Abrupt temperature changes in the northern North Atlantic occurred frequently throughout the last glaciation as shown by proxy records from Greenland ice-cores, deepsea cores, and Norway speleothems. Many of these variations occurred in irregular sawtooth cooling cycles which sometimes ended with the deposition of thick layers of ice-rafted debris (IRD) in the deep ocean that are known as Heinrich events. The lithologies of most of the IRD deposits are consistent with widespread surges of the Laurentide Ice-Sheet that may have resulted from the accumulation of deformable sediments in portions of the ice-sheet bed. An alternative conceptual model proposed here to explain the sawtooth coolings and the surges involves repetitive jökulhlaups from a Hudson Bay lake dammed by ice at the mouth of Hudson Strait. The slow sawtooth coolings may be explained by storm track diversion due to progressive coverage of the lake by icebergs, and the surges by abrupt losses of water pressure and buttressing ice-shelves at all ice-sheet fronts in the lake when the ice-dams failed.