Balbas et. al. use cosmogenic berylium-10 dating methods to further constrain the timing of ice sheet retreat, as well as the potential pathways for megafloods from both Lake Missoula and Lake Columbia. Read this fascinating Geology article summarizing their findings.
In summary, our new chronological information suggests the following:(1) Blockage of the Clark Fork river by the Purcell Trench lobe by ca. 18.2 ka, resulting in Missoula floods following the Columbia River valley.(2) Blockage of the Columbia River valley by the Okanogan lobe before 15.4 ± 1.4 ka, which shunted Missoula flood water south across the Channeled Scablands.(3) The final Missoula floods at ca. 14.7 ± 1.2 ka, signaling retreat of the Purcell Trench lobe from the Clark Fork valley, yet these floods entered a glacial Lake Columbia still impounded by the Okanogan lobe.(4) Down-Columbia floods at ca. 14 ka from breakouts of glacial Lake Columbia, signaling the retreat and final damming of the Columbia Valley by the Okanogan lobe