These valleys originally were streams that flowed to the south. The moraine formed a series of lakes in the valleys. Drainage was still to the south over the moraine until the glacier retreated far enough to the north to allow escape of the waters along the southern edge of the glacier.
These valleys initially served as tributaries that flowed to the south. The moraine formed a series of reservoirs in the valleys. Drainage continued to be directed towards the south over the moraine until the glacier retreated far enough northwards to allow the waters to escape along the southern edge.