Cracking the problem of river growth
A general mathematical theory that predicts how cracks spread through materials like glass and ice can also predict the direction in which rivers will grow, according to a new MIT study. In fracture mechanics, the theory of local symmetry predicts that, for example, a crack in a wall will grow in a direction in which the surrounding stress is symmetric around the crack’s tip. Scientists at MIT have now applied this theory to the growth of river networks, finding that as a river fed by groundwater cuts through a landscape, it will flow in a direction that maintains symmetric pressure from groundwater around the river’s head. The group tested the theory on 255 streams in the Florida Panhandle, and found that streams grow in a direction consistent with symmetry. The local groundwater flow — and specifically, the height of the underlying water table — therefore plays a large role in directing a river...