The slump was triggered by an earthquake of magnitude 7.3, 150 miles south of the Island of Newfoundland, Canada, at the edge of the relatively shallow continental shelf.
On November 18, 1929, a major earthquake occurred 150 miles south of Newfoundland, Canada, along the southern edge of the Grand Banks. This magnitude 7.3 event was felt as far away as New York and Montreal. Damage on land was concentrated on Cape Breton Island in the northern part of Nova Scotia where chimneys were overthrown or cracked. Highways in Nova Scotia were blocked by landslides. Aftershocks, some of magnitude 6, were experienced in both Newfoundland and Nova Scotia. A tsunami that was triggered by the earthquake caused extensive destruction on the coast of Newfoundland and killed a number of people.
Dense coastal settlements along the south and east coasts of Newfoundland have long been a feature of this part of Canada because of the fish resources provided by the banks. The Grand Banks is the largest of them. They mark the seaward limit of the continental shelf and they constitute the most extensive area of banks anywhere along the North American coast.
Because they are shallow they serve as a rich habitat for fish as they are constantly being enriched by nutrients from both the southward moving cold Labrador Current and the northward-moving warm Gulf Stream. In recent years, with the increasing use of bigger and bigger fishing vessels and their use of trawl nets with which to scour the sea bottom, over fishing has almost destroyed some stocks of fish and local residents have had to find alternative livelihoods.
The earthquake’s epicenter was 6,000 feet below sea level and the landslide it caused was multi-faceted. It constituted a massive submarine slump involving a number of small landslides, adding up in aggregate to more than two hundred cubic miles of debris. The many smaller slides were spread out over a distance of seventy miles along the edge of the continental shelf. As the smaller landslides were coalescing into one big mass they formed into a mixed current hundreds of feet thick.
This current as part of the whole overall landslide swept down slope at the edge of the continental shelf at a speed of fifty feet per second, cutting twelve transatlantic cables in numerous places as it moved. About 80,000 square miles of the seafloor was covered with sediment to a depth of ten feet. It was one of the biggest turbidity currents ever identified either historically or in the geological record.
The main story from this earthquake was the tsunami that followed. It was felt along the eastern seaboard as far as South Carolina and across the Atlantic in Portugal. Approximately two and a half hours after the earthquake the tsunami struck the southern part of Newfoundland as three main pulses, causing local sea levels to rise as high as twenty-two feet. At the heads of several long narrow bays the momentum of the tsunami carried water as high as eighty-five feet.
This giant mountain of water claimed a total of twenty-eight lives, twenty-seven of them drowned and a young girl never recovered from her injuries and died a few years later. This was Canada’s largest documented loss of life directly related to an earthquake, although oral traditions of First Nations people record stories of entire villages being destroyed by tsunamis.
More than forty local villages in southern Newfoundland were affected, where numerous homes, ships, businesses, livestock, and fishing gear were destroyed. Also lost were more than 280,000 pounds of salt cod. Total property losses were estimated at more than $1 million. Many buildings were lifted off their foundations and they floated away. The ferocity of the tsunami was not restricted to the land; it also tore up the seabed. This destruction of the seabed was believed by many to be the dominant factor in poor fish catches during much of the Great Economic Depression that followed in the years of the 1930s.
The provincial capital of Newfoundland, St. John’s, and the rest of the world did not immediately know of the devastation caused by the tsunami. The only telegraph line from the Burin Peninsula had, coincidentally and unfortunately, gone out of service just prior to the earthquake. When word did finally get out, help came quickly. A relief committee of the government, including doctors and nurses, arrived at communities on the south coast of Newfoundland on the afternoon of November 22. Recovery assistance was also provided by the Red Cross.