The word tsunami usually brings to mind seismic waves in the Pacific or the Indian Oceans. Eighty five years ago today, an major earthquake, in the Atlantic, approximately 250 km south of Newfoundland along the southern edge of the Grand Banks, caused a tsunami that slammed into the Newfoundland coast.
On November 18, 1929, at 5:02 PM local time, the Grand Banks was rocked by a magnitude 7.2 earthquake. The earthquake triggered a large underwater landslide, which severed 12 submarine transatlantic cables. The landslide also generated a tsunami which raced towards Newfoundland at speeds of up to 140 km/hr, before slowing to about 40 km/hr in shallower water. Three waves would crash into Newfoundland’s Burin Peninsula, flooding dozens of communities and washing entire homes out to sea. Twenty eight residents would die in tsunami’s path.
As recounted by Newfoundland and Labrador Heritage: Despite the magnitude of the earthquake which precipitated the tsunami, no one in Newfoundland and Labrador anticipated the approaching danger. Large-scale seismic events are rare in eastern North America and virtually non-existent in Newfoundland and Labrador; in 1929, the country did not even possess a seismograph or tide gauge which could warn of the tsunami. Moreover, a recent storm had severed the single telegraph line linking the Burin Peninsula with the rest of the island; it was not until almost three days after the tsunami struck that the Squires government learned of the disaster and was able to send help….
At about 7:30 p.m., residents along the Burin Peninsula noticed a rapid drop in sea level as the lowest point of the tsunami’s first wave, known as a trough, reached the coast. As the water receded, it exposed portions of the ocean floor that were normally submerged and caused boats docked at various harbours to tumble over onto their sides. Minutes later, three successive waves hit the shore and water levels rose dramatically. In most places, the sea level swelled three to seven metres above normal, but in some of the peninsula’s long narrow bays, such as at Port au Bras, St. Lawrence, and Taylor’s Bay, the water rose by between 13 and 27 metres.
The force of the waves lifted houses off their foundations, swept schooners and other vessels out to sea, destroyed stages and flakes, and damaged wharves, fish stores, and other structures along the peninsula’s extensive coastline. Approximately 127,000 kilograms of salt cod were also washed away by the tsunami, which affected more than 40 communities on the Burin Peninsula. At Point au Gaul, giant waves destroyed close to 100 buildings as well as much of the community’s fishing gear and food supplies; St. Lawrence lost all of its flakes, stages, and motor boats. Government assessment later placed property damage on the Burin Peninsula at $1 million.
Worse than the damage to property, however, was the loss of human life. The tsunami killed 28 people in southern Newfoundland, which is more than any other documented earthquake-related event in Canadian history. Twenty-five victims drowned during the disaster (six bodies were washed out to sea and never found) and another three later died from shock or other tsunami-related conditions. The deaths were confined to six communities: Allan’s Island, Kelly’s Cove, Point au Gaul, Lord’s Cove, Taylor’s Bay, and Port au Bras. Fortunately, the tsunami struck on a calm evening when most people were still awake and could quickly react to the rising water; many managed to evacuate their homes and flee to higher ground.
Mostly taken from http://www.visionlearning.com/blog/2013/11/20/day-cables-broke/
Nov. 18, 1929: The Day the Cables Broke
November 20, 2013 by Julia Rosen
Today, a veritable superhighway of data rushes below the surface of the frigid North Atlantic. Every second, thousands of gigabytes whiz back and forth between North America and Europe on one of dozens of telecommunication cables that snake along the seafloor, transmitting emails, tweets, pictures, music — the everyday stuff of our digital lives.
In fact, a physical line of communication has linked the two continents since the first telegraph cable spanned the ocean back in 1858 (it was capable of transmitting just a few words per hour, and that was still a big improvement over shipping letters across the sea!). In 1929, however, these telegraph cables did more than connect the world: through an accident of geologic happenstance, they helped scientists discover a whole new phenomenon known as a turbidity current.
However, one seemingly inconsequential detail held the clue to the truth: from records of when they lost communication, the telegraph companies reported that six of the cables broke immediately at the time of the earthquake, but the remaining cables broke sequentially, and at progressively deeper depths, over the next 13 hours. Oddly, none of the cables lying higher up on the shallow continental shelf were damaged. All of the explanations offered at the time struggled to explain this slow, regular pattern of breakage, leaving some scientists with a nagging feeling that they were missing something.
Independently of the Grand Banks earthquake, a few geologists and oceanographers in the 1930s had begun to hypothesize about the possibility of underwater avalanches. In particular, a scientist named Reginald Daly from Harvard University suggested in 1936 that slurries of sediment and water might develop on the continental shelf, and since they would be heavier than the “clean water” around them, they could accelerate and flow down the continental slope. He dubbed these debris flows “turbidity currents” and argued that they could have carved steep submarine gorges that dissect the continental slope, features which were revealed by seafloor mapping expeditions just a few years before. Unfortunately, Daly lacked any evidence that ocean turbidity currents were real and for the next twenty years, geologists continued to debate their existence, using theoretical predictions and laboratory experiments to support their arguments.
It wasn’t until 1952 that two scientists — Bruce Heezen and Maurice Ewing of Columbia University — put all the pieces of the puzzle together. They were aware of Daly’s turbidity hypothesis, still untested, when at last, they realized that the Grand Banks cable breaks provided the first proof of a turbidity current in action: an underwater debris flow careening down the continental slope at the speed of an automobile would produce exactly the observed pattern of cable breaks and spare those on the continental shelf. They proposed that earthquakes could be a common trigger for turbidity currents, a fact we now know to be true.
Heezen and Ewing’s explanation for the 1929 event has now been universally accepted, and the Grand Banks telegraph cables are credited with documenting the first turbidity current ever observed by humans. After decades of further research, scientists now know that the turbidity current caused by the Grand Banks earthquake carried more than 200 cubic kilometers of debris more than 1,100 kilometers, depositing it across vast areas of the deep ocean — the cables didn’t stand a chance.
Knowing the time the cables broke in succession allowed an estimate of the speed of the turbidity currents: up to 55mph.
Bruce Heezen and Maurice Ewing were prominent oceanographers at Lamont Doherty Earth Observatory and the manner of Bruce’s death is an adventurous sea story.
Thanks Alan. Very interesting.
Have heard of this tsunami some years ago thanks for doing the story and keep up the good story,s from around the world .
Gerald