  Over a smooth complex projective curve, we study an algebraic versal
deformation space with fixed determinant of a coherent sheaf. The algebraic
versal deformation space decomposes into a disjoint union of Shatz strata,
namely locally closed subschemes which parametrize coherent sheaves with common
Harder-Narasimhan types. We study the geometry and local topology of large
unstable strata and their behavior along boundaries.
