This is true. Ah ha! Much more detail here: http://www.sciencemag.org/content/341/6149/997.full http://www.sciencemag.org/content/341/6149/997.full Seems that

This is true. Ah ha! Much more detail here: http://www.sciencemag.org/content/341/6149/997.full http://www.sciencemag.org/content/341/6149/997.full Seems that in some parts of the upper canyon, the ice configuration likely leads water away, but in the lower part, it controls the direction of water flow.