Two vast ancient glacial lakes which long ago gushed out of what is now northern Canada into the North Atlantic caused the most abrupt cold snap of the past 10,000 years, scientists said yesterday. Researchers at the University of Colorado in Boulder estimated that more than one trillion cubic metres of water drained from the Agassiz and Ojibway lakes in the Hudson Bay region about 8,200 years ago. The vast outflow occurred when an ice dam from a remnant of the Laurentide Ice Sheet, which once covered much of North America, collapsed.