  The simplest patterns of qualitative changes on the configurations of lines
of principal curvature} around umbilic points on surfaces whose immersions into
$\mathbb R^3$ depend smoothly on a real parameter (codimension one umbilic
bifurcations) are described in this paper. Global effects, due to umbilic
bifurcations, on these configurations such as the appearance and annihilation
of periodic principal lines, called also principal cycles, are also studied
here.
