Testing northwest drainage from Lake Agassiz using extant ice margin and strandline data

Extant data on shorelines and ice margins in the glacial Lake Agassiz basin defines the limits of Lake Agassiz through deglacial time. The ice sheet margin had not retreated far enough northwards by the beginning or end of the Younger Dryas chronozone for the lake to drain northwest. However, once Lake Agassiz reached the Campbell Beach stage at ∼10,800–10,300 cal BP, then projections of Lake Agassiz strandlines were higher than the topography allowing for the first possible pathway to the northwest. This relationship is used to reject the recent assertion that there was northwest drainage from Lake Agassiz at the beginning and end of the Younger Dryas chronozone.