Tsunami 1929:

The earth's continents are constantly eroding, and the erosional detritus is carried mainly by rivers (but on occasion by wind and by glacial ice) to settle in the sea on the continental shelves. Ocean waves and tidal currents sort the material over time and move it to, and over, the continental shelf edge. Until the early 1950s, the processes of moving these erosional sediments down into the deep ocean was not really known or understood by earth scientists.

It was an event quite unknown in the lives of most who felt it in Atlantic Canada. The surface wave magnitude (Ms) 7.2 earthquake of Monday, November 18, 1929 struck at 5:02 p.m. N.S.T. in the late afternoon -- seventy-five years ago. The hypocentre was some 18 km below the seafloor of the northwest Atlantic Ocean, at the mouth of the Laurentian Channel in 2 km of water depth on the continental slope south of the Burin Peninsula on the south coast of what was then the British colony of Newfoundland. It was felt as far away as Montréal, in the New England states as far south as New York City, and there is even a serendipitous felt report in Bermuda of a probable seismic 'surface wave'; it registered on seismographs around the world. It is still remembered by older residents of the Atlantic Provinces as the only felt earthquake experienced in their lives. Onshore the damage from the earthquake's shaking was restricted to some slumping and minor building damage in Cape Breton Island; some chimneys were dislocating resulting in subsequent chimney fires in the next few days. Newfoundland, despite its proximity to the epicentre, experienced virtually no physical damage onshore.

Two-and-a-half hours after the event, on a dead calm, bright, moonlit night, on a rising high tide, three main pulses of a tsunami arrived, quite unexpectedly, along the coast of the Burin Peninsula, with amplitudes of 2 to 7 m. There was an initial slow withdrawal of the sea to expose ocean floor in places never before seen by local inhabitants, then the water returned in three positive pulses that rose 2 to 7 m above sealevel. The height and forward momentum of the arriving tsunami caused the runup to rise to as much as 13 m above sealevel at the ends of the long narrow harbours such as Port au Bras, St. Lawrence, Little Lawn Harbour, Lawn, Lord's Cove, Taylor's Bay, and Lamaline. Twenty-eight persons lost their lives, and the fishing capability of the coastal communities was devastated.

There was as yet no road to connect the communities to each other or to link the Burin Peninsula to the rest of Newfoundland to the north. Landline telegraph communications with the rest of the Island had been broken by a storm two days earlier, and the tsunami took out the land lines between the coastal communities. In St. Lawrence the telegraph station ended up floating in the harbour. The Burin had to cope on its own for two-and-a-half days before a coastal ferry named the PORTIA, which had a working wireless radio, arrived on the scene. Despite the success of wireless 17 years earlier during the TITANIC disaster, the local communities had no radio sets, and while a wireless was available on the DAISY situated in Burin harbour, no-one knew how to operate it to get a message out!

The tsunami was seen in Cape Breton Island, Nova Scotia, at about 8:00 p.m. A.S.T. on November 18th, where it did minor damage. The one possible death in Nova Scotia has been shown to be false and was based on incomplete information. The tsunami refracted counterclockwise around the Avalon Peninsula to arrive in the Bonavista area about 1:30 a.m. N.S.T. the next morning. The tsunami was physically seen along the coast of Nova Scotia as far southwest as Lunenburg, and in Bermuda at about 8:00 p.m. local time in the evening. It rose in Halifax Harbour, where it flowed over the gates of the commercial drydock at Halifax Shipyards for five minutes and is recorded on the tide gauge record. The only tide gauge operating in Atlantic Canada to record the tsunami was in Halifax; the British had not yet installed a tide gauge anywhere in Newfoundland (or in Bermuda).

The tsunami travelled at about 615 km/hr south and eastwards in the deep ocean; the tsunami travelled at about 105 km/hr over the shallower continental shelf of Canada north and westwards. The tsunami was recorded on tide gauges as far south as Charleston, South Carolina, in the United States, in the Azores, and on the west coast of Portugal. The tide gauge records for the United Kingdom were destroyed during WW II bombings. The rather high water recalled by many Newfoundlanders as the "tidal wave" on the next morning of Tuesday, November 19, 1929 was not the tsunami. It was a significant storm surge of an early winter storm that had tracked up the Atlantic coast from New England and the Maritimes over the past day. It snowed that day on the Burin and turned bitterly cold, making life even more miserable for people affected by the tsunami.

At the instant of the earthquake, five transAtlantic telegraph cables broke in numerous places near the top of the continental slope as the underwater landslides began to move down into deeper water. Over the next two hours, seven more cables parted progressively in deeper and deeper water, and more distant from the initial breaks. The repairs to the twenty-eight breaks in the twelve transAtlantic telegraph cables required all available cable ships, and repairs stretched well into 1930. At the time, the mechanism of the seafloor disruption was not understood, and was not successfully worked out for some 23 years. It is now known that the earthquake's strong vibrations shook loose and mobilized up to 200 cubic kilometres of ocean floor sediments on the continental slope. The underwater slump, or landslide, travelled downslope, initially at speeds of up to 50 to 70 km/hr, as a slurry of water and sediment, now called a "turbidity current".

The turbidity current then slowed and eventually travelled over 1,200 km from its source out across the Sohm Abyssal Plain, laying down a thin layer of graded sediment -- material that had initially been deposited over thousands of years on the upper Continental Slope, and was now in 3,000 to 4,000 m water depth. This process of filling the ocean basins by an ongoing series of turbidity currents is now recognised as a very important final step of a process that moves sediments from the rivers and coasts of the continent, out onto the continental shelves, over the shelf break, and then down into the ocean basins as turbidity currents.

There is still an ongoing debate as to whether other earthquakes, in what is now known as the Laurentian Slope seismic source zone, could cause other slumps and tsunamis. One other apparent slump was reported nearby in October of 1884 when three transAtlantic cables all broke in one area at about the same time, south of the Tail of the Banks. The continental slope of Atlantic Canada, when mapped by deep ocean sidescan sonar, or other swath-mapping multi-beam sonar techniques, shows substantial evidence of other downslope mass movements, though the ages and frequency of these events is not known. A number of the apparent slump scars may reflect slow creep events rather than catastrophic landslides such as occurred 75 years ago south of Newfoundland. Only the rapid underwater landslides will create a tsunami. Much like moving one's leg rapidly to one side in a bathtub, the rapid movement of the ocean floor creates a very long wavelength, low amplitude, fast-moving, gravity wave on the ocean's surface -- a 'tsunami'.

It is popularly believed by many Newfoundlanders that the collapse of the fisheries and the loss of the eel grass in the early 1930s were a direct result of the 'tidal wave'; this observation appears to be unfounded. The onshore geological signature of the 1929 tsunami has been found in many of the harbours along the south coast of the Burin. At Taylor's Bay the tsunami's signature clearly shows as a band of white sand about 10 cm down in the brown peat (see photograph at the Dalhousie University Department of Earth Sciences website ). A case study at St. Lawrence, and a careful mapping survey in Taylor's Bay, have allowed the zone of tsunami runup to be mapped. In St. Lawrence, community growth has gone forward without regard to the 1929 runup zone or a possible recurrence. In contrast, the village of Taylor's Bay has never recovered from its losses on that fateful November 18th evening. Documenting of community folklore has allowed a rich oral history of the event, songs, stories, poems, photographs, and myths surrounding the event, to be documented throughout the Burin Peninsula.  

 

Reference to materials on this page provided by Maritime Museum of the Atlantic