We consider the binormal flow equation, which is a model for the dynamics
of vortex filaments in Euler equations. Geometrically it is a flow of curves in three dimensions, explicitly connected to the 1-D Schr¨odinger map with values on the 2-D sphere,
and to the 1-D cubic Schr¨odinger equation. Although these equations are completely
integrable we show the existence of an unbounded growth of the energy density. The
density is given by the amplitude of the high frequencies of the derivative of the tangent
vectors of the curves, thus giving information of the oscillation at small scales. In the setting of vortex filaments the variation of the tangent vectors is related to the derivative of
the direction of the vorticity, that according to the Constantin-Fefferman-Majda criterion
plays a relevant role in the possible development of singularities for Euler equations
