There is no apparent source for so much coarse sediment on the slumped areas of the muddy continental slope. We therefore infer that there was a large volume of sand and gravel available in the upper fan valley deposits before the earthquake. This coarse sediment was discharged from sub-glacial meltwater streams when the major ice outlet through the Laurentian Channel was grounded on the upper slope during middle Wisconsinan time. This sediment liquefied during the 1929 event, and the resulting flow was augmented by slumping of proglacial silts and gas-charged Holocene mud on the slope. Although earthquakes of this magnitude probably have a recurrence interval of a few hundred years on the eastern Canadian margin, we know of no other deposits of the size of the 1929 turbidite off eastern Canada. For such convulsive events, both a large-magnitude earthquake and a sufficient accumulation of sediment are required.
