We study topology change in M theory compactifications on Calabi-Yau
three-folds in the presence of G flux (the four form field strength). In
particular, we discuss vacuum solutions in strongly coupled heterotic string
theory in which the topology change is inevitable within a single spacetime
background. For rather generic choices of initial conditions, the field
equations drive the Kahler moduli outside the classical moduli space of a
Calabi-Yau manifold. Consistency of the solution suggests that degenerate flop
curves - just as wrapped M theory fivebranes - carry magnetic charges under the
four form field strength.Comment: 21 pages, LaTeX, 2 figures (eps