  We study the behavior of bundles of superconducting vortices when increasing
the magnetic field using scanning tunneling microscopy and spectroscopy (STM/S)
at 100 mK. Pinning centers are given by features on the surface corrugation. We
find strong net vortex motion in a bundle towards a well defined direction. We
observe continuos changes of the vortex arrangements, and identify small
displacements, which stress and deform the vortex bundle, separated by larger
re-arrangements or avalanches, which release accumulated stress.
