Almost perfect example of alternate bars in a river: the result of an instability mechanism related to a uniform flow in a straight channel with erodible bottom. The picture was taken from the mountain Gonzen above Sargans (Switzerland), close to the border with Liechtenstein. The pictured river is the Rhine. The development of such patterns can mathematically be understood by so-called weakly nonlinear stability analysis -- Ginzburg-Landau equations, as shown in the PhD thesis of Ralph Schielen (Utrecht University, 1995). See for instance `bars and bends' for more about river morphology. Nice and unexpected example of buckling in an axially loaded cylinder. The load had probably been applied accidentally to this roll of toilet paper ... There is a mathematical explanation for this buckling phenomenon.