waves-Tsunamis, Bulletin No. 198, Fisheries Research Board of Canada,
Ottawa, 337p.
8. Murty, T.S., and Wigen, S.O. 1976. Tsunami behavior on the Atlantic coast of Canada and some similarities to
the Peru coast. Proc. IUGG Symp. tsunamis and tsunami Res. Jan. 29-Feb. 1, 1974. Wellington, N.Z., R. Soc.
N.Z. Bull. 15:51-60.
9. Bucher, W.H. 1940. Submarine Valleys and Related Geologic Problems of the North Atlantic. Geol. Soc. Am.
Bull. 51: 489-512.
10. Heezen, B.C., and Ewing, M. 1952. Turbidity currents and submarine slumps and the 1929 Grand Banks
earthquake. Am. J. Sci. 250: 849-873.
11. Murty, T.S. (1979). Submarine Slide-Generated Water Waves in Kitimat Inlet, J. of British Columbia, Phys.
Res., Vol. 84, No. C12, 7777-7779.
12. Casagrande, L. (1977). Kitimat Arm B.C. Slide of April 27, 1975. Unpubl. manuscript. Casagrande
Consultants, 40 Massachusetts Avenue, Arlington, Mass. 30 pp. and Appendices.
13. Brown, W.E. (1975). Underwater Subsidence at Kitimat: Sunday 27 April, 1975 (Unpubl. man., Institute of
Ocean Sciences, Patricia Bay, Fisheries and Environment Canada, Sidney, B.C. 8 pp.
14. Miloh, T and H.L. Strein (1978). Tsunami effects at coastal sites due to offshore faulting, tectonophysics, vol.
46, 347-356.
15. Dunbar, D.S., LeBlond, P.H. and Murty, T.S. (1989a). Evaluation of Tsunami Amplitudes for Pacific Coast of
Canada, Progress in Oceanography, Vol. 26, 115-177.
16. Dunbar, D.S., LeBlond, P.H. and Murty, T.S. (1989b). Maximum Tsunami Amplitudes and Associated
Currents on the Coast of British Columbia, Science of Tsunami Hazards, Vol. 7, No. 1, 3-44.
184