  If one assumes solar and LSND neutrino oscillations to explain the
corresponding data, then the atmospheric neutrino deficit cannot be
accommodated within the Standard Model with three light flavors, unless one
ignores the data's zenith-angle dependence. We propose a novel solution to this
problem by postulating large anomalous diagonal $\nu_\tau$-quark interactions
which affect $\nu_\mu - \nu_\tau$ oscillations traversing the Earth and induce
the observed zenith-angle dependence.
