  We give a complete description of the behavior of the volume function at the
boundary of the pseudoeffective cone of certain Calabi-Yau complete
intersections known as Wehler N-folds. We find that the volume function
exhibits a pathological behavior when N>=3, we obtain examples of a
pseudoeffective R-divisor D for which the volume of D+sA, with s small and A
ample, oscillates between two powers of s, and we deduce the sharp regularity
of this function answering a question of Lazarsfeld. We also show that
h^0(X,[mD]+A) displays a similar oscillatory behavior as m increases, showing
that several notions of numerical dimensions of D do not agree and disproving a
conjecture of Fujino. We accomplish this by relating the behavior of the volume
function along a segment to the visits of a corresponding hyperbolic geodesics
to the cusps of a hyperbolic manifold.
