A newly identified mechanism that controls the spacing of river basins in growing mountain systems is reported in a study published online this week in Nature Geoscience. A constant relationship between the position of mountain divides and the number of river-system outlets has been observed in nature, but the processes controlling this connection had been previously unknown.

Stephane Bonnet used laboratory experiments to model the topography of a mountain range while combining the effects of the upward motion of the mountain range and asymmetric precipitation ― in which a mountain range blocks the movement of rain-producing clouds, casting a "shadow" of dryness behind the range. He found that the mountain divide responded to these conditions by migrating towards the dry side of the range. And as it did, channels on the dry side of the range began to split, forming more rivers and smaller but more plentiful drainage basins.

Bonnet suggests that evidence of this process can be found in the Aconquija Range of Argentina.